Heterozygosity, genetic similarity and extra‐pair paternity variation in two populations of rock sparrow Petronia petronia: a within and between populations comparison

Abstract

Extra-pair paternity (EPP) has been broadly reported in socially monogamous bird species and it has been hypothesized that females engage in extra-pair copulations to increase the genetic variability of the offspring and to reduce the risk of inbreeding and genetic incompatibilities. This hypothesis makes two predictions: within populations, females should engage with more dissimilar/heterozygous males and, among populations, females should pursue more frequently EPP in populations characterized by a lower genetic variability and a higher homozygosity. However, support is still unclear throughout literature, and usually involves the study of a single population. We compared a peripheral population of rock sparrow Petronia petronia living at the marginal distribution of the species and characterized by a high EPP level (> 50%) (Italian Alps) with a population located in the centre of the species' distribution (central Spain), to understand if variations in EPP could be linked to differences in mean heterozygosity and genetic similarity both between and within populations. EPP in the Spanish population was 18.1%, three times lower than that observed in the Alpine one (51.2%), and this difference remained fairly constant across different years. Supporting the between populations prediction, we found lower heterozygosity and reduced allelic richness in the Alpine population compared to the Spanish one. In contrast, social and extra-pair males, as well as within and extra-pair offspring, did not significantly differ in terms of genetic similarity and heterozygosity within brood in either population. Social and extra-pair males did not differ in tarsus size, body weight or yellow badge size, suggesting that females were not choosing extra-pair partners based on heterozygosity, genetic similarity or phenotypic quality. Although based on a limited sample in the within population analysis, our results indicate that EPP may evolve in response to a low level of genetic variability in the population.

Extra‐pair paternity correlates with genetic diversity, but not breeding density, in a Neotropical passerine, the black catbird

“…heritable variance in quality). Across populations, this hypothesis predicts that EPP should increase with overall genetic diversity (Liu et al 2015, Corregidor‐Castro et al 2022) and with increasing inter‐individual variation in male quality (Petrie and Lipsitch 1994). Within populations, females paired to low‐quality males, or to genetically similar males, should be more likely to seek extra‐pair mates in order to increase the genetic quality or diversity of their offspring (Blomqvist et al 2002, Richardson et al 2005).…”

Low Extra-Pair Paternity and Polygamy in the Common Kingfisher Alcedo atthis

“…Extra-pair mating in birds is common; fewer than 25% of bird species are socially as well as genetically monogamous (Griffith et al , 2002; Brouwer & Griffith, 2019), while the extent of extra-pair paternity (EPP) varies greatly, ranging from 0 to up to 62% (Warkentin et al ., 1994; Kleven et al , 2008; Hajduk et al , 2021). It may even vary between different populations of the same species (e.g., Evans et al ., 2009, Corregidor-Castro et al ., 2022) and generally can be influenced by habitat fragmentation (Evans et al ., 2009), latitude (Valcu et al ., 2021), synchronicity of breeding (Stutchbury & Morton, 1995) or by a high density of breeding individuals (Westneat & Sherman, 1997).…”

“…The involvement of males in extra-pair copulation (EPC) is mainly explained by the enhancement of male breeding productivity, while high-quality males (genetically diverse, phenotypically superior, in good body condition) can be expected to sire larger progenies (Kempenaers et al , 1992; Petrie & Kempenaers, 1998; Dyrcz et al , 2005; Badás et al , 2020). By participating in extrapair copulations, females enhance the probability of good genes for their offspring (Jennions & Petrie, 2000), genetic compatibility and diversity (Johnsen et al ., 2000; Tregenza & Wedell, 2000; Corregidor-Castro et al, 2022) or avoid inbreeding (Brooker et al, 1990; Brouwer et al ., 2017). In addition, females may also benefit directly from provisioning by the extra-pair male, having access to additional food resources or help with nest defence (Gray, 1997; Townsend et al ., 2010).…”