Vasquez David, Willoughby Anna, Davis Andrew K
Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, 24061, United States of America.
Department of Evolutionary Anthropology, Duke University, Durham, North Carolina, 27708, United States of America.
PLoS One. 2015 Apr 1;10(4):e0121614. doi: 10.1371/journal.pone.0121614. eCollection 2015.
The effects of non-lethal parasites may be felt most strongly when hosts engage in intense, energy-demanding behaviors. One such behavior is fighting with conspecifics, which is common among territorial animals, including many beetle species. We examined the effects of parasites on the fighting ability of a saproxylic beetle, the horned passalus (Odontotaenius disjunctus, Family: Passalidae), which is host to a non-lethal nematode, Chondronema passali. We pitted pairs of randomly-chosen (but equally-weighted) beetles against each other in a small arena and determined the winner and aggression level of fights. Then we examined beetles for the presence, and severity of nematode infections. There was a non-significant tendency (p = 0.065) for the frequency of wins, losses and draws to differ between beetles with and without C. passali; non-parasitized individuals (n = 104) won 47% of their fights while those with the parasite (n = 88) won 34%, a 13% difference in wins. The number of nematodes in a beetle affected the outcome of fights between infected and uninfected individuals in an unexpected fashion: fighting ability was lowest in beetles with the lowest (p = 0.033), not highest (p = 0.266), nematode burdens. Within-fight aggression was highest when both beetles were uninfected and lowest when both were infected (p = 0.034). Collectively, these results suggest the nematode parasite, C. passali, is associated with a modest reduction in fighting ability in horned passalus beetles, consistent with the idea that parasitized beetles have lower energy available for fighting. This study adds to a small but growing body of evidence showing how parasites negatively influence fighting behavior in animals.
当宿主进行激烈的、消耗能量的行为时，非致命性寄生虫的影响可能会最为明显地体现出来。其中一种行为就是与同种个体争斗，这在领地性动物中很常见，包括许多甲虫种类。我们研究了寄生虫对一种食菌甲虫——有角扁甲（Odontotaenius disjunctus，扁甲科）战斗能力的影响，这种甲虫是一种非致命性线虫——扁甲软骨线虫（Chondronema passali）的宿主。我们在一个小场地中让随机挑选（但体重相等）的甲虫两两对决，确定战斗的胜负以及攻击水平。然后我们检查甲虫是否感染线虫以及感染的严重程度。感染和未感染扁甲软骨线虫的甲虫在胜负和平局的频率上存在不显著的差异趋势（p = 0.065）；未感染寄生虫的个体（n = 104）在47%的战斗中获胜，而感染寄生虫的个体（n = 88）获胜率为34%，获胜率相差13%。甲虫体内线虫的数量以一种意想不到的方式影响着感染和未感染个体之间战斗的结果：线虫负担最轻的甲虫（p = 0.033）战斗能力最低，而非线虫负担最重的甲虫（p = 0.266）。当两只甲虫都未感染时，战斗中的攻击性最强，而当两只都感染时攻击性最弱（p = 0.034）。总体而言，这些结果表明线虫寄生虫扁甲软骨线虫与有角扁甲甲虫战斗能力的适度下降有关，这与受寄生虫感染的甲虫可用于战斗的能量较低的观点一致。这项研究进一步补充了少量但不断增加的证据，表明寄生虫如何对动物的战斗行为产生负面影响。
