Radical loss of an extreme extra-pair mating system

Sjouke A Kingma,Anne Peters,Michelle L Hall,Gernot Segelbacher

doi:10.1186/1472-6785-9-15

Sjouke A Kingma, Anne Peters + Show 2 more

Open Access

https://doi.org/10.1186/1472-6785-9-15

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Abstract

BackgroundMating outside the pair-bond is surprisingly common in socially monogamous birds, but rates of extra-pair paternity (EPP) vary widely between species. Although differences in life-history and contemporary ecological factors may explain some interspecific variation, evolutionary forces driving extra-pair (EP) mating remain largely obscure. Also, since there is a large phylogenetic component to the frequency of EPP, evolutionary inertia may contribute substantially to observed EP mating patterns. However, the relative importance of plasticity and phylogenetic constraints on the incidence of EP mating remains largely unknown.ResultsWe here demonstrate very low levels of EPP (4.4% of offspring) in the purple-crowned fairy-wren Malurus coronatus, a member of the genus with the highest known levels of EPP in birds. In addition, we show absence of the suite of distinctive behavioral and morphological adaptations associated with EP mating that characterize other fairy-wrens. Phylogenetic parsimony implies that these characteristics were lost in one speciation event. Nonetheless, many life-history and breeding parameters that are hypothesized to drive interspecific variation in EPP are not different in the purple-crowned fairy-wren compared to its promiscuous congeners.ConclusionSuch radical loss of an extreme EP mating system with all associated adaptations from a lineage of biologically very similar species indicates that evolutionary inertia does not necessarily constrain interspecific variation in EPP. Moreover, if apparently minor interspecific differences regularly cause large differences in EPP, this may be one reason why the evolution of EP mating is still poorly understood.

Highlights

Mating outside the pair-bond is surprisingly common in socially monogamous birds, but rates of extra-pair paternity (EPP) vary widely between species
Adaptations to extra-pair mating: morphology and behavior In M. coronatus, we found none of the male morphological adaptations for EP mating that are characteristic of other members of the genus (Fig. 1)
High infidelity has been assumed to occur in all fairywrens (e.g., [9,13,14]), we here show a marked exception: M. coronatus' mating system rather approaches genetic monogamy, with EPP rates being even lower than the average 18.7% of broods observed in socially monogamous birds [2]

Summary

Introduction

Mating outside the pair-bond is surprisingly common in socially monogamous birds, but rates of extra-pair paternity (EPP) vary widely between species. Differences in lifehistory and contemporary ecological factors may explain some interspecific variation, evolutionary forces driving extra-pair (EP) mating remain largely obscure. The relative importance of plasticity and phylogenetic constraints on the incidence of EP mating remains largely unknown. Phylogenetic constraints on EP mating are important, with over 50% of the interspecific variation being explained at the level of families or orders [2,5], suggesting that contemporary ecological factors may (sometimes) play a secondary role [5]. The relative importance of phylogenetic constraints on one hand and plasticity on the other in determining interspecific variation in EPP rates remains largely unknown

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