Biology subjects

Gunderson, A. R.

Publications and source records attributed to Gunderson, A. R..

7 recordsLinked to original sources

bioRxiv2026

Climate variability and the paradox of plasticity

Adaptive phenotypic plasticity is expected to evolve when environmental conditions change predictably over time. This has led to the hypothesis that ectotherms in environments with low temperature seasonality, such as the tropics, should evolve lower thermophysiological plasticity than those from more seasonal environments (the Climate Variability Plasticity Hypothesis, or CVHP). Yet, empirical support for the CVHP is incredibly low, creating a need to identify other factors that can help explain how thermal plasticity evolves. Here, we use numerical models to show that the evolution of constitutive thermal tolerance breadth greatly affects the evolutionary benefits of thermal plasticity. In particular, tolerance breadth interacts with within- and between-season temperature variation in ways that can confound expectations of the CVHP, including conditions in which organisms from less seasonal environments benefit 30 most from expressing plasticity. Our findings indicate that a more holistic view of the relationship between thermophysiology and environmental temperature is needed to explain the evolution of thermal plasticity across climatic gradients.

evolutionary biology↗

bioRxiv2026

No adaptive plasticity in the heat tolerance of lizard sperm

O_LIAdaptive phenotypic plasticity can help organisms cope with global warming by increasing their heat tolerance, yet most research has focused on whole-organism traits. Much less is known about thermal plasticity at the gamete level despite increasing evidence that reproduction, and particularly sperm function, is especially sensitive to heat. C_LIO_LIWe tested for plasticity in sperm heat tolerance in two ways: via male thermal acclimation (pre-ejaculate stage) and via sperm cell heat hardening (post-ejaculate stage) in brown anole lizards (Anolis sagrei). We also measured plasticity in several other sperm and ejaculate traits in response to male thermal acclimation. C_LIO_LITo test for effects of male thermal acclimation, adult males were exposed to one of two ecologically realistic, fluctuating temperature regimes that either mimic cool spring conditions or projected future summer conditions for eight weeks. Throughout this period, we repeatedly measured sperm heat tolerance (LT50), baseline motility, and sperm count. We also measured sperm morphology at the end of thermal acclimation. We predicted that males in the warmer treatment would produce more heat tolerant sperm. C_LIO_LITo test for post-ejaculate heat hardening, we compared the heat tolerance of ejaculated sperm that either did or did not experience a high but non-lethal temperature prior to heat tolerance measurement. C_LIO_LIWe found no plasticity in sperm heat tolerance due to either male thermal acclimation or sperm cell heat shock. Long-term thermal acclimation of males did not increase sperm heat tolerance, nor change motility, sperm count, or sperm morphology. We also found no evidence for post-ejaculate heat hardening, as exposing sperm cells to mild sublethal heat shock did not enhance sperm heat tolerance. C_LIO_LIOur results indicate that gametic traits have limited capacity for plastic adjustment to thermal stress, which is broadly consistent with the low levels of thermal plasticity found for whole-organism thermal tolerance across ectotherms. This highlights the vulnerability of reproductive traits to rising temperatures and the importance of evolutionary and behavioral responses to buffer organisms from climate change. C_LI

ecology↗

bioRxiv2024

Extreme lead tolerance in an urban lizard

Lead (Pb) is an extremely toxic heavy metal pollutant pervasive in many environments with serious health consequences for humans and wildlife. We found that Cuban brown anole lizards (Anolis sagrei) in New Orleans, USA, have the highest mean (955{+/-}877 {micro}g/dL; N = 40) and individual (3,192 {micro}g/dL) blood lead levels of any free-living vertebrate reported to date. Unexpectedly, this extreme field lead exposure did not decrease performance in whole-organism traits commonly affected by lead (balance, sprint speed, endurance). To identify toxicity thresholds, we employed a 60-day lead-dosing experiment and found that the brown anole blood lead threshold for decreased whole-organism performance is over an order of magnitude higher than the already extreme mean field concentration (10,600 {micro}g/dL). Transcriptomic analysis of brain and liver from lizards in high and low lead sites revealed minor effects of lead exposure. However, several of the differentially expressed genes function in metal ion homeostasis and oxygen carrying capacity, pointing to cellular mechanisms that may contribute to high lead tolerance in these animals. The brown anole may be the most lead-tolerant vertebrate known to date and has the potential to serve as a powerful model system to help us understand mechanisms of lead tolerance.

