The sea snail Littorina fabalis is a gastropod mollusk that is present in numerous rocky intertidal areas of much of the Galician coast and that is characterized, among many other aspects, by the polymorphism of the color of its shells. Aware of this fact and willing to study its causes, the researcher from the Marine Research Center of the University of Vigo (CIM-UVIGO) Daniel Estévez focused his doctoral thesis on the study of the different aspects related to the fact that this chromatic polymorphism has remained stable over the last decades. It was three years of research and study in which he tried to answer multiple questions, including whether there is a frequency-dependent selection mechanism in the Galician populations of this species, how it works, which is the component of effectiveness most related to the color of the shell and whether genetic drift can explain the changes in frequency in the different characters.
“L. fabalis shows a clear polymorphism of color and banding pattern in the shell that, in the A Coruña village of Abelleira, in the heart of the Muros e Noia estuary, has remained stable for more than 21 years,” explains the author of the thesis, a researcher in the Department of Biochemistry, Genetics and Immunology, who emphasizes that after all the work carried out over the three years he dedicated to writing this study, it is clear that one of the most plausible mechanisms to explain the maintenance of color over time is a frequency-dependent sexual selection that is caused by a negative preference exercised by males.
This explanation has, according to the researcher, its main defense in the fact that the most frequent pairs are those between different colors, which would also be a consequence of a negative preference. On the other hand, for the banding pattern, no evidence of frequency-dependent sexual selection was found, but they did find an inverse relationship between a component of global effectiveness and the frequency of banded individuals in the population. “It is interesting that, in both characters, genetic drift -an evolutionary force that would explain the changes in frequency due to chance- would sufficiently explain the changes in polymorphism when these are not exaggerated from year to year, while it does not explain them when they are more pronounced”, emphasizes Estévez, who considers that this would indicate that both the color and the banding pattern are maintained over time by the joint action of both drift and natural selection, the intensity of these two alternating depending on the magnitude of the changes in polymorphism.
Key studies to establish conservation plans for this species
The results of this doctoral thesis, directed by CIM-UVIGO researchers Juan Galindo and Emilio Rolán and defended at the Faculty of Biology, now allow the scientific community to get closer to predicting biological evolution in different natural populations of this species. “Knowing how genetic diversity varies allows us to evaluate how these populations would withstand environmental changes and disturbances,” explains the researcher, while underlining the fact that when establishing conservation or exploitation plans for a given resource, it is always essential to know these aspects in the different organisms of a given ecosystem.
Source: DUVI
