Territoriality: Attempting a One-Two Punch

In my major Ph.D. project, I questioned the idea that territoriality is a good or useful description of Anolis lizards’ mating systems. When I began working on this question, I planned to primarily use an empirical approach, measuring the movement patterns and mating patterns of a population of Anolis sagrei in a way that didn’t depend on territoriality. But anticipating future criticism, I realised that because I’d be working in one population of one species, my empirical work could readily and reasonably be dismissed as an aberration without a broader foundation on which to place it.

This realization led to the historical review in which my Ph.D. advisor Jonathan Losos and I examined the history of research on Anolis territoriality. I’ve written about this historical research quite a bit before, but haven’t said much about the empirical work, leaving the two complementary halves of this project unintegrated. That’s partly been because the empirical work wasn’t published until recently. But it’s also because in contextualizing the problem tackled by the empirical paper, I have to basically recount the whole of the historical review. There really hasn’t been room to talk about both in a single venue, and there still isn’t, but I’m going to tell you a bit more about the empirical paper to balance things out. You’ve heard a little about it before–I wrote field notes about one of the males in this study (interesting addendum: U131 fathered none of the offspring of the females he encountered!) and about a tiny survey of green anoles that we conducted concurrently.

The empirical paper is now published, in the Proceedings of the Royal Society B! Here’s an awesome press release about the study from UCSB that will give you the gist of it, but in short what we did was:

• Catch and mark almost every lizard we saw, and then measure the spatial locations of as many lizards as we could by repeatedly surveying as big an area as we could.
• Make a map of all the trees within our sampling area.
• Measure the body size and estimate the population-level growth rate of males
• Collect a subset of the females, bring them into the lab, and collect the DNA of their offspring.
• Devise a mathematical approach to estimating encounters between males and females from data on their spatial locations. Combined this with the growth-rate estimate to calculate the size of males at their encounters with females.
• Use DNA sequencing to figure out the likely fathers of the females’ offspring; we leaned on the estimates of male-female encounters to do so.
• Use a clever and (I think!) pretty original approach to quantifying sexual selection on body size and movement patterns by comparing the traits of males that encountered females to the traits of the subset of those males that actually fathered offspring.

In sum what we found was that male and female movement patterns spanned larger areas and were more dynamic than many of us had previously imagined, that females encounter multiple potential mates, that at least 60% and possibly up to 80% of females  mate with multiple males, and that sexual selection acts on male body size as well as males’ spatial extent and the timing of male-female encounters. I’ll let you read the press release and the paper itself to learn more about what we found (here it is on BioRxiv, essentially the same paper but freely accessible)!

Viewed together, I hope the historical and empirical papers make a convincing case that we’ve been looking at Anolis mating systems in a limited way for a long time, and that other, newer ways of quantifying mating systems in ways that don’t depend on territoriality can yield both interesting and sensible results. I see this work as opening up an arena of questions, both in Anolis and in other taxa where mating systems have been described in a static way for a long period of time.

I’m very proud of this paper. I remember a phase of grad school when I found it impossible to convince people that this work would turn out interesting, or maybe it was just that my own self-doubt prevented me from seeing others’ interest and support for this research. It remains true that this is one study of one population of one species, and it may well be that I turn out to be all wrong. Perhaps new explorations of Anolis mating systems will eventually lead us back to territoriality. But even if that’s the case, I feel confident that, thanks to this work, we’ll be able to approach that or any description of Anolis mating systems with clearer, more skeptical, and more discerning eyes.

This won’t be the last you’ll be hearing from me on this subject of lizard mating systems; for one, there are responses to our historical review that are in the process of being published, and we’ll have a chance to respond to them. I’m very excited to engage in an actual scientific dispute, and will do my best to do so respectfully and productively, especially since I have on-the-record views about what makes such disputes annoying. But in terms of research, I seem to be heading in other directions, which I think will be related to this work but maybe not directly. So I wanted to make sure that I put down here, all in one place, what I see this project as and what I hope it will achieve. Let me know what you think!