<b>Experimental drought suppresses amphibian pathogen yet intensifies transmission and disrupts protective skin microbiome</b>

Shifting precipitation regimes driven by global climate change can alter vertebrate behavior and host-symbiont relationships, potentially compromising host resistance to pathogen invasion. In Brazil's Atlantic Forest, a biodiversity hotspot, prior research identified drought as a key factor disrupting the skin microbiome, contributing to a die-off of pumpkin toadlets due to the invasive waterborne fungal pathogen Batrachochytrium dendrobatidis (Bd). However, observational studies cannot distinguish the direct effect of moisture on Bd growth from increased amphibian activity during wet breeding seasons. Using field enclosures, we experimentally tested the influence of drought conditions on host microhabitat use, Bd disease dynamics, and the composition and predicted Bd-inhibitory function of cutaneous bacterial communities. Each tent housed ecologically realistic densities of Brachycephalus pitanga, a micro-endemic pumpkin toadlet. We simulated a short-term drought in half of the enclosures using translucent tarp coverings. To track individual toadlets, we identified their unique markings and collected skin swabs biweekly over three months. We then implemented molecular techniques to quantify Bd loads and characterize skin bacterial diversity and composition over time. Our findings indicate that while drought may reduce overall Bd loads on hosts, this effect is partially offset by an increase in the use of water-filled areas of the enclosures and by a disruption of the protective host skin microbiome. This study provides valuable insights into the cascading impacts of climate change on animal behavior, host-symbiont interactions, and disease dynamics.全球气候变化驱动的降水格局变化，可改变脊椎动物的行为模式及其与共生体的互作关系，进而可能削弱宿主对病原体入侵的抵抗能力。在作为全球生物多样性热点区域的巴西大西洋森林中，既往研究已证实干旱是破坏皮肤微生物组的关键诱因，其通过入侵性水生真菌病原体蛙壶菌（Batrachochytrium dendrobatidis, Bd）导致南瓜蟾蜍种群大规模死亡。然而，现有观测研究无法厘清潮湿繁殖季两栖动物活动增强，与湿度对Bd生长的直接作用之间的因果关联。本研究借助野外围栏实验，探究了干旱条件对宿主微生境选择、Bd病害动态，以及皮肤细菌群落组成与潜在抗Bd功能的影响。每个实验围栏均按照生态合理密度放养了皮坦加短头蟾（Brachycephalus pitanga）——一种狭域特有的南瓜蟾蜍物种。研究团队通过半透性防水布覆盖半数实验围栏，模拟短期干旱环境。为追踪每只蟾蜍个体，研究人员通过其独特的体表斑纹进行识别，并在为期三个月的实验周期内每两周采集一次皮肤拭子样本。随后通过分子实验技术定量检测Bd负载量，并动态刻画皮肤细菌的多样性与群落组成特征。研究结果显示，尽管干旱可降低宿主体表的整体Bd负载量，但该效应会被两方面因素部分抵消：一是蟾蜍对围栏内积水区域的利用频次显著提升，二是宿主保护性皮肤微生物组的结构遭到破坏。本研究为理解气候变化对动物行为、宿主-共生体互作以及病害动态的级联效应提供了重要的科学参考。