Jf. Arnaud et al., Spatial analysis of allozyme and microsatellite DNA polymorphisms in the land snail Helix aspersa (Gastropoda : Helicidae), MOL ECOL, 10(6), 2001, pp. 1563-1576
The genetic structure of the land snail Helix aspersa was investigated for
21 populations collected along a road located in the polders of the Bay of
Mont-Saint-Michel (Brittany, France), following a sampling scheme the area
of which did not exceed 900 m in length. A total of 369 individuals were ge
notyped for five enzymatic markers and seven microsatellite loci. We used s
equential hierarchical F-statistics at different spatial scales and spatial
autocorrelation statistics to explore recent historical patterns involved
in the observed genetic distribution. Whatever the statistics used, congrue
nt levels of spatial genetic substructuring across loci were demonstrated,
excepted for one allozyme locus. Overall spatial genetic arrangement matche
d in a substantial fashion theoretical predictions based on the limited dis
persal power of land snails. Positive autocorrelation over short-distance c
lasses may result from the development of genetically distinct patches of i
ndividuals organized in family-structured colonies. Therefore, spatial sign
atures of average I correlograms can be viewed as the expression of a stepp
ing-stone model of population structure, sometimes involving external migra
tional events. Overall, the revealed pattern of population subdivision on a
microgeographical scale was suggestive of a neighbourhood structure. Final
ly, microsatellite loci are especially suitable for the detection of small
genetic clustering, and combining different classes of markers offers the p
otential to gain further insight into the description of spatial genetic va
riability over short temporal and geographical scales.