séminaire du vendredi

"Variable selection in a variable world: the evolution of multiple sexual ornaments in a passerine" - Alexis Chaine du Laboratoire CNRS Évolution et Diversité Biologique de Moulis - vendredi 21 mars 2008 à 11h, Amphithéâtre Monge, bât. Gabriel
Many species have multiple sexually selected signals despite costs associated with production and maintenance of multiple ornaments. To overcome such costs, there must be distinct benefits to having many costly traits. I explored the role of both male-male competition and female mate choice in the evolution of four plumage signals in a passerine, the lark bunting Calamospiza melanocorys, over five breeding seasons. Signals of social rank, or badges of status, can greatly reduce the costs of conflict and strife in social groups, but it remains unclear what advantage multiple status signals can carry. In lark buntings, multiple traits are used to resolve social conflict, but the utility of each trait depends on both the context in which they are used and degree of escalation in the contest. Models of the evolution of male sexual ornaments via female choice assume consistent directional mate preferences, yet this assumption is rarely tested. We found highly dynamic selection on male traits across years due to flexible female choice. Examination of some causes for flexible female choice reveal that fluctuations in female decisions are in part associated with direct benefits related to raising offspring which likely change from year to year. This result indicates much more complexity in female choice decisions than have been previously assumed and the implications of these results for sexual selection will be explored. Together these results provide support for two underappreciated mechanisms that affect the evolution of multiple sexual ornaments and will likely change our perspective on sexual selection and female choice.

Alexis Chaine
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