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Genetic relationships among suspected contact zone populations of Helix aspersa (Gastropoda: Pulmonata) in Algeria

1996; Springer Nature; Volume: 77; Issue: 2 Linguagem: Inglês

10.1038/hdy.1996.116

1365-2540

Annie Guiller, Marie-Agnès Coutellec-Vreto, Luc Madec,

Aquatic Invertebrate Ecology and Behavior

In Maghreb, the land snail Helix aspersa consists of two anatomically and biochemically divergent groups of populations between which the separation occurs roughly to the east of the Lesser Kabylia. To document the patterns of migration across the suspected contact zone between these two geographical entities, we have analysed changes in allele frequencies at 13 polymorphic allozyme loci in five intermediate Algerian populations ranging from Azeffoun (Great Kabylia) to El Hedaick (Skikda), thus including three western and two eastern colonies. Multivariate analyses and exact tests for population differentiation were used to show the genetic divergence between samples; deviations from panmixia were calculated to account for the effect of migration. Whereas some loci showed abrupt changes in allelic composition across the hybrid zone, some others were introgressed, especially into eastern populations in the central colony of Djemila. It is tempting to ascribe this allelic distribution to gene exchanges between populations on the east and west. However, the large number of private alleles found in adjoining populations apparently does not support this explanation, although such an increase in rare alleles has been observed in other hybrid zone surveys. In addition, it may be that this discrepancy between the patterns of common and private allele variation may result from the time since contact occurred. Whatever the explanation of this finding, the genetic structure in Djemila, and particularly the large linkage disequilibria observed, indicates population mixing. Although not ruling out the possibilities of tectonic events and of human transport, the most likely hypothesis for contacts between eastern and western populations are that these result from climatic phenomena during the Quaternary.