ecology↗

bioRxiv2024

The heat sensitivity of sperm in the lizard Anolis sagrei

The heat sensitivity of reproduction is a critical determinant of population persistence under climate change. However, the heat sensitivity of gametes is poorly known relative to adults. We developed a method to measure the heat tolerance of lizard sperm cells, and used the method to test several aspects of sperm cell thermal biology in the brown anole lizard (Anolis sagrei). We estimated the repeatability of sperm traits by measuring heat tolerance and baseline motility of ejaculated sperm from the same individuals multiple times over 21 days. To investigate co-adaptation of sperm and adult thermal traits, we tested for a correlation between sperm heat tolerance and the heat tolerance of adults that produced them. Furthermore, we tested for effects of episodic heat stress experienced by males on sperm performance. Sperm heat tolerance and motility were both repeatable, consistent with evolutionary potential, though there was clear evidence for environmental effects on these traits as well. Contrary to the expectation of thermal co-adaptation, we found no correlation between sperm and adult heat tolerance. A single, episodic extreme heat event experienced by adult males immediately impaired sperm motility, consistent with detrimental effects of adult heat stress on stored sperm. Our study adds to the mounting evidence that sperm are heat-sensitive and represent a vulnerability to global warming, but also suggest evolutionary potential for thermal adaptation at the gamete level. Summary statementThis study investigates gamete heat sensitivity in lizards, revealing heat tolerance and repeatability in sperm thermal traits. These findings are essential for understanding reproductive responses to climate change.

zoology↗

bioRxiv2022

Trade-offs between baseline thermal tolerance and thermal tolerance plasticity are much less common than it appears

Thermal tolerance plasticity is a core mechanism by which organisms can mitigate the effects of climate change. As a result, there is a need to understand how variation in tolerance plasticity arises. The Baseline Tolerance/Plasticity Trade-off Hypothesis (hereafter referred to as the Trade-off Hypothesis, TOH) has recently emerged as a potentially powerful explanation. The TOH posits that organisms with high baseline thermal tolerance have reduced thermal tolerance plasticity relative to those with low baseline tolerance. Many studies have found support for the TOH. However, this support must be regarded cautiously because the most common means of testing the TOH can yield spurious trade-offs due to regression to the mean. I acquired data for 25 previously-published analyses that supported the TOH at the intraspecific level and reanalyzed them after applying a method that adjusts plasticity estimates for regression to the mean. Only six of the 25 analyses remained statistically significant after adjustment, and effect size and variance explained decreased in all cases. The few data sets in which support for the TOH was maintained after adjustment point to areas of future study, but are too few to make generalizations at this point. In sum, regression to the mean has led to a substantial overestimation of support for the TOH and must be accounted for in future tests of the hypothesis.

physiology↗

bioRxiv2022

Humanization of wildlife gut microbiota in urban environments

Urbanization is rapidly altering Earths environments, demanding investigations of the impacts on resident wildlife. Here, we show that urban populations of coyotes (Canis latrans) and crested anole lizards (Anolis cristatellus) acquire gut microbiota constituents found in humans, including the gut bacterial lineages most significantly associated with urbanization in humans (e.g., Bacteroides). Comparisons of urban and rural wildlife and human populations revealed significant convergence of the gut microbiota among urban host populations. Remarkably, all microbial lineages found in humans that were overrepresented in urban wildlife relative to rural wildlife were also overrepresented in urban humans relative to rural humans. These results indicate parallel effects of urbanization on human and wildlife gut microbiota and suggest spillover of bacteria from humans into wildlife in cities.

ecology↗

bioRxiv2021

Testing for genetic assimilation with phylogenetic comparative analysis: Conceptual, methodological, and statistical considerations

Genetic assimilation is a process that leads to reduced phenotypic plasticity during adaptation to novel conditions, a potentially important phenomenon under global environmental change. Null expectations when testing for genetic assimilation, however, are not always clear. For instance, the statistical artifact of regression to the mean could bias us towards detecting genetic assimilation when it has not occurred. Likewise, the specific mechanism underlying plasticity expression may affect null expectations under neutral evolution. We used macroevolutionary numerical simulations to examine both of these important issues and their interaction, varying whether or not plasticity evolves, the evolutionary mechanism, trait measurement error, and experimental design. We also modified an existing reaction norm correction method to account for phylogenetic non-independence. We found: 1) regression to the mean is pervasive and can generate spurious support for genetic assimilation; 2) experimental design and post-hoc correction can minimize this spurious effect; and 3) neutral evolution can produce patterns consistent with genetic assimilation without constraint or selection, depending on the mechanism of plasticity expression. Additionally, we re-analyzed published macroevolutionary data supporting genetic assimilation, and found that support was lost after proper correction. Considerable caution is thus required whenever investigating genetic assimilation and reaction norm evolution at macroevolutionary scales.

evolutionary biology↗