A group of small tropical primates is breaking the trend, however—recent research demonstrates that several dwarf lemurs in Madagascar undergo seasonal hibernation periods for up to eight months of the year. While it had previously been known that the western fat-tailed dwarf lemur (Cheirogaleus medius) spends seven months of the year hibernating in tree holes (Dausmann et al. 2004), until recently there was no evidence for any other primate undertaking significant hibernation periods.

(Cheirogaleus crossleyi)

A recent paper in Nature’s open access journal, Scientific Reports, however, presents brand-new evidence of hibernation in two other species, the Sibree’s dwarf lemur (C. sibreei) and the Crossley’s dwarf lemur (C. crossleyi; sometimes called the furry-eared dwarf lemur), both of which occur in east-central Madagascar’s high altitude forests (Blanco et al. 2013). While it may not seem as though primates would need to hibernate on a tropical island, Madagascar’s mountainous regions can indeed experience temperatures that dip below freezing—a significant thermoregulatory challenge for a squirrel-sized primate. Thus, a  group of researchers from the University of Hamburg, the University of Antananarivo, and Duke University decided to see if the overwintering strategies of eastern dwarf lemurs resembled that of the western species.

The researchers managed to trap dwarf lemurs prior to hibernation season, and outfitted each animal with a collar that featured both a radio transmitter and a temperature sensor. The collars allowed the animals to be located after they had retreated to their hibernacula, in addition to tracking fluctuations in body temperature while the lemurs were hibernating.

The results were surprising and fascinating. Not only do these tropical lemurs hibernate for 3-6 months out of the year, the arboreal primates actually spend their hibernation underground, despite their lack of adaptations for a fossorial lifestyle. The lemurs nestled 10-40 cm beneath a the forest’s floor of secondary roots and humus, no small feat for an animal that gives every appearance of a life optimized for the treetops. Each lemur denned up alone, and they used just one or two hibernacula sites per season.

From Blanco et al. (2013)

This underground hibernation habit is extremely interesting; the other lemur species known to hibernate, C. medius, uses tree hollows exclusively. The researchers suggest that this difference in hibernation sites could be partially due to constraints imposed by soil type: soil in C. medius’ habitat is hard and dry, unlike the soft soils of the eastern forests.  Another significance of the findings about hibernacula choice is that the eastern species use tree hollows for their normal resting periods during the non-hibernation season, meaning that hibernation is an event with a very specific site selection pattern, rather than just an extended rest in their usual shelters.

Temperature data from the collars showed that C. sibreei and C. crossleyi tend to keep their body temperatures more stable while hibernating than does C. medius, which may highlight another advantage of subterranean hibernation. Soil provides more resistance to ambient temperature fluctuations than hollow trees, meaning that the eastern species are better insulated during their long rest than their western relative.

A final noteworthy aspect of this study is that C. sibreei and C. crossleyi are basal species within their branch of the lemur phylogeny. This raises the question of whether their hibernation patterns may be an ancestral condition for dwarf lemurs. Further studies on other species and populations will provide further insights into just how widespread these behaviors are among upland lemur species, in addition to yielding discoveries about how these small tropical mammals have adapted their metabolic physiology to achieve such long stretches of dormancy.

Blanco, M., Dausmann, K., Ranaivoarisoa, J., & Yoder, A. (2013). Underground hibernation in a primate Scientific Reports, 3 DOI: 10.1038/srep01768

Dausmann, K.H., Glos, J., Ganzhorn, J.U., Heldmaier, G. (2004). Hibernation in a tropical primate. Nature 429, 825-826.

Image source:

http://www.abicko.cz/clanek/precti-si-priroda/9874/sto-let-ztraceny-maki-znovu-objeven.html

Tasmanian devil suffering from DFTD

About a year and a half ago, I wrote about devil facial tumor disease (DFTD), the transmissible cancer that is pushing the Tasmanian devil closer and closer to the edge of extinction (see that post for a detailed discussion about the biology of contagious cancer). In the mean time, scientists have continued to press onward in pursuit of a way to stop DFTD’s spread and attempt to prevent the extinction of this unique and endangered marsupial. Last month, a fascinating and promising new discovery about DFTD was published in the Proceedings of the National Academy of Sciences (Siddle et al. 2013), and it looks as though there may actually be a light at the end of the tunnel for those who have worked so hard to understand and beat the disease—and for the devils themselves, of course.

As you might remember from my earlier post, there are two known transmissible cancers, DFTD and canine transmissible venereal tumor (CTVT), a sexually transmitted strain of cancer found in dogs and a few wild canids. Although DFTD is invariably fatal, CTVT rarely kills its hosts. Why? This question was a key starting point for Siddle and colleagues as they embarked on this new study. The researchers reasoned that the vast difference in mortality rate between the two diseases indicates that there must be something different about how the DFTD cells and CTVT cells interact with host immune systems.

Before we dive farther into the study, let’s have a very basic refresher course on mammalian immune responses. In order to recognize non-self cells (ie, those resulting from an infection or another foreign source), the immune system’s T-cells rely upon signals from the major histocompatibility complex (MHC) molecules that are displayed on the outside of the cell walls. These are the signals that tell the animals’ body, “this cell is mine, let it go about its business in peace,” or “Invader! Attack!” The expression of MHC molecules is controlled by a dizzying array of transcription factors, cytokines, DNA promoter elements, and epigenetic changes that occur over the course an organism’s development. Through their control of MHC activity, these factors influence the ability of the immune system to recognize “non-self” cells that need to be isolated and destroyed.

The progression of CTVT infection is interesting from an MHC perspective. For the first couple of months after an animal is infected, its CTVT cells don’t express MHC—the tumors fly under the immunological radar. Starting three to nine months after infection, however, the cells finally begin to express the MHC signals, and this allows lymphocytes to recognize the tumor cells as a problem and go in for the attack (Pérez et al. 1998; Hsiao et al. 2008). This is likely why CTVT is nowhere near as fatal as DFTD.

Now, it had long puzzled researchers that DFTD cells can be grafted between individuals with no rejection effect whatsoever—the animal’s body cannot tell that the tumor came from another devil. This is not due to extreme genetic similarity between devils—they have sufficient genetic variation that their immune systems should recognize a cell from another individual. (Sidebar: One often-told story is that cheetahs are famously so genetically homogenous that captive animals fail to reject skin grafts from other cheetahs, even without anti-rejection drugs . . . but newer research on wild cheetahs has shown that although there is indeed very low MHC variation, they are not as immunologically vulnerable as once thought).

So, back to devils. We have a transmissible cancer with a 100% mortality rate, and with cells that can be shuffled around between individuals with no alarm from the immune system…it seems clear that we needed a better understanding of exactly what is going on with the MHC molecules on DFTD cells.

