Molecular genetic evidence for parallel evolution in a marine gastropod, Littorina subrotundata

Abstract

Littorina subrotundata from wave-exposed rocky shores differ consistently in shell and radula morphology from those found in wave-protected salt-marshes. To determine if the two morphological forms of this gastropod represent separate species, clades, or ecotypes, DNA sequencing and single-stranded conformational polymorphism (SSCP) analysis were used to assay variation in a 480 bp fragment of the mitochondrial cytochrome-b gene. Several nested analyses of molecular variance (AMOVA) were then performed to test if grouping populations by geographical region or habitat type better explained the distribution of cytochrome-b haplotypes among some northeastern Pacific populations. The analysis by geographic region resulted in a significant variance component that explained 53% of the variance, whereas the analysis by habitat type was not significant. These results, along with previous studies showing that the differences in shell morphology among different forms have a heritable component, suggest that the two forms are ecotypes and not separate species or clades as had been previously proposed. These results also imply that each ecotype has evolved independently in each geographic area and that the morphological similarity of individuals from the same habitat type is most likely the result of parallel evolution.

Molecular Evidence for Repetitive Parallel Evolution of Shell Structure in Clausiliidae (Gastropoda, Pulmonata)

“…The morphology of shells might be more often subject to parallel evolution than we have thought so far. Evidence for parallel evolution of two morphological forms has been found before in the marine gastropod Littorina subrotundata by Kyle and Boulding (1998). These authors conclude that the different forms are ecotypes.…”

The species flocks of lacustrine gastropods: Tylomelania on Sulawesi as models in speciation and adaptive radiation

“…The finding of largely species-specific radula types and the correlation between trophic morphology and substrate in Tylomelania as well as marked niche differences in species von Rintelen et al, 2007) suggest a strong role for ecological factors in speciation in these snails. In gastropods, studies on intertidal marine species of Littorina have indicated differentiation across ecotones and assortative mating between morphs (Johannesson et al, 1995;Kyle & Boulding, 1998;Wilding et al, 2001). The limnic gastropods of Sulawesi offer excellent opportunities to test the importance of these factors in freshwater.…”

Molecular genetic analyses of species boundaries in the sea

“…Species of gastropods have been even more extensively investigated. The genus Littorina, for example, has a long history of study [see recent works by Reid et al (1996), Grahame et al (1997), Tatarenkov & Johannesson (1998), and Kyle & Boulding (1998)]. Other genera that have been recently analyzed include Hydrobia (Ponder & Clark, 1988), Stramonita (Liu et al, 1991), Alviniconcha (Denis et al, 1993), Trochus (Borsa & Benzie, 1993), Tectus (Borsa & Benzie, 1993), Austrocochlea (Parsons & Ward, 1994), Drupella (Johnson & Cumming, 1995), Columbella (Oliverio, 1995), Patella (Côrte-Real et al, 1996a,b;Ridgway et al, 1998), Nassarius (Sanjuan et al, 1997), Nucella (Kirby et al, 1997;Marko, 1998), and Dendronotus (Thollesson, 1998).…”

“…The multipronged attack on the population structure of Crassostrea across the Gulf of Mexico and Atlantic coast of North America (see most recently Hare & Avise, 1998) has shown that different techniques can give fundamentally different answers for reasons that still remain unclear. In Littorina, closely related pairs of taxa that occur in different habitats have in some studies been shown to exhibit reproductive barriers across environmental gradients within a site but, in other cases, samples from different environments within sites are more similar genetically than are those samples which are geographically isolated but environmentally similar (Kyle & Boulding, 1998;Tatarenkov & Johannesson, 1998). Some of this complexity is probably due to the proximity of the divergences being studied in all three genera (see Discussion), but is such complexity lying below the surface in the many other groups that have yet to be investigated so intensively?…”