Population biology, genetic structure, and mating system parameters in freshwater snails

Abstract

Summary. Freshwater gastropods can reproduce by both uniparental and biparental means. In particular, self-fertilization in the hermaphrodite pulmonates (Basommatophora) and apomictic parthenogenesis in prosobranchs are viable alternatives to biparental sexuality in several species. The coexistence of different mating systems within and among extant populations provides opportunities to examine the forces directing their evolution. We review the models predicting genetic structure in subdivided populations, with an emphasis on the effects of inbreeding. Empirical population genetic data on freshwater pulmonates suggest a marked loss of genetic variability under selfing. We also consider the genetic and demographic factors thought to influence mating system evolution, and highlight approaches that should be used to estimate mating system parameters and inbreeding depression. We mainly draw empirical examples from our population biological studies on tropical species in the planorbid Bulinus and the European stream limpet, Ancylus fluviatilis. These ongoing studies contribute to a deeper understanding of the evolution of selfing versus outcrossing.

Partial selfing, ecological disturbance and reproductive assurance in an invasive freshwater snail

“…First, this species inhabits a wide range of more or less temporary habitats varying in openness (eg ponds versus rivers). As a consequence, population size is likely to vary dramatically through time because of drying out events or floods (reviewed in Städler and Jarne, 1997). Second, P. acuta is the commonest species in isolated habitats (ie ponds) of the area studied here (reviewed in Henry, 2002), in accordance with its invasive status (Dillon et al, 2002;Bousset and Jarne, unpublished data).…”

“…Major arguments are the over-representation of selfcompatible species among long-distance colonizing species (reviewed in Pannell and Barrett, 1998), the repeated evolution of selfing populations or species from outcrossing ancestors in constraining habitats (eg Dole, 1992), and the occurrence of autogamous characters in populations experiencing chronically low density (eg Dole, 1992;Städler and Jarne, 1997). More direct arguments are derived from studies on plant pollination showing that selfing correlates with pollen-vector unreliability and/or low plant population density (eg Lloyd, 1980;Watkins and Levin, 1990;Fausto et al, 2001).…”

“…Freshwater snails are good candidates for such a work (Jarne and Charlesworth, 1993;Städler and Jarne, 1997). P. acuta predominantly outcrosses, probably because of strong inbreeding depression (Jarne et al, 2000;Henry et al, 2003;Tsitrone et al, 2003b).…”

Contrasting the distribution of phenotypic and molecular variation in the freshwater snail Biomphalaria pfeifferi, the intermediate host of Schistosoma mansoni

“…Populations of freshwater snails are also experiencing cycles of drought and flood, which amplitude depends on habitat characteristics. Environmental stochasticity can result in repeated bottlenecks and extinctions (Städler and Jarne, 1997;Keller and Douglas, 2008). This was approached here through habitat openness (open versus closed) and permanence (temporary versus permanent).…”

“…Freshwater snails of the Basommatophoran group offer excellent biological models to address these issues (Städler and Jarne, 1997;Charbonnel et al, 2002c;Chapuis et al, 2007;Escobar et al, 2008).…”