DOI: 10.5061/dryad.jb10h
title: Data from: Size selection by a gape-limited predator of a marine snail: insights into magic traits for speciation

description: The intertidal snail Littorina saxatilis has repeatedly evolved two
 parallel ecotypes assumed to be wave adapted and predatory shore crab
 adapted, but the magnitude and targets of predator-driven selection are
 unknown. In Spain, a small, wave ecotype with a large aperture from the
 lower shore and a large, thick-shelled crab ecotype from the upper shore
 meet in the mid-shore and show partial size-assortative mating. We
 performed complementary field tethering and laboratory predation
 experiments; the first set compared the survival of two different
 size-classes of the crab ecotype while the second compared the same
 size-class of the two ecotypes. In the first set, the large size-class of
 the crab ecotype survived significantly better than the small size-class
 both on the upper shore and in the laboratory. In the second set, the
 small size-class of the crab ecotype survived substantially better than
 that of the wave ecotype both on the upper shore and in the laboratory.
 Shell-breaking predation on tethered snails was almost absent within the
 lower shore. In the laboratory shore crabs (Pachygrapsus marmoratus) with
 larger claw heights selected most strongly against the small size-class of
 the crab ecotype, whereas those with medium claw heights selected most
 strongly against the thin-shelled wave ecotype. Sexual maturity occurred
 at a much larger size in the crab ecotype than in the wave ecotype. Our
 results showed that selection on the upper shore for rapid attainment of a
 size refuge from this gape-limited predator favors large size, thick
 shells, and late maturity. Model parameterization showed that
 size-selective predation restricted to the upper shore resulted in the
 evolution of the crab ecotype despite gene flow from the wave ecotype
 snails living on the lower shore. These results on gape-limited predation
 and previous ones showing size-assortative mating between ecotypes suggest
 that size may represent a magic trait for the thick-shelled ecotype.
description: Tethering data November
 2013 crab ecotypeTethering results for
 November 2013 at high and mid intertidal levels at Cabo Silleiro with 4 mm
 crab ecotype and 9 mm crab ecotype. 2nd sheet has codes for shell
 fragments.Cabo Silleiro field tethering
 Nov 12-29 2013 rev2 input
 simple.xlsxTethering April June
 2014 4mm crab and wave ecotypesTethering results for
 April to June 2014 at high, mid, and low intertidal levels at Cabo
 Silleiro with 4 mm crab ecotype and 4 mm wave ecotype. 2nd sheet has codes
 for shell fragments.Cabo Silleiro field tethering
 April June 2014 rev10
 simple.xlsxECIMAT1 crab ecotype 4mm
 9mm by day cw ph simpleLab experiment 1 with
 marbled shore crabs offered ten snails of 4 mm crab ecotype and ten snails
 of 9 mm crab ecotype every two days.ECIMAT2 crab wave
 ecotypes 4mm by day cw ph simpleLab experiment 2 -
 marbled shore crabs offered ten 4mm wave ecotype and ten 4 mm crab ecotype
 snails every two daysshell
 length_weight_thickness_morphometrics ver 2Shell measurement, shell
 weight, shell thickness, gender, maturity, geometric morphometric
 measurements for natural size range above 3 mm for crab ecotype and wave
 ecotype.GM
 corregido lenght_weight_thickness_morphometrics ver 2
 simple.xlsx