Do ornaments, arrival date, and sperm size influence mating and paternity success in the collared flycatcher?

Abstract

Males advertise their intrinsic parental and/or genetic qualities by the size of secondary sexual ornaments. Moreover, they compete with one another for the best territory and males who arrive first at the breeding ground usually have an advantage in this competition. Females may consider multiple male qualities simultaneously and prefer the one most important for their fitness in the current context. They can further improve their fitness by selecting the best care-giver as their social mate and engaging in an extra-pair copulation with a genetically superior male. In such cases, sperm competition arises in the female reproductive tract and its outcome may be affected by the sperm morphology of both the social and extra-pair male. Here, we tested these ideas in the collared flycatcher (Ficedula albicollis), a species with context-dependent choice of social partners and frequent extra-pair paternity. We recorded male arrival to breeding sites, manipulated their forehead patches, and measured sperm size. In contrast to a previous study in a Swedish population, males with enlarged patches were non-significantly less successful late in the season while no such difference was found early in the season. Besides this tendential seasonal interaction, arrival date did not affect mating and paternity success or male fitness, and the same was true for sperm size. These results suggest different benefits of male ornamentation and female mate choice between populations and call for more replicated research within and between species. The fitness of a male of a migratory species might be affected by several pathways. First, early arrival should confer benefits in the form of best territory choice. Second, in a dichromatic and sexually promiscuous species, secondary sexual ornaments are considered by females both in the choice of social and extra-pair mates. Third, by modifying sperm traits, males may outmatch their rivals in sperm competition. These ideas have usually been tested in isolation. In this experimental study, we tested the joint effect of all of these factors on the genetic fitness of males. We found little evidence for the dependence of male reproductive success on either sperm morphology or plumage ornamentation which is in contrast to other populations of the species. Our study calls for replicated research both in well-established fields like mate choice and emerging ones like sperm competition.