Geographic Ranges, Population Structure, and Ages of Sexual and Parthenogenetic Snail Lineages

Abstract

Abstract. Asexual reproduction is thought to doom organisms to extinction due to mutation accumulation and parasite exploitation. Theoretical models suggest that parthenogens may escape the negative effects of conspecifics and biological enemies through escape in space. Through intensive sequencing of a mitochondrial DNA (mtDNA) and a nuclear intron locus in sexual and parthenogenetic freshwater snails (Campeloma), I examine three questions: (1) Are sexual mtDNA lineages more restricted geographically than parthenogenetic mtDNA lineages? (2) Are independent parthenogenetic lineages shorter lived than sexual lineages? and (3) Do parthenogens have higher intraindividual nuclear sequence diversity and form well-differentiated monophyletic groups as expected under the Meselson effect? Geographic ranges of parthenogenetic lineages are significantly larger than geographic ranges of sexual lineages. Based on coalescence times under different demographic assumptions, asexual lineages are short lived, but there is variation in clonal ages. Although alternative explanations exist, these results suggest that asexual lineages may persist in the short term through dispersal, and that various constraints may cause geographic restriction of sexual lineages. Both allotriploid and diploid Campeloma parthenogens have significantly higher allelic divergence within individuals, but show limited nuclear sequence divergence from sexual ancestors. In contrast to previous allozyme evidence for nonhybrid origins of diploid Campeloma parthenogens, cryptic hybridization may account for elevated heterozygosity.

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

“…For a given species, asexual forms have a broader geographic distribution and are more frequently found in environments that are generally classified as marginal than their sexual relatives from which, presumably, they originated (Bell 1982;Lynch 1984;Suomalainen et al 1987;Schwander & Crespi 2009). A number of different but not mutually exclusive hypotheses have been proposed to account for geographic parthenogenesis (Glesener & Tilman 1978;Bell 1982;Lynch 1984;Kirkpatrick & Barton 1997;Peck et al 1998;Haag & Ebert 2004;Kearney 2005;Johnson 2006;Lundmark & Saura 2006). According to the "post glacial invasion hypothesis", parthenogenetic lineages would have had significant ecological success and spread from southern core refugia more efficiently than sexual ones in the areas that were strongly affected by the Pleistocene glacial cycles (Hewitt 1999).…”

Evolutionary Origin and Phylogeography of the Diploid Obligate Parthenogen Artemia parthenogenetica (Branchiopoda: Anostraca)

“…Parthenogenetic organisms tend to have broadly distributed genetic lineages, wider geographic distributions than their sexual relatives, and a propensity to occur in marginal areas (see [1] and references therein). Several non-exclusive hypotheses have been put forward to explain this phenomenon, ranging from their better colonisation abilities through reproductive assurance (i.e.…”

Population genetic structure of sexual and parthenogenetic damselflies inferred from mitochondrial and nuclear markers

“…The use of mitochondrial DNA to study sexual-asexual lineage divergence can lead to invalid age estimates, due to the extinction of sexual lineages, an inadequate sampling, or if sexual populations have diverged considerably (see Johnson, 2006;and references therein). In our case, we found a single mutational step between sexual and parthenogenetic lineages suggesting a very recent origin for the parthenogenetic lineages.…”