Age-dependent trajectories differ between within-pair and extra-pair paternity success.

Y.‐H Hsu,J Schroeder,T Burke,S Nakagawa,A Girndt,I S Winney,M J P Simons

doi:10.1111/jeb.13058

Abstract

Reproductive success is associated with age in many taxa, increasing in early life followed by reproductive senescence. In socially monogamous but genetically polygamous species, this generates the interesting possibility of differential trajectories of within-pair and extra-pair siring success with age in males. We investigate these relationships simultaneously using within-individual analyses with 13years of data from an insular house sparrow (Passer domesticus) population. As expected, we found that both within- and extra-pair paternity success increased with age, followed by a senescence-like decline. However, the age trajectories of within- and extra-pair paternity successes differed significantly, with the extra-pair paternity success increasing faster, although not significantly, in early life, and showing a delayed decline by 1.5years on average later in life compared to within-pair paternity success. These different trajectories indicate that the two alternative mating tactics should have age-dependent pay-offs. Males may partition their reproductive effort between within- and extra-pair matings depending on their current age to reap the maximal combined benefit from both strategies. The interplay between these mating strategies and age-specific mortality may explain the variation in rates of extra-pair paternity observed within and between species.

Highlights

Age-dependent paternity success, a change with age in the number of offspring sired by a male, has been described in many taxa (Hoikkala et al, 2008, Carazo et al, 2011, Schroeder et al, 2012, Tarof et al, 2012, Lebigre et al, 2013)
The age-related increase in paternity success may result from older males being of high genetic quality, as evidenced by their viability (Fisher, 1930, Hamilton & Zuk, 1982, Brooks & Kemp, 2001)
High genetic quality can result in higher offspring fitness, and females may choose these older males as social and genetic sires for their offspring

Summary

Introduction

Age-dependent paternity success, a change with age in the number of offspring sired by a male, has been described in many taxa (Hoikkala et al, 2008, Carazo et al, 2011, Schroeder et al, 2012, Tarof et al, 2012, Lebigre et al, 2013). In a socially monogamous but genetically polygamous system, the costs and benefits of within- and extra-pair matings to males probably differ, such that these two avenues to paternity success might have different age trajectories This possibility has only been indirectly investigated once (Lebigre et al, 2013; but see below for further discussion), with the remaining studies either focusing on other mating systems (Auld et al, 2013, Froy et al, 2013, Hayward et al, 2013, Zhang et al, 2015, Caudill et al, 2016), in systems where extra-pair mating is rare and being neglected (Aubry et al, 2009, Bouwhuis et al, 2012, Zabala & Zuberogoitia, 2015), or mixing within-pair and extra-pair paternity successes instead of estimating them separately (Hatch & Westneat, 2007, Schroeder et al, 2012, Froy et al, 2013, Harris et al, 2016). The prediction of age-related increase in paternity success is consistent with the robust pattern supported by meta-analyses that, in birds, extra-pair fathers tend to be older than within-pair fathers (Akçay & Roughgarden, 2007, Cleasby & Nakagawa, 2012, Hsu et al, 2015)

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Conclusion