Bandilla M, Hakalahti-Sirén T, Valtonen E T
Department of Biological and Environmental Science, P.O. Box 35, FIN-40014, University of Jyväskylä, Finland.
Int J Parasitol. 2007 Oct;37(12):1343-9. doi: 10.1016/j.ijpara.2007.04.004. Epub 2007 Apr 21.
Argulus coregoni is an ectoparasite primarily infesting freshwater salmonids. Sexually reproducing parasites such as A. coregoni are confronted with a dilemma between finding a mate and the costs involved in doing so; if mating partners are unavailable on a host, by leaving to search for a mate on a new host, the parasite is exposed to risks such as predation and energy loss. The utilization of chemical cues could enhance the probability of finding a host and/or a suitable mating partner and thus decrease the level of costs associated with detachment from the host. In this study we constructed a Y-maze arena to determine if adult A. coregoni respond to mate- and host-related chemical cues. We also tested the directional response towards light, since it has been suggested that photic cues are the most important cues for juvenile A. coregoni locating a host. Our results showed that both sexes were attracted to light and fish odour. Free-swimming A. coregoni males responded to chemical cues produced by adult females but not vice versa. The hierarchy of these stimuli was analyzed by pitting the cues against one another in the Y-maze, showing that light was the most salient stimulus for both male and female parasites. Moreover, male parasites were more strongly attracted towards light and fish odour than female odour. In another experiment in a semi-natural environment, we examined whether the ability of A. coregoni males to detect female odour influences their host choice. Free-swimming males did not preferentially infest fish infected with female parasites over parasite-free fish. We suggest that a hierarchy of stimulus responses exists, whereby free-swimming parasites first respond to host-related signals and most dominantly to visual cues. However, cues connected to mate finding may become a priority for late adult stages and/or once the parasite has attached to the host.
河鲈锚头鳋是一种主要寄生于淡水鲑科鱼类的体外寄生虫。像河鲈锚头鳋这样进行有性繁殖的寄生虫面临着寻找配偶与为此付出的代价之间的两难困境；如果在宿主身上找不到交配对象，离开去新宿主上寻找配偶时，寄生虫就会面临被捕食和能量损失等风险。利用化学信号可以提高找到宿主和/或合适交配对象的概率，从而降低与脱离宿主相关的代价水平。在本研究中，我们构建了一个Y型迷宫场地，以确定成年河鲈锚头鳋是否对与配偶和宿主相关的化学信号做出反应。我们还测试了对光的定向反应，因为有人提出光信号是幼年河鲈锚头鳋定位宿主的最重要信号。我们的结果表明，雌雄两性都被光和鱼的气味所吸引。自由游动的河鲈锚头鳋雄虫对成年雌虫产生的化学信号有反应，而雌虫则不然。通过在Y型迷宫中让这些信号相互竞争来分析这些刺激的等级，结果表明光对雌雄寄生虫来说都是最显著的刺激。此外，雄性寄生虫对光和鱼的气味的吸引力比对雌性气味的吸引力更强。在另一个半自然环境实验中，我们研究了河鲈锚头鳋雄虫检测雌虫气味的能力是否会影响它们对宿主的选择。自由游动的雄虫并没有优先感染感染了雌虫的鱼，而不是未感染寄生虫的鱼。我们认为存在一个刺激反应等级，即自由游动的寄生虫首先对与宿主相关的信号做出反应，最主要的是对视觉信号做出反应。然而，与寻找配偶相关的信号可能在成年后期和/或一旦寄生虫附着在宿主上后成为优先考虑因素。
