Sex-specific additive genetic variances and correlations for fitness in a song sparrow (Melospiza melodia) population subject to natural immigration and inbreeding.

Matthew E Wolak,Pirmin Nietlisbach,Lukas F Keller,Jane M Reid,Peter Arcese

doi:10.1111/evo.13575

Abstract

Quantifying sex-specific additive genetic variance (VA ) in fitness, and the cross-sex genetic correlation (rA ), is prerequisite to predicting evolutionary dynamics and the magnitude of sexual conflict. Further, quantifying VA and rA in underlying fitness components, and genetic consequences of immigration and resulting gene flow, is required to identify mechanisms that maintain VA in fitness. However, these key parameters have rarely been estimated in wild populations experiencing natural environmental variation and immigration. We used comprehensive pedigree and life-history data from song sparrows (Melospiza melodia) to estimate VA and rA in sex-specific fitness and underlying fitness components, and to estimate additive genetic effects of immigrants alongside inbreeding depression. We found evidence of substantial VA in female and male fitness, with a moderate positive cross-sex rA . There was also substantial VA in male but not female adult reproductive success, and moderate VA in juvenile survival but not adult annual survival. Immigrants introduced alleles with negative additive genetic effects on local fitness, potentially reducing population mean fitness through migration load, but alleviating expression of inbreeding depression. Our results show that VA for fitness can be maintained in the wild, and be broadly concordant between the sexes despite marked sex-specific VA in reproductive success.

Highlights

The magnitude of additive genetic variance (VA) in fitness governs the rate of adaptive trait evolution and the expected increase in population mean fitness (Fisher 1930; Robertson 1966; Price1970), and thereby links adaptation and population persistence (Bell 2013; Gomulkiewicz and Shaw 2013; Carlson et al 2014; Shaw and Shaw 2014)
28% of offspring are sired by extra-pair males (Sardell et al 2010), creating opportunities for individual males to gain or lose substantial reproductive success compared to their sociallypaired female (Reid et al 2011a, 2014b; Reid and Sardell 2012)
The posterior modes were similar in both sexes, and the lower 95% highest posterior density credible intervals (95%CI) limits did not converge towards zero (Table 1)

Summary

Introduction

The magnitude of additive genetic variance (VA) in fitness governs the rate of adaptive trait evolution and the expected increase in population mean fitness (Fisher 1930; Robertson 1966; Price1970), and thereby links adaptation and population persistence (Bell 2013; Gomulkiewicz and Shaw 2013; Carlson et al 2014; Shaw and Shaw 2014). VA in sex-specific fitness and 2 fitness components, and corresponding cross-sex and within-sex rAs, are key parameters shaping the total VA for fitness that emerges and is maintained following selection (Lewontin 1974; Rose 1982; 52 Chippindale et al 2001; Brommer et al 2007; Kruuk et al 2008; Walsh and Blows 2009; Walling et al 2014)

Methods

Results

Conclusion