Year: 2024

Hello Anolophiles!

Could anyone use a free undergraduate field assistant this summer for any squamate evolution or conservation projects, preferably outside of the U.S.? I am an undergraduate student in Drs. Emily Lemmon and Frank Burbrink’s labs with $5k from a merit based scholarship that I need to spend this summer on my “educational enrichment”. I’m hoping to use my funding to support any living, travel, research, and lost wages expenses associated with being a field assistant for anyone doing squamate research any time between May and the end of July 2024. My current research focuses on phylogeography of North American herps, but I’m eager to assist with any project on any squamate, ideally though not necessarily in the neotropics. I’m looking to learn new field techniques, work with a new biological system, have wonderful discussions on all sorts of herpetological matters with a new research mentor(s), and find inspiration for anticipated upcoming graduate studies.

I have experience with molecular lab methods (DNA extraction, gel electrophoresis, Qubit quantification), museum methods (toe clipping and dissection for tissue extraction, posing and formalin fixing specimens), field methods (lassoing lizards, nocturnal herpetofaunal field surveys, dipnetting, roadcruising), data visualization and statistical analyses in R, and science communication. I’m happy to work in challenging and remote field conditions; the more bugs, venomous snakes, and stinging plants the better, though I would like to come back alive and in one piece. Let me know if you could potentially use a field assistant at povenika@gmail.com , and I would be happy to send along a CV and letters of recommendation.

I woke up after spending the whole night in motion and listening to the engine noise as a crib song. Some years ago, it had been a crab boat in Alaska and it was now equipped to do biological research in the northwest of Mexico. I am here after a few talks with Armando Escobedo; he told me about an amazing project to describe the diet of the lizards living on Maria Cleofas Island. My experience with lizards and trophic niches was scare, but I was motivated to learn about it. “Not every day I have the opportunity to meet the Marías Islands.”

This island with a biblical name, María Cloefas Island, is home to four lizard species. Anolis nebulosus (Clouded Anole), Aspidoscelis communis (Colima Giant Whiptail), Ctenosaura pectinata (Western Spiny-tailed Iguana), and a recently described endemic leaf-toed gecko, Phyllodactylus cleofasensis. After taking  breakfast on the boat deck, Rafael (an undergraduate student like me), Armando and I were taken to the island in a small boat to evaluate the dietary variation of lizard species.

Fieldwork team and lizard species in María Cleofas Island

The main goal of our study was to describe the trophic niche of the lizard community, given that the species differ in foraging strategy. We expected to observe higher prey diversity in the active forager (Aspidoscelis communis) compared to the three sit-and-wait foraging species. Also, due to their different habitat use, we expected that the arboreal species (Anolis nebulosus and Ctenosaura pectinata) would share similar dietary niches, and that the terrestrial species (Aspidoscelis communis) might exhibit a partial dietary niche overlap with them. Finally, we expected that the saxicolous and nocturnal species (Phyllodactylus cleofasensis) would have the most distinct prey diversity.

We visited the island during eight weeks between 2017 and 2018. We performed diurnal and nocturnal surveys in all available habitats to manually capture individuals of the four lizards on the island. We obtained stomach contents from a total of 115 individuals using the stomach flushing technique. From this total of samples, 37 belonged to Anolis nebulosus, 11 to Aspidoscelis communis, 36 to Phyllodactylus cleofasensis, and 31 to Ctenosaura pectinata. Despite the movement of the ship, I could check the stomach contents under the stereoscope, and begin to determine the occurrence of each prey item eaten by each lizard species, for later calculatation of their prey diversity and determination of whether the lizards were generalists or specialists, as well as their degree of inter-individual specialization. Furthermore, we looked for similarities within species; therefore, we calculated their food resource overlap and their similarity index. In addition, we performed some analyses to examine differences in each food niche method and to determine if there was a difference in the prey eaten by each species and between years of surveys.

Insects, skin remains, and vegetal matter found in the stomach contents of the species.

We discovered, surprisingly, a wide variety of arthropods within the stomach contents of the lizards, regardless of their foraging strategy and habitat use! We identified 19 types of prey items such as insects, arachnids, gastropods, and centipedes, with a clear prevalence of beetles, spiders, and vegetation matter in the diets of the lizards. The diet of Anolis nebulosus was the most diverse, composed of 15 items, mostly arthropods, some vegetation matter, and their own skin remains. Aspidoscelis communis consumed 11 prey items, mostly arthropods, while Phyllodactylus cleofasensis consumed 10 prey items, mostly arthropods, some vegetation matter, and their own skin remains. We found nine items for Ctenosaura pectinata; surprisingly, we found a lower amount of vegetation matter, and the rest were arthropods.

Prey items found in the stomach contents of each species.

The Clouded Anole showed the highest richness of prey items in their stomachs; however, it was not the species with the highest prey diversity. Despite this, Anolis nebulosus exhibited greater prey diversity compared to other insular and continental populations. This expansion of its trophic niche could be attributed to the low predation pressure and high intraspecific competition on the island, which also influenced the phenotypic and behavioral plasticity of the species.

The actively foraging species Aspidoscelis communis showed the highest diversity of prey values. Phyllodactylus cleofasensis showed a significant variety of prey, while Ctenosaura pectinata displayed the lowest values across all three measures of food niche diversity. Thus, Anolis nebulosus, Aspidoscelis communis¸ and Phyllodactylus cleofasensis were generalist species with an increase in inter-individual specialization, while Ctenosaura pectinata remained close to the threshold between specialist-generalist feeding habits and little or no inter-individual specialization.

