Temporal stability and directional change in a color cline of a marine snail from NW Spain

The evolution and maintenance of color clines is a classic topic of research in evolutionary ecology.However,studies analyzing the temporal dynamics of such clines are much less frequent,due to the difficulty of obtaining reliable data about past color distributions along environmen-tal gradients.In this article,we describe a case of decades-long temporal stability and directional change in a color cline of the marine snail Littorina saxatilis along the coastal inlet of the Ria de Vigo(NW Spain).L.saxatilis from this area shows a clear color cline with 3 distinct areas from the innermost to the more wave-exposed localities of the Ria:the inner,protected localities show an abundance of fawn-like individuals;the intermediate localities show a high diversity of colors;and the outer,wave-exposed localities show populations with a high frequency of a black and lineated morph.We compare data from the 1970s and 2022 in the same localities,showing that the cline has kept relatively stable for at least over half a century,except for some directional change and local variability in the frequency of certain morphs.Multiple regression analyses and biodiversity measures are presented to provide clues into the selective pressures that might be involved in the maintenance of this color cline.Future research avenues to properly test the explanatory power of these selective agents as well as the possible origins of the cline are discussed.

Limited proteomic response in the marine snail Melarhaphe neritoides after long-term emersion

Rocky intertidal organisms are commonly exposed to environmental gradients, promoting adapta-tions to these conditions. Emersion time varies along the intertidal range and in the supralittoralzone is frequently larger than a single tidal cycle, even lasting for weeks. The planktonic-dispersinggastropod Melarhaphe neritoides is a common species of the high shore, adapted to reduce waterloss in order to survive during long-term emersion. In this study, we investigated the molecular re-sponse, at the proteome level, of M. neritoides collected in high-shore tide pools to a series ofemersion periods, from 8 to 24 days, in laboratory conditions. We compared this response to indi-viduals maintained submerged during this period, because this was their original habitat. We alsoincluded a reversion treatment in the study, in which emersed individuals were returned to the sub-merged conditions. Although we detected an increase in overall protein concentration with longeremersion periods, contrary to general expectation, the two dimensional electrophoresis （2DE）-based proteomic analysis did not show significant differences between the treatments at the levelof individual protein spots, even after an emersion period of 24 days. Our results suggest that themetabolism remains unaltered independent of the treatment carried out or the changes are verysubtle and therefore difficult to detect with our experimental design. We conclude that M. neri-toides could be equally adapted to emersion and submersion without drastic physiologicalchanges.

Proteomic analysis of F_(1)hybrids and intermediate variants in a Littorina saxatilis hybrid zone

Proteomic analysis was carried out on the Crab(upper-shore)and Wave(lower-shore)ecotypes of Littorina saxatilis from a hybrid zone at Silleiro Cape,Spain.Proteome profiles of individual snails were obtained.Protein expression in F_(1)hybrid snails bred in the laboratory and snails with intermediate shell phenotypes collected from the mid-shore were compared with Crab and Wave ecotypes using analytical approaches used to study dominance.Multivariate analysis over many protein spots showed that the F_(1)snails are distinct from both ecotypes but closer to the Wave ecotype.The intermediate snails are highly variable,some closer to the Crab and others to the Wave ecotype.Considered on a protein by protein basis,some proteins are significantly closer in expression to the Crab and others to the Wave ecotype for both F_(1)and intermediate snails.Furthermore,a significant majority of proteins were closer in expression to the Wave ecotype for the F_(1),consistent with the multivariate analysis.No such significant majority toward either the Crab or Wave ecotype was observed for the intermediate snails.The closer similarity of F_(1)and Wave ecotype expression patterns could be the result of similar selective pressures in the similar mid-shore and low-shore environments.For a significantly larger number of proteins,intermediate snails were closer in expression to the ecotype having the lower expression,for both Crab and Wave ecotypes.This is somewhat unexpected as lower expression might be expected to be an indication of impairment of function and lower fitness.Proteomic analysis could be important for the identification of candidate proteins useful for gaining improved understanding of adaptation and barriers to gene flow in hybrid zones.