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Littorina brevicula is one of the most common gastropods in the supralittoral zone around Japan. The northernmost population of this species is around Hokkaido and the determinant of this northern limit is likely seawater and air temperature. To reconstruct an evolutionary history of this species, we investigated genetic differentiation among 12 populations (three from Hokkaido, six from Honshu and three from Kyushu) using a mitochondrial DNA marker (partial sequence of the NADH dehydrogenase 6 gene). The haplotype network showed shallow genetic divergence within the species, suggesting a bottleneck followed by population expansion. One major haplotype that occurred in 70.5% of all individuals examined was the most frequent in every population sampled. A second major haplotype was abundant around Kyushu but not found in Hokkaido. This skewed haplotype distribution resulted in significant genetic differentiation along the north-south axis of Japan. The importance of the southern clade, which included the second major haplotype, was supported by population genetic analyses of datasets that excluded either the southern clade or the northern clades. The north-south differentiation remained when datasets that excluded the northern clades were used, but disappeared when datasets that excluded the southern clade were used. The combined evidence of shallow divergence and the north-south population structure suggests that the L. brevicula population around Japan once declined and then expanded and colonized northward. Although the time of population reduction and recolonization could not be precisely estimated, the observation that this species is absent further north in Japan suggests that it would have been unable to survive in northern Japan during the last glacial maximum (LGM) and therefore recolonization likely occurred after the LGM, probably from south to north. [ABSTRACT FROM AUTHOR]

Species occupying different ecological niches may evolve ecotypes that differ in size as a result of divergent selection on this trait. Size differences may affect mate preference and cause deviations from random mating. Several marine snails of the genus Littorina have ecotypes that differ in size and earlier studies have shown strong assortative mating between differently sized ecotypes in at least one of these species, L. saxatilis. Here we studied male mate choice in two ecotypes of the congeneric L. fabalis that differ in size. We found mating to be nonrandom, because males of the large ecotype followed the mucus trails and copulated with females of their own large ecotype more than with females of the smaller ecotype. Males of the smaller ecotype showed no strong preference, but tended to copulate more with females of the large ecotype than with their own females. Further experiments using the small ecotype showed that mate choice was size-based, with a general preference of the males to mate large females. It seems likely that the partial reproductive barrier that we describe somewhat impedes gene flow between the two ecotypes of L. fabalis, a result that corroborates earlier observations of a weak, but significant, gene-flow barrier across zones where the two ecotypes overlap and hybridize. [ABSTRACT FROM AUTHOR]

Three unknown Littorina species were revealed by allozyme study of snails from the northwestern Pacific. One of them was found in Kasatka Bay (Pacific coast of Iturup Island, south Kurile Islands) together with L. sitkana, which it resembled in anatomical features, but the genetic distance between these species was D=0.622. The second one was found in Tauiskaya Inlet (northern part of Okhotsk Sea) and was again similar to L. sitkana in morphological and anatomical features, but D=1.160. The third species was found in Egvekinot Inlet (Anadyrskiy Gulf, Bering Sea) in sympatry with L. natica, to which was close genetically (D=0.256) although it differed in shell shape. [ABSTRACT FROM AUTHOR]

Although Littorina littorea (L.) exhibits a relatively consistent pattern of vertical distribution throughout the North Atlantic, ranging from the mid-intertidal to the shallow subtidal zone, its horizontal distribution and abundance are highly variable. In this study, we first described the snail's horizontal distribution patterns on Appledore Island, ME, USA and then asked whether wave exposure, rugosity, predator density (e.g. Carcinus maenas and Cancer borealis), the percentage of the substrate covered by Ascophyllum nodosum, Chondrus crispus, Polysiphonia spp., and ephemeral green algae, or the percentage of uncovered substrate (bare rock) were correlated with L. littorea abundance in the intertidal zone (0.6 to 0.0 4;m relative to Mean Lower Low Water [MLLW]) and the shallow subtidal zone (−1.5 to −3.0 4;m MLLW) at nine study sites. Intertidal densities of L. littorea were highly variable across sites, ranging from 0 to >600 4;m−2. In this zone, L. littorea density showed a significant positive correlation with rugosity and percentage of bare rock. Densities were very low in the subtidal zone (range: 0–19 4;m−2) and varied little among sites. Exploratory multiple regression analysis suggested that L. littorea density was positively correlated with the density of C. maenas in the shallow subtidal zone. Additionally, snails in the subtidal zone had thicker shells than snails of the same size in the intertidal zone. Our results suggest that structural elements of the habitat, such as rugosity and percentage of uncovered substrate, are among the most important predictors of L. littorea abundance on moderately protected, rocky intertidal shores. [ABSTRACT FROM AUTHOR]

Here we present data concerning the ability of two littorinids to remain attached to a slate substratum as a dislodging force is applied vertically. Specimens of Littorina littorea (L.) and L. obtusata (L.) were attached to a simple pulley and sandflow system which applied force to the animals at a constantly increasing rate until the animals released from the substratum. Three aspects of tenacity were measured: force required to remove the winkles from the substratum; time taken for removal; and final displacement at removal. For L. littorea the mean force required (1.09 N), the mean displacement (8.9 mm) and the mean time taken (185 s) were all found to be significantly greater than those recorded for L. obtusata (means = 0.60 N, 7.5 mm and 102 s, respectively). However, when animal size was taken into account there was no significant difference in either force or time required for removal, although L. obtusata showed a greater displacement than did L. littorea. Animal dry flesh weight was not a useful predictor of any of the tenacity variables. Rugosity of the slate substrata was shown to have a significant effect on all tenacity variables, greater forces being required to remove both species of winkle from smooth substrata than from rough substrata. This also generally held true when animal size was accounted for. The results of these experiments, although insufficient to identify the mechanism(s) of attachment, do discount the mechanism of ‘muscular grip’, since greater tenacity would be expected on rough substrata. Whether winkles were immersed or emersed had no significant effect on any of the tenacity variables. Recorded tenacities suggest that many L. littorea and L. obtusata would be dislodged by the direct forces created by breaking waves. [ABSTRACT FROM AUTHOR]

We investigated variation in shell size and shape of marine snail species of the Littorina saxatilis complex (L. saxatilis, L. compressa and L. arcana) using geometric morphometric methods. These morphologically similar periwinkle species that are common in the European intertidal have presented many problems for diagnosis based on morphology alone. A discriminant analysis demonstrated that geometric morphometrics is very efficient for diagnosing individuals to species among sympatric populations. We successfully diagnosed an average of 96% of the specimens (with 85.7–100% correct diagnosis for specific comparisons). The diagnosis capability of this method is absolute at the population level. This makes the technique potentially useful for the design of manipulative field or laboratory experiments. Moreover, a geometric-morphometric analysis was also accomplished in two snail ecotypes (H and M) of L. saxatilis from rocky shores of NE England which are apparently adapted to different degrees of wave exposure. We found that the H (exposed) ecotype has a relatively rounded shell shape with a bigger aperture, whereas the M (protected) ecotype has a smaller aperture. [ABSTRACT FROM AUTHOR]