Spread of amphibian chytrid fungus across lowland populations of Túngara frogs in Panamá

Chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is an emergent infectious disease partially responsible for worldwide amphibian population declines. The spread of Bd along highland habitats ( > 500 m a.s.l.) of Costa Rica and Panamá is well documented and has been linked to amphibian population collapses. In contrast, data are scarce on the prevalence and dispersal of Bd in lowland habitats where amphibians may be infected but asymptomatic. Here we describe the spread (2009 to 2014) of Bd across lowland habitats east of the Panamá Canal (< 500 m a.s.l.) with a focus on the túngara frog (Physalaemus [Engystomops] pustulosus), one of the most common and abundant frog species in this region. Highland populations in western Panamá were already infected with Bd at the start of the study, which was congruent with previous studies indicating that Bd is enzootic in this region. In central Panamá, we collected the first positive samples in 2010, and by 2014 we detected Bd from remote sites in eastern Panamá (Darién National Park). We discuss the importance of studying Bd in lowland species, which may serve as potential reservoirs and dispersers of Bd to highland species that are more susceptible to chytridiomycosis.

由真菌病原体蛙壶菌（Batrachochytrium dendrobatidis，简称Bd）引发的壶菌病（Chytridiomycosis）是一种新发传染病，亦是全球两栖动物种群衰退的部分诱因。Bd在哥斯达黎加与巴拿马的高地生境（海拔高于500米，above sea level，缩写a.s.l.）中的传播已有充分文献记载，且与两栖动物种群崩溃紧密关联。与之形成鲜明对比的是，目前关于低地生境中Bd的流行率与传播扩散的研究数据较为匮乏——在这类生境中，两栖动物可能已感染Bd但无明显临床症状。本研究记录了2009年至2014年间，Bd在巴拿马运河以东海拔低于500米（a.s.l.）的低地生境中的传播动态，研究重点为泡蟾（túngara frog，*Physalaemus [Engystomops] pustulosus*）——该区域最常见且种群规模最为繁盛的蛙类物种之一。研究启动之初，巴拿马西部的高地种群已感染Bd，这与此前研究得出的“Bd在该区域呈地方性动物流行”的结论高度吻合。在巴拿马中部区域，研究团队于2010年采集到首批Bd阳性样本；至2014年，我们在巴拿马东部的偏远样地（达连国家公园）中也检测到了Bd。本研究最后探讨了在低地蛙类物种中开展Bd研究的重要意义：这类物种可能充当Bd的潜在储存宿主与传播媒介，将病原体扩散至对壶菌病更为易感的高地两栖动物种群中。