Egg viability and egg mass underlie immune tradeoffs and differences between urban and rural lizard egg yolk physiology.

Urbanization can cause innumerable abiotic and biotic changes that have the potential to influence the ecology, behavior, and physiology of native resident organisms. Relative to their rural conspecifics, urban Side-blotched Lizard (Uta stansburiana) populations in southern Utah have lower survival prospects and maximize reproductive investment via producing larger eggs and larger clutch sizes. While egg size is an important predictor of offspring quality, physiological factors within the egg yolk are reflective of the maternal environment and can alter offspring traits, especially during energetically costly processes, such as reproduction or immunity. Therefore, maternal effects may represent an adaptive mechanism by which urban-dwelling species can persist within a variable landscape. In this study, we assess urban and rural differences in egg yolk bacterial killing ability (BKA), corticosterone (CORT), oxidative status (d-ROMs), and energy metabolites (free glycerol and triglycerides), and their association with female immune status and egg quality. Within a laboratory setting, we immune challenged urban lizards via lipopolysaccharide injection (LPS) to test whether physiological changes associated with immune system activity impacted egg yolk investment. We found urban females had higher mite loads than rural females, however mite burden was related to yolk BKA in rural eggs, but not urban eggs. While yolk BKA differed between urban and rural sites, egg mass and egg viability (fertilized vs. unfertilized) were strong predictors of yolk physiology and may imply tradeoffs exist between maintenance and reproduction. LPS treatment caused a decrease in egg yolk d-ROMs relative to the control treatments, supporting results from previous research. Finally, urban lizards laid a higher proportion of unfertilized eggs, which differed in egg yolk BKA, CORT, and triglycerides in comparison to fertilized eggs. Because rural lizards laid only viable eggs during this study, these results suggest that reduced egg viability is a potential cost of living in an urban environment. Furthermore, these results help us better understand potential downstream impacts of urbanization on offspring survival, fitness, and overall population health.

Glucocorticoids, energy metabolites, and immunity vary across allostatic states for plateau side-blotched lizards (Uta stansburiana uniformis) residing in a heterogeneous thermal environment.

Reptiles rely on thermal heat exchange to achieve body temperatures (Tbody ) conducive to maintaining homeostasis. Diurnal changes in the thermal environment are therefore liable to influence allostatic mediation of survival processes (e.g., immunity) during environmental challenges or stressors. However, the extent to which Tbody prompts individual variation in physiology remains largely unexplored in reptiles. Our study tested how circulating energy-mobilizing hormone, energy metabolites, and immunity can vary across basal and stress-induced allostatic states for plateau side-blotched lizards (Uta stansburiana uniformis) residing in a heterogeneous thermal environment. We collected baseline and acute stress blood samples from male lizards to compare changes in plasma corticosterone (CORT), glucose, and bacterial killing ability (BKA) in relation to each other and Tbody . We hypothesized each physiological parameter differs between allostatic states, whereby stress-induced activity increases from baseline. At basal and stress-induced states, we also hypothesized circulating CORT, glucose, and BKA directly correspond with each other and Tbody . We found both CORT and BKA increased while glucose instead decreased from acute stress. At basal and stress-induced allostatic states, we found CORT to be directly related to Tbody while BKA was inversely related to CORT. We also found BKA and glucose were directly related at baseline, but inversely related following acute stress. Overall, these results demonstrate allostatic outcomes from acute stress in a free-living reptile and the role of temperature in mediating energetic state and immunity. Future research on reptilian allostasis should consider multiple environmental conditions and their implications for physiological performance and survival.