Siddle and colleagues proceeded to isolate three cell lines from DFTD tumors, using a devil fibroblast cell line as a control. They cultured these cell lines in the lab, and conducted a series of tests to look at the activity of genes regulating MHC expression. They also checked to see if the DFTD cells exhibit structural abnormalities that could affect MHC recognition.

Siddle et al. (2013) show that DFTD cells do not express MHC molecules on their cell surfaces—in other words, they act like Trojan horses for the cancer, with no signal to the immune system that the tumor cells are a cause for concern. It turns out that DTFD cells down-regulated genes that are required for antigen processing, ultimately leading to a lack of MHC expression on the outside of the tumor cells. Without that signal from the MHC molecules, the immune system is oblivious to this sinister presence, and the cancer proliferates until it has killed the animal—explaining why this disease has a 100% mortality rate. The loss of gene expression was due to epigenetic modifications of the regulatory units, not to structural abnormalities of the tumor cells themselves.

Yes, this is quite upsetting news for a devil.

The discoveries didn’t stop there. Siddle’s group also tried treating the tumor cells with two substances: an antifungal drug called Trichostatin A, which is known to affect the activity of genes involved in MHC regulation, and a cytokine called interferon gamma, which had previously been shown to limit the growth of CTVT tumors. Both treatments resulted in a reactivating of the MHC gene activity, allowing the DFTD cells to be labeled as cause for alarm.

The upshot of this is intriguing: the authors suggest that the new discovery could yield a vaccine against DFTD. If devils can be inoculated with DFTD cells that have their MHC machinery reactivated, we may have finally found a way to allow the devils’ immune systems to fight off the tumor cells.

There is still much work to be done before this solution becomes a reality, of course. There are other ways the DFTD cells try to evade the immune system, and further research is needed to determine the best way way to strip the tumors of as many defenses as possible. Still, this is an exciting advance. For a species as close to the extinction abyss as the Tasmanian devil, good news can be scarce, and this study is definitely a cause for hope.

Hsaio YW, et al. (2008). Interactions of hos IL-6 and IFN-gamma and cancer-derived TGF-beta1 on MHC molecule expression during tumor spontaneous regression. Cancer Immunology, Immunotherapy, 57 (7), 1091-1104.

Pérez J, Day MJ, Mozoz E. (1998). Immunohistochemical study of hte local inflammatory infiltrate in spontaneous canine transmissible venereal tumour at different stages of growth. Veterinary Immunology and Immunopathology, 64 (2), 133-147.

Siddle HV, Kreiss A, Tovar C, Yuen CK, Cheng Y, Belov K, Swift K, Pearse AM, Hamede R, Jones ME, Skjødt K, Woods GM, & Kaufman J. (2013). Reversible epigenetic down-regulation of MHC molecules by devil facial tumour disease illustrates immune escape by a contagious cancer. Proceedings of the National Academy of Sciences of the United States of America, 110 (13), 5103-8 PMID: 23479617

All images sourced from Wikimedia Commons.

Cape fox (Vulpes chama)

Kamler et al. started with a very basic hypothesis: that the densities of both foxes would be higher on the jackal-free property than on the property that was open to jackals. Basic mesopredator release effect, right? But the researchers wanted to dig deeper. They posed a series of other predictions as well, based on knowledge about life histories of both fox species.
First, they predicted that both foxes would have smaller range sizes on the jackal-free property. This is because the foxes would no longer have to roam around in order to avoid and seek refuge from jackals, and could concentrate their activities on the highest quality habitat, reducing the space needed to sustain each family group. Similarly, it was predicted that both foxes would show different habitat selection patterns on the jackal-free property, since they could concern themselves primarily with resource availability rather than the relative risk from jackals in different vegetation types.

Bat-eared fox (Otocyon megalotis)

The next set of predictions took into consideration how differences in the natural history of the two fox species might affect their responses to jackal removal. Kamler et al. predicted that the group size of bat-eared foxes would decrease, but not group size of Cape foxes. They also predicted that Cape foxes would shift more of their activity to the daytime, becoming more diurnal in the absence of jackals, but that bat-eared foxes would not change their temporal activity patterns.
Finally, Kamler et al. predicted that there would be decreases in activity overlap between the two fox species when jackals were not present. This is because they would no longer be squeezed into microhabitats or other zones that provided lower predation risk, and would be free to spread out and stake out their own zones of the jackal-free property.
The team set out surveying the canids on both properties. For the foxes, they installed a radio telemetry collar on at least one member of each family group, so that each group could be located and observed in order to track population abundance and density. Telemetry data was also used to record movement patterns, which allowed estimation range size for each species. Scent stations and scat counts  were used to track jackal densities. Habitat selection was determined by comparing the proportion of different habitat types that were available to the actual proportion they represented in the animals’ home ranges. In order to examine activity patterns, the researchers determined the proportion of moving telemetry detections of each animal in each of three temporal categories: day, sunset, and night. They also measured prey abundance for each species, to control for the potential effects of differential resource availability.
The researchers’ efforts yielded fascinating results, some expected and some unexpected. This study included quite a few predictions covering multiple species, so I’ll cover it with an itemized summary of the predictions and corresponding results.
Prediction:
Lower densities of both foxes on non-jackal property.
Findings:
The Cape fox density was three times higher on the fenced property . . . but bat-eared fox density actually decreased by 37% in the absence of jackals, contrary to the prediction. The authors suggested that this was likely due to differences in termite abundance on the two properties, with the benefits of a jackal-free zone being overridden by the lower availability of the bat-eared fox’s favorite menu item.
Prediction:
Smaller range sizes for both foxes on non-jackal property.
Findings:
Both the Cape and bat-eared foxes demonstrated significantly smaller home range sizes where there were no jackals, consistent with the prediction. It appears that when foxes don't have to worry about dodging jackals and can focus on finding the richest resource sites, they can afford to reduce the area they occupy on a regular basis.
Prediction:
Both foxes would select for significantly different habitat types on non-jackal property.
Findings:
Neither fox showed significantly different habitat preferences in the absence of jackals. The bat-eared fox did show more of a tendency towards using bushveld habitat where jackals were absent (p = 0.069), possibly to take advantage of the termite berry plant that was more abundant than on the jackal-friendly property. Although not quite statistically significant, this does suggest that difference in food resources between the two sites were driving bat-eared fox habitat selection, not the presence or absence of jackals. Note that the definitions of the different habitat types were not based on resource abundance, so this is not necessarily inconsistent with the finding that foxes reduce their range sizes on the jackal-free property.
Prediction:
Smaller group sizes for bat-eared foxes on non-jackal property.
Findings:
Bat-eared fox group size was 48% smaller on the non-jackal property. Group size in this species seems to serve a vigilance function against jackal predation, thus the foxes may not need to stick together in such large numbers when predation risk is significantly lowered.
Prediction:
Cape foxes would become more diurnal in the absence of jackals.
Findings:
This was indeed the case, with 10-13% of telemetry signals of Cape foxes being recorded during the day time on the jackal-free property, compared to only 0-2% where jackals were abundant. The reason that bat-eared foxes did not show the same effect (and were not expected to) is that they primarily track their activity patterns to those of their prey, northern harvester termites. These insects are active at night for most of the year, creating a situation in which it is lucrative for bat-eared foxes to be nocturnal as well, despite the risk of jackal predation.
Prediction:
Decrease in spatial overlap of Cape and bat-eared foxes in the absence of jackals.
Findings:
The core areas of the Cape and bat-eared foxes overlapped less on the jackal-free property, indicating that they were able to partition den sites and other resources more broadly when they didn’t need to worry about predation risk from jackals.

