Phenotypic and genetic differentiation between two chromosomal taxa of the gastropod Nucella lapillus at Galician rocky shores (NW Spain).

Abstract

In certain North Atlantic rocky shores, 2 chromosomal lineages of Nucella lapillus have been observed at different extremes of an environmental gradient. Here, we have determined the presence of this chromosomal polymorphism, resulting from Robertsonian translocations, in populations of the Iberian Peninsula spanning a similar gradient. Interestingly, we have found monomorphic populations (2n = 26) across the gradient while we only found polymorphic populations (2n = 27-36) in certain exposed microhabitats, and never both types of populations together. These chromosomal lineages differ morphologically and genetically in a manner that can be successfully discriminated, based on their morphology (95% of success) and molecular variation (99.9% of success), in the studied set of samples, and so considering these data this could potentially represent isolated evolutionary lineages or taxa. This situation is discussed in relation to the data available in previous studies in this and other geographical areas for this species. The new findings do not solve the problem of the Robertsonian polymorphism known to exist in this species, but it could perhaps suggest a new approach to solve it, suggesting a wide geographical comparison between the 2 taxa to confirm if they represent evolutionary isolated lineages or maintain a certain degree of hybridization.