Department of Zoology, University of Cambridge, Cambridge, UK.
Biol Lett. 2013 Aug 21;9(5):20130573. doi: 10.1098/rsbl.2013.0573. Print 2013 Oct 23.
Many brood parasitic birds lay eggs that mimic their hosts' eggs in appearance. This typically arises from selection from discriminating hosts that reject eggs which differ from their own. However, selection on parasitic eggs may also arise from parasites themselves, because it should pay a laying parasitic female to detect and destroy another parasitic egg previously laid in the same host nest by a different female. In this study, I experimentally test the source of selection on greater honeyguide (Indicator indicator) egg size and shape, which is correlated with that of its several host species, all of which breed in dark holes. Its commonest host species did not discriminate against experimental eggs that differed from their own in size and shape, but laying female honeyguides preferentially punctured experimental eggs more than host or control eggs. This should improve offspring survival given that multiple parasitism by this species is common, and that honeyguide chicks kill all other nest occupants. Hence, selection on egg size in greater honeyguides parasitizing bee-eaters appears to be imposed not by host defences but by interference competition among parasites themselves.
许多巢寄生鸟类所产的蛋在外观上与宿主的蛋相似。这种情况通常是由于宿主具有辨别能力，会拒绝与自己的蛋不同的蛋，从而产生了选择。然而，寄生蛋也可能受到寄生虫自身的选择，因为对于产卵的寄生雌鸟来说，检测和破坏另一只在同一宿主巢中由不同雌鸟产下的寄生蛋是有利的。在这项研究中，我通过实验测试了大蜜导（Indicator indicator）蛋的大小和形状的选择来源，这与它的几个宿主物种的蛋的大小和形状有关，所有这些宿主物种都在黑暗的洞穴中繁殖。它最常见的宿主物种不会对在大小和形状上与自己不同的实验蛋产生歧视，但产卵的蜜导鸟会优先刺破实验蛋，而不是宿主蛋或对照蛋。鉴于这种物种的多次寄生很常见，而且蜜导鸟的雏鸟会杀死所有其他巢居者，因此，对蜜蜂食蜂鸟寄生的大蜜导鸟的蛋大小的选择似乎不是由宿主的防御机制引起的，而是由寄生虫自身的干扰竞争引起的。