So, that is a lot to absorb, and now we are much more informed about the ways that jackal presence affects the lives of small foxes in South Africa. But what is the take-home message of this study?

A key  implication is the the fact that the exclusion of jackals affected two similarly-sized foxes in very different ways on some parameters. As the authors put it, “several sublethal effects were species-specific, probably due to different evolutionary histories of the fox species and related constraints on behavioral plasticity." The 'good fences make good neighbors' premise seems to hold up for Cape foxes, which dramatically increased their densities and shifted their activity patterns when jackals were excluded. The bat-eared foxes, however, appear to be primarily limited by food resource. The bat-eareds actually showed a density response that was dramatically opposite that which would be predicted in a mesopredator release situation.
These results illustrate the fact that we cannot consider species interactions to be isolated from life history factors such as diet and social structure. Although there is still much evidence for mesopredator release effects in many systems, we cannot take for granted that small predators are primarily controlled by large ones. Foxes must avoid being eaten, but foxes must also eat. Future studies in other systems, including those with intact apex predator assemblages, will provide better insights into the conditions and possible resource “tipping points” that determine whether a small predator is controlled primarily by resource constraints or risk from larger predators.

To end with something comical, I recently had an interesting incident during my own data collection that involved a black-backed jackal. A big male jackal and a white-tailed mongoose (Ichneumia albicauda) showed up at a trap to investigate the bait at the same time.

The jackal got quite cocky, and greedily rushed to monopolize the bait that had attracted them both to the site . . .

. . . and proceeded to spend a night in jail as a result, while the white-tailed mongoose got to go on its merry way.

The bigger guy doesn't always come out ahead!

Gehrt, S. D. & Clark, W. R. (2003). Raccoons, coyotes, and reflections on the mesopredator release hypothesis. Wildlife Society Bulletin, 31, 836-842.

Helldin, J. O., Liberg, O., & Gloersen, G. (2006). Lynx (Lynx lynx) killing red foxes (Vulpes vulpes) in boreal Sweden: Frequency and population effects. Journal of Zoology, 270, 657-663.

Kamler, J., Stenkewitz, U., & Macdonald, D. (2013). Lethal and sublethal effects of black-backed jackals on cape foxes and bat-eared foxes Journal of Mammalogy, 94 (2), 295-306 DOI: 10.1644/12-MAMM-A-122.1

Myers, R. A., Baum, J. K., Chepherd, T. D., Powers, S. P., & Peterson, C. H. (2007). Cascading effects of the loss of apex predatory sharks from a coastal ocean. Science, 315, 1846-1850.

Young chimpanzee (Pan troglodytes). Image via WikimediaCommons

Both camps make valid points. While there may be nothing wrong with valuing a species based on the fact of its right to exist as an entity alone, scientists often don’t fully drive home information about the ecosystem-wide effects that losses of these animals could have. Yes, it is a crying shame to lose a large, intelligent, beautiful animal, but what about all of the thousands of less charismatic organisms that will also be impacted if the elephants, tigers, and gorillas disappear?

Publicists crow about the importance of charismatic animals to protect species that share their habitats, but often they don’t actually give much attention or publicity to the details and mechanisms behind interactions on the metaphorical “flagship.” This overlooks many critical facts about species dynamics, and misses the opportunity to educate people about the complexity of ecological communities—teaching them why even non-photogenic species are key links in the chain of life, and that nothing can be valued or protected in isolation. Also, it is critical for non-scientists to understand that even these flagship species are dependent upon an enormous supporting cast, and just preserving them in zoos is not enough to ensure ecological viability in the long-term.

Fortunately, some ecologists are putting effort into investigating just how the disappearance of key species affects—and is affected by—entire ecological communities. A  study in the most recent issue of  Proceedings of the Royal Society B provides just such an example (Effiom et al. 2013). African primates consume vast quantities of fruit and vegetation, and often transport seeds in the process. These species—the largest seed dispersers for many trees in dense African forests—are also being decimated by the bushmeat trade. This is clearly devastating to primate populations. But what about all of those fruit trees that are suddenly losing critical seed dispersal services? This is precisely the issue that Effiom et al. sought to investigate.

Drill (Mandrillus sphinx). Photo by Matt Sabbath, via WikimediaCommons

Their study was conducted in southeastern Nigeria, home to a plethora of primate species, including gorillas, chimpanzees, the spectacular drills, and a number of smaller monkeys. The researchers surveyed plants and animals in two different types of sites: protected areas, and non-protected areas that experience significant hunting pressure. These surveys consisted of transects to document abundances of mammals, which were assigned to four categories:  “large primates” (gorillas, chimps, and drills), “other monkeys,” “large rodents” (which often act as seed predators), and ungulates. They also censused both mature trees and seedlings. Trees were classified by their method of seed dispersal: whether their seeds are transported by 1) large primates, 2) other mammals, or 3) “wind or ballistic ejection” (sounds exciting, right?).

Map of study area (Effiom et al. 2013)

The researchers compared the results of these surveys between the protected and hunted zones. Because primates are both heavily hunted for the bushmeat trade and critical seed dispersers, the researchers expected primates to be less abundant in the hunted zones, and hypothesized that if this was indeed the case, seedlings of primate-dispersed trees would also be scarcer in the hunted zones, while the abundance and species composition of mature trees and seedlings of non-primate dispersed trees would not differ between the two treatments.

The results strongly supported this hypothesis. First, there were stark and ominous differences in the species composition of protected and hunted areas. The hunted areas housed just one third of the number of primate groups as the protected areas, while rodent populations were fourteen times higher in the hunted areas. The number of ungulates was also twice as high in hunted areas as in protected zones, although this difference did not prove to be statistically significant. In other words, in zones that are open to hunting, it appears that primate populations decline dramatically, while rodent and ungulate populations manage to expand, possibly released from top-down pressures by loss of the larger animals impacted by hunting.

As predicted, the decimation of primate populations had a profound impact on the tree composition of hunted areas. Although mature trees of all dispersal types were comparably abundant between treatments, there were significantly fewer seedlings of primate-dispersed trees in the hunted zones. This altered seedling composition is a window into the forest's future. The upcoming generation of trees will have a much different population structure than their forebears, due to the precipitous loss of primates in recent years. Once this cohort of seedlings has matured, the forest itself will look profoundly different.

