Caves Eleanor M, Stevens Martin, Spottiswoode Claire N
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK
Centre for Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Penryn Campus, Penryn, Cornwall TR10 9FE, UK.
Proc Biol Sci. 2017 May 17;284(1854). doi: 10.1098/rspb.2017.0272.
When mimicry imposes costs on models, selection may drive the model's phenotype to evolve away from its mimic. For example, brood parasitism often drives hosts to diversify in egg appearance among females within a species, making mimetic parasitic eggs easier to detect. However, when a single parasite species exploits multiple host species, parasitism could also drive host egg evolution away from other co-occurring hosts, to escape susceptibility to their respective mimics. This hypothesis predicts that sympatric hosts of the same parasite should partition egg phenotypic space (defined by egg colour, luminance and pattern) among species to avoid one another. We show that eggs of warbler species parasitized by the cuckoo finch in Zambia partition phenotypic space much more distinctly than do eggs of sympatric but unparasitized warblers. Correspondingly, cuckoo finch host-races better match their own specialist host than other local host species. In the weaver family, parasitized by the diederik cuckoo , by contrast, parasitized species were more closely related and overlapped extensively in phenotypic space; correspondingly, cuckoos did not match their own host better than others. These results suggest that coevolutionary arms races between hosts and parasites may be shaped by the wider community context in which they unfold.
当拟态给被模拟者带来代价时，自然选择可能会促使被模拟者的表型朝着远离其模仿者的方向进化。例如，巢寄生常常驱使宿主在同一物种内的雌性个体间使卵的外观多样化，从而使模仿性的寄生卵更容易被察觉。然而，当单一寄生虫物种利用多种宿主物种时，寄生作用也可能驱使宿主卵的进化远离其他同时存在的宿主，以避免受到各自模仿者的影响。这一假说预测，同一寄生虫的同域宿主物种之间应该在物种间划分卵的表型空间（由卵的颜色、亮度和图案定义），以相互避开。我们发现，在赞比亚，被杜鹃雀寄生的莺类鸟卵在表型空间上的划分比同域但未被寄生的莺类鸟卵要明显得多。相应地，杜鹃雀的宿主种群与其特定的宿主相比，与其他当地宿主物种的匹配度更高。相比之下，在被迪德里克杜鹃寄生的织布鸟家族中，被寄生的物种亲缘关系更近，在表型空间上广泛重叠；相应地，杜鹃与其特定宿主的匹配度并不比与其他宿主的匹配度更高。这些结果表明，宿主与寄生虫之间的协同进化军备竞赛可能受到它们所处的更广泛群落背景的影响。
