Abstract
Within hybrid zones of socially monogamous species, the number of mating opportunities with a conspecific can be limited. As a consequence, individuals may mate with a heterospecific (social) partner despite possible fitness costs to their hybrid offspring. Extra-pair copulations with a conspecific may thus arise as a possible post hoc strategy to reduce the costs of hybridization. We here assessed the rate of extra-pair paternity in the hybrid zone between all-black carrion crows (Corvus (corone) corone) and grey hooded crows (C. (c.) cornix) and tested whether extra-pair paternity (EPP) was more likely in broods where parents differed in plumage colour. The proportion of broods with at least one extra-pair offspring and the proportion of extra-pair offspring were low overall (6.98% and 2.90%, respectively) with no evidence of hybrid broods having higher EPP rates than purebred nests.
Highlights
In stable zones of secondary contact and hybridization, species have diverged to a degree that they still interbreed but do not collapse back into one (Price, 2008)
The observed extra-pair paternity rates of 6.98% per brood and 2.90% across all offspring are much lower than a previous estimate from a carrion crow population (N = 59 nests) in which most pairs breed cooperatively (EPP rate 26% per brood; Baglione et al, 2002)
The only three broods of unassisted pairs all had no extra-pair paternity, which is consistent with the link between EPP rate and breeding system described across bird species (Brouwer & Griffith, 2019)
Summary
In stable zones of secondary contact and hybridization, species have diverged to a degree that they still interbreed but do not collapse back into one (Price, 2008). Reproductive isolation between hybridizing taxa can be maintained through pre- and post-zygotic barriers to gene flow (Irwin, 2019), such that heterospecific pairings are either largely avoided by assortative mating (prezygotic barriers; Mayr, 1942) or hybrid offspring suffer a reduction in fitness (post-zygotic barriers; Barton & Hewitt, 1989; Hatfield & Schluter, 1999). Additional potential post-zygotic effects, such as reduced egg size or hatching success of hybrid pairs, have been discussed (Saino, 1990; Saino & Bolzern, 1992; Saino & Villa, 1992) It may be advantageous for members of hybrid pairs to seek extra-pair copulations with conspecifics. We first quantify the number of extra-pair young in nests from the hybrid zone and test whether extra-pair behaviour occurs more frequently in heterospecific pairings
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
