Category: New Research Page 13 of 67

Winning Symposium t-shirt design by Eric-Alain Parker

Calling all anole aficionados! Spots for the Seventh Anole Symposium on March 17-18, 2018 at the Fairchild Tropical Garden in Miami, Florida are starting to fill up! We have a limited number of spots for attendees and fewer still for presentations. If you have already registered, great! If you haven’t, please do so soon to guarantee your spots. Registering now does not require you to also pay now  – registrants will be contacted in early 2018 to pay the $100 registration fee. Submitting an abstract is not also required at this stage, and can be amended to the registration at a later date.

Photographs of a subset of lacertid lizard species used in this study. From the left top to the right bottom: Acanthodactylus beershebensis, Lacerta bilineata, Dalmatolacerta oxycephala, Podarcis melisellensis, Tropidosaura gularis, Podarcis siculus, Heliobolus lugubris, Algyroides nigropunctatus, Lacerta media.

The vast array of signals used in animal communication is a continuous source of awe and a hot topic in evolutionary and behavioral research. One important factor contributing to the signal diversity we witness today is ‘signal efficacy’: the ability of a signal to travel efficiently through the environment and attract the receiver’s attention. With this in mind, natural selection is expected to mold signal design for maximum efficacy of information transmission and detectability, leading to signal variation among populations/species living in different environments. To illustrate, a recent study by Tess Driessens and colleagues assessed the degree of variation in the dewlap design of Anolis sagrei by comparing 17 populations distributed across the Caribbean (Fig. 1).

Fig. 1 — Phylogenetic relationships among 17 Anolis sagrei populations. Pie charts illustrate dewlap pattern proportions for each population per sex (black = solid; light grey = marginal; dark grey = spotted). Photographs represent male and female dewlaps of typical individuals from every population.

Their findings showed large interpopulational variation in dewlap size, pattern, and color, and more interesting, they established a link between the dewlap design of brown anoles and the environment they live in. Lizards occurring in more ‘xeric’ environments had a higher proportion of solid dewlaps with a higher UV reflectance; lizards inhabiting ‘mesic’ environments had predominantly marginal dewlaps showing high reflectance in red. This was true for both males and females. Like Ng et al. (2011) and their observations on dewlap variation in A. distichus across an environmental gradient, Driessens et al. (2017) interpret their findings as evidence for adaptive divergence of a signaling apparatus.

Surprisingly though, while there are numerous great examples of comparative studies finding support for convergent evolution in visual and acoustic signaling systems, (e.g. Endler 1992; Fleishman 1992; Nicholls & Goldizen 2006, to say a few), similar (comparative) studies, but then, on the phenotype of chemical signals are almost entirely lacking. This is probably due to the combination of only very recent developments in chemical analytical and statistical comparative tools, the time researchers need to assemble a large-scale multi-species chemical dataset, and perhaps due to our own predisposition to visual and auditory signals. Currently, the proper analytical tools for studying natural products chemistry are available and affordable, permitting comprehensive taxon-wide research on the evolution of chemical signal diversity and design. Ultimately, there has never been a better time as now to be a comparative chemical ecologist.

Photograph of the cloacal region of a male lacertid lizard (Lacerta agilis), showing his numerous femoral pores with protruding glandular secretion.

Finally, three Belgians, two Spaniards and one Greek (sounds like the start of a joke with ample potential) took up the challenge to examine variation in the chemical signal design of lizards. Although underrepresented in studies on chemical signal diversity, lizards are an excellent group for investigating chemical signal evolution, as many of them they bear numerous glands on their thighs that secrete waxy substances, which they deposit while moving through their habitat. These secretions are often considered the leading source of chemical signals involved in lizard communication.

The study started with a quest. A quest to collect gland secretions of as many species as possible (within a PhD timeframe). Luckily, we were fortunate enough to be able to count on the help of many collaborators (Shai Meiri, Chris Broeckhoven, …). We focussed on lacertid lizards, as they are a species-rich family distributed over a wide geographical area, and known to rely strongly on chemical communication in several contexts.

In total, we sampled secretions from 64 species throughout, Europe, Africa, and Asia, covering a wide array of habitats and climate regions: from the Mediterranean maquis over the alpine meadows in the Pyrenees Mountains, to the sandy Israeli dunes and the Kalahari Desert of South Africa (Fig. 2). Back in the lab, we determined the chemical composition and chemical ‘richness’ (number of different chemical compounds) of the secretions using GC-MS, and obtained climate data for all catch-localities from online databases.

