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Extrapair mating between relatives in the barn swallow: a role for kin selection?

ABSTRACT: Why do females of many species mate with more than one male? One of the main hypotheses suggests that female promiscuity is an insurance mechanism against the potential detrimental effects of inbreeding. Accordingly, females should preferably mate with less related males in multiple or extrapair mating. Here we analyse paternity, relatedness among mating partners, and relatedness between parents and offspring, in the socially monogamous North American barn swallow (Hirundo rustica erythrogaster). In contrast to the inbreeding avoidance hypothesis, we found that extrapair mating partners were more related than expected by random choice, and tended to be more related than social partners. Furthermore, extrapair mating resulted in genetic parents being more related to their extrapair young than to their withinpair young. We propose a new hypothesis for extrapair mating based on kin selection theory as a possible explanation to these findings.

SUBMITTER: Kleven O

PROVIDER: S-EPMC1626374 | biostudies-literature | 2005 Dec

REPOSITORIES: biostudies-literature

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Extrapair mating between relatives in the barn swallow: a role for kin selection?

Kleven Oddmund O Jacobsen Frode F Robertson Raleigh J RJ Lifjeld Jan T JT

Biology letters 20051201 4

Why do females of many species mate with more than one male? One of the main hypotheses suggests that female promiscuity is an insurance mechanism against the potential detrimental effects of inbreeding. Accordingly, females should preferably mate with less related males in multiple or extrapair mating. Here we analyse paternity, relatedness among mating partners, and relatedness between parents and offspring, in the socially monogamous North American barn swallow (Hirundo rustica erythrogaster) ...[more]

PMID: 17148214

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Project description:Variation in intensity and targets of sexual selection on multiple traits has been suggested to play a major role in promoting phenotypic differentiation between populations, although the divergence in selection may depend on year, local conditions or age. In this study, we quantified sexual selection for two putative sexual signals across two Central and East European barn swallow (Hirundo rustica rustica) populations from Czech Republic and Romania over multiple years. We then related these differences in selection to variation in sexual characters among barn swallow populations. Our results show that tail length and ventral coloration vary between populations, sexes, and age classes (first-time breeders vs. experienced birds). We found that selection on tail length was stronger in first-time breeders than in experienced birds and in males than in females in the Romanian population, while these differences between age groups and sexes were weak in Czech birds. We suggest that the populational difference in selection on tail length might be related to the differences in breeding conditions. Our results show that ventral coloration is darker (i.e., has lower brightness) in the Romanian than in the Czech population, and in experienced birds and males compared with first-time breeders and females, respectively. The sexual difference in ventral coloration may suggest sexual selection on this trait, which is supported by the significant directional selection of ventral coloration in first-time breeding males on laying date. However, after controlling for the confounding effect of wing length and tarsus length, the partial directional selection gradient on this trait turned nonsignificant, suggesting that the advantage of dark ventral coloration in early breeding birds is determined by the correlated traits of body size. These findings show that ventral coloration may be advantageous over the breeding season, but the underlying mechanism of this relationship is not clarified.

Project description:BackgroundIn diverse taxa, photoperiodic responses that cause seasonal physiological and behavioural shifts are controlled by genes, including the vertebrate Clock orthologues, that encode for circadian oscillator mechanisms. While the genetic network behind circadian rhythms is well described, relatively few reports exist of the phenological consequences of and selection on Clock genes in the wild. Here, we investigated variation in breeding phenology in relation to Clock genetic diversity in a long-distance migratory bird, the barn swallow (Hirundo rustica).Methodology/principal findingsIn a sample of 922 adult barn swallows from a single population breeding in Italy we found one very common (Q(7)) and three rare (Q(5), Q(6), Q(8)) length variants of a functionally significant polyglutamine repeat. Rare (2.9%) Q(7)/Q(8) heterozygous females, but not males, bred significantly later than common (91.5%) Q(7)/Q(7) females, consistent with the expectation that 'long' alleles cause late breeding, as observed in a resident population of another bird species. Because breeding date depends on arrival date from migration, present results suggest that the association between breeding date and Clock might be mediated by migration phenology. In addition, fecundity selection appears to be operating against Q(7)/Q(8) because late migrating/breeding swallows have fewer clutches per season, and late breeding has additional negative selection effects via reduced offspring longevity. Genotype frequencies varied marginally non-significantly with age, as Q(7)/Q(8) frequency showed a 4-fold reduction in old individuals. This result suggests negative viability selection against Q(7)/Q(8), possibly mediated by costs of late breeding.Conclusions/significanceThis is the first study of migratory birds showing an association between breeding phenology and Clock genotype and suggesting that negative selection occurs on a phenologically deviant genotype. Low polymorphism at Clock may constrain microevolutionary phenological response to changing climate, and may thus contribute to the decline of barn swallow populations.

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Extrapair mating between relatives in the barn swallow: a role for kin selection?

Publications

Extrapair mating between relatives in the barn swallow: a role for kin selection?

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