DOI: 10.5061/dryad.7fn18
title: Data from: Ecological speciation in an island snail: evidence for the parallel evolution of a novel ecotype and maintenance by ecologically dependent postzygotic isolation

description: 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.
description: 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.