Fig. 2 — Map showing the sample localities of the 64 lizard species under study.

Our gathered data showed considerable variation in the chemical richness and composition of lacertid secretion. Shared-ancestry failed to explain among-species patterns of variation, hinting that chemical signals may change relative rapidly. Most interestingly, our findings revealed a strong relationship between the environmental conditions species live in and the chemical composition of their glandular secretions. On the one hand, lizards living in ‘xeric’ environments, characterized by high temperatures and arid conditions, contained higher proportions of stable and heavy-weight compounds in their secretions. Hot and dry conditions increase the evaporation rate of chemicals, and so, decreasing the longevity of a signal. Stable and heavy-weight compounds most likely reduce evaporation rate and counteract the rapid signal fade-out through evaporation, generating a highly persistent scent-mark. On the other hand, species inhabiting wet, humid conditions produced highly aromatic and low-weight secretions containing numerous different compounds. This chemical mix probably creates a volatile-rich signal that can be used for long-distance airborne communication.

While we cannot deny that these findings of convergent evolution in the design of chemicals signals are fascinating, some would say this outcome is not unexpected.

“[…] a cadre of scientists has taken the […] view, that convergence is the expectation, that it is pervasive, and that we should not be surprised to discover that multiple species […] have evolved the same features to adapt to similar environmental circumstances. From this perceived ubiquity, the scientists draw a broader conclusion: evolution is deterministic, driven by natural selection to repeatedly evolve the same adaptive solutions to problems posed buy the environment. — J. Losos (Improbable Destinies, p. 33)

Nonetheless, I am confident to state that using by far the largest comparative dataset amassed to-date to examine patterns of chemical signal divergence, we have provided strong evidence for a significant relationship between chemical signal design and prevailing environmental conditions, which may results from differential selection on signaling efficacy (Baeckens et al. 2017).

A male slender anole (Anolis limifrons)

A walk through a tropical rainforest can reveal astonishing forms and colors of organisms – from vibrant poison frogs and coral snakes to the vegetative camouflage of stick insects and other cryptic creatures. Perhaps some of the most dramatic displays of variation can occur between the sexes, where males and females can differ so greatly in appearance that they resemble different species. Research in many systems has demonstrated that much of this variation is driven by sexual selection, the force responsible for the evolution of traits that are important for acquiring mates. Individuals may invest as much energy as possible into such sexually selected traits because doing so will give them a competitive advantage for mate acquisition. These traits are therefore considered condition dependent, as their expression is dependent upon the energetic condition of the individual that possesses them. While condition dependence has been the subject of many studies, it is not well known how it may vary between closely related species that share the same traits. If closely related species vary in condition dependence of their shared traits, then this implies that condition dependence could be important for the evolutionary diversity of sexually selected traits.

The lowland rainforest at the La Selva Biological Station in Costa Rica

Together with students from Grinnell College and Reed College, and as part of an OTS (Organization for Tropical Studies) course that I took as an undergraduate at the University of Virginia, we took to the lowland jungles of Costa Rica to answer this question. We studied two anole species from Costa Rica, the slender anole (Anolis limifrons) and the ground anole (Anolis humilis). Specifically, we tested whether several traits that they had in common exhibited condition dependence, including dewlap size, aspects of jaw morphology, and sprinting speed. To test for condition dependence, we first calculated two conventional indices of body condition, the residual index and the scaled mass index, which both take into account an organism’s mass, given its length. We then obtained residuals from the relationship between our variables of interest (dewlap size, jaw width, jaw length, and sprint speed) and snout-vent length (a measure of body length), which allowed us to control for the fact that trait sizes often scale with the overall size of an animal. Finally, we used bivariate linear regressions to test the effect of our indices of body condition on our residual traits of interest, with a significant positive relationship suggesting condition dependence. We found that dewlap size (a trait important for sexual signaling) and jaw width (a trait important for bite force and male combat) exhibited condition dependence in ground anoles, but not in slender anoles. In contrast, neither sprint speed nor jaw length were condition-dependent in either species. Importantly, the presence of condition dependence in one species, but not the other, implies that the condition dependence of shared traits is evolutionarily labile. Additionally, by detecting condition dependence in the dewlap of ground anoles, which have a larger dewlap given their body length when compared to slender anoles, our findings may indicate that the strength of sexual selection differs between these two species. Lastly, our research suggests that variation in condition dependence of the dewlap among species could contribute to the extraordinary diversity of dewlaps in the Anolis genus.

