SOURCE-SINK POPULATIONS IN MEDITERRANEAN BLUE TITS - EVIDENCE USING SINGLE-LOCUS MINISATELLITE PROBES

Long term studies on population biology of Blue tits (Parus caeruleus L.) in Mediterranean habitats have shown that in patchy landscapes lif e-history traits seem to be adapted to the predominant type of habitat , where reproductive success is higher. The ''source-sink hypothesis' suggests that differences in the local production of fledglings result in an asymmetrical gene flow from rich deciduous habitats (''source'' ) to evergreen poor habitats (''sink''), preventing local adaptation i n evergreen habitats. In this study we used single-locus minisatellite DNA probes to test the following predictions of the source-sink hypot hesis: 1) source and sink populations are not genetically differentiat ed; 2) amount of gene flow is ranked in the following decreasing order : between source and sink habitats, among source habitats and among si nk habitats; and 3) linkage disequilibrium is higher in sink than in s ource populations. Results were consistent with these three prediction s, and with previous results obtained using other approaches. Results clearly support a source-sink functioning of Blue tit populations in s outhern France mosaic landscapes, and emphasise the need of combining genetic and ecological studies to understand the functioning of natura l populations.