The problem doesn’t stop there. As we saw, seed predators (mostly rodents) increased dramatically in hunted zones, creating a double-whammy for trees that suddenly faced reduced seed dispersal in addition to increased consumption of seeds by animals. The researchers’ conclusions are not optimistic: “The predicted future state is a forest with few, if any, large-seeded species dispersed by primates.”

All of this creates a final, "big picture" issue to consider. Removing primates causes declines in recruitment of the trees that they use for food…meaning that in the future, these hunted zones are likely to be suboptimal habitat (having much sparser food resources). Thus, even in the highly unlikely event of a complete cessation of primate hunting, these habitats will be unlikely to support pre-hunting densities of primates again. Take away the animal, the plants it interacts with declines, and it becomes harder for the animal to move back into the neighborhood, furthering inhibiting seed dispersal of the fruit trees that are left…and the situation continues in an unfortunate feedback loop.

Effiom et al. (2013) briefly discuss the bushmeat trade as a primary driver of hunting in this part of Africa. They cite two primary forces that are increasing these hunting pressures: increasing human populations and the encroachment of road networks into dense forest, facilitated by the timber industry. Although the bushmeat crisis is often portrayed to be perpetrated by locals due to their own taste for wild animals (Effiom et al. do not make this claim, just for the record), the truth is that local people co-existed with wildlife for millennia before Europeans showed up. Locals did hunt many of wild animals, of course, but in a managed way that didn’t result in complete decimation of populations.

Image credit: National Geographic

The opening of Africa to international trade, however, has fueled much demand for wildlife products across the globe—from people desiring the novelty of a primate steak to the demand for primate parts as traditional medicinal remedies, and everything in between.  One investigation showed that between 4,000 and 29,000 tons of illegal bushmeat is imported into the UK alone every year (Kümpel 2005)—and that is only what was detected. It is estimated that the market for bushmeat generates several billion dollars every year (Brashares et al. 2011). So although westerners often blame Africans for the bushmeat crisis, that perception is far removed from reality.

The take-home message of Effiom et al. (2013)'s study is that hunting primates—which is a growing problem due to market demand from the bushmeat trade—is not just an issue for monkeys and apes, but for the ecological structure of the forest itself. As we’ve seen from some of the bushmeat investigations, this is not a local problem. This is a problem fueled by global market demand. Solutions will depend on wide public awareness about how eating key species can result in a complete overhaul of the landscape itself. Food for thought.

Gorilla (Gorilla gorilla). Image courtesy of WikimediaCommons

Effiom, E., Nunez-Iturri, G., Smith, H., Ottosson, U., & Olsson, O. (2013). Bushmeat hunting changes regeneration of African rainforests Proceedings of the Royal Society B: Biological Sciences, 280 (1759), 20130246-20130246 DOI: 10.1098/rspb.2013.0246

Few things are more important for a carnivore's survival than having a lethal bite. The critical mechanics underlying bite force have significantly influenced carnivore evolution--they determine morphology, hunting behavior, and prey selection. As such, these adaptations carry both evolutionary and ecological significance.

Another, less tangible aspect of carnivore life is also tightly linked to hunting behavior: social structure. Individuals that hunt in cooperative groups, such as wolves (Canis lupus), can subdue larger prey than if they were hunting solo. For example, a pack of grey wolves can take down an elk (Cervus canadensis), which weighs up to 5  times as much as a lone wolf.

Just as hunting behavior influences sociality, sociality is thought to have influenced the physical evolution of carnivores in turn. The “social brain hypothesis” suggests that social species need larger brains than solitary species. Within this framework, social species need more cognitive capacity to process the communication and coordination required to both hunt cooperatively and manage social dynamics within the group (Dunbar 1998; Holekamp 2007).

So, we have two significant lifestyle issues influencing carnivore evolution: physical structures needed to provide the power to subdue prey, and social dynamics that also influence physical structures by requiring larger brain volumes. How do these two influences on carnivore cranial structure interact with one another?

Some research has suggested that there are physical trade-offs between brain and brawn, with the need for strong jaws putting a constraint on brain volume. For example, Wroe and Milne (2007) examined carnivorous marsupials and eutherians and found a trade-off between brain volume capacity and the strength of primary jaw adductors. This effect raises the question of whether bite force, by constraining brain volume, can also influence the evolution of social structure.

Recently, a group of researchers from Brazil and the U.K. undertook a study to investigate this issue for a specific group of carnivores, the family Canidae (Damasceno et al. 2013). Canids are especially interesting in this framework, because they display a wide range of morphological and ecological traits as well as a broad spectrum of sociality. The researchers explored the relationship between bite force and brain volume and compared these measurements across all of the world’s canid species.

The authors used two metrics for both bite force and brain volume. For brain volume, they first used raw volume as calculated from cranial measurements. Because brain volume is known to be influenced to some degree by body size, they also calculated a “brain volume quotient” (BVQ) by dividing brain volume by total skull length.

Rather than just using jaw adductor strength, bite forces were determined via the “beam theory,” which uses the cross-sectional area of cranial muscles that are critical to the biting/holding motions used to subdue prey, in addition to the distances between some of the muscles and critical joints, such as the temperomandibular joint in the jaw. Once again, bite force is known to be influenced by body size, so a correction factor was applied to produce a “bite force quotient” (BFQ).

The analyses involved two main questions:

1)   Do species with the largest absolute brain size also have the largest absolute bite forces, and are BVQs and BFQs similarly correlated?

2)   Do species with the biggest brain volumes have the weakest bites?

The results were intriguing and not entirely what one might expect. First, although absolute brain volume and absolute bite force were correlated across the board, BVQ and BFQ were not. Interestingly, the only species that did show strong correlations between BVQ and BFQ were “group hunting hypercarnivores,” species that hunt cooperatively and eat nearly entirely meat (in contrast to the high degree of omnivory found in some of the smaller, less social species). These species included the dhole (Cuon alpinus), bush dog (Speothos venaticus), and African wild dog (Lycaon pictus).

Dhole (Cuon alpinus). Photo from Wikimedia Commons.

Bush dogs (Speothos venaticus). Photo via Wikimedia Commons.

African wild dogs (Lycaon pictus).
Photo by Anne-Marie Hodge

Despite the expectations of the “social brain hypothesis,” which predicts that high sociality leads to larger brains, the grey wolf (Canis lupus) ranked 10^th out of the 32 species in terms of BVQ.  In fact, four small, non-social foxes ranked higher than the wolf on this measure. The wolf is both hypercarnivorous and a group hunter, though, so what’s going on here?

