Abstract
Species with variable mating systems provide a unique opportunity to investigate whether females receive direct fitness benefits from additional male partners. The direct benefits provide an obvious explanation for why females would breed polyandrously, in a situation where males clearly do not attain their optimal reproductive success. Evidence for these direct benefits is, however, mixed. Here, we present a detailed study of the breeding biology of the dunnock, Prunella modularis, which inform an investigation into the effects of the social mating system on the reproductive success in a population of dunnocks in Southern New Zealand. We studied 80 different social groups over the course of three breeding seasons. Dunnocks in our population presented a variable mating system, with socially monogamous (45%), socially polyandrous (54%) and socially polygynandrous (1%) groups being observed in the same breeding season. We did not observe any polygynous social units in our study period although polygyny exists in the population. We found little difference in the numbers of eggs laid, and egg volume between monogamous and polyandrous nests. However, polyandrous groups had better hatching and fledging success than monogamous groups (composite d = 0.385, 95% CI: 0.307 to 0.463). Overall our results support the notion that polyandry is beneficial for females.
Highlights
There is little intra-specific variation in social breeding systems, with one form being commonly the only one observed in a population
Some females might breed in socially polyandrous groups, gaining direct fitness benefits conferred by additional paternal care
We investigated whether the types of social mating system affected breeding parameters and nest survival in our population
Summary
There is little intra-specific variation in social breeding systems, with one form (e.g., monogamy) being commonly the only one observed in a population. This is especially the case for bird species, in some instances, the genetic breeding system could provide another dimension of variation [1,2]. Some species exhibit variable breeding systems, in which two or more types of social units occur during the reproductive season (e.g., pukeko, Porphyrio porphyrio, [6]) In these species, the outcome of sexual conflict over mating optima is more readily observed. A replication using the same species in a different population is likely to provide us with fresh insights
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