Parasites can negatively affect the reproductive success of hosts. Placental species may be particularly susceptible, because parasite-induced stress during pregnancy could potentially influence embryo development. Here, we examine the consequences of a trematode infestation (black spot disease, BSD) for fetal development and adult behavior in 19 natural populations of the placental live-bearing fish species Poeciliopsis retropinna (Poeciliidae) in Costa Rica. First, we observed substantial variation in parasite infestation among populations which correlated with a number of local environmental conditions (elevation, river width, depth, and flow velocity). Furthermore, we observed substantial variation in parasite infestation among females within populations associated with maternal age and size. We found that the infestation rate significantly influenced embryonic development, with more heavily parasitized females producing smaller and worse-conditioned offspring at birth, possibly, because a costly immune response during pregnancy limits, either directly or indirectly, nourishment to developing embryos. Finally, a behavioral experiment in the field showed that the infestation rate did not affect an individual’s boldness. Our study indicates that in placental live-bearing fish parasite infestation leads to reduced embryo provisioning during pregnancy, resulting in a smaller offspring size and quality at birth potentially with negative implications for offspring fitness.

寄生虫会对宿主的繁殖成功产生负面影响。胎盘物种可能特别敏感，因为怀孕期间寄生虫诱发的压力可能会影响胚胎发育。在这里，我们检查胎盘活轴承鱼种类的19个自然种群吸虫感染的胎儿发育和成人行为的后果（黑点病，BSD）Poeciliopsis retropinna（Poeciliidae）在哥斯达黎加。首先，我们观察到种群中寄生虫侵扰的显着变化，这与许多当地环境条件（海拔，河流宽度，深度和流速）相关。此外，我们观察到与产妇年龄和体型有关的人群中，女性中寄生虫侵扰的差异很大。我们发现出没率显着影响了胚胎的发育，更多地被寄生的雌性在出生时会产下更小，条件更差的后代，这可能是因为怀孕期间代价高昂的免疫反应直接或间接地限制了对发育中的胚胎的营养。最后，在该领域进行的一项行为实验表明，出没率并没有影响一个人的胆识。