Author: Brooke Bodensteiner Page 1 of 2

Measuring Anolis thermal tolerances has been a hallmark of many studies since the heydays of thermal physiological studies in the mid-to-late 1900’s. However, studies examining the factors affecting thermal tolerances of embryos are still relatively sparse. In the symposium “Beyond CTmax and CTmin: Advances in Studying the Thermal Limits of Reptiles and Amphibians” at the ninth World Congress of Herpetology, Joshua Hall – PhD candidate in the Warner lab at Auburn University – explored critical thermal maximum temperatures in Anolis sagrei during development. He sought to determine (1) How we should measure embryonic CTmax? (2) What is the ecological relevance of embryonic CTmax? And (3) Are there differences between acute and chronic CTmax?

Previous work from Pruett and Warner, determined that constant incubation temperatures resulted in a chronic CTmax of 35°C for A. sagrei. Meanwhile, Joshua tested three methodologies of creating an acute CTmax during incubation including: heat shock, thermal ramp, and thermal fluctuations. All three methodologies showed an acute CTmax of ~45/46°C; there was consistency across methodologies as well as an extremely large difference found between chronic and acute CTmax. Additionally, Josh examined what data were available via the Reptile Developmental Data Base to examine chronic CTmax in nine other squamate species (ranging from 28-36°C). Of those nine species from previously collected data, four had measures of acute CTmax, and in all four cases the acute CTmax was higher than the chronic CTmax. Lastly, Josh recommends that researchers use the terminology acute and chronic when describing CTmax and that more work should be done to better determine the relationships between chronic and acute CTmax in an ecological context. Super cool work, looking into the future of thermal physiological work!

Ectotherms are well known for having an inordinate fraction of their biology linked to thermal conditions. Many of their demographic vital rates and life-history traits are influenced by temperature-dependent physiological processes. This connection between temperature and physiology is particularly apparent during embryonic development, especially in oviparous species lacking parental care after eggs are laid. Jenna Pruett, a PhD candidate in the Warner lab at the University of Auburn, investigated the effect of constant egg incubation temperatures across life stages in the brown anole. Many studies of this nature lack enough temperature treatments to fully characterize the thermal reaction norm and frequently do not follow the offspring past hatching. Jenna sought to fill these knowledge gaps by answering the questions:  1) How does constant incubation temperature affect embryonic development? 2) Do these effects vary across a small geographic scale? and 3) Do effects carry over into later life stages?

To do this Jenna incubated ~350 brown anole (Anolis sagrei) eggs from different locations across eight different constant incubation temperatures. When examining hatching success, temperature seemed to be the only driver of success. Meanwhile, hatchling mass had a significant interaction between temperature and location potentially indicating that lizards at specific locations respond differently to different thermal regimes during development. Overall, she found that geographic variation doesn’t impact hatching success but changes how phenotypes respond to temperature.

The second part of the experiment involved a large release and recapture experiment on experimental spoil islands off the coast of Florida. Hatchlings were released early and late in the summer and then were recaptured the following fall and spring to determine survival to recapture. Jenna found that survival to recapture was influenced by incubation temperature, release date, and an interaction between the two, showing that timing is everything and that in this case the optimal temperature for the greatest survival varied across life stages.

Shelby Irwin, a junior in Michele Johnson’s lab at Trinity University, presented a poster on her summer research in Thomas Sanger’s lab at Loyola University examining hatchling behavior in Anolis sagrei after incubation in thermally stressful conditions. In the lab, Irwin and colleagues incubated A. sagrei eggs under a standard (27°C) and elevated (34°C) thermal regimes to investigate impacts on hatchling phenotype and behavior.

It has been previously noted that thermal stress during development can affect craniofacial development, but Shelby was interested in if there was also an impact on behavior of hatchlings. After hatching, lizards from both the standard and elevated thermal regimes were run through a gambit of exploratory (prey interactions, novel object, and open-field test) and social trials (conspecific and predator interactions). They found that “hot” hatchlings were less aggressive and exhibited less exploratory behaviors. Their findings add to the growing body of research investigating the impacts of a warming world, particularly with regards to sensitive periods in thermally sensitive species.

Anolis shrevei. Photograph by Miguel Landestoy.

Post-doc Vincent Farallo presented work, co-authored by Martha Muñoz, in the behavioral physiology session on the importance of incorporating physiology and behavior when assessing how species, especially montane endemics, will be impacted by climate change. Vincent and Martha compared correlative models and mechanistic niche models to better understand how climate change may impact three anoles from the island of Hispaniola, Anolis shrevei, A. armouri, and A. cybotes. When predicting future ranges of these species using correlative modeling, Farallo and Muñoz saw that the ranges of the mountain-top endemics A. shrevei and A. armouri shrink, whereas the range of the widespread species A. cybotes remains the same under future climate change predictions. Comparing these findings to mechanistic niche modeling, which uses organismal physiology and behavior to help predict future activity times within current ranges, they found that all three species will increase activity times within the mountain-top endemic ranges.

