Living on the edge: parasite prevalence changes dramatically across a range edge in an invasive gecko

Species interactions can determine range limits, and parasitism is the most intimate of such interactions. Intriguingly, the very conditions on range edges likely change host-parasite dynamics in nontrivial ways. Range edges are often associated with clines in host density and with environmental transitions, both of which may affect parasite transmission. On advancing range edges, founder events and fitness/dispersal costs of parasitism may also cause parasites to be lost on range edges. Here we examine the prevalence of three species of parasite across the range edge of an invasive gecko, Hemidactylus frenatus, in northeastern Australia. The gecko’s range edge spans the urban-woodland interface at the edge of urban areas. Across this edge, gecko abundance shows a steep decline, being lower in the woodland. Two parasite species (a mite and a pentastome) are coevolved with H. frenatus, and these species become less prevalent as the geckos become less abundant. A third species of parasite...物种相互作用可决定物种分布范围的边界，而寄生作用（parasitism）是这类相互作用中最为紧密的一种。令人感兴趣的是，分布边界处的环境条件很可能以非平凡的方式改变宿主-寄生虫动态（host-parasite dynamics）。分布边界往往与宿主密度的渐变群（clines）以及环境过渡区域相关，这两类因素均可能影响寄生虫的传播。对于正在扩张的分布边界而言，奠基者效应（founder events）以及寄生作用带来的适合度/扩散成本，也可能导致寄生虫在分布边界处丢失。本研究针对澳大利亚东北部入侵壁虎（Hemidactylus frenatus）的分布边界，调查了三种寄生虫的感染率（prevalence）。该壁虎的分布边界横跨城市区域边缘的城市-林地交错带。沿该分布边界，壁虎的种群丰度呈现急剧下降趋势，林地中的种群丰度显著更低。两种寄生虫（一种螨类和一种舌形虫）与H. frenatus存在协同进化关系，且随着壁虎种群丰度下降，这两种寄生虫的感染率也随之降低。第三种寄生虫……