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 life-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 in evergreen habitats. In this study we used single-locus minisatellite DNA probes to test the following predictions of the source-sink hypothesis: 1) source and sink populations are not genetically differentiated; 2) amount of gene flow is ranked in the following decreasing order: between source and sink habitats, among source habitats and among sink habitats; and 3) linkage disequilibrium is higher in sink than in source populations. Results were consistent with these three predictions, and with previous results obtained using other approaches. Results clearly support a source-sink functioning of Blue tit populations in southern France mosaic landscapes, and emphasise the need of combining genetic and ecological studies to understand the functioning of natural populations.