Microevolution in Solatopupa landsnails (Pulmonata Chondrinidae): genetic diversity and founder effects

Abstract

Enzyme variability at 28 presumptive gene loci was studied, by standard starch gel electrophoresis, in 30 populations belonging to the five recognized species of the landsnail Solatopupa from its entire NW Mediterranean range. Six genetically differentiated groups can be identified among the 30 populations sampled. These are distinguished by two to 19 diagnostic loci, different levels of genetic variability and populations genetics. They are also significantly different as far as the D values are considered. There is no evidence of gene flow among them. Genetically inferred groups correspond in four cases to morphologically distinguished species. In contrast, S. similis, as identified by morphological features, is likely to be a complex of at least two cryptic species. Populations and species of Solatopupa are characterized by: high fixation of alternative alleles both within and between species; medium‐lo‐low levels of genie variation; heterozygote deficiency; sharp genetic differentiation among population within species; restricted gene flow; and high genetic distances. Genetic variability is partly associated with climatic factors related to moisture. Both deterministic and stochastic processes may play a part in the genetic differentiation of Solatopupa snails. Founder events seem to be the main factor affecting the genetic structure of populations and perhaps also speciation. Solatopupa populations display many attributes of populations that may be expected to undergo speciation events involving reorganization of the whole genome after a founder event.

Allozyme versus discrete morphologic characters in the phylogenetic analysis of the land snailSolatopupa(Pulmonata, Chondrinidae)

“…Their population distribution pattern is always of an insular type. The genetic structure of populations and, perhaps, also the speciation process are mainly affected by stochastic factors such as the founder effect (Boato, 1988).…”

“…Allozyme data were derived form previous studies (Boato & Rodino, 1986;Boato, 1988) concerning the electrophoretically detectable genetic variability at 28 gene loci and 30 populations belonging to all species and from the whole genus range.…”

“…Moreover, as Nei himself stressed in a recent review (1987), the process of allele frequency change or gene substitution in populations must be very much taken into account in reconstructing phylogenetic trees, with particular care for the effects of stochastic factors. In Solatopupa snails, stochastic processes such as the random genetic drift and the founder effect are known to be important in determining the genetic structure and composition of populations (Boato, 1988). Random genetic drift is the evolutionary force invoked by the probabilistic model (Edwards & Cavalli-Sforza, 1964) underlying the maximum likelihood CONTML method proposed by Felsenstein (1981).…”

Genetic differentiation reflects geological history in the Azorean land snail, Leptaxis azorica

“…Most authors agree that Flores (2 My) Thomaz et al, 1996). In general, a higher susceptibility for genetic drift and natural selection in land snails can be related to their generally patchy distributions caused by their limited dispersal ability and/or dependence on specific (micro-) ecological conditions (eg Boato, 1988;Schilthuizen and Lombaerts, 1994). Nevertheless, while there is no a priori reason to assume rate heterogeneity and/or the existence of coadapted gene complexes (eg Davison and Clarke, 2000) within Laa, our results show some evidence for stronger effects of genetic drift in the populations of Lae (and Laf) which are characterised by lower values for A and H (see eg Leberg, 1992).…”

“…Most genetic variation present in L. azorica is contained in four OTUs (Lam, Lae, Law and Laf) that coincide with (former) islands. The genetic distances between the four OTUs are typical for congeneric (allopatric) species in several families of pulmonate land snails (eg Boato, 1988;Chiba, 1993;Johnson et al, 2000). Nevertheless, genetic distances do not provide a yardstick for discriminating between taxonomic levels, and considerable differentiation between conspecific populations is not uncommon in land snails (eg Selander and Kaufman, 1975;Ochman et al, 1987).…”