被巢寄生鳥當作目標的很多鳥類已學會拒絕寄生鳥的卵，但它們卻很少有排斥寄生鳥的幼鳥的——如果這些幼鳥得以孵化出來的話,，即便這些幼鳥與它們自己的幼鳥在大小上的差別顯而易見,。同一物種內(nèi)的寄生是較為罕見的一種巢寄生形式，在其中幼鳥拒絕的確會發(fā)生,。
研究人員對此進行了一系列幼鳥交叉養(yǎng)育實驗,，實驗對象是美洲黑鴨。實驗結(jié)果表明,，父母利用一窩中的第一只作為一個模板來孵化,，并以此作為依據(jù)來判斷以后所孵化的是否有可能是潛在入侵者的后代。這種學習規(guī)則也許可解釋為什么幼鳥識別作為針對鳥類巢寄生的一種寄主防衛(wèi)手段令人迷惑不解地不存在：對大多數(shù)物種間寄生形式的寄主來說，幼鳥識別可能是起反作用的,，因為入侵者通常孵化得早,，有很好的機會成為同窩幼鳥的模板。（生物谷Bioon.com）
生物谷推薦原始出處：
Nature 463, 223-226 (14 January 2010) | doi:10.1038/nature08655
Coots use hatch order to learn to recognize and reject conspecific brood parasitic chicks
Daizaburo Shizuka1 & Bruce E. Lyon1
1 Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, California 95064, USA
Correspondence to: Daizaburo Shizuka1 Correspondence and requests for materials should be addressed to D.S.
Avian brood parasites and their hosts provide model systems for investigating links between recognition, learning, and their fitness consequences1, 2, 3, 4. One major evolutionary puzzle has continued to capture the attention of naturalists for centuries: why do hosts of brood parasites generally fail to recognize parasitic offspring after they have hatched from the egg5, 6, 7, 8, 9, even when the host and parasitic chicks differ to almost comic degrees7? One prominent theory to explain this pattern proposes that the costs of mistakenly learning to recognize the wrong offspring make recognition maladaptive10. Here we show that American coots, Fulica americana, can recognize and reject parasitic chicks in their brood by using learned cues, despite the fact that the hosts and the brood parasites are of the same species. A series of chick cross-fostering experiments confirm that coots use first-hatched chicks in a brood as referents to learn to recognize their own chicks and then discriminate against later-hatched parasitic chicks in the same brood. When experimentally provided with the wrong reference chicks, coots can be induced to discriminate against their own offspring, confirming that the learning errors proposed by theory can exist10. However, learning based on hatching order is reliable in naturally parasitized coot nests because host eggs hatch predictably ahead of parasite eggs. Conversely, a lack of reliable information may help to explain why the evolution of chick recognition is not more common in hosts of most interspecific brood parasites.
