Data from: Ecological speciation in an island snail: evidence for the parallel evolution of a novel ecotype and maintenance by ecologically dependent postzygotic isolation

Speciation is the process by which reproductive isolation evolves between populations. Two general models of speciation have been proposed: ecological speciation, where reproductive barriers evolve due to ecologically based divergent selection, and mutation-order speciation, where populations fix different mutations as they adapt to similar selection pressures. I evaluate these alternative models and determine the progress of speciation in a diverse group of land snails, genus Rhagada, inhabiting Rosemary Island. A recently derived keeled-flat morphotype occupies two isolated rocky hills, while globose-shelled snails inhabit the surrounding plains. The study of one hill reveals that they are separated by a narrow hybrid zone. As predicted by ecological speciation theory, there are local and landscape level associations between shell shape and habitat, and the morphological transition coincides with a narrow ecotone between the two distinct environments. Microsatellite DNA revealed a cline of hybrid index scores much wider than the morphological cline, further supporting the ecological maintenance of the morphotypes. The hybrid zone does not run through an area of low population density, as is expected for mutation-order hybrid zones, and there is a unimodal distribution of phenotypes at the centre, suggesting that there is little or no prezygotic isolation. Instead, these data suggest that the ecotypes are maintained by ecologically dependent postzygotic isolation (i.e. ecological selection against hybrids). Mitochondrial and Microsatellite DNA indicate that the keeled-flat form evolved recently, and without major historical disruptions to gene flow. The data also suggest that the two keeled-flat populations, inhabiting similar rocky hills, have evolved in parallel. These snails provide a complex example of ecological speciation in its early stages.,Lats, longs and mean spire (ahell shape) index for each siteGeographic coordinates (decimal degrees ;wgs 84), and mean spire index (with standard error and standard deviation) for each sample site in the study area. Data collected in field with hand held GPS.Individual shell measurements at each transect siteShell measurements (shell height, shell width) and the spire index (shell height/shell width) at each site. Data collected with calipers accurate to 0.1 mm.Microsatellite genotypesMultilocus microsatellite genotypes. Allele codes indicate fragment length (bp). data flie formated as 1 allele per column, 2 alleles per locus. Transect, site and individual number all provided.Estimates of habitat variables at each siteField measurements of the local habitat at each sample site.Estimates of population density across the collapsed transectEstimates of population density (density of live snails per square meter) at each site along the collapsed transect. Data collected during sampling.Rosemary Rhagada COI sequences666 bp fragments of the mitochondrial gene Cytochrome Oxidase subunit I from 263 snails collected from the main study area. The first number in the title is the transect number, the second is the site number and the third is the individual number (Transect_Site_Individual). The dataset is edited and aligned. Sequences with the same name followed by the letter B were collected from the same site on different occasions (i.e., 8_1_4 and 8_1_4B). The sequences have been edited and aligned.,