Higher Rate of Male Sexual Displays Correlates with Larger Ventral Posterior Amygdala Volume and Neuron Soma Volume in Wild-Caught Common Side-Blotched Lizards, <b><i>Uta stansburiana</i></b>

Abstract

Several areas of the vertebrate brain are involved in facilitating and inhibiting the production of sexual behaviors and displays. In the laboratory, a higher rate of sexual displays is correlated with a larger ventral posterior amygdala (VPA), an area of the brain involved in the expression of sexual display behaviors, as well as larger VPA neuronal somas. However, it remains unclear if individuals in the field reflect similar patterns, as there are likely many more selective pressures in the field that may also modulate the VPA architecture. In this study, we examined variation in VPA volume and neuron soma volume in wild-caught common side-blotched lizards (Uta stansburiana) from two different populations. In a population from Nevada, males experience high predation pressure and have decreased sexual display rates during the breeding season, whereas a population in Oregon has lower levels of predation and higher rates of male sexual displays. We found that wild-caught males from the population with lower display rates also exhibited decreased VPA volume and VPA neuron cell soma volume, which may suggest that decreased display rate, possibly due to increased predation rate, covaries with VPA attributes.

The effects of early-life and intergenerational stress on the brain

“…Previous studies found variation in avian hippocampal volume with concurrent changes in hippocampal neuron soma sizes [109,110]. Similarly, studies have found variation in brain region volume and neuron soma size within the region of interest in lizards [65,111], suggesting that neuron size may partially contribute to volumetric changes. However, we also measured variation in neuron soma size and found that there is not a concomitant change in neuron soma volume in the medial cortex.…”

“…We used standard, unbiased stereological techniques (Stereo-Investigator, Microbrightfield, Williston, VT; Leica M400B microscope) optimized for this species (all coefficient of errors <0.011 [62]) to estimate medial and dorsal cortical volumes and neuron soma volume in the medial cortex. We also measured telencephalon volume (minus medial and dorsal cortical volumes) to assess if population of origin and stress treatment effects were specific to the cortices or representative of global changes within the brain [63][64][65]. The left and right hemispheres of the medial cortex, dorsal cortex and the remainder of the telencephalon were contoured in their entirety at 5×.…”

Neural control of reproduction in reptiles

“…Kabelik et al (2006) found that male tree lizards ( Urosaurus ornatus ) had a significantly larger AMY than females, and males exhibited seasonal changes in AMY volume, with the AMY larger during August and September compared to other months. In another example, wild‐caught male common side‐blotched lizards ( Uta stansburiana ) with lower display rates also exhibited lower average volume and neuron soma volume in the AMY (LaDage et al, 2022). Overall, the AMY exhibits seasonal morphological changes in most reptilian species studied.…”