DOI: 10.5061/dryad.t4kv200
title: Data from: Contrasting genetic structure of sympatric congeneric gastropods: do differences in habitat preference, abundance, and distribution matter?

description: Aim: The relationship of population genetics with the ecology and
 biogeography of species may be explored by comparing phenotypically
 similar but ecologically different congeners with overlapping ranges. We
 compared genetic differentiation between two congeneric rocky intertidal
 gastropods across a major portion of their sympatric range. We
 hypothesized that the habitat generalist with high abundance and
 continuous distribution would exhibit comparatively less genetic
 differentiation than the habitat specialist with low abundance and a
 fragmented distribution. Location: Northeast Atlantic from the northwest
 Iberian Peninsula to southern British coastline. Taxon: Gastropoda,
 Trochidae, Steromphala (formerly Gibbula) Methods: Field surveys were
 conducted to assess presence/absence and abundance of Steromphala
 umbilicalis (generalist) and S. pennanti (specialist) at 23 localities
 along ~1800 km coastline. We isolated polymorphic microsatellite markers
 for both species (seven loci for S. umbilicalis and eight for S. pennanti)
 and used these to genotype 187 S. umbilicalis and 157 S. pennanti
 individuals. We used standard population genetic analyses to compare
 patterns of genetic differentiation between species in relation to the
 field surveys. Results: Steromphala pennanti showed a more fragmented
 distribution, significantly lower abundance, and greater genetic
 differentiation than S. umbilicalis. One S. umbilicalis population towards
 the north of the range (southern Britain) was genetically distinct from
 all other sampled populations. Steromphala pennanti showed greater genetic
 differentiation between three southern localities, which may be
 attributable to its fragmented distribution and lower abundance because of
 limited availability of its preferred fucoid habitat in this region. We
 also suggest that oceanographic currents could be associated with regional
 genetic structure. Main conclusions: The habitat generalist showed high
 local abundances, continuous distribution and low regional genetic
 differentiation across much of its range. We found the opposite pattern
 for the habitat specialist. Our study highlights the importance of
 considering ecological (e.g. abundance, habitat preferences) and abiotic
 variables (e.g. ocean currents and temperature) for understanding
 differences in genetic structure of sympatrically distributed congeners.
description: Steromphala pennanti
 microsatellitesFragment sizes of
 different microsatellite markers for Steromphala pennanti DNA samples.
 Column one gives the individual (P=Point du Chay, SJ=St Jean de Luz,
 LOC=Loctudy, V=Vilagarcia, H=Cap de la Hague, SV=San Vicente de la
 Barquera); other columns give marker names. Absent data is represented by
 "-1".S_pennanti_msats.csvSteromphala umbilicalis microsatellitesFragment sizes of different microsatellite markers for Steromphala umbilicalis DNA samples. Column one gives the individual (B=Biarritz, C=Cap de Carteret, LOC=Loctudy, LP=Les Pierrieres, S=San Vicente de la Barquera, SW=Swanage, V=Vilagarcia); other columns give marker names. Absent data is represented by "-1".S_umbilicalis_msats.xlsxAbundance of S. umbilicalis and S. pennantiDifferent localities' (column 1) timed search (individuals/minute) abundance estimates of Steromphala umbilicalis (column two) and Steromphala pennanti (column 3). Localities north of the habitat gap labelled "1" in column 4, south of the habitat gap labelled "2".timesearch_abundances.csv