Sommer Simone, Rakotondranary Solofomalla Jacques, Ganzhorn Jörg U
Evolutionary Genetics, Leibniz-Institute for Zoo- and Wildlife Research Alfred-Kowalke-Strasse 10, Berlin, 10315, Germany ; Institute for Experimental Ecology, University of Ulm Albert-Einstein Allee 11, Ulm, 89069, Germany.
Department of Animal Ecology and Conservation, University of Hamburg, Biozentrum Grindel Martin-Luther-King Platz 3, Hamburg, 20146, Germany.
Ecol Evol. 2014 Dec;4(24):4751-65. doi: 10.1002/ece3.1311. Epub 2014 Dec 2.
Understanding the drivers of species adaptations to changing environments on the one hand and the limits for hybridization on the other hand is among the hottest questions in evolutionary biology. Parasites represent one of the major selective forces driving host evolution and at least those with free-living stages are at the same time dependent on the ecological conditions of their host's habitat. Local immunological adaptations of host species to varying parasite pressure are therefore expected and might represent the genetic basis for ecological speciation and the maintenance of recently diverged species. Madagascar provides one of the rare examples where two partially sympatric primate species (Microcebus griseorufus, M. murinus) and their hybrids, as well as an allopatric species (M. cf rufus) live in close proximity along a very steep environmental gradient ranging from southern dry spiny bush to gallery forest to evergreen eastern humid rain forest, thus mimicking the situation encountered during extensions and retreats of vegetation formations under changing climatic conditions. This system was used to study parasite infection and immune gene (MHC) adaptations to varying parasite pressure that might provide selective advantages to pure species over hybrids. Parasite burdens increased with increasing humidity. M. griseorufus, M. murinus, and their hybrids but not M. rufus shared the same MHC alleles, indicating either retention of ancestral polymorphism or recent gene flow. The hybrids had much higher prevalence of intestinal parasites than either of the parent species living under identical environmental conditions. The different representation of parasites can indicate a handicap for hybrids that maintains species identities.
一方面，了解物种适应不断变化的环境的驱动因素，另一方面了解杂交的限制，是进化生物学中最热门的问题之一。寄生虫是推动宿主进化的主要选择力量之一，至少那些具有自由生活阶段的寄生虫同时依赖于其宿主栖息地的生态条件。因此，可以预期宿主物种对不同寄生虫压力的局部免疫适应，这可能代表生态物种形成和维持最近分化物种的遗传基础。马达加斯加提供了一个罕见的例子，两个部分同域分布的灵长类物种（灰红倭狐猴、小鼠狐猴）及其杂交种，以及一个异域分布的物种（rufus亚种），沿着从南部干燥多刺灌木丛到长廊林再到东部湿润常绿雨林的非常陡峭的环境梯度近距离生活，从而模拟了在不断变化的气候条件下植被形成的扩张和退缩过程中遇到的情况。这个系统被用来研究寄生虫感染和免疫基因（MHC）对不同寄生虫压力的适应，这可能为纯种物种提供相对于杂交种的选择优势。寄生虫负担随着湿度的增加而增加。灰红倭狐猴、小鼠狐猴及其杂交种，而不是rufus亚种，共享相同的MHC等位基因，这表明要么保留了祖先的多态性，要么存在近期的基因流动。在相同环境条件下生活的杂交种的肠道寄生虫患病率比任何一个亲本物种都要高得多。寄生虫的不同表现可能表明杂交种存在劣势，这有助于维持物种的特性。
