In a previous study, we showed that Spiroplasma, a maternally transmitted endosymbiotic bacterium of Drosophila hydei, enhances larval to adult survival of its host when exposed to oviposition attack by the parasitoid wasp Leptopilina heterotoma. The mechanism by which Spiroplasma enhances host survival has not been elucidated. To better understand this mechanism, we compared the growth of wasp larvae in Spiroplasma-infected and uninfected hosts. Our results indicate that wasp embryos in Spiroplasma-infected hosts hatch and grow normally for ~2 days, after which their growth is severely impaired, compared to wasps developing in uninfected hosts. Thus, despite their reduced ability to complete development in Spiroplasma-infected hosts, developing wasps may exert fitness costs on their hosts that are manifested after host emergence. The severity of these costs will influence the degree to which this protective mechanism contributes to the long-term persistence of Spiroplasma in D. hydei. We therefore examined survival to 10-day-old adult stage and fecundity of Spiroplasma-infected flies surviving a wasp treatment. Our results suggest detrimental effects of wasp attack on longevity of Spiroplasma-infected adult flies. However, compared to Spiroplasma-free flies exposed to wasps, Spiroplasma-infected flies exposed to wasps have ~5 times greater survival from larva to 10 day-adult. The relative fecundity of wasp-attacked Spiroplasma-infected females was ~71% that of un-attacked Spiroplasma-free females. Our combined survival and female fecundity results suggest that under high wasp parasitism, the reproductive fitness of Spiroplasma-infected flies may be ~3.5 times greater than that of uninfected females, so it is potentially relevant to the persistence of Spiroplasma in natural populations of D. hydei. Interestingly, Spiroplasma-infected males surviving a wasp attack were effectively sterile during the 3-day period examined. This observation is consistent with the expectation that, as a maternally transmitted symbiont, there is little selective pressure on Spiroplasma to enhance the reproductive fitness of its male hosts.

中文翻译：

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果蝇内共生体螺旋体对寄生蜂发育和被蜂攻击的苍蝇幸存者的生殖健康的影响

在之前的一项研究中，我们发现 Spiroplasma 是一种母系传播的 Drosophila hydei 内共生细菌，当暴露于寄生蜂 Leptopilina 异体瘤的产卵攻击时，其宿主的幼虫到成虫的存活率提高。Spiroplasma 增强宿主存活的机制尚未阐明。为了更好地理解这种机制，我们比较了螺旋原体感染和未感染宿主中黄蜂幼虫的生长。我们的结果表明，与在未感染宿主中发育的黄蜂相比，螺旋原体感染宿主中的黄蜂胚胎孵化并正常生长约 2 天，之后它们的生长受到严重损害。因此，尽管它们在螺旋体感染宿主中完成发育的能力降低，但发育中的黄蜂可能会对宿主产生适应度成本，这在宿主出现后表现出来。这些成本的严重程度将影响这种保护机制在多大程度上有助于螺旋原体在 D. hydei 中的长期存在。因此，我们检查了 10 天大成虫阶段的存活率和在黄蜂治疗中幸存下来的螺旋原体感染果蝇的繁殖力。我们的研究结果表明黄蜂攻击对螺旋体感染成年果蝇的寿命有不利影响。然而，与暴露于黄蜂的无螺旋体苍蝇相比，暴露于黄蜂的螺旋体感染苍蝇从幼虫到 10 天的成虫存活率高约 5 倍。被黄蜂攻击的螺旋体感染雌性的相对繁殖力是未攻击的无螺旋体的雌性的 71%。我们的综合存活率和雌性繁殖力结果表明，在黄蜂寄生率高的情况下，螺旋原体感染的果蝇的繁殖适应性可能约为 3。比未感染的雌性高 5 倍，因此它可能与 D. hydei 自然种群中螺旋原体的持久性有关。有趣的是，在被检查的 3 天期间，在黄蜂攻击中幸存下来的螺旋原体感染雄性实际上是不育的。这一观察结果与预期一致，即作为母系传播的共生体，螺旋原体几乎没有选择压力来增强其雄性宿主的生殖健康。