Constraints on the adaptive potential of ectotherms to climate change

Anthropogenic climate change is rapidly altering global thermal regimes. While these shifts threaten all biodiversity, ectothermic organisms are particularly at risk because their physiological functions rely heavily on temperature. While rapid evolutionary adaptation has been proposed as a potential pathway to survival, the adaptive potential of ectotherms may be inherently limited by evolutionary constraints. In this dissertation, I combine theoretical and empirical approaches to investigate how these constraints may influence the adaptive capacity of ectotherms to climate change across three critical axes: performance, metabolism, and reproduction. In Chapter 1, I employ individual-based simulations to evaluate how genetic correlations that underlie thermal performance curves (TPCs) affect population persistence in warming climates. I find that, while some genetic correlations constrain adaptation, others, particularly the thermodynamic effect, can actively facilitate it by promoting trait variation that yields phenotypes pre-adapted to warming. Consequently, forecasting ectotherm extinction risk without accounting for these genetic architectures risks generating fundamentally flawed predictions. In Chapter 2, I investigate the “cost-of-living squeeze” (COLS) in wild western fence lizards (Sceloporus occidentalis) along an elevational gradient. Integrating mark-recapture surveys, laboratory metabolic measurements, and biophysical simulations, I find that COLS acts as a potent selective agent, particularly in warmer, low-elevation environments. Selection favors individuals with highly sensitive metabolic reaction norms but low metabolic baselines, a strategy that minimizes resting energetic costs while in thermal refugia. Lastly, in Chapter 3, I develop and validate a process-based optimality model formalizing the century-old “cold-climate hypothesis” regarding the evolution of lizard viviparity. This model mechanistically demonstrates that fine-scale thermal environments, interacting with life-history trade-offs, drive the evolution of gestation length to navigate the impossibility of maximizing fitness across all life stages simultaneously. Ultimately, this dissertation demonstrates that evolutionary constraints significantly dictate whether ectotherms can adapt to warming environments. Advancing accurate vulnerability forecasting will require characterizing specific trait correlations, understanding the evolutionary potential of phenotypic plasticity, and utilizing rigorous biophysical modeling of microhabitats rather than broad macroclimatic approximations. By integrating constraints on performance, metabolism, and reproduction, this work provides a mechanistically grounded framework for predicting ectotherm survival in a changing world.

Level thesis:degree_level

Doctorate Degree

Year dc:date.issued

2026

Author dc:creator

• Garcia Costoya, Guillermo

Advisor dc:contributor.advisor

• Logan, Michael L

Committee members dc:contributor.committeemember

• Forister, Matthew L
• Riddell, Eric A
• Riddle, Misty R
• Williams, Perry J

• Climate change
• Cost-of-living Squeeze
• Ectotherms
• Evolutionary constraints
• Thermal Performance Curves
• Viviparity

Language dc:language.iso

en_US, English

Repository record dc:identifier.uri

https://scholarwolf.unr.edu/handle/11714/11846

OAI identifier oai:identifier

oai:scholarwolf.unr.edu:11714/11846