A comparative analysis of the evolution of imperfect mimicry

摘要

Although exceptional examples of adaptation are frequently celebrated, some outcomes of natural selection seem far from perfect. For example, many hoverflies (Diptera: Syrphidae) are harmless (Batesian) mimics of stinging Hymenoptera. However, although some hoverfly species are considered excellent mimics, other species bear only a superficial resemblance to their models and it is unclear why this is so. To evaluate hypotheses that have been put forward to explain interspecific variation in the mimetic fidelity of Palearctic Syrphidae we use a comparative approach. We show that the most plausible explanation is that predators impose less selection for mimetic fidelity on smaller hoverfly species because they are less profitable prey items. In particular, our findings, in combination with previous results, allow us to reject several key hypotheses for imperfect mimicry: first, human ratings of mimetic fidelity are positively correlated with both morphometric measures and avian rankings, indicating that variation in mimetic fidelity is not simply an illusion based on human perception; second, no species of syrphid maps out in multidimensional space as being intermediate in appearance between several different hymenopteran model species, as the multimodel hypothesis requires; and third, we find no evidence for a negative relationship between mimetic fidelity and abundance, which calls into question the kin-selection hypothesis. By contrast, a strong positive relationship between mimetic fidelity and body size supports the relaxed-selection hypothesis, suggesting that reduced predation pressure on less profitable prey species limits the selection for mimetic perfection.%贝氏拟态物种是潜在的猎物物种，它们对捕食者是无害的，但能够通过它们与味道不好的猎物物种的相似性而获得保护。令人吃惊的是，很多贝氏拟态物种似乎是相当中庸的模仿者，尽管可能存在很大的演化压力来促使它们提高自己的模仿能力。这篇论文对无害的食蚜蝇物种进行了形态学和系统发生学分析，这种食蚜蝇能以不同成功率模仿能刺痛捕食者的膜翅目昆虫。本文作者们排除了几个假设：比如说，不完美的模仿是人的认识上的一个错觉：或者说，不完美的模仿实际上是多头下注的一个手段，即同时模仿几个膜翅目昆虫物种。