Author: Hanna Wegener

The gold dust day gecko was introduced to Hawaii in the 1980s. It is ecologically similar to the green anole, which was introduced to Hawaii in the 1950s.

Hawaii has no native herpetofauna, aside from sea turtles. Human-mediated introductions between the 1950s and 1980s have created an interesting new guild of arboreal and diurnal lizards: the green anole (Anoles carolinensis), the gold dust day gecko (Phelsuma laticauda) and the brown anole (A. sagrei ).

Amber Wright next to her poster on Saturday

Phelsuma laticauda belongs to a genus that is endemic to Madagascar with almost 50 species, that are known for their incredible color patterns. Anolis carolinensis and P. laticauda are thought to be ecologically similar and thus potential competitors.

Amber Wright’s research investigates whether and how the three species partition their habitat when they occur in sympatry and how that might affect species abundance. Using field observations and morphological data, she found that the three species overlap in body size and habitat use, which suggests that they are potential competitors for food resources and perch sites.

Enclosure experiment.

Preliminary data show that abundance decreases when ecologically similar species are present.

In a pilot study, Amber used seven 10x10m plots to simulate different community scenarios: only one species, two species and all three species. Anolis carolinensis and A. sagrei seem to be interacting similarly to populations outside of Hawaii: coexistence with reduced densities and increased perch heights of A. carolinensis. When all three species were present, P. laticauda perched higher than usual, presumably to avoid competition with A. carolinensis. Future work will focus on long term effects of species composition on resource partitioning and abundance of each species.

Previous research in the Warner lab has shown that temperature during egg development influences fitness and performance in Anolis sagrei. In particular, a warmer incubation temperature increases sprint speed. The breeding season of A. sagrei spans from March through October, with lower temperatures early in the season and higher temperatures late in the season. Phil Pearson, a masters student in the Warner Lab, conducted an experiment to test whether embryos are developmentally adapted to their incubation temperature. He collected eggs from two temporally-separated cohorts and incubated them under two different temperatures, simulating seasonal temperature differences. He found that late season hatchlings had higher egg survival when incubated under late season temperature. Regardless of incubation temperature, late season embryos had higher sprint speed, larger body size and longer tails. This might compensate for the late start, since they are competing with early cohort individuals in the population.

Late season hatchlings have higher sprint speed regardless of incubation temperature

Overall, this suggests that timing of oviposition has greater effect on morphology and performance than incubation temperature. Future analysis will show whether timing of oviposition affects survival. Phil released the hatchlings on small islands to measure fitness using a mark-recapture approach and will hopefully present his findings at future meetings.

Color variation of Anolis conspersus on Grand Cayman. Spotted individuals (left) are found in the west of the island and vermiculated ones (right) are found in the east.

Christopher Peterson, a masters student in the Fitzpatrick Lab at the University of Tennessee, studies color variation of Anolis conspersus on Grand Cayman. He found that lizards from eastern Grand Cayman are vermiculated and individuals from the west side are spotted. He hypothesized that color variation along the east-west axis might be due to climatic variation, habitat differences or population structure. He sampled multiple sites across the island and measured air temperature, relative humidity, degree of leaf coverage (shade), perch roughness and perch connectivity. Using a hierarchical Bayesian logistic regression, Christopher did not find correlations between body coloration and climatic variation or habitat differences. He found, however, that spotted individuals have significantly longer tails and vermiculated ones are larger (SVL) on average. Genome wide SNPs will reveal whether population structure can explain variation in coloration between eastern and western populations.

Andrew Battles from the Kolbe Lab gave a talk at JMIH presenting data on performance-habitat relationships comparing lizard performance on rough and smooth surfaces. The data were collected on Guana Island in the British Virgin Islands using Anolis cristatellus and A. stratulus as study species. Andrew and his advisor, Jason Kolbe, were interested in whether lizards perform differently on artificial and natural surfaces.

Major differences between natural and artificial habitats

They used three different running tracks (37°-incline rough track,  90°-incline rough track, 90°-incline smooth track), assuming that artificial surfaces are smoother than natural ones. The rough tracks consisted of a board covered in window screen and the smooth track was a plain 2-by-4 board. They used a high-speed camera to measure maximum velocity, how often a lizard paused during the run and how often it slipped. While both species ran significantly slower, paused and slipped more often on the smooth surface, A. cristatellus performed even worse than A. stratulus. Andrew and Jason then conduced a field survey to test whether lizards in a human-modified habitat use both artificial and natural perches. In addition, they rated roughness of natural and artificial perches. When both types of perches were available, lizards used artificial perches more often than natural ones.

In human-modified habitats, lizards were found mostly on artificial perches

This is surprising, because artificial perches are significantly smoother than natural ones and lizards perform worse on smooth surfaces. Possible explanations are that other factors such as food availability and/ or predation may drive habitat selection on artificial substrates.

Anolis cybotes sitting on a rock. Image from Discover Life.

Martha Muñoz presented data on how shifts in behavior constrain evolution of thermophysiology and drive morphological differentiation in the Anolis cybotes complex. The A. cybotes complex occurs across a large altitudinal range on the Caribbean island of Hispaniola and Martha was interested in whether and how lizards are adapted to thermal differences at different elevations. Martha tested whether body temperatures differ between lizards found in the different thermal habitats. Sampling more than 400 individuals, Martha did not find differences in body temperature between the populations. This is surprising because ambient temperature differed by more than 10 degrees Celsius between the low and high elevation localities.

So, if temperatures differ so dramatically among the different altitudinal habitats, how do lizards maintain similar body temperatures? Habitat use data from the two populations show that the high elevation lizards use rocky substrates more often than low elevation lizards, which are mostly found on tree trunks and other types of vegetation. Data obtained by using copper models that measure temperature as a lizard would experience it in a given habitat show that rock habitats are too hot at lower altitudes, but ideal at higher ones. This suggests that lizards keep their body temperatures stable by shifting from arboreal habitat type to rocks in higher elevations.

Martha then asked whether similarity in body temperature was matched with similarity in underlying thermal physiology. In ectotherms such as lizards, the ability to perform a task is dependent on temperature such that is optimized over a narrow range and then drops at lower and higher temperatures until the animal is immobilized. She found that lizards from all populations have similar preferred temperatures, and so their underlying physiologies do not appear to be evolving.

While thermoregulation keeps thermal physiology stable, the shift in structural habitat affects morphology. Martha measured morphological characters such as head shape, limb proportions, and lamella number to test whether habitat use has driven morphological change. Martha found that lizards in high elevations have wider and flatter heads and shorter limbs than populations in lower habitats. Thus, she found that a thermoregulatory behavior impedes physiological evolution while simultaneously driving morphological evolution.