To reiterate their findings, they showed that when incorporating behavior and physiology, montane endemic species will increase potential activity time under climate change.  However, their widespread competitor will also see increased activity, indicating the montane endemics are still likely at risk, but not directly from warming temperatures.  Understanding the mechanism of species decline will be critical for mitigating the impacts of climate change.

Frequently phenotypic evolution is rapid on islands, resulting in many ecologically diverse species. Most of what we know about the faster evolution on islands has been through the examination of morphological diversity. By utilizing species-rich Anolis lizards, Dr. Martha Muñoz and collaborators were able to examine the island effect with regards to rates and patterns of evolution through a different lens: thermal physiological trait diversity. Muñoz et al. examined the evolutionary dynamics of cold tolerance, body temperature, and heat tolerance in island and mainland anoles. They discovered faster heat tolerance evolution in the mainland lineages, and that island and mainland anoles are evolving towards separate trait optima with island lizards having a higher upper thermal limit. A higher optima and slower evolutionary rates are consistent with the Bogert Effect, in which organisms are shielded from selection because of behavioral buffering such as thermoregulatory behavior. Cold tolerance did not differ between habitats, not surprisingly due the fact that lower physiological limits cannot be behaviorally buffered against selection. Despite island and mainland anoles occurring in similar thermal environments, island lizards thermoregulate more. Consequently, the ecological opportunity (fewer predators and/or competitors) provided on islands may be reducing the costs of thermoregulation and slowing down, rather than accelerating evolution of certain traits. This study highlights the importance of other phenotypic axes that organisms diversify along in an adaptive radiation, such as physiological diversification, and that behavior can elucidate or drive patterns shaping evolution.

Jenna in search of brown anole eggs.

Maternal nest-site choice plays an important role in determining the developmental environment of oviparous organisms, but even so, almost nothing is known about anole nest-site choice. Jenna Pruett (Ph.D. student in Dan Warner’s lab at Auburn) and company set out to examine what microhabitats female Anolis sagrei are choosing to lay their eggs in on the Warner Lab’s experimental intercoastal islands, and to experimentally manipulate eggs by altering nest microhabitat locations in the field. Jenna found 100% of eggs under some type of cover object (rocks, leaf litter, etc.)  and quantified nest habitats in comparison to what was available in the environment, finding that moms choose nest sites that were cooler and moister habitats than what was available on the island overall.

The second part of this study involved taking 400 eggs (200 placed in June and 200 placed in August) from the lab breeding colony and incubating them in the field across all island microhabitat types. The control eggs were sealed in a Petri dish to ensure a constant moisture supply throughout incubation. Survival was higher in the control eggs with constant moisture and higher in August. They found that survival probability decreased as the incubation temperature increased and that hatchling body condition improved with increased soil moisture.

To top off this very neat study, Jenna was the winner of the Division of Animal Behavior best student presentation award, the Marlene Zuk Award. Congratulations Jenna!

Dan Warner (left) and Tim Mitchell (right) beside their poster on impacts of population density and time of hatching on survival and early life phenotypes of Anolis sagrei

Tim Mitchell a post-doctoral researcher at University of Minnesota with Emilie Snell-Rood presented his work from his prerious post doc in Dan Warner’s lab where he investigated the impacts of density and timing of hatching on the survival and growth of Anolis sagrei hatchings. Seeking to specifically address these questions:

How does investment in offspring size and number shift seasonally?

Does the timing of hatching influence survival or growth in the field?

And does adult density influence survival or growth of hatchlings in the field?

Adult anoles were brought into the lab on three different dates and breeding was split into three corresponding windows of time: Cohort 1 (February 23^rd – April 27^th), Cohort 2 (June 18^th – July 30^th), and Cohort 3 (September 5^th – October 15^th).  On experimental islands, adult densities were manipulated to create high and low lizard densities. Hatchlings from cohorts 1, 2, and 3 were released onto high and low adult density islands in June, August, and October, respectively, and researchers returned the following spring to recapture the marked lizards.

Breeding in the lab revealed a seasonal shift from producing more smaller offspring early to producing fewer larger offspring later in the season. Adult densities on the islands did not affect hatchling survival, but there was a substantial survival advantage to being an early-hatched lizard. Size and growth of hatchlings were influenced both by timing of hatching and the adult densities. So happy to catch up with my academic family and see the cool research they are doing!