Sherratt Thomas N, Beatty Christopher D
Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada.
Am Nat. 2003 Oct;162(4):377-89. doi: 10.1086/378047. Epub 2003 Oct 16.
It is widely argued that defended prey have tended to evolve conspicuous traits because predators more readily learn to avoid defended prey when they are conspicuous. However, a rival theory proposes that defended prey have evolved such characters because it allows them to be distinguished from undefended prey. Here we investigated how the attributes of defended (unprofitable) and undefended (profitable) computer-generated prey species tended to evolve when they were subject to selection by foraging humans. When cryptic forms of defended and undefended species were similar in appearance but their conspicuous forms were not, defended prey became conspicuous while undefended prey remained cryptic. Indeed, in all of our experiments, defended prey invariably evolved any trait that enabled them to be distinguished from undefended prey, even if such traits were cryptic. When conspicuous mutants of defended prey were extremely rare, they frequently overcame their initial disadvantage by chance. When Batesian mimicry of defended species was possible, defended prey evolved unique traits or characteristics that would make undefended prey vulnerable. Overall, our work supports the contention that warning signals are selected for their reliability as indicators of defense rather than to capitalize on any inherent educational biases of predators.
人们普遍认为，具有防御能力的猎物往往会进化出显著的特征，因为当它们很显眼时，捕食者更容易学会避开有防御能力的猎物。然而，另一种对立的理论认为，有防御能力的猎物进化出这些特征是因为这能让它们与无防御能力的猎物区分开来。在这里，我们研究了有防御能力（无利可图）和无防御能力（有利可图）的计算机生成的猎物物种在受到觅食人类的选择时，其特征是如何倾向于进化的。当有防御能力和无防御能力物种的隐蔽形态在外观上相似但显眼形态不同时，有防御能力的猎物变得显眼，而无防御能力的猎物则保持隐蔽。事实上，在我们所有的实验中，有防御能力的猎物总是会进化出任何能使它们与无防御能力的猎物区分开来的特征，即使这些特征是隐蔽的。当有防御能力的猎物的显眼突变体极其罕见时，它们经常会偶然克服最初的劣势。当对有防御能力的物种进行贝氏拟态是可能的时候，有防御能力的猎物会进化出独特的特征，这些特征会使无防御能力的猎物变得易受攻击。总的来说，我们的研究支持这样一种观点，即警告信号之所以被选择，是因为它们作为防御指标的可靠性，而不是为了利用捕食者任何固有的认知偏差。