One of the biggest structural contributors to bite force is tooth row reduction (Van Valkenburgh 2007), which is strikingly apparent in other carnivore groups, such as the Felidae and Mustelidae. Most canids have 2 upper and 3 lower molars, but bush dogs have reduced their molar count 1 upper and 2 lower, dholes have 2 upper and 2 lower, and African wild dogs have the standard 2 upper and 3 lower. The wolf, however, has the same number of molars as the African wild dog, showing no significant specialization.

African wild dogs play-fighting.
Photo by Anne-Marie Hodge.

So, the African wild dog actually doesn’t deviate from the standard canid molar count, despite having one of the top BFQs, and the  wolf has the same molar count as the wild dog, but has a pretty unimpressive BFQ. Besides tooth row reduction, how else, might bite force increase brain volume? An example of another adaptation that increases both parameters is the widening of the occipital bones, which both increases intracranial space and strengthens the neck muscles, simultaneously providing more “brain space” and increasing the ability to subdue prey. The other hypercarnivores with the highest BFQs in this study also have relatively wide snouts, deeper jaws, larger anterior teeth, and elongated trigonid blades on the first molars. All of these features distinguished the high-BFQ/high-BVQ hypercarnivores from the wolf.

Thus, the authors suggest that the failure of the wolf's high sociality to push it up in the BVQ or BFQ rankings suggests that skull shape, not sociality, might be the biggest determinant of BVQ. The authors also note that although the three species with the highest BVQs also happened to have the highest BFQs, the two metrics were not correlated across the board, showing that they are independent variables amongst canid species.

Another interesting insight that emerged from this analysis is that all of the canids with the very lowest BFQs are desert species: side-striped jackals (Canis adustus), kit foxes (Vulpes macrotis), Ethiopian wolves (C. simensis), and bat-eared foxes (Otocyon megalotis). The authors suggest that arid, resource-poor environments force carnivores to be opportunistic feeders, negating the benefits of skull morphology optimized for hypercarnivory. Bat-eared foxes are invertebrate specialists, and unsurprisingly had skull morphologies least like those of the hypercarnivores, with 4-5 molars.

Bat-eared fox (Otocyon megalotis).
Photo by Anne-Marie Hodge.

The results of this study are fascinating and should spur further research with other carnivore taxa. Even the canids with the most forceful bites are no competitors for the bite forces of some non-canid species within the Mustelidae, Hyaenidae, and Dasyuridae (Wroe et al. 2005). Thus there still might be a brain-brawn trade off between families. In addition, measuring intelligence in animals (and humans, for that matter) is difficult at best, and the jury is out on how brain volume actually relates to metrics we would refer to as "intelligence."

The primary take-home message, though, is that these data strongly challenge the idea of such a trade-off within the Canidae, showing that once bite force and brain volume are adjusted for body size, increasing bite strength actually may facilitate higher brain volumes, the largest of which appeared only in species with the complex social systems required for cooperative hunting. In other words, these hypercarnivores are probably not dumb jocks. As we saw with the gray wolf, being social may not be enough to boost brain size on its own; structural features related to bite force appear to be key as well. Perhaps the wolf’s bark is worse than its bite after all?

Gray wolf (Canis lupus). Photo via Wikimedia Commons.

References
Damasceno, E., Hingst-Zaher, E., & Astúa, D. (2013). Bite force and encephalization in the Canidae (Mammalia: Carnivora) Journal of Zoology DOI: 10.1111/jzo.12030
Dunbar, R.I.M. 1998. The social brain hypothesis. Evol. Anthropol. 6, 178–190.

Van Valkenburgh, B. 2007. Déjà vu: the evolution of feeding morphologies in the Carnivora. Integr. Comp. Biol. 47:147–163.

Wroe, S., McHenry, C. & Thomason, J.J. 2005. Bite club: comparative bite force in big biting mammals and the prediction of predatory behaviour in fossil taxa. Proc. Biol. Sci. 272:619–625.

Wroe, S. & Milne, N. 2007. Convergence and remarkably consistent constraint in the evolution of the carnivore skull shape. Evolution 61:1251–1260.

One of my favorite species so far is the slender mongoose (Galerella sanguinea), mainly because I am fascinated by the morphological variation I’ve observed in the individuals that I’m capturing out here (all of the photos in this post are of animals that I've caught over the past month). I’ve seen a range of eye-fur color combinations, and even managed to capture a real prize: a leucistic male! All of this variability has me highly intrigued, and so I’ve been reading up on slender mongoose taxonomy a bit. It turns out they are notoriously polymorphic, and at one point as many as 70 different subspecies had been described (Kingdon 1997).

Leucistic slender mongoose, adult male

The genus Galerella consists of a group of species that—not without some controversy—was carved out of the larger mongoose genus Herpestes. Galerella includes an array of small (less than 1 kg), diurnal mongoose species that share a general set of features, yet there is debate about how many species actually belong in the genus, and no molecular  (Veron et al. 2004; Perez et al. 2006) or morphological (Taylor and Goldman 1993) analyses have shown the genus to be monophyletic.

Amidst this uncertainty, the two species most widely accepted as being “legitimate” members of the group are the grey mongoose (G. pulverulenta) and the slender mongoose (G. sanguinea). In contrast, the classification of the black mongoose (G. nigrata) has been kicked around quite a bit—it is sometimes defined as a species all to itself, and at other times assigned as a subspecies of either the grey or slender. Although the black mongoose does have cranial features that distinguish it from both of these potentially synonymous species, the issue had yet to be tackled using molecular data until recently.

Due of the lack of genetic information on this group of species, researchers from the University of Queensland recently sought to examine the evolutionary affinities of the black mongoose, with a special focus on potential hybridization with the slender mongoose (Rapson et al. 2012). They added another layer to their study by investigating whether species divergence times showed any relationship to major climatic shifts or events.

The study was conducted primarily using animals from northwest Namibia (the black mongoose occurs only in northwestern Namibia and southern Angola). Approximately 20% of the samples collected from black mongoose were thought to be hybrids, based on what appeared to be intermediate morphological characteristics. Using small tissue samples taken from ear notches, the researchers sequenced the cytochrome b and nuclear β-fibrinogen intron for black mongoose, slender mongoose, and potential hybrids. They also examined microsatellite loci, in order to use molecular clocks to determine how long ago the different mongoose lineages diverged from one another.

The results showed that the average percentage of divergence between black and slender mongoose Cytb sequences was 8.5%. For comparison’s sake, the grey and slender mongoose differ by about 10.1%. Despite this slightly lower level of divergence, the analyses did indeed show that black mongoose Cytb sequences form a monophyletic group, and that it appears this lineage split from that of the slender mongoose approximately 3.85-4.27 million years ago.

The timing of this event is extremely intriguing when considered in context of climate dynamics. The estimated divergence time falls within the Plio-Pleistocene period, which was a time of significant shifts in the animal community composition across Africa. The planet was beginning to go through a cooling period (Lisiecki & Raymo 2007), resulting in aridification and reduction of forest cover in South Africa.

