Neuroendocrine correlates of juvenile amphibian behaviors across a latitudinal cline

We assessed the macrogeographic and neuroendocrine correlates of behavioral variation exhibited by juveniles, an important life stage for dispersal, across the expansive range of the wood frog. By rearing animals from eggs in a common garden then using a novel environment test, we uniquely demonstrated differential expression of juvenile behaviors among 16 populations spanning 8° latitude. On the individual level, cluster analysis indicated three major behavior profiles and principal component analysis resolved four unique axes of behavior, including escape, foraging, food intake, feeding efficiency. We found that increased escape behavior was associated with blunted adrenocorticotropic hormone (ACTH)-induced circulating corticosterone (CORT), however, foraging and food intake behaviors were not associated with either resting or ACTH-induced CORT. At the population level, the expression of foraging behaviors increased with latitude while food intake behaviors declined with latitude, which raised several hypotheses of eco-evolutionary processes likely driving this variation. Given that these behaviors covary along the same ecological gradient as locally adapted developmental traits, genomic studies in this species could provide deep insights into how HPA/I activity is associated with the eco-evolutionary processes that structure intraspecific variation in morphology and behavior.本研究针对林蛙（wood frog）广泛分布区内的幼体——这是扩散过程的关键生命阶段——所展现的行为变异，探究其大地理尺度关联与神经内分泌调控基础。我们通过将蛙卵孵化后开展同质园（common garden）饲养，并结合新环境测试实验，前所未有地在跨越8个纬度的16个林蛙种群中证实了幼体行为表现存在显著分化。在个体层面，聚类分析（cluster analysis）显示出三类主要行为表型；主成分分析（principal component analysis）则解析出四类独立的行为维度，涵盖逃避行为、觅食行为、摄食量与摄食效率。研究发现，逃避行为的增强与促肾上腺皮质激素（adrenocorticotropic hormone, ACTH）诱导的循环皮质酮（corticosterone, CORT）的钝化反应相关；但觅食行为与摄食量均未与基础皮质酮水平或ACTH诱导的皮质酮水平存在关联。在种群层面，觅食行为的表达随纬度升高而增强，而摄食量则随纬度升高呈下降趋势，这一结果引出了若干关于驱动该行为变异的生态进化过程的假说。鉴于这些行为与本地适应的发育性状沿相同生态梯度协同变异，对该物种开展基因组学研究，可深入解析下丘脑-垂体-肾上腺/肾间组织（HPA/I）轴的活性，如何与塑造种内形态与行为变异的生态进化过程相关联。