Congruence between starch gel and polyacrylamide gel electrophoresis in detecting allozyme variation in pulmonate land slugs

Abstract

The predominantly selfing slug species Arion (Carinarion) fasciatus, A. (C.) silvaticus and A. (C.) circumscriptus are native in Europe and have been introduced into North America, where each species consists of a single, homozygous multilocus genotype (strain), as defined by starch gel electrophoresis (SGE) of allozymes. In Europe, the "one strain per species" hypothesis does not hold since polyacrylamide gel electrophoresis (PAGE) of allozymes uncovered 46 strains divided over the three species. However, electrophoretic techniques may differ in their ability to detect allozyme variation. Therefore, several Carinarion populations from both continents were screened by applying the two techniques simultaneously on the same individual slugs and enzyme loci. SGE and PAGE yielded exactly the same results, so that the different degree of variation in North American and European populations cannot be attributed to differences in resolving power between SGE and PAGE. We found four A. (C.) silvaticus strains in North America indicating that in this region the "one strain per species" hypothesis also cannot be maintained. Hence, the discrepancies between previous electrophoretic studies on Carinarion are most likely due to sampling artefacts and possible founder effects.

Molecular systematics of the Carinarion complex (Mollusca: Gastropoda: Pulmonata): a taxonomic riddle caused by a mixed breeding system

“…The present mtDNA data confirm that North American Carinarion populations are genetically impoverished compared to European populations (six vs. 50 haplotypes, respectively) (Geenen et al ., 2003). This implies that earlier protein electrophoretic data of North American Carinarion (Chichester, 1967; McCracken & Selander, 1980) may be not sufficiently representative to decide about taxonomic issues.…”

“…To further evaluate the allozyme based genetic impoverishment of the North American Carinarion spp. (Geenen et al ., 2003), nucleotide diversities (π) (Nei, 1987) within the three nominal morphospecies in Europe and North America were calculated based on the p‐distance in MEGA, version 2.1 (Kumar et al ., 2001) and compared for the two geographical regions.…”

“…produce heterozygous individuals, suggesting the occurrence of facultative outcrossing and possibly even of interspecific hybridization (Jordaens et al ., 1996, 2000). Further analyses by Geenen et al . (2003) showed that the different conclusions of the allozyme studies of European and (introduced) North American populations were not due to technical discrepancies, but most probably to the lower amount of allozyme variation in the North American populations.…”

Population Genetics and Identity of an Introduced Terrestrial Slug: Arion subfuscus s.l. in the North-east USA (Gastropoda, Pulmonata, Arionidae)

“…Given that the lower molecular genetic diversity in NE USA A. subfuscus s.s. was not due to a sampling bias (Figure 4), the dramatic loss of genetic diversity in the NE USA populations is most likely the result of founder effects. Extensive allozyme studies of native European and introduced North American Carinarion populations also suggested founder effects because, although a sampling bias could not be excluded, 46 MLGs were found in Europe, but only six were found in North America (Geenen et al, 2003).…”