Rapson et al. (2012) suggest that as southern Africa cooled and savanna habitats retreated, the slender mongoose population may have split into at least two groups: one contingent followed the savannas to keep up with the happy hunting grounds, and the other stuck it out on the increasingly dry, rocky dunes that remained in what is now northwestern Namibia. As both the distance and the environmental gradient between the two populations increased, reproductive isolation and adaptation to local conditions could have led to the development of a new species, which we know as the black mongoose today.

The globe has warmed up again since the Plio-Pleistocene cooling, however, allowing the habitat zones of the slender and black mongoose to come back in contact. The authors suggest that this secondary contact actually increased divergence, as mechanisms encouraging assortative mating became increasingly adaptive in contact zones. This is definitely possible, but reproductive isolation is not yet complete. Putative hybrids were shown to possess  both black and slender mongoose genes, showing that there is still gene flow between the two species in areas of sympatry. The fact that all of the Cytb sequences of apparent hybrids clustered with black mongoose suggests that these species might undergo “unidirectional hybridization,” in this case meaning that female black mongoose are more likely to participate in cross-species matings than are female slender mongoose.

Although the main focus of this study was the validity of the black mongoose as a species, the results for the slender mongoose Cytb sequencing were intriguing as well. It appears that G. sanguinea itself is not monophyletic, and that individuals from central and southern Africa may actually be different species. The study was limited by its lack of samples from east Africa (Uganda and Tanzania were represented by a single museum specimen each, and no individuals from Kenya or other east African countries within the slender’s range were included). It appears that the jury is still out on where these populations (including the animals I’m currently catching in my traps) fit in the taxonomic scheme.

Slender mongoose; adult female and juvenile male sharing a trap.

The link that Rapson et al. show between climate dynamics and a putative speciation event is fascinating, and it will be interesting to stay abreast of further studies that shed light on how the same shifting climate envelopes influenced the evolution of other species during the Plio-Pleistocene period. Meanwhile, it seems as though the black mongoose has been validated as a taxonomic entity, for the moment at least. This is also of interest from a conservation standpoint, because if the black mongoose is a species in its own right, it is one with an extremely limited distribution--a very significant risk factor for extinction.

Works Cited

Kingdon, J. 1997. A Field Guide to African Mammals. Academic Press, London.

Lisiecki, L. & Raymo, M. E. 2007. Plio-Pleistocene climate evolution: trends and transitions in glacial cycle dynamics. Quaternary Science Reviews 26:56-69.

Perez, M., Li, B., Tillier, A., Cruaud, A., & Veron, G. 2006. Systematic relationships of the bushy-tailed and black-footed mongooses (genus Bdeogale, Herpestidae, Carnivora) based on molecular, chromosomal and morphological evidence. J. Zool. Syst. Evol. Res. 44:251–259.
Rapson SA, Goldizen AW, & Seddon JM (2012). Species boundaries and possible hybridization between the black mongoose (Galerella nigrata) and the slender mongoose (Galerella sanguinea). Molecular phylogenetics and evolution, 65 (3), 831-9 PMID: 22940151
Taylor, M.E. & Goldman, C.A. 1993. The taxonomic status of the African mongooses, Herpestes sanguineus, H. nigratus, H. pulverulentus and H. ochraceus (Carnivora: Viverridae). Mammalia 57:375–391.

Veron, G., Colyn, M., Dunham, A.E., Taylor, P., & Gaubert, P. 2004. Molecular systematics and origin of sociality in mongooses (Herpestidae, Carnivora). Mol. Phylogenet. Evol. 30:582–598.

A study recently published in the journal Behavioral Ecology and Sociobiology sheds light on this issue (Ward & Currie 2013). The “flocking together” in this case is examined in two species of fish, the three-spined stickleback (Gasterosteus aculeatus) and the banded killifish (Fundulus diaphanus), both of which are known to move around in large shoals. Both species also exhibit extremely low variation in size between individuals comprising a given group, so Ward and Currie sought to examine how the fish manage to accomplish this size-sorting strategy.

Much research has shown that: 1) moving around in large groups reduces individual risk from predation, a sort of "safety in numbers" effect (Neill & Cullen 1974); and 2) often, the more similar your appearance to that of the other members of your group, the greater your risk reduction (Krause et al. 2000). This begs the question, though: how does an animal like a fish or a bird, or even a mammal, know what it looks like? With the exception of humans—and some dolphins and apes—few animals are capable of self-recognition even in the vanishingly rare instance of having access to a reflective surface.

Ward and Currie investigated this phenomenon in their study of sticklebacks and killifish. They hypothesized that there must be some sensory mechanism that allows fish to identify whether a conspecific is similar on an important aspect of phenotype, even in the absence of a visual concept of one's own appearance.

The authors note that previous work has shown that fish can visually assess whether they are within about 20% of the size of another member of their species (Ranta et al. 1992; Krause & Godin 1994). Many shoals, however, show much less than 20% variation in size. This strongly suggests that fish must have some other, more precise, form of size discrimination as well.  Fish use chemosensory cues for a wide variety of behaviors, and chemical cues have already been shown to help fish determine the body size of potential predators. In light of this, Ward and Currie hypothesized that a chemosensory stimuli might underlie their perception of body size when forming shoals.

The researchers collected individuals within two different size classes for each species. After an acclimation period in the lab, the fish were put into “flow channels” that circulated water from a reservoir bucket through the channel and then out a drain, creating an artificial current carrying water from two reservoirs. This created a “stream” of water from each reservoir on each side of the channel, with a neutral zone in the middle. The "focal fish” (the one in the channel) had the option to either swim in the stream with an individual of its own size class, a smaller or larger fish, or neither, based on chemical cues from the water streaming in from the reservoirs. A two-stream channel was also created to test whether fish would choose to swim in the stream of any conspecific or in a neutral zone.

The results? The fish “selected” the chemical cues taken from individuals that were of their own size class by a very significant margin, and they similarly preferred to swim in the stream of a conspecific than a neutral zone in the two-stream test. All of this strongly supports the hypothesis that fish use chemosensory information from the surrounding water to determine whether another member of their species is of a similar size. This is important, because it confirms that there is no need to visually assess one’s own size in order to determine the relative size of another individual.

All of the fish in this experiment were fed the same food items and kept in the same tank conditions during a control period leading up to the data collection, to avoid any bias based on dietary composition or other environmental factors. The authors point out, however, that size-based differences in diet (i.e., bigger fish can eat bigger and/or different prey) may enhance the difference in chemical cues, creating even stronger signals to inform fish about body size in natural settings.

