Genetic structure of the common terrestrial pulmonate snail, Cryptozona siamensis (Pfeiffer, 1856), in Thailand

Abstract

Allozyme variation was examined in 432 specimens of the pulmonate snail, Cryptozona siamensis, from 24 localities across three regions of Thailand plus an additional population from Malaysia. Although this snail is a cosmopolitan species it was predicted that C. siamensis should exhibit a large degree of genetic subdivision across these regions due to a low level of inter-population gene flow. To test this hypothesis, 10 enzyme systems were screened using horizontal starch gel electrophoresis, from which 14 presumed allozyme loci were scored and 13 found to be polymorphic. For these 13 polymorphic loci the expected heterozygosity levels were moderate (Hexp = 0.036-0.183, mean = 0.101). Genetic differentiation among the samples was low, with a low FST value (0.254) and genetic distance (D = 0.000-0.124, mean = 0.034) and no significant isolation by distance (IBD) across the whole sampled range of Thailand or Thailand plus Malaysia. However, an IBD pattern in the population substructure in the central Thailand region was detected. The low FST and moderate Hexp values in various populations of C. siamensis suggests a high degree of gene flow/migration between populations across the three geographic regions of Thailand (northern, central and southern) as well as the sampled population in Malaysia, perhaps associated with the anthropochoric effect of snail dispersal. The apparent IBD in the central Thailand region could be the consequence of local dynamics though this region. © 2011 Elsevier Ltd.