Life-history and demographic spatial variation in Mediterranean populations of the opportunistic polychaete <Emphasis Type="Italic">Ophryotrocha labronica</Emphasis> (Polychaeta,Dorvilleidae)

The spatial scale of life-history and demographic variation was investigated in the opportunistic polychaete Ophryotrocha labronica La Greca and Bacci. Individuals were collected along the Italian coasts from three thermally different biogeographical regions of the Mediterranean Sea. For each region, populations from four harbours were considered, and for each harbour, two sites were examined. Life-history and demographic traits were investigated after one generation under a common garden experiment, and their variation at the three spatial scales was assessed. All the traits showed high variability with regard to site. A number of life-history and all demographic traits also varied according to the biogeographical region. Conversely, no differences were found between harbours, suggesting that geographical isolation did not contribute to phenotypic variation. Results confirmed the central role of local conditions for the evolution of life history in species colonizing heterogeneous environments, but they also pointed to the importance of large-scale factors in shaping the phenotypic responses of O. labronica, demonstrating the need for a multi-scale approach for obtaining a good measure of natural variation in widespread opportunistic species.