The genetic architecture of hybridisation between two lineages of greenshell mussels

Abstract

A multidisciplinary approach has identified sigmoidal genetic clines on the east and west coasts in central New Zealand where low-density ecological interactions occur between northern and southern lineages of the endemic greenshell mussel, Perna canaliculus. The sigmoidal clines indicate the existence of a mussel hybrid zone in a region of genetic discontinuities for many continuously distributed coastal taxa, in particular marine invertebrates. Examination of the genetic architecture of the hybrid zone revealed the differential contribution of individual microsatellite loci and/or alleles to defining the zone of interaction and no evidence of increased allelic richness or heterozygosity inside versus outside the hybrid zone. Genomics cline analysis identified one locus in particular (Pcan1-27) as being different from neutral expectations, thereby contributing to lineage differentiation. Estimates of contemporary gene flow revealed very high levels of within-lineage self-recruitment and a hybrid zone composed mostly (~85%) of northern immigrants. Broad scale interpretation of these results is consistent with a zone of genetic interaction that was generated between 0.3 and 1.3 million years before present at a time of pronounced global sealevel change. At that time, the continuous distribution of the greenshell mussel was split into northern and southern groups, which differentiated to become distinct lineages, and which have subsequently been reunited (secondary contact) resulting in the generation of the hybrid zone at~42°S.

Genetic and morphological evidence of a geographically widespread hybrid zone between two crocodile species,Crocodylus acutusandCrocodylus moreletii

“…Indeed, the geographic location of a hybrid zone may reflect differences in the environmental preferences of the species, resulting in a mosaic or an environmental gradient (Confitti et al . ; Gardner & Wei ), like the complex mosaic hybrid zone along Europe observed for the marine mussels Mytilus edilus and Mytilus galloprovincialis (Fraïsse et al . ).…”

“…Hybrid zones can exhibit coincident geographic clines in trait values or allele frequencies. Some hybrid zones exhibit show sharp clines over short geographic distances (greenshell mussel, Perna canaliculus; Gardner & Wei 2015), whereas clines in other systems extend throughout large geographic regions (marine mussels; Fra€ ısse et al 2014). More complex patterns, such as mosaic hybrid zones that show steep clines between habitat patch boundaries, have also been documented (e.g.…”

“…; Harrison et al 1987;Ross & Harrison 2002). Indeed, the geographic location of a hybrid zone may reflect differences in the environmental preferences of the species, resulting in a mosaic or an environmental gradient (Confitti et al 2015;Gardner & Wei 2015), like the complex mosaic hybrid zone along Europe observed for the marine mussels Mytilus edilus and Mytilus galloprovincialis (Fra€ ısse et al 2014). The longterm evolutionary outcome of hybridization is less clear in cases where no sharp transitions are involved and hybrid zones are naturally diffuse.…”

Emerging patterns of genetic variation in the New Zealand endemic scallop Pecten novaezelandiae

“…There is thus uncertainty about the timing of the north–south split, about the mechanism(s) that caused its origin, and why most species are affected, but not all (Wei et al . ; Gardner & Wei ).…”