Department of Biological Sciences, California Polytechnic State University, San Luis Obispo, California, USA,
School of Medicine, University of California Davis Medical Center, Sacramento, California, USA,
Brain Behav Evol. 2023;98(3):160-170. doi: 10.1159/000529692. Epub 2023 Feb 16.
The hippocampus plays an important role in spatial navigation and spatial learning across a variety of vertebrate species. Sex and seasonal differences in space use and behavior are known to affect hippocampal volume. Similarly, territoriality and differences in home range size are known to affect the volume of the reptile hippocampal homologues, the medial and dorsal cortices (MC, DC). However, studies have almost exclusively investigated males and little is known about sex or seasonal differences in MC and/or DC volumes in lizards. Here, we are the first to simultaneously examine sex and seasonal differences in MC and DC volumes in a wild lizard population. In Sceloporus occidentalis, males display territorial behaviors that are more pronounced during the breeding season. Given this sex difference in behavioral ecology, we expected males to have larger MC and/or DC volumes than females and for this difference to be most pronounced during the breeding season when territorial behavior is increased. Male and female S. occidentalis were captured from the wild during the breeding season and the post-breeding season and were sacrificed within 2 days of capture. Brains were collected and processed for histology. Cresyl-violet-stained sections were used to quantify brain region volumes. In these lizards, breeding females had larger DC volumes than breeding males and nonbreeding females. There was no sex or seasonal difference in MC volumes. Differences in spatial navigation in these lizards may involve aspects of spatial memory related to breeding other than territoriality that affect plasticity of the DC. This study highlights the importance of investigating sex differences and including females in studies of spatial ecology and neuroplasticity.
海马体在多种脊椎动物物种的空间导航和空间学习中起着重要作用。已知性别和季节性差异会影响空间利用和行为，从而影响海马体体积。同样，领地性和巢穴范围大小的差异已知会影响爬行动物海马体同源物，即内侧和背侧皮质（MC、DC）的体积。然而，这些研究几乎专门调查了雄性，而对蜥蜴中 MC 和/或 DC 体积的性别和季节性差异知之甚少。在这里，我们首次同时研究了野生蜥蜴种群中 MC 和 DC 体积的性别和季节性差异。在西部箱龟中，雄性表现出更明显的领地行为，这种行为在繁殖季节更为明显。鉴于行为生态学中的这种性别差异，我们预计雄性的 MC 和/或 DC 体积会大于雌性，并且这种差异在繁殖季节最为明显，因为此时领地行为会增加。雄性和雌性的西部箱龟在繁殖季节和繁殖后季节从野外捕获，并在捕获后 2 天内被处死。收集大脑并进行组织学处理。用 Cresyl-violet 染色的切片用于量化脑区体积。在这些蜥蜴中，繁殖期雌性的 DC 体积大于繁殖期雄性和非繁殖期雌性。MC 体积没有性别或季节性差异。这些蜥蜴的空间导航差异可能涉及与繁殖有关的空间记忆方面，而不是与领地性有关的方面，这会影响 DC 的可塑性。这项研究强调了研究性别差异和包括雌性在内的空间生态学和神经可塑性研究的重要性。
