Evol Ecol Res 5: 345-362 (2003)     Full PDF if your library subscribes.

Co-evolutionary dynamics of egg appearance in avian brood parasitism

Fugo Takasu*

Department of Information and Computer Sciences, Nara Women’s University, Kita-Uoya Nishimachi, Nara 630-8506, Japan

e-mail: takasu@ics.nara-wu.ac.jp


In avian brood parasitism, interactions between parasites and their hosts lead to a co-evolutionary process called an arms race. Field studies have shown that many host species have evolved an ability to recognize and reject parasite eggs that look unlike their own and that some parasites lay eggs of sophisticated mimicry. Egg appearance is a crucial factor that determines the reproductive success both of the parasites and their hosts in the arms race. The appearance of eggs, however, is a quantitative trait and the variation within a population could critically affect the dynamics of the arms race; parasite individuals that lay eggs more similar to those of the host are more likely to reproduce successfully, whereas host individuals that lay eggs more unlike those of the parasite have a better chance of rejecting parasitism and reproducing, which would de-stabilize the parasites’ good mimicry. To explore the arms race for egg appearance, I constructed a model described by an integro-difference equation. The temporal change of the ‘distributions’ of egg appearance along a continuous spectrum was analysed both for the parasite and host populations. The model analyses show that (1) a conventional view of an arms race – ‘parasites chasing their hosts escaping from the parasites’ – is realized in the early stage of the dynamics, but (2) the distributions of egg appearance finally converge to discrete point-distributions (polymorphism) even when any continuous distributions are used as the initial state. The latter might be relevant to the maintenance of polymorphism of egg appearance. Based on the model analysis, I discuss the implications of this model for general (co)evolutionary processes for quantitative traits and suggest a new modelling framework to account for such processes.

Keywords: arms race, avian brood parasitism, co-evolution, egg appearance, ideal free evolution, quantitative trait.

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