If you would like to read the full paper, published in the Journal of Experimental Zoology Part A, go to:http://onlinelibrary.wiley.com/doi/10.1002/jez.2076/epdf

The 11th Latin American Congress of Herpetology is underway right now at the Museo de Zoología QCAZ at Pontificia Universidad Católica del Ecuador. Although I could not attend, I have been following the meeting vicariously as attendees have been using the Twitter hashtag #latinherps to document the meeting.  From those tweets alone, it appears the meeting has featured a series of fantastic talks, including many on anoles. If you are not a Twitter user you can still follow along by clicking more below to see all tweets from the Congress. Finally to Congress attendees, if any of you are interested, it would be great to have you contribute Anole Annals posts (or even comments below) on talks from the meeting.

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Amy Yackel Adams presents at JMIH 2017.

All anole field biologists have been there, right? It’s the middle of the night, and you’re walking around the forest searching for sleeping lizards in the trees. You’re probably wearing a headlamp, so the bugs are flying around your face, and your eyes start to strain as you get sleepy and you’re entering hour three or four of the search. This searcher fatigue could lead to the kinds of unintentional bias that can interfere with our research. But there’s good news when it comes to anoles, as Amy Yackel Adams, a statistician with the USGS in Fort Collins, Colorado, reported on the last day of JMIH.

Dr. Yackel Adams works with a Rapid Response Team whose goal is to prevent the spread of the worst invasive species. When a report came in of a sighting of a brown tree snake on the island of Saipan (in the Northern Mariana Islands, western Pacific Ocean), the team of experienced herpers deployed to Saipan and began intensive nightly surveys to assess the possibility of a brown tree snake population there.  Luckily, they didn’t find any of these snakes in the surveys, but they did log 20,000+ sightings of other vertebrates! These included emerald tree skinks, several species of geckos, a variety of small mammals, and the green anole (Anolis carolinensis). Dr. Yackel Adams saw an opportunity to use this rich dataset to statistically test for two types of bias that could occur in such surveys – searcher fatigue (both across the 4-hour nightly searches, and across the up-to-31 day deployment), and searcher bias in taxon detection.

The team of 29 searchers covered a total of 387 km of transects during the 31 days, and found a total of 5,800 sleeping green anoles during this time. (Wow!!) In terms of short-term searcher fatigue, there was a slight decrease in tree skink and mammal sightings as the night progresses, and gecko sightings were generally stable over the night, but far MORE green anoles were sighted in the later hours of the night. And over the long term, skinks and anoles were MORE likely to be detected the more nights a searcher worked, and there was no evidence of long-term searcher fatigue.  So, that’s why my take-home message was “nobody gets tired of looking for anoles!”

There was, however, significant taxonomic bias among the searchers – for example, the skink-to-anole sighting ratios ranged from 0.86 to 9.5. Dr. Yackel Adams concluded that this type of bias could be a real problem for certain kinds of studies, and we should be aware that differences among sightings by our survey team members could be potentially problematic in statistical analyses.

Chris Thawley presents at JMIH 2017.

For most of the history of life on earth, the only sources of light at night were the moon and stars. Yet with the invention and rapid spread of electric light, species around the world now face a novel evolutionary pressure: artificial light at night, or ALAN. Artificial light likely has an especially strong effect on animals in city habitats, such as the urban-adapted brown anole lizard, Anolis sagrei. Chris Thawley and Jason Kolbe at the University of Rhode Island set out to determine whether brown anoles were negatively impacted by ALAN.

In addition to their abundance in urban environments, brown anoles are a particularly good species for this study.  Previous studies of brown anoles have shown that photoperiod influences the onset of reproduction at the beginning of the breeding season, and that several behavioral traits change under artificial light. In addition, work by Moore and Menaker has shown that pineal production of melatonin in this species is significantly altered by photoperiod.  So, would ALAN influence brown anole growth and reproduction?

Chris and Jason collected lizards from south Florida and set up a lab experiment where some lizards experienced a normal photoperiod, and others were exposed to ALAN that mimicked landscape lighting. Their results were quite unexpected! ALAN actually increased female growth, resulted in eggs laid earlier in the season, and increased the reproductive output of small females – but did not affect the number or mass of eggs or hatchlings.  And, ALAN females did not exhibit more stress (measured via circulating corticosterone) than control females.

So are brown anoles just superlizards? Do they have no trade-offs that result from ALAN? Chris suggested that it’s possible that such trade-offs may appear in studies over a longer time period, or in traits not measured here. Or, perhaps ad libitum food and the absence of predators in the lab remove the costs of ALAN. Or, maybe these really are indefatigable lizards!