By demonstrating that fish use chemical cues to determine the size of conspecifics relative to themselves, this study demonstrates the importance of chemical cues for a critical aspect of fish behavior. As water quality becomes more and more of a concern in many areas, awareness of whether or not these signaling mechanisms are impaired by changing temperature, pH, or chemical composition of the water will be critical. Future research on the precise chemicals involved in these interactions will also be interesting. This is definitely a line of inquiry to keep an eye on!

References

Krause J., Godin J. G. J., Brown B. (1998) Body length variation within multi-species fish shoals: the effects of shoal size and number of species. Oecologia 114:67–72.

Krause J., Hoare D.J., Croft D., Lawrence J., Ward A., Ruxton G.D., Godin J.G.J., James R. (2000) Fish shoal composition: mechanisms and constraints. Proc R Soc Lond B 267:2011–2017.

Neill S. R. S., Cullen J. M. (1974) Experiments on whether schooling by their prey affects hunting behavior of cephalopods and fish pred- ators. Journal of Zoology 172:549–569.

Ranta E., Lindstrom K., Peuhkuri N. (1992) Size matters when 3-spined sticklebacks go to school. Animal Behavior 43:160–162.
Ward, A., & Currie, S. (2013) Shoaling fish can size-assort by chemical cues alone. Behavioral Ecology and Sociobiology DOI: 10.1007/s00265-013-1486-9

By Luca Galuzzi, via Wikimedia Commons

The giraffe’s neck actually contains the same number of cervical (neck) vertebrae found in nearly all other mammals. (For a discussion of the very few mammals to deviate the magic number of seven cervicals, see this Endless Forms post). The rate at which these vertebrae develop relative to other parts of the giraffe’s body, including its head and overall body mass, however, has not been adequately explored.

The gangly, awkward teenage period is painful enough even for those of us that are not destined to end up as awkwardly gangly as giraffes for the rest of our lives.  This state of comical disproportion (in our eyes, of course) is not an entirely lifelong condition for giraffes, however: they are born with extended but not extremely long necks, and their cervicals don’t begin to extend rapidly until later in life (Van Sittert et al. 2010). But just how rapidly, relative to the rest of the body? Is there a difference between male and female growth patterns? What can the answers to these questions tell us about the evolutionary roots of the giraffe’s long neck?

These questions motivated a group of researchers from the University of Wyoming and the Centre for Veterinary Wildlife Studies at the University of Pretoria to investigate growth patterns of the necks and heads of giraffes, and their findings appear in a recent issue of the Journal of Zoology (Mitchell et al. 2013). They analyzed numerous morphological measurements in order to determine whether neck growth scaled allometrically with head and body growth—ie, whether the neck maintained a consistent size ratio with the rest of the giraffe’s body, or whether a giraffe goes through an “awkward teen phase” with proportions that are skewed relative to those of mature adults. The researchers also compared growth patterns between the sexes and examined sexual dimorphism to determine whether developmental patterns differ between males and females.

It turns out that there is no significant difference between male and female giraffes in neck growth rate (measured by both neck mass and neck length), but that in both sexes the neck length did indeed increase at a faster rate than body mass. The rates of neck and body growth rates are similar to one another in youngsters, but the necks outpace body mass once puberty hits, elongating out of proportion to the growth of the rest of the body. In other words, there is now scientific evidence that giraffes go through a gangly teenage stage.

Juvenile giraffe, via the "Wind and Sea" blog

Interestingly, a giraffe’s head actually grows at a slower rate than its overall body mass. Males did end up with slightly heavier heads and necks, due to thicker ossicones and skull bones. The researchers attribute this to basic differences in sex steroid levels, and it should also be noted that males have a much longer total growth period during their lives than do females. These factors underlie the slight male:female body size differential typically found even in mammals that lack significant sexual selection dynamics. Giraffe head and neck growth rates and the ratio of neck mass to total body mass both remained similar between the sexes,  meaning that they differ a bit in size but not in basic growth pattern.

This low degree of sexual dimorphism in skull and neck proportions has important implications for our understanding of giraffe evolution and biology. If giraffe necks had developed due to pressures from one form of sexual selection, dubbed "female choice," we would expect to find one sex (in the mammal world it would typically be the males) with profoundly more extreme features. In this form of sexual selection,  extreme features would provide the basis for the other sex (typically the females, sorry guys) to choose a mate from their array of suitors based on display characteristics of some sort, some more exaggerated than others. In the other type of sexual selection--"male-male competition"--giraffes would use their massive necks to battle for access to mates, which themselves would exhibit little aesthetic choosiness and would just go with the males that were the most successful at winning fights.

There are popular video clips of giraffes engaging in dramatic bouts of “necking”, in which they appear to fight by swinging their long necks and heavy heads at each other like weapons.  On the surface, it seems like this may represent sexual selection via male competition. Mitchell et al., however, point out that studies have shown that large males rarely participate in these activities, and it’s more often immature males with female-like head and neck sizes that do all of the “fighting” in order to establish a dominance hierarchy. Most importantly, the winners of the fights don’t go on to acquire more mates (Pratt & Anderson 1982).

Giraffes possess an extremely exaggerated feature, to be sure, but the lack of difference between males and females tells us that it’s unlikely this was due to sexual selection. This makes it much more likely that some form of enhanced resource utilization or physiological efficiency was the mechanism for neck elongation over evolutionary time.

The issue is far from resolved, however. Alternative mechanisms require further research and testing before they can claim to have “won” as evolutionary explanations for the length of giraffe necks. Moreover, there have been noteworthy back-and-forth on the validity of these theories. Some studies have suggested that giraffes rarely browse at the full height that their necks can reach (Young & Isbell 1991). Also, in order to “out-reach” other browsers, they would only need to reach two meters into the canopy, not five meters, and being that high off the ground actually makes it harder to see predators such as lions that slink along the ground (Cameron & Du Toit 2005).  Conversely, although Cameron & Du Toit (2007) found that 57% of the forage consumed by giraffes grew below two meters, i.e. in the height range of other herbivores, they suggest that the giraffe’s long neck allows it exclusive access leaves in the center of shrubs and bushes by reaching down from above. All of this will require broader and deeper investigation, of course, and in the end it is likely that the selective pressure that have produced such long necks is attributable to more than one precise factor.

Although it is most famous for its long neck, the giraffe exhibits an array of highly specialized features, and Mitchell et al. review a few fun facts about giraffe morphology. For example, relative to total cranial mass, the sinus cavities of giraffes are massive relative to those of other artiodactyls, allowing the development of such an enormous head without the skull becoming debilitatingly heavy. In addition, the cervical vertebrae close to the head are lighter than those lower in the neck, further decreasing the mechanical stress of holding a head that high on a neck that long. The occipital condyles, which allow the head to rotate on the neck, have such a wide range of motion that the giraffe can actually partially lay the top of its head along its neck while feeding, a sort of reverse flamingo strategy. Fancy, no?

