Résumé
Knowledge of the scale of dispersal and the mechanisms governing gene flow
in marine environments remains fragmentary despite being essential for
understanding evolution of marine biota and to design management plans. We
use the limpets Patella ulyssiponensis and Patella rustica as models for
identifying factors affecting gene flow in marine organisms across the
North-East Atlantic and the Mediterranean Sea. A set of allozyme loci and
a fragment of the mitochondrial gene cytochrome C oxidase subunit I were
screened for genetic variation through starch gel electrophoresis and DNA
sequencing, respectively. An approach combining clustering algorithms with
clinal analyses was used to test for the existence of barriers to gene
flow and estimate their geographic location and abruptness. Sharp breaks
in the genetic composition of individuals were observed in the transitions
between the Atlantic and the Mediterranean and across southern Italian
shores. An additional break within the Atlantic cluster separates samples
from the Alboran Sea and Atlantic African shores from those of the Iberian
Atlantic shores. The geographic congruence of the genetic breaks detected
in these two limpet species strongly supports the existence of
transpecific barriers to gene flow in the Mediterranean Sea and
Northeastern Atlantic. This leads to testable hypotheses regarding factors
restricting gene flow across the study area.