Rowland Hannah M, Ihalainen Eira, Lindström Leena, Mappes Johanna, Speed Michael P
School of Biological Sciences, University of Liverpool, Biosciences Building, Crown Street, Liverpool L69 7ZB, UK.
Nature. 2007 Jul 5;448(7149):64-7. doi: 10.1038/nature05899.
In the first clear mathematical treatment of natural selection, Müller proposed that a shared warning signal (mimicry) would benefit defended prey species by sharing out the per capita mortality incurred during predator education. Although mimicry is a mainstay of adaptationist thinking, there has been repeated debate on whether there is a mutualistic or a parasitic relationship between unequally defended co-mimic species. Here we show that the relationship between unequally defended species is mutualistic. We examined this in a 'novel world' of artificial prey with wild predators (great tit, Parus major). We kept the abundance of a highly defended prey ('model') constant and increased the density of a moderately defended prey ('defended mimic') of either perfect or imperfect mimetic resemblance to the model. Both model and defended mimic showed a net benefit from a density-dependent decrease in their per capita mortality. Even when the effect of dilution through density was controlled for, defended mimics did not induce additional attacks on the model, but we found selection for accurate signal mimicry. In comparison, the addition of fully edible (batesian) mimics did increase additional attacks on the model, but as a result of dilution this resulted in no overall increase in per capita mortality. By ignoring the effects of density, current theories may have overestimated the parasitic costs imposed by less defended mimics on highly defended models.
在对自然选择的首次清晰数学处理中，米勒提出，共享的警示信号（拟态）将通过分摊捕食者学习过程中产生的人均死亡率，使受保护的猎物物种受益。尽管拟态是适应主义思想的支柱，但关于防御能力不同的共同拟态物种之间是互利关系还是寄生关系，一直存在反复的争论。在这里，我们表明防御能力不同的物种之间的关系是互利的。我们在一个有野生捕食者（大山雀，Parus major）的人工猎物“新环境”中对此进行了研究。我们保持一种高度受保护的猎物（“模型”）的数量不变，增加一种与模型具有完美或不完美拟态相似性的中度受保护猎物（“受保护拟态者”）的密度。模型和受保护拟态者都从人均死亡率随密度的下降中获得了净收益。即使通过密度控制了稀释效应，受保护拟态者也不会引发对模型的额外攻击，但我们发现了对准确信号拟态的选择。相比之下，添加完全可食用的（贝氏）拟态者确实增加了对模型的额外攻击，但由于稀释，这并没有导致人均死亡率的总体增加。由于忽略了密度的影响，当前理论可能高估了防御能力较弱的拟态者对高度受保护模型造成的寄生成本。
