Leary Christopher J, Ralicki Hannah F, Laurencio David, Crocker-Buta Sarah, Malone John H
University of Mississippi, Department of Biology, University, Mississippi, United States of America.
University of Connecticut, Department of Ecology & Evolutionary Biology, Storrs, Connecticut, United States of America.
PLoS One. 2018 Jan 11;13(1):e0191183. doi: 10.1371/journal.pone.0191183. eCollection 2018.
Amphibians inhabiting montane riparian zones in the Neotropics are particularly vulnerable to decline, but the reasons are poorly understood. Because environmental contaminants, endocrine disruption, and pathogens often figure prominently in amphibian declines it is imperative that we understand how these factors are potentially interrelated to affect montane populations. One possibility is that increased precipitation associated with global warming promotes the deposition of contaminants in montane regions. Increased exposure to contaminants, in turn, potentially elicits chronic elevations in circulating stress hormones that could contribute to montane population declines by compromising resistance to pathogens and/or production of sex steroids regulating reproduction. Here, we test this hypothesis by examining contaminant levels, stress and sex steroid levels, and nematode abundances in male drab treefrogs, Smilisca sordida, from lowland and montane populations in Costa Rica. We found no evidence that montane populations were more likely to possess contaminants (i.e., organochlorine, organophosphate and carbamate pesticides or benzidine and chlorophenoxy herbicides) than lowland populations. We also found no evidence of elevational differences in circulating levels of the stress hormone corticosterone, estradiol or progesterone. However, montane populations possessed lower androgen levels, hosted more nematode species, and had higher nematode abundances than lowland populations. Although these results suggested that nematodes contributed to lower androgens in montane populations, we were unable to detect a significant inverse relationship between nematode abundance and androgen level. Our results suggest that montane populations of this species are not at greater risk of exposure to contaminants or chronic stress, but implicate nematodes and compromised sex steroid levels as potential threats to montane populations.
栖息在新热带地区山地河岸带的两栖动物尤其容易数量减少，但其原因却鲜为人知。由于环境污染物、内分泌干扰和病原体在两栖动物数量减少中常常起着重要作用，因此我们必须了解这些因素如何相互关联从而影响山地种群。一种可能性是，与全球变暖相关的降水增加促进了污染物在山地地区的沉积。反过来，污染物暴露增加可能会导致循环应激激素长期升高，这可能会通过削弱对病原体的抵抗力和/或调节繁殖的性类固醇的产生，导致山地种群数量下降。在这里，我们通过检测来自哥斯达黎加低地和山地种群的雄性灰树蛙（Smilisca sordida）体内的污染物水平、应激和性类固醇水平以及线虫丰度来验证这一假设。我们没有发现证据表明山地种群比低地种群更易受污染物影响（即有机氯、有机磷和氨基甲酸酯类农药或联苯胺和氯苯氧基除草剂）。我们也没有发现应激激素皮质酮、雌二醇或孕酮的循环水平存在海拔差异的证据。然而，山地种群的雄激素水平较低，寄生的线虫种类更多，线虫丰度也比低地种群更高。尽管这些结果表明线虫导致了山地种群雄激素水平降低，但我们未能检测到线虫丰度与雄激素水平之间存在显著的负相关关系。我们的研究结果表明，该物种的山地种群接触污染物或遭受慢性应激的风险并不更高，但表明线虫和性类固醇水平受损是山地种群的潜在威胁。
