Genetic diversity and mixed reproduction in Eucypris virens (Crustacea: Ostracoda)

Inbreeding and outbreeding depression in geographical parthenogensHeterocypris incongruensandEucypris virens(Crustacea: Ostracoda)

“…virens samples were from six different vernal pools located between Mistretta and Nicosia (Sicily, Italy) where we found little evidence of inbreeding and where sexual populations coexist with polyploid asexual ones (Rossi et al 2008;Adolfsson et al 2009). These Sicilian populations have a surprisingly close genetic relationship with a clonal population found in Great Britain (Schön et al 2000;Rossi et al 2008). H. incongruens samples were from two different sites (Littoral and Fondaria) of the Espolla temporary pond (42…”

“…These species are among the most genetically variable ostracods reported and showed a very high level of clonal diversity that is generally linked with local adaptation (Rossi et al 2006;Rossi et al 2008). Polyploid lineages were found in both species indicating that hybridization may be a route to parthenogenesis but not a major driving force in geographic parthenogenesis (Schön et al 2000;Rossi et al 2006;Rossi et al 2008;Adolfsson et al 2009). …”

“…The most established viewpoint is that this pattern has evolved due to the higher colonisation ability of asexuals ). On the other hand, the frequent transition from sexual to asexual reproduction and the interbreeding with sexual congeners explain the persistence of asexuality, the generation of polyploid lineages and the high clonal diversity reported in nonmarine ostracods (Havel & Hebert 1989;Chaplin et al 1994;Little & Hebert 1994;Turgeon & Hebert 1994;Turgeon & Hebert 1995;Chaplin & Hebert 1997;Little & Hebert 1997;Schön et al 2000;Cywinska & Hebert 2002;Little 2005;Rossi et al 2006;Rossi et al 2008;Adolfsson et al 2009). In general, populations of sexual species and sexual populations of geographic parthenogens showed agreement of genotype frequencies with HardyWeinberg expectations at single loci, random associations at pairs of loci and little evidence of inbreeding was reported (Havel et al 1990;Little & Hebert 1994;Turgeon & Hebert 1995;Finston 2002).…”

“…Asexual populations of E. virens are widespread throughout Europe while males are only found in the Mediterranean region where they sometimes live in sympatry with partenogenetic females (Schön et al 2000;Rossi et al 2008;Martins et al 2009). The circum-Mediterranean distribution of H. incongruens bisexual populations is in accordance with the hypothesis that this region retained several southern refugia during the last glaciation although bisexual populations are also found at higher latitudes ).…”

Viability selection on body size in a non-marine ostracod

“…Assuming an evolutionary equilibrium (i.e., the mean body size in each population would be the result of past directional selection), stabilizing selection would be predicted in cold and hot ponds, and considering the TSR, larger sizes should be found in the cold ponds, compared with the hot pond. However, many forces could produce and maintain disequilibria in ostracods (e.g., periodic bottlenecks, low heritability of body size, cyclic parthenogenesis, gene-flow, see Chaplin et al, 1994;Schon et al, 2000;Baltanas et al, 2002;Rossi et al, 2008). In this case, positive or negative directional selection would be predicted if the optimum value is above or below the actual one.…”