Andale Andale Arriba Arriba

If you are my age, the saying "Andale Andale, Arriba Arriba" should immediately conjure memories of Speedy Gonzales and his ability to do everything REALLY fast.

Andale Andale Arriba Arriba 

It turns out that Speedy is not only a cartoon creation -- Dave is trying to emulate "Speedy" by flying to Puerto Rico last Wednesday, checking into Parador El Combate, and then instantly turning the room into his private laboratory.

Dave's set-up at Parador El Combate

As of today, he has already collected all the lizards he needs (30 male A. cristatellus) and completed half of his experiment, which involves measuring the visual grasp reflex of males to seven different stimuli. He will be back in Durham on Sunday, data in hand. As Speedy likes to say, "Andale Andale, Arriba Arriba." 

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.