The zone of sympatry and hybridization of Mytilus edulis and M. galloprovincialis, as described by intron length polymorphism at locus mac-1

Abstract

Intron-size variation at the actin gene locus mac-1 was used to characterize mussel, Mytilus spp., populations in the approximately 2000-km wide zone of contact and hybridization ('hybrid zone') between M. edulis and M. galloprovincialis in western Europe. Twenty-five samples were collected in 1995-99 in locations within the hybrid zone and from reference populations of each species. We used correspondence analysis on the matrix of allelic frequencies to determine which alleles are characteristic of each species, and to characterize samples along the genetic gradient between M. edulis and M. galloprovincialis. In the hybrid zone, some samples exhibited mac-1 allele frequencies that were typical of M. edulis; other samples were distributed along the M. edulis/M. galloprovincialis gradient and displayed variable levels of intergradation that were not correlated with geography. Some of the latter samples exhibited significant heterozygote deficiencies. The simple admixture hypothesis (Wahlund effect) could not be rejected for two-fifths of the samples. The hybrid zone thus appeared as a mosaic of populations which are either pure M. edulis, or hybrid between M. galloprovincialis and M. edulis, or a mixture of the foregoing with M. galloprovincialis individuals. These results were consistent with published allozyme data, suggesting that they can be extended to the entire nuclear genome. M. edulis mac-1 alleles were present at moderate frequency in Atlantic M. galloprovincialis, and at significantly lower frequency in some Mediterranean samples. This pattern was homogeneous over a broad geographical range within each basin. It was not evident that introgression of M. edulis into M. galloprovincialis presently occurs south of the zone of contact. We propose that the distinctness of the Atlantic M. galloprovincialis population results from past introgression by M. edulis alleles.

Adaptive genetic variation distinguishes Chilean blue mussels (Mytilus chilensis) from different marine environments

“…Mytilus species are prone to produce hybrid in geographical areas where two sibling species coexist (Daguin et al. 2001; Toro et al. 2004a), given the opportunity to introgress alleles from one species into the other, producing higher F ST when these loci are evaluated in the genome of the recipient species.…”

Endemic North African Quercus afares Pomel originates from hybridisation between two genetically very distant oak species (Q. suber L. and Q. canariensis Willd.): evidence from nuclear and cytoplasmic markers

“…Alleles diagnostic of a given species were pooled in two synthetic alleles (S for Q. suber and C for Q. canariensis) per locus. Alleles common to both species were assigned according to their coordinates on the first axis of a correspondence analysis realised on the pure Q. suber and Q. canariensis populations (see Daguin et al, 2001). HI was estimated per locus and over all loci for each Q. afares individual, and then averaged per population.…”

Intron polymorphism (EPIC-PCR) reveals phylogeographic structure of Zacco platypus in China: a possible target for aquaculture development

“…This kind of marker, the subject of recent publications (Dixon et al, 1996;Villablanca et al, 1998;Bierne et al, 2000;Daguin et al, 2001) is promising for intraspecific structure description; however, basic knowledge is still missing and several technical problems must still be solved.…”