The paths of parallel evolution and their genetic crossroads
One of the first steps in ecological speciation is the formation of locally adapted ecotypes. Taxa experiencing the same divergent selection pressure over a large geographic range may evolve similar ecotypes independently in different locations, a process called parallel evolution. Although the study of parallel phenotypic evolution has contributed to our knowledge about adaptation and speciation, the genetic mechanisms underlying this process are still largely unknown.
The marine/terrestrial transition at the intertidal zone is a natural laboratory: this ecological transition is one of the most violent in nature, and its intensity varies locally with the slope of the shore, and at a larger scale with the amplitude of tides and the climate. Recent studies on Littorina species (marine intertidal gastropods), have highlighted their potential for studying parallel divergent evolution. We have chosen the flat periwinkle, L. fabalis , a common intertidal gastropod, as our focal species. L. fabalis is widely distributed throughout NE Atlantic coasts. Two locally adapted ecotypes, ‘Large ecotype in Moderately exposed habitats’ (LM) and ‘Small-Sheltered ecotype’ (SS), can be found throughout Northern Europe, while three other ecotypes were described for Iberia, associated with different algae genera located in different parts of the intertidal zone. The presence of multiple ecotypes in different locations is probably determined by both biotic and abiotic environmental factors, and makes this species among the most interesting for studies of parallel evolution and speciation.
This international project will employ an innovative sampling design and a multidisciplinary approach focusing on ecology, morphology, genomics, transcriptomics and modelling, with the aim of identifying and characterizing loci under disruptive selection among ecotypes in different geographic regions. This will allow us to shed light on the genetic mechanisms of ecotype evolution and more specifically, to understand if parallel divergent evolution evolves through the same genetic paths. In other words, how repeatable is ecotype evolution?
Roger Kenneth Butlin, Emilio Rolán-Alvarez, Petri M. Kemppainen, Juan Antonio Gabaldón Estevan, Juan Galindo Dasilva, Katja Nowick, Christine Altenrath