Prey-group diversity index and trophic niche breadth index of each species.

Based on habitat preferences, we expected that arboreal species (Ctenosaura pectinata and Anolis nebulosus) would exhibit similar prey diversity, and also that the actively foraging species, Aspidoscelis communis, would exhibit a greater prey variety compared to Ctenosaura pectinata. Our results through the different trophic niche approaches aligned with these expectations. Surprisingly, Phyllodactylus cleofasensis, despite being a nocturnal forager, demonstrated similar individual specialization as Anolis nebulosus.

Niche overlap and similarity among the lizard species.

The results from the discriminant functional analysis showed distinctive dietary patterns among lizard species. Aspidoscelis communis exhibited a diet divergence from the other lizard species; part of its diet could potentially be confused with Ctenosaura pectinata’s diet, while the diet of Phyllodactylus cleofasensis showed similarity with the diet of Anolis nebulosus (and vice versa). Finally, the diet of Ctenosaura pectinata had a relatively low overlap with Anolis nebulosus.

Diet overlap derived from the number of prey items per stomach among lizard species.

Our research on the lizard community of María Cleofas Island has not only demonstrated the wide dietary diversity among species, but has also expanded our understanding of trophic relationships in island ecosystems. Moreover, with this study, we have challenged conventional assumptions about resource partitioning and dietary niche diversity in insular ecosystems.

Don’t forget to take a look at the original paper; you will find some other amazing observations!

Rachana applying fluorescent powder to a wild brown anole

This post is an update of one from 2020. Below is the old post based on a presentation by Rachana Bhave at the 2020 SICB meetings. Rachana has now done the genetic parentage studies and published the cool paper in Behavioral Ecology. Here’s the abstract of the paper:

In promiscuous species, fitness estimates obtained from genetic parentage may often reflect both pre- and post-copulatory components of sexual selection. Directly observing copulations can help isolate the role of pre-copulatory selection, but such behavioral data are difficult to obtain in the wild and may also overlook post-copulatory factors that alter the relationship between mating success and reproductive success. To overcome these limitations, we combined genetic parentage analysis with behavioral estimates of sizespecific mating in a wild population of brown anole lizards (Anolis sagrei). Males of this species are twice as large as females and multiple mating among females is common, suggesting the scope for both pre- and post-copulatory processes to shape sexual selection on male body size. Our genetic estimates of reproductive success revealed strong positive directional selection for male size, which was also strongly associated with the number of mates inferred from parentage. In contrast, a male’s size was not associated with the fecundity of his mates or his competitive fertilization success. By simultaneously tracking copulations in the wild via the transfer of colored powder to females by males from different size quartiles, we independently confirmed that large males were more likely to mate than small males. We conclude that body size is primarily under pre-copulatory sexual selection in brown anoles, and that postcopulatory processes do not substantially alter the strength of this selection. Our study also illustrates the utility of combining both behavioral and genetic methods to estimate mating success to disentangle pre- and post-copulatory processes in promiscuous species.

And here’s the post from 2020:

If you’ve ever tried to note how often lizards mate, you’ve likely found yourself staring at an individual for hours at a time, sometimes with little to no movement at all, let alone observing copulations! Further, if you’re unable to catch the animal after your behavioral observations, you may not be able to draw any conclusions about traits that influence how successful an individual is at mating with another.

Rachana Bhave, a fourth year PhD candidate in Bob Cox’s lab at University of Virginia, studies pre- and post-copulatory sexual selection in brown anoles (Anolis sagrei). One of her interests includes estimating mating rates in the wild and, in particular, testing if traits such as body size directly influence these rates. Given the power required to detect selection statistically, using simple behavioral observations can be inefficient. Further, because selection is a measure of covariance between phenotype and fitness, one needs phenotypic values for each individual within her analyses. Thankfully, Rachana was able to come up with a robust technique to estimate mating rates using an island population of brown anoles in Florida: fluorescent powders!

To understand how size affects mating rate in the brown anole, Rachana and colleagues caught 153 adult male lizards in May and 128 adult male lizards in July, weighed them, and then assigned them to one of four fluorescent powder treatments. Each mass quartile was painted with a unique color of fluorescent powder on their cloaca and released to their initial capture location. After two days, all females on the island were captured and their cloaca were examined under UV light to look for the presence and color of fluorescent powder, which would suggest that she mated with a painted male. Using this technique, Rachana found that within two days, 24% of the captured females had mated in May and 48% had mated in July. These rates were shockingly high for such a short time frame!

A) Powdering an adult male brown anole; B) copulating brown anoles; C) powder visible on the cloaca of a female brown anole, evidence of copulation
Images from Rachana’s poster

Further, she found that both larger males and larger females mated significantly more than smaller males and females across the two sampling periods. Interestingly, 2% of females had multiple colors on their cloacas, which suggests they mated multiple times with males from different size classes in the two-day span. Because multiple matings within the same size class would be undetectable, this is likely an underestimation of multiple matings in the wild.

Next, Rachana plans to quantify male reproductive success using genetic parentage analysis to begin to tease apart how pre- and post-copulatory selection influences selection. We are all looking forward to her results next year! Meanwhile, you can take a look at her poster to find out more on her website.