By Marcus Obal, via Wikimedia Commons

References:

Cameron, E.Z. & du Toit, J.T. (2005). Social influences on vigilance behaviour in giraffes, Giraffa camelopardalis. Animal Behaviour. 69:1337–1344.
Mitchell, G., Roberts, D., van Sittert, S., & Skinner, J. (2013). Growth patterns and masses of the heads and necks of male and female giraffes. Journal of Zoology DOI: 10.1111/jzo.12013

Pratt, D.M. & Anderson, V.H. (1982). Population, distribution, and behaviour of giraffe in the Arusha National Park, Tanzania. Journal of Natural History 16:481–489.

Van Sittert, S. J.; Skinner, J. D.; Mitchell, G. (2010). From fetus to adult – An allometric analysis of the giraffe vertebral column. Journal of Experimental Zoology Part B Molecular and Developmental Evolution 314B(6):469–79.

Young, T.P. & Isbell, L.A. (1991). Sex differences in giraffe feeding ecology: energetic and social constraints. Ethology 87:79–89.

It is important to keep in mind, however, that modern birds are not the only feathered creatures to have ever walked—or, perhaps, danced—the earth. There is now abundant evidence that at least some dinosaurs sported feathers as well. (The theory birds are descended from dinosaurs and the debate surrounding that issue are beyond the scope of this post but certainly worth reading up on if that's all new to you). This revelation has opened up new realms of investigation involving signaling behavior and social cues related to the arrangement and coloration of dinosaur feathers. Unfortunately, data on integumentary details are exceedingly difficult to obtain from the fossil record—which is one reason it took us so long to figure out that many dinosaurs were feathered in the first place.

In a forthcoming issue of the journal Acta Palaeontologica Polonica, three paleontologists posit that fossilized oviraptors possessed structural features that are characteristic of those found in modern birds with ornamental tails (Persons 2012). For example, in the early oviraptor Similicaudipteryx, the last caudal vertebrae (the tip of the “tailbone”) are fused into a structure known as a “pygostyle," which was long thought to be a feature exclusive to modern birds. There is no evidence that Similicaudipteryx was a flying species, and Persons et al. suggest that the bone and muscle structures that can be discerned from the fossil remains are consistent with those seen in birds with tail displays that don't aid in flying but do functional as flashy ornaments, such as peacocks, turkeys, and birds of paradise (note that these birds are not completely flightless, the tails just don't contribute to optimal flight). Some species do indeed favor form over function, and apparently the trend may have started way back in the Mesozoic.

Pygostyle (Henderson State University)

Specifically, Persons et al. point to the presence of a series of numerous small vertebrae at the base of the tail and evidence of large, distally extended caudal muscles. These features would have given the tail a good deal of flexibility—perfect for “shaking its tail feathers” to attract mates. Similicaudipteryx’s good looks were not limited to its posterior: the dapper species sported a bony crest that also may have functioned in display behavior, either to attract mates or to intimidate competitors.

These assertions are, of course, subject to skepticism due to the limitations of the fossil record. This is part of science—publishing new perspectives or conclusions and allowing the scientific community to contribute further analyses and information--ultimately either supporting or discarding the idea. What is unquestionable, however, is that this paper signifies just how far paleontology has come in recent years. New finds and new technology have yielded broader an deeper information about the details of what dinosaurs actually looked like, how they moved, and how they might have interacted in their ancient world. As demonstrated by Persons et al., our increasing knowledge of dinosaur ornamentation and muscle structure means that areas of inquiry—behavior, social structure, mating systems, for example—that have long been of interested can finally be tackled scientifically. Worthy of a tail shake, no?

Persons, S. W., Currie P. J., and Norrell, M. A. (2013). Oviraptorosaur tail forms and functions Acta Palaeontologica Polonica DOI: 10.4202/app.2012.0093

Like many migratory species, humpback whales (Megaptera novaeangeliae) were long thought to have designated geographic areas along their migration routes for specific activities: a region for breeding, other regions for foraging and feeding, et cetera. One of the most lauded characteristics of humpback courtship is the complex “singing” behavior involved in their courtship displays (to hear one for yourself, see this video). A new study conducted by researchers from U.S. Naval Postgraduate School, the University of California-Santa Barbara and Duke University, however, suggests that humpbacks may emit courtship calls not only in their traditional breeding grounds, but outside of the “breeding zone” as well, and sometimes even perform these complex calls while in the process of making foraging dives (Stimpert et al. 2012).

 In order to study calling behavior during foraging, suction-cup tags were attached to ten individual humpbacks in the Western Antarctic Peninsula. This region of Antarctica is known to be a rich foraging ground, where humpbacks gather to consume masses of krill (Nowacek et al. 2011). Although there were previous reports of whales singing courtship songs outside of breeding areas, no one had yet either described individual songs from the Antarctic region’s rich feeding grounds or recorded what other activities the whale was doing at the time the song was produced. Thus, the new study by Strimpert et al. sought to address an important question: what is the behavioral context of courtship displays performed outside of traditional breeding regions?

Study region: West Antarctic Peninsula (Strimpert et al. 2012)

The suction-tag data showed that the whales did indeed emit calls outside of traditional breeding areas, and at least two individuals produced songs with acoustic qualities matching those used in courtship displays. One individual even appeared to manage the feat of producing these courtship calls while in the process of performing a deep (greater than 100 meters) foraging dive. Although there is a potential that the tag devices recorded calls from nearby whales rather than the individual to which the device was affixed, the researchers note that aggregated individuals usually engage in the same types of activities when together, and the call during a deep dive could not have been recorded from an individual remaining near the surface.

The primary takeaway from this study is: rather than strictly compartmentalizing their breeding and feeding behaviors into different geographic regions, humpbacks apparently are able to multitask. They were observed advertising their mating availability while also performing deep foraging dives in feeding areas thousands of miles from traditional warm-water breeding grounds.

The fact that whales can multitask in such a way is interesting from a behavioral as well as a physiological standpoint: producing the correct sounds while moving down in the water column likely requires tight vocal modulation in response to increasing water pressure. Another noteworthy finding was that the whales in this study produced songs while they were foraging in groups, which is unusual: on breeding grounds whales normally sing either while solitary or while escorting mother/calf pairs.

The significance of these findings should not be understated. The data essentially show that the paradigm of a strict breeding-feeding dichotomy is a simplistic and probably inaccurate way to frame humpback whale behavior. Multitasking allows whales much more complexity in their feeding behavior and social interactions, in addition to both their temporal and their spatial ecology. In addition, if this rigid trade-off pattern is not accurate for humpbacks, it is likely that many other species have much more complex, multi-faceted behavior patterns than traditional models might suggest.

Alison K. Stimpert, Lindsey E. Peavey, Ari S. Friedlaender, Douglas P. Nowacek (2012). Humpback Whale Song and Foraging Behavior on an Antarctic Feeding Ground PLoS ONE, 7 (12)