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Hybridization and adaptive mate choice in flycatchers


Hybridization in natural populations is strongly selected against when hybrid offspring have reduced fitness. Here we show that, paradoxically, pairing with another species may offer the best fitness return for an individual, despite reduced fitness of hybrid offspring. Two mechanisms reduce the costs to female collared flycatchers of pairing with male pied flycatchers. A large proportion of young are sired by conspecific male collared flycatchers through extra-pair copulations, and there is a bias in favour of male offspring (which, unlike females, are fertile) within hybrid pairs. In combination with temporal variation in breeding success, these cost-reducing mechanisms yield quantitative predictions about when female collared flycatchers should accept a male pied flycatcher as a mate; empirical data agree with these predictions. Apparent hybridization may thus represent adaptive mate choice under some circumstances.

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Figure 1: Male share of paternity in relation to pairing type in flycatcher families.
Figure 2: Effect of pairing type on sex ratio and viability of brood.
Figure 3: Numbers of recruited offspring and grand-offspring for each pairing type.
Figure 4: Breeding time, reproductive success, and mating decisions in flycatchers.


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We thank the many people that helped to collect data from the Swedish and Czech study populations, particularly J. Träff for providing access to mixed pairs in Sweden, and M. Kral for access to Czech data. P. R. Grant, L. E. B. Kruuk, J. Merilä and T. Price commented on a previous version of the manuscript. The work was funded by grants from the Swedish Natural Sciences Research Council, the Norwegian Research Council, an Erasmus grant to T.V., and by a Royal Society University Research Fellowship to B.C.S.

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Correspondence to Ben C. Sheldon.

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Veen, T., Borge, T., Griffith, S. et al. Hybridization and adaptive mate choice in flycatchers. Nature 411, 45–50 (2001).

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