Morphometric diversity of the mussel Brachidontes pharaonis in different coastal environments

Abstract

In the debate on how and why biodiversity evolves spatially and temporally and in an attempt to assess the further effects of anthropogenic activities, the ability of marine invertebrate to express a large spectrum of phenotypical plasticity can have a central role. The ability of a single genotype to produce more than one alternative form of morphology and/or physiological state should be larger in species living in highly changing waters like shallow habitats. Invertebrates, there, usually experience ample changes of temperature and food availability on annual, seasonal, diurnal and hourly bases which are the two main drivers leading the life histories of these organisms. In such circumstances they are expected to have a larger ability to express plastic phenotypic traits respect to species living under more stable conditions. Hence, the geometric morphometry is informative in understanding if morphology of sessile bivalves significantly changes as a function of different conditions of environmental variability. Here we focus on Brachidontes pharaonis as a model of our morphometric study as it spans intertidal, subtidal and shallow Mediterranean habitats with a range of physical and biological characteristics, colonising valuable shallow habitats. Specimens where collected from habitats at different degree of thermal variability throughout the Sicily: shallow waters (Stagnone di Marsala and Vendicari lagoons), some typical intertidal marine substrates and from pillars of a power plant (T. Imerese). Geometric morphometric analysis carried out on 248 specimens by means the MakeFan6 and MophoJ 1.01 softwares allowed us to individuate differences in the shell shape. Significant differences of morphotypes appeared to be variable with temperature in that shallow specimens formed a significant distinct cluster respect to marine organisms although we detected a partial overlapping among them, while power plant specimens were at all different from all other mussels.