Evaluation of Elevated Ploidy and Asexual Reproduction as Alternative Explanations for Geographic Parthenogenesis in Eucypris Virens Ostracods

Abstract

Transitions from sexual to asexual reproduction are often coupled with elevations in ploidy. As a consequence, the importance of ploidy per se for the maintenance and spread of asexual populations is unclear. To examine the effects of ploidy and asexual reproduction as independent determinants of the success of asexual lineages, we sampled diploid sexual, diploid asexual, and triploid asexual Eucypris virens ostracods across a European wide range. Applying nuclear and mitochondrial markers, we found that E. virens consists of genetically highly differentiated diploid sexual populations, to the extent that these sexual clades could be considered as cryptic species. All sexual populations were found in southern Europe and North Africa and we found that both diploid asexual and triploid asexual lineages have originated multiple times from several sexual lineages. Therefore, the asexual lineages show a wide variety of genetic backgrounds and very strong population genetic structure across the wide geographic range. Finally, we found that triploid, but not diploid, asexual clones dominate habitats in northern Europe. The limited distribution of diploid asexual lineages, despite their shared ancestry with triploid asexual lineages, strongly suggests that the wider geographic distribution of triploids is due to elevated ploidy rather than to asexuality.

Can resource costs of polyploidy provide an advantage to sex?

“…This idea has found support from studies such as that of Stenberg et al (2003), who contended that broad distribution of triploid vs. diploid asexual weevils suggested an intrinsic advantage of polyploidy (also see Adolfsson et al, 2010). More broadly, Stenberg et al (2003) presented evidence for 'geographical polyploidy,' a pattern analogous to geographical parthenogenesis, in which polyploid forms, regardless of sexuality, also tend to be found in higher latitudes (also see Suomalainen et al, 1987).…”

“…Some authors have pointed to advantages and disadvantages of asexuality per se as an explanation for these different distributional patterns (Levin, 1975;Glesener and Tilman, 1978;Bell, 1982;Jensen et al, 2002;Frantz et al, 2006;Ben-Ami and Heller, 2007;Martins et al, 2008). However, several authors have instead suggested that polyploidy is a more likely explanation (Bierzychudek, 1985;Beaton and Hebert, 1988;Lundmark and Saura, 2006;Adolfsson et al, 2010). For example, Bierzychudek (1985) pointed out that asexuality was so frequently associated with polyploidy in plants that it was 'premature' to implicate sex as a causal factor for distributional differences between asexual and sexual plant taxa (also see Suomalainen et al, 1987).…”

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

“…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).…”

Pseudamnicola Paulucci, 1878 (Caenogastropoda: Truncatelloidea) from the Aegean Islands: a long or short story?

“…According to the phylogenetic analysis and p-distance values for COI, the studied Pseudamnicola populations can be assigned to 16 clades, most of which are probably distinct species, according to the GMYC and ABGD analysis. The GMYC procedure has been applied in several previous studies Papadopoulou et al 2009a, b;Adolfsson et al 2010;Pagès et al 2010;Powell et al 2011;Vuataz et al 2011), including some on molluscs (Nekola et al 2009;Lorion et al 2010;Jörger et al 2012;Jörger and Schrödl 2013). Reliability of species delimitated by GMYC has also been discussed in the literature (e.g.…”