Laboratorio Ecotono, Universidad Nacional del Comahue, Pasaje Gutiérrez N° 1125, Bariloche 8400, Argentina.
School of Life Sciences, University of Sussex, Brighton BN1 9QG, United Kingdom.
J Insect Physiol. 2019 Jul;116:49-56. doi: 10.1016/j.jinsphys.2019.04.008. Epub 2019 Apr 20.
Parasites are an important selection pressure for all organisms, and host immune responses are key in shaping host-parasite interactions. Host species with strong immune defences may be expected to experience lower parasitism; on the other hand, investment in immune function is costly, so hosts that have evolved to invest more in immune defence may be expected to have been under greater selection pressure from parasites. Disentangling the coevolutionary dynamics requires comparative studies that quantify the immune responses of potential hosts of parasites in a community, but such studies are rare. Here, we studied the immune defences of six leaf-cutting ant species in a community for which their relationships with phorid fly parasitoid species are known. We tested whether the strength of the baseline immune defences of the different ant species correlated positively or negatively with parasitoid load (number and abundance of parasitoid species exploiting the ant species), and host specialization of parasitoid species (the proportion of specialist parasitoids using each host). We measured four immune variables: i) the encapsulation response to a standard challenge, levels of ii) phenoloxidase (PO) and iii) prophenoloxidae (PPO) immune enzymes, and iv) the number of haemocytes. We found that ant species differed in their encapsulation response, PO levels and number of haemocytes, and that there was a positive, not negative, correlation across ant species between the strength of several of the immune variables and parasitoid load, but not for host specialization. This is in keeping with the hypothesis that higher parasitoid load selects for greater investment in immune defences. Our results suggest that immunity may be an important factor accounting for the dynamics of host-parasitoid interactions in this community. Similar community-level studies may be insightful, both for understanding host-parasite community ecology and for applications such as biocontrol.
寄生虫是所有生物的重要选择压力，而宿主的免疫反应是塑造宿主-寄生虫相互作用的关键。具有强大免疫防御能力的宿主物种可能会经历较低的寄生虫感染率；另一方面，免疫功能的投资是有代价的，因此那些进化出更多免疫防御投资的宿主可能会受到寄生虫更大的选择压力。要解开这种协同进化的动态，需要进行比较研究，量化群落中寄生虫潜在宿主的免疫反应，但这种研究很少。在这里，我们研究了一个群落中六种切叶蚁物种的免疫防御能力，这些物种与 phorid 蝇寄生蜂物种的关系是已知的。我们测试了不同蚂蚁物种的基础免疫防御强度是否与寄生虫负荷（利用蚂蚁物种的寄生虫物种数量和丰度）以及寄生蜂物种的宿主专化性（利用每个宿主的专性寄生蜂比例）呈正相关或负相关。我们测量了四个免疫变量：i）对标准挑战的包埋反应，ii）酚氧化酶（PO）和 iii）原酚氧化酶（PPO）免疫酶的水平，以及 iv）血球数量。我们发现，蚂蚁物种在包埋反应、PO 水平和血球数量方面存在差异，并且在几种免疫变量的强度与寄生虫负荷之间存在正相关，而不是负相关，但与宿主专化性无关。这与寄生虫负荷越高选择更多免疫防御投资的假设一致。我们的研究结果表明，免疫可能是解释这个群落中宿主-寄生虫相互作用动态的一个重要因素。类似的群落水平研究可能具有启发性，既可以帮助我们理解宿主-寄生虫群落生态学，也可以应用于生物防治等领域。
