Soler M, Soler J J, Martinez J G, M Ller A P
Departamento de Biología Animal y Ecología, Facultad de Ciencias, Universidad de Granada, E-18071, Granada, Spain.
Zoological Institute, Copenhagen University, Universitetsparken 15, DK-2100, Copenhagen Ø, Denmark.
Evolution. 1995 Aug;49(4):770-775. doi: 10.1111/j.1558-5646.1995.tb02312.x.
Why should the hosts of brood parasites accept and raise parasitic offspring that differ dramatically in appearance from their own? There are two solutions to this evolutionary enigma. (1) Hosts may not yet have evolved the capability to discriminate against the parasite, or (2) parasite-host systems have reached an evolutionary equilibrium. Avian brood parasites may either gain renesting opportunities or force their hosts to raise parasitic offspring by destroying or preying upon host eggs or nestlings following host ejection of parasite offspring. These hypotheses may explain why hosts do not remove parasite offspring because only then will hosts avoid clutch destruction by the cuckoo. Here we show experimentally that if the egg of the parasitic great spotted cuckoo Clamator glandarius is removed from nests of its magpie Pica pica host, nests suffer significantly higher predation rates than control nests in which parasite eggs have not been removed. Using plasticine model eggs resembling those of magpies and observations of parasites, we also confirm that great spotted cuckoos that have laid an ejected egg are indeed responsible for destruction of magpie nests with experimentally ejected parasite eggs. Cuckoos benefit from destroying host offspring because they thereby induce some magpies to renest and subsequently accept a cuckoo egg.
为什么巢寄生鸟类的宿主会接受并抚养那些在外观上与自己的后代有显著差异的寄生后代呢？对于这个进化之谜有两种解释。（1）宿主可能尚未进化出辨别寄生虫的能力，或者（2）寄生虫 - 宿主系统已达到进化平衡。鸟类巢寄生者可能通过在宿主将寄生后代逐出后破坏或捕食宿主的卵或雏鸟，从而获得再次筑巢的机会，或者迫使宿主抚养寄生后代。这些假说或许可以解释宿主为何不清除寄生后代，因为只有这样宿主才能避免杜鹃对其一窝卵的破坏。在此我们通过实验表明，如果将寄生性大斑凤头鹃的卵从其喜鹊宿主的巢中移除，这些巢遭受的捕食率会比未移除寄生虫卵的对照巢显著更高。利用类似喜鹊卵的橡皮泥模型卵以及对寄生虫的观察，我们还证实，产下被逐出卵的大斑凤头鹃确实会导致带有实验性被逐出寄生虫卵的喜鹊巢被破坏。杜鹃通过破坏宿主后代而受益，因为这样能促使一些喜鹊再次筑巢，并随后接受一枚杜鹃卵。
