Microspatial genetic structure in the land snail helix aspersa (Gastropoda: helicidae)
The microspatial genetic structure of allele frequencies at seven isozyme loci was examined for 15 populations of the land snail Helix aspersa sampled in a village from Brittany (north-western France). Spatial heterogeneity of allele frequencies was highly significant (P < 0.001). Fixation indices reflected nonrandom mating within neighbourhoods and a slight but consistent differentiation between colonies (FST=0.044; P < 0.01). Analyses of gene flow or genetic distances failed to reveal a significant relationship with geographical distance, probably because of the complexity of environmental heterogeneity. However, matrix comparisons between genetic distances and connectivity networks among adjacent colonies (Gabriel-connected graph) yielded a significant correlation in every case, indicating a 'step-by-step' relationship between neighbouring localities. Moreover, most of the allozymes were spatially structured and showed (i) a gradual isolation of colonies with increasing geographical distances, and (ii), for some correlogram profiles, a circular gradient illustrating a multidirectional colonization of the village. The probable existence of disperser individuals allowed us to suggest a metapopulation model which would explain the maintenance of such animals in fragmented habitats where anthropogenic disturbances and extinction/recolonization events are commonly observed.
Arnaud
J
UMR CNRS 6553, Service de Zoologie et d'Ecophysiologie, Universite de Rennes I, Campus de Beaulieu, Avenue du Gal Leclerc, 35042 Rennes cedex, France; UMR CNRS 6553, Service de Parasitologie Pharmaceutique, Universite de Rennes I, Avenu.
Madec
L
Bellido
A
Guiller
A