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The evolution of the social and genetic mating system of purple-crowned fairy-wrens Malurus coronatus

The evolution of the social and genetic mating system of purple-crowned fairy-wrens Malurus coronatus

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KINGMA, Sjouke Anne, 2011. The evolution of the social and genetic mating system of purple-crowned fairy-wrens Malurus coronatus [Dissertation]. Konstanz: University of Konstanz

@phdthesis{Kingma2011evolu-14786, title={The evolution of the social and genetic mating system of purple-crowned fairy-wrens Malurus coronatus}, year={2011}, author={Kingma, Sjouke Anne}, address={Konstanz}, school={Universität Konstanz} }

The evolution of the social and genetic mating system of purple-crowned fairy-wrens Malurus coronatus eng Kingma, Sjouke Anne terms-of-use Kingma, Sjouke Anne In this thesis, I describe my research on the causes and consequence of extra-pair (EP) mating and cooperative breeding in a passerine bird, the purple-crowned fairy-wren, Malurus coronatus. These costly behaviours are common aspects of animal mating systems, but how these are evolutionarily adaptive has puzzled biologists for decades. Why do females copulate with males outside their pair-bond? Why do some individuals assist in raising other individuals’ offspring? These questions were addressed based on detailed field-observations, combined with molecular analyses. Overall, relatedness among individuals is shown to be important in determining fitness benefits of both EP mating and cooperative behaviour in M. coronatus, and therefore predicts whether individuals engage in particular behaviours. In turn, as EP mating reduces relatedness among individuals, this appears to have important implications for the evolution of cooperative behaviour in general.<br /><br /><br />Females in many bird species actively pursue EP mating, but understanding why they do so (or why not) has generally proven challenging. I show that EP mating functions mainly in inbreeding avoidance in M. coronatus: broods of females paired with a first-order relative had almost 15 times higher rates of EPP than broods of females with an unrelated partner. Inbreeding resulted in increased hatching failure of eggs, and therefore EP mating in this species constitutes an adaptive mechanism to avoid large costs of inbreeding.<br />While EP mating is adaptive in M. coronatus, overall levels of EPP are considerably lower (4-6% of offspring) than in its highly promiscuous congeners (40-80%). This is surprising, because life-history features that determine costs or benefits of EP mating (e.g., the extent of paternal care and incestuous pairings) appear rather similar between the species. Possibly, M. coronatus females are restricted in EP mating by relatively low density and breeding synchrony that limit access to fertile EP males. Within M. coronatus, variation in such factors indeed explained part of the variation in EP mating, but females in an incestuous pairing actively overcame such constraints by synchronizing breeding with fertility of unrelated neighbouring males. Thus, EP mating behaviour is shaped by a complex interplay between benefits and constraints and the relative importance of those can be actively modulated by females. Moreover, minor changes in the costs, benefits and/or constraints can have far-reaching effects, suggesting that EP mating can evolutionarily be a rather flexible behaviour.<br /><br /><br />Cooperative behaviour that does not yield benefits for survival or reproductive success is in contrast with natural selection theory, and how such seemingly altruistic behaviour can persist is a prevailing topic in evolutionary biology. I show that helpers in M. coronatus feed siblings more than unrelated nestlings. Because helpers improve reproductive success and breeder survival, this supports the prediction of the kin-selection theory that helpers gain inclusive fitness of increased gene-transfer through relatives. Additionally, direct benefits also appear important in explaining variation in helper investment: less related helpers feed nestlings more when they are more likely to inherit the breeder position, probably to augment groups with future helpers. This therefore provides one solution of the puzzle how cooperation among non-related individuals can remain evolutionarily stable.<br /><br /><br />Helpers in M. coronatus are mostly males and breeder females may therefore benefit most from producing sons. Nonetheless, I did not find evidence for the hypothesis that females should adjust offspring sex ratio to overproduce males. One possibility is that sex-bias in long-term fitness returns is too small to drive evolution of sex ratio adjustment mechanisms, and this requires more in depth investigation.<br /><br /><br />The finding that helpers in M. coronatus have substantial beneficial effects on breeder survival and reproductive success is in strong contrast with its promiscuous congeners, in which such effects are much smaller. Since kinship is a major driver of apparently altruistic behaviour, low rates of EPP could contribute to cooperative behaviour. In a comparative study among 37 bird species, I show that this is a general pattern as enhancement of reproductive success and breeder survival by helpers is more frequent in species with lower levels of EPP. This result likely explains why cooperative breeding is associated with relatively low rates of EPP in general, and strongly suggests that the genetic mating system plays an important role in the evolution of social systems in animals.<br /> 2011-09-01T07:39:43Z 2011 2011-09-01T07:39:43Z

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