Gibson Cara M, Hunter Martha S
College of Agriculture and Life Sciences, Department of Entomology, The University of Arizona, Tucson, AZ 85721-0036, USA.
Appl Environ Microbiol. 2009 May;75(10):3115-9. doi: 10.1128/AEM.00361-09. Epub 2009 Mar 13.
Heritable bacterial symbionts are widespread in insects and can have many important effects on host ecology and fitness. Fungal symbionts are also important in shaping their hosts' behavior, interactions, and evolution, but they have been largely overlooked. Experimental tests to determine the relevance of fungal symbionts to their insect hosts are currently extremely rare, and to our knowledge, there have been no such tests for strictly predacious insects. We investigated the fitness consequences for a parasitic wasp (Comperia merceti) of an inherited fungal symbiont in the Saccharomycotina (Ascomycota) that was long presumed to be a mutualist. In comparisons of wasp lines with and without this symbiont, we found no evidence of mutualism. Instead, there were significant fitness costs to the wasps in the presence of the yeast; infected wasps attacked fewer hosts and had longer development times. We also examined the relative competitive abilities of the larval progeny of infected and uninfected mothers, as well as horizontal transmission of the fungal symbiont among larval wasps that shared a single host cockroach egg case. We found no difference in larval competitive ability when larvae whose infection status differed shared a single host. We did find high rates of horizontal transmission of the fungus, and we suggest that this transmission is likely responsible for the maintenance of this infection in wasp populations.
可遗传的细菌共生体在昆虫中广泛存在，并且对宿主的生态和适应性有许多重要影响。真菌共生体在塑造宿主的行为、相互作用和进化方面也很重要，但它们在很大程度上被忽视了。目前，用于确定真菌共生体与其昆虫宿主相关性的实验测试极为罕见，据我们所知，对于严格食肉的昆虫还没有这样的测试。我们研究了一种长期被认为是互利共生体的子囊菌门酵母亚门遗传真菌共生体对寄生蜂（Comperia merceti）适应性的影响。在有和没有这种共生体的黄蜂品系比较中，我们没有发现互利共生的证据。相反，在有酵母存在的情况下，黄蜂存在显著的适应性代价；受感染的黄蜂攻击的宿主较少，发育时间较长。我们还研究了受感染和未受感染母亲的幼虫后代的相对竞争能力，以及真菌共生体在共享单个宿主蟑螂卵鞘的幼虫黄蜂之间的水平传播。我们发现，感染状态不同的幼虫共享单个宿主时，幼虫竞争能力没有差异。我们确实发现真菌的水平传播率很高，并且我们认为这种传播可能是这种感染在黄蜂种群中得以维持的原因。
