Infected with Love: A Viral Aphrodisiac in Crickets
Like many other insects, field crickets (Gryllinae) use a courtship song to attract potential mates and initiate mating. A team of researchers headed by Shelley Adamo at Dalhousie University has recently discovered a surprising trigger which speeds up this dating process - a virus. In their recent article “A viral aphrodisiac in the cricket Gryllus texensis” published in the Journal of Experimental Biology, the researchers found that a pathogenic insect virus (iridovirus) is able to modify the sexual behavior of male field crickets.
The researchers paired male and female crickets and measured the time it took for male crickets to initiate their courtship song. When compared to healthy male crickets, infected male crickets were at least twice as fast to begin their song routine. The infection also did not impair the mating behavior of female crickets. Female crickets mounted a courting male cricket in the same period of time, independent of whether the female crickets were healthy or infected by the virus. Many chronic illnesses can impair the feeding behavior and anti-predator defenses of crickets, which in turn can suppress their mating potential. However, this aphrodisiac iridovirus had no such effect. Infected crickets were able to maintain their weight and remained quite agile with intact anti-predator defenses.
An intriguing finding of the study was that the virus-infected crickets became sterile despite their increased sex drive. The sperm cells of infected male crickets showed little or no movement and the ovaries of infected female crickets were depleted of eggs. The researchers surmised that the accelerated cricket mating behavior may reflect an adaptive strategy of the virus to enhance its transmission during the physical contact that takes place during mating. Some of their data supported this hypothesis. Roughly half of the infected crickets transmitted the virus to uninfected mates. The researchers could not detect the virus in the sex organs of the crickets and thus concluded that the transmission probably took place via simple physical contact such as by grooming each other's antennae with their mouthparts.
There are important limitations of this study. The numbers of individual crickets in some of the experimental groups were rather low (n=4 or 5) which makes it difficult to generalize these findings. The study also did not provide any definitive mechanistic explanations for the multitude of effects that the virus had. How did the virus accelerate the courtship behavior while at the same time inducing sterility in the infected hosts? Was there a common molecular pathway involved? The researchers found decreased total circulating protein levels in the infected crickets, but this does not really explain how the virus turned the crickets into trigger-happy troubadours.
The findings of Adamo and colleagues need to be replicated with a larger sample of cricket populations. If these findings are confirmed, then they represent a fascinating example of how viruses can modify the sexual behavior of an infected host to maximize their own propagation.
Adamo, S., Kovalko, I., Easy, R., & Stoltz, D. (2014). A viral aphrodisiac in the cricket Gryllus texensis Journal of Experimental Biology DOI: 10.1242/jeb.103408