Giant, fertile city spiders: behind the scenes
I was excited to see the attention around an interesting spider-focused paper published in PLOS last week, titled "Urbanisation at Multiple Scales Is Associated with Larger Size and Higher Fecundity of an Orb-Weaving Spider" by Lizzy Lowe, Shawn Wilder, and Dieter Hochuli. This work ignited creativity in headlings around the world, including things like "City living makes spiders big, fat and fertile, researchers say" or "Our hot, bright cities are spawning gigantic spiders".
Lowe et al. looked at how body size, lipid reserves and ovary weight of a spider (Nephila plumipes) varies in relation to urbanization in and around Sydney (Australia), and found that spiders in areas of increased ubanization were indeed larger than their cousins in the country, and were also more fertile. So, indeed, fat and fertile spiders, in a relative sense, were more common in urban areas. I touched base with Lizzy to discuss this research, and get a behind-the-scenes glimpse at how this work was done, and its broader implications.
CB: There is a lot of literature out there about effects of urbanization on wildlife, plants, invasive species, etc, but the idea of using “spiders” as a model taxon in this context is somewhat novel. What inspired you to tackle the effects of urbanization on spiders?
LL: Spiders are a fantastic model for urbanisation in Australia. Firstly there are quite a few iconic species which are urban exploiters, huntsmen, red backs and of course Nephila. But also we have really amazing spider biodiversity in Australia. and there are just as many species which don’t do well in urban areas. I am hoping to use these differing responses to urbanisation to work out which traits (morphological, physiological or behavioural) allow some spiders, but not others, to thrive in urban areas. I also just really love spiders, I’ve found so many cool species living in such unlikely places that it makes for a very interesting study system.
CB: It’s one thing to document changes in species distributions in urban areas, but something entirely different to consider effects on ‘fitness’ measures of spiders (e.g., size, reproductive capacity). What are the challenges and benefits of looking more deeply at these measure of fitness?
LL: The benefit of looking at size and condition of these spiders it’s possible to develop a better understanding of the mechanisms underlying their success in urban areas. For example we know that they live there, but this way we can find out which components of urban systems are actually allowing them to benefit. In this case we found associations with hard surfaces and lack of vegetation. Obviously these are at this stage, just associations and the next step of this is to formulate a more mechanistic approach. The challenge is that the manipulation of things such as temperature or “urbanisation” in the field can be very difficult. We have worked around this in some ways by doing transplant experiments but it is still difficult to directly assess the effects of the environmental variables on growth and development in the field.
CB: The media has been all over this paper, in part because it makes a great headline e.g., “SPIDERS IN CITIES ARE GIANTS”. If you were to write the headline for your paper, what would you write, and why? Related, what are the “big picture” and broad consequences of your research if you project 20-30 years into the future, when cities are even more pervasive than they are now.
LL: I actually wrote my own opinion piece on this work which I called “City spiders are getting bigger — but that’s a good thing”. The first part of this title is the editor wanting to draw in readers and the second is my appeal to the readers to consider the broader implications of this rather than just running for their insect spray. I find it fascinating that ANYTHING can live in cities considering all the modifications that we’ve made compared to their natural environments. There are so many studies now showing that green space and access to nature is essential for human wellbeing and health. So we should be looking at increasing not just the biodiversity of our urban areas but the functionality of these systems too. If you want to have functioning ecosystems in urban areas spiders are a vital part of this.
CB: The field and laboratory work was probably quite challenging and interesting: can you share any anecdotes arising from your field and lab work?
LL: I get lots and lots of strange questions and looks while I’m out in the field poking and collecting my spiders. But I really love this because it gives me the chance to explain to the public what I’m doing and why it’s important. Most of the time they agree!
But my best story from this piece of work actually comes from the lab. Shawn and I trialed a few ways to measure the lipid content of these spiders. Shawn had previously used freeze drying to do this with locusts and it worked perfectly, so we decided to give it a go with the spiders. We put them in the -80 degrees freezer for a few days and then popped them into the freeze drier. But these spiders can get VERY fat and some must not have been quite frozen in the middle because they actually did pop. We got the vials out and it looked like a minor explosion had happened in each one, there were spider guts splattered on the inside (see photo attached, and there were many that were much worse). So the first project of my PhD ended with me blowing up spiders in a freeze drier, pretty cool really!
Finally, a BIG thanks to Lizzy for agreeing to answer a few questions about this outstanding research. You can follow her on twitter!