Molecular and morphological patterns of introgression between two large white‐headed gull species in a zone of recent secondary contact

Abstract

Incomplete reproductive isolation promotes gene flow between diverging taxa. However, any gene encoding for traits involved in the reproductive barriers will be less prone to introgression than neutral markers. Comparing introgression rates among loci is thus informative of the number and functions of loci involved in the reproductive barriers. This study aimed at identifying possible mechanisms of restriction to gene flow across a zone of recent secondary contact between Larus argentatus and Larus cachinnans by comparing introgression patterns for nine microsatellite loci, a fragment of mitochondrial DNA and a set of phenotypic traits. The low linkage disequilibrium between neutral nuclear markers indicated introgression without any barrier to gene flow. However, asymmetric introgression of mitochondrial DNA suggested that interspecific crosses may be more successful in one direction. The introgression rate for phenotypic traits was variable and low compared to neutral molecular markers. This was particularly evident in colouration of bare parts: individuals with intermediate colouration were scarcer in sympatry than expected if the genomes recombined freely. We hypothesized that one of these variables, the orbital ring colour, may play a role in mate choice, acting as an incomplete premating barrier through assortative mating. This study emphasizes that multilocus approaches are useful to discriminate among possible mechanisms responsible for the maintenance of hybrid zones.

Hybridization of glaucous gull (Larus hyperboreus) and herring gull (Larus argentatus) in Iceland: mitochondrial and microsatellite data

“…The argument was that cluster II harboured more variation in L. argentatus and that it had been supported by nuclear AFLP (de Knijff et al 2001). This is also supported by the recent study by Gay et al (2007) on introgression between L. cachinnans (a descendant from the AraloCaspian refugium) and L. argentatus.…”

“…Snell suggested that the claimed hybrids in Iceland were light-winged argentatus originating from Scandinavia and that no hybridization between the two species in Iceland occurs. Along with all the previously mentioned cases of hybridization in gulls, genetic research strongly suggests that gene flow among large white-headed gulls is in fact extensive in many parts of the world (Crochet et al 2002(Crochet et al , 2003Liebers et al 2004;Gay et al 2007). Thus, the haplotype and allele sharing in Icelandic L. hyperboreus and L. argentatus observed in this study should not be surprising.…”

“…Studies by Bell (1996) and Crochet (2000) indicated that the situation in gulls was more complex than simple surveys of plumage phenotypes or allozyme variation had shown. Similarly, more recent genetic studies on herring gulls and related species have shown discrepancies between gene trees and the taxon phylogeny, resulting from incomplete lineage sorting and/or hybridization (Crochet et al 2002(Crochet et al , 2003Liebers et al 2004;Gay et al 2007). Genetic work by Liebers et al (2004) on L. hyperboreus from Novaja Semlija, Svalbard and Baffinland indicated a phylogeographical split between Europe and America, and a similar split was described between the European L. argentatus and the American L. smithsonianus.…”

“…Larus smithsonianus!Larus hyperboreus in the Mackenzie Delta, Canada (Spear 1987), Larus glaucescens! Larus occidentalis on the Pacific coast of North America (Bell 1996), Larus argentatus!Larus fuscus in western France (Yesou 1991), L. argentatus!Larus cachinnans in Russia (Panov & Monzikov 1999) and Poland (Gay et al 2007), and L. argentatus!L. hyperboreus in Iceland (Ingólfsson 1970).…”

Tests of multiple molecular markers for the identification of Great Spotted and Syrian Woodpeckers and their hybrids

“…The utility of nuclear markers for identification of species and their hybrids has been shown for introns (e.g., Pacheco et al 2002;Nadachowska and Babik 2009), single nucleotide polymorphisms (SNP; e.g., Väli et al 2010;Hohenlohe et al 2011), and microsatellites (e.g., Gay et al 2007;Väli et al 2010). A combined set of nuclear and mitochondrial markers may be the best option for species and their hybrids identification, especially in birds, when hybridizing species diverged recently and share a high proportion of alleles (e.g., Gay et al 2007;Väli et al 2010).…”