Can You See Me?

After a somewhat tortuous path, Dave's paper demonstrating signal modulation in response to predation pressure just came out in the Proceedings of the National Academy of Sciences. This study nicely illustrates the advantages of using a replicated design to conduct behavioral experiments under natural conditions. Such experiments are often characterized by unpredictability that can test the perseverance of any field biologist. In the case of this study, we had to endure tropical storms, the scorching sun, poisonwood, millions of sand-flies, and hundreds of horse-flies, in order to be prepared for the precise moment when a male Anolis sagrei would display. All of these nuisances were only exacerbated by a daily routine that included dealing with low tides that required walking in and out of islands carrying at least 20 pounds of video equipment. Kudos to Dave for collecting such a nice dataset. 

Dave feels fully hydrated after drinking two litters
 of his favorite "water"  

Dave walking to island (# 1) and wondering 
where is all the water

It has been long proposed that prey species should decrease the conspicuousness of their displays if predation risk is high. However, experimental data supporting this prediction are relatively rare, particularly for movement-based visual signals.  This study shows that A. sagrei can quickly decrease the amplitude of their head-bobs in the presence of the larger and predatory curly-tailed lizard. As illustrated by the figure below, anoles exposed to curly-tails decrease the amplitude of their displays by up to 60%. It should be noted that results presented in the study were collected in 2011, only three years after the beginning of the experiment. Therefore, the change has occurred relatively quickly. It is highly likely that this reduction in amplitude was already present in 2010; however, due to weather conditions we weren’t able to collect data for every island. 

Maximum amplitude of head-bob displays given by males Anolis sagrei  in the control and experimental islands

A second finding, which in my opinion can be a game changer in terms of how predation can impact individual fitness, is that a reduction in the amplitude of head-bob displays results in a much smaller signal active space (see figure). By integrating the motion detection parameters of the sensory system of A. sagrei, Dave was able to elegantly demonstrate that a reduction in the amplitude of head-bobs greatly reduces the signal active space of males on predator islands. For a territorial lizard that depends on signaling to attract females and to keep potential rivals away from its territory, a smaller active space should result in a reduction in reproductive success. This is an open question waiting to be answered! 

Differences in the active space of the signal between control and experimental islands. The inner circle corresponds to the active space in the presence of curly-tailed 

Another equally interesting implication of Dave's findings is the potential for changes in social dynamics resulting from smaller territory sizes.  For example, are males that were previously unable to secure territories now able to do so when the territory sizes of dominant males are reduced? Last but not least, are the results due to plasticity alone (i.e., modulation based on the perceived risk of predation) or is there some heritable variation in head-bob amplitude or accuracy of modulation that favors certain individuals? Our working hypothesis is that both of these likely interact. 

Popular press coverage:

Science News  
PhysOrg

      

Bahamian Toast

After a couple of days out on the cays, I am happy to report that our experiment has survived the power of Hurricanes Irene and Sandy. On a number of cays, A. sagrei has bounced back to densities suggestive of viable populations. A great example is Cay #1, which had only two anoles last year, but now has double-digit lizards. One Pine has similarly recovered and currently supports thriving populations of both A. sagrei and Leiocephalus.   

Manuel paint-gun in hand, marking lizards as part of population density estimates at One Pine

To celebrate the continuation of our experiment, Jonathan gave a truly Bahamian toast by chugging a 2-liter bottle of Goombay Punch.

Jonathan celebrating the continuation of our experiment  

Few Lizards and Bad Weather

Today was our first day out in the cays and our observations are mixed. Some cays appear to have extremely low population densities of anoles, and on a few others there is a high probability that A. sagrei populations are locally extinct. There is clear evidence that the surge from Hurricane Sandy, on some of our cays, was over one meter high, which is nearly as high as the tallest vegetation on some islands.

Note seaweeds nearly in the top of vegetation

However, it should be noted that the weather today was not the best for lizard catching: it was relatively windy and cloudy and included a heavy downpour. Because of the rain, tomorrow should be a great day for lizard activity, so we are holding out hope that our islands might be in better shape than today’s observations suggest. 

Dave and Jonathan having fun in the rain

We Are Back

Snappas an Abaco must visit grill and one of Dave Steinberg favorite relaxing spots.

We are back in Abaco and ready to begin our field season. If you are a follower of the blog, you might recall that last year we had serious problems due to hurricanes. The population density of anoles on a number of our study islands was very close to extinction levels. We are looking forward to tomorrow, our first day of this year's census, to get a better idea of the fate of populations. Have they bounced back or gone locally extinct? If the populations have increased in number, are there any phenotypic changes after passing through a bottleneck? Stay tuned for possible answers to these questions, which will be posted throughout the following weeks. 

Good Luck In College

Gabrielle has finished her project in which she was evaluating the visual acuity of Anolis evermanni. This project was part of her senior thesis at the the North Carolina School of Science and Mathematics. To test the visual acuity of the lizards, she used the same behavioral paradigm that we developed to demonstrate associative learning and cognitive abilities in anoles. As is the case with most behavioral projects there were a few bumps in the road. Nevertheless, Gabrielle was always excited about what the lizards will do and it was great to have her as part of the team.  

Gabrielle and her "lizards" note, 

how the anole is attentive to the block 

Back in the NYT ...

What an exciting few days here in the Chipojo Lab. Dr. Alex Gunderson (as you can see in the post below) successfully defended his dissertation on Friday . . . 

And now Manuel Leal is back in the New York Times!

A view inside the lizard chamber.

The lab is extremely excited that our research have been featured in the Science Section of the New York Times for a THIRD time! That says a lot about the ability of our work to interest a general audience, something that we take very seriously and are especially proud of.

Manuel Leal and Brian Powell's study on behavioral flexibility in Anolis evermanni is featured in an article on reptile cognition. You can read more about the research or watch a short video that discusses the work here. For those of you too lazy to click the link, I've included a magnificent photo of El Jefe below. CONGRATS!!!!

FELICIDADES

Please welcome the newly minted Dr. Alexander "Alejandro" Gunderson. Alejandro has successfully defended his dissertation work on thermal ecology in anoles.

Alex and Dave pouring champagne to begin the celebration 

This is a bittersweet moment for the Chipojo Lab. I am extremely happy that Alex was able to complete an ambitious project, one that I am certain will have a major impact on the methods that are currently used to predict the effects of global warming. To be clear, this is not a "proud" advisor blowing "hot air" about his graduate student. If you don’t believe me, please take a minute to read three of the papers that are already published and formed the core of Alex's dissertation. (Alex’s fourth chapter is currently under review in American Naturalist.) Yes, this is not a typo, three out of the four chapters of Alex's dissertation are already published, including a paper in Functional Ecology and another in American Naturalist.

Dr. Gunderson!!!!!!!!!  

We are going to miss Alex. For my part, Alex is my second graduate student, which means that I am still trying to figure out my "job" as an advisor. However, I feel very lucky, because having Alex as a student made advising a walk in the park and extremely rewarding. My only job was to keep him humble. FELICIDADES ALEJANDRO