Department of Biology, University of North Carolina, Chapel Hill, NC, USA.
Proc Biol Sci. 2010 Apr 7;277(1684):1041-8. doi: 10.1098/rspb.2009.2000. Epub 2009 Dec 2.
In Batesian mimicry, a harmless species (the 'mimic') resembles a dangerous species (the 'model') and is thus protected from predators. It is often assumed that the mimetic phenotype evolves from a cryptic phenotype, but it is unclear how a population can transition through intermediate phenotypes; such intermediates may receive neither the benefits of crypsis nor mimicry. Here, we ask if selection against intermediates weakens with increasing model abundance. We also ask if mimicry has evolved from cryptic phenotypes in a mimetic clade. We first present an ancestral character-state reconstruction showing that mimicry of a coral snake (Micrurus fulvius) by the scarlet kingsnake (Lampropeltis elapsoides) evolved from a cryptic phenotype. We then evaluate predation rates on intermediate phenotypes relative to cryptic and mimetic phenotypes under conditions of both high- and low-model abundances. Our results indicate that where coral snakes are rare, intermediate phenotypes are attacked more often than cryptic and mimetic phenotypes, indicating the presence of an adaptive valley. However, where coral snakes are abundant, intermediate phenotypes are not attacked more frequently, resulting in an adaptive landscape without a valley. Thus, high-model abundance may facilitate the evolution of Batesian mimicry.
贝氏拟态中，一种无毒的物种（“拟态者”）与一种危险的物种（“模型”）相似，从而免受捕食者的侵害。人们通常认为，拟态表型是从隐蔽表型进化而来的，但不清楚一个种群如何通过中间表型过渡；这些中间表型可能既没有隐蔽的好处，也没有拟态的好处。在这里，我们询问中间表型是否随着模型丰度的增加而受到选择压力的削弱。我们还询问了在一个拟态进化枝中，拟态是否是从隐蔽表型进化而来的。我们首先提出了一个祖先特征状态重建，表明珊瑚蛇（Micrurus fulvius）被猩红王蛇（Lampropeltis elapsoides）模仿的拟态是从隐蔽表型进化而来的。然后，我们在高模型丰度和低模型丰度两种条件下，评估了中间表型相对于隐蔽表型和拟态表型的捕食率。我们的结果表明，在珊瑚蛇稀少的地方，中间表型比隐蔽表型和拟态表型更容易受到攻击，这表明存在一个适应性低谷。然而，在珊瑚蛇丰富的地方，中间表型并不经常受到攻击，导致没有低谷的适应性景观。因此，高模型丰度可能有助于贝氏拟态的进化。
