Spatial and temporal patterns of parthenogenesis and parasitism in the freshwater snail Melanoides tuberculata

Abstract

The Red Queen hypothesis predicts that sex should be more common in populations heavily infested with parasites, than in those without. This hypothesis was investigated in the aquatic snail Melanoides tuberculata, in which both sexual and parthenogenetic individuals exist in natural populations, and some populations are heavily infested by trematodes. The presence of fertile males and the higher genetic diversity of bisexual populations are indicative of sexual reproduction. We compared sites in 1990, 1999, and 2001, and we looked for a positive correlation between male and parasite frequencies. Male frequency was not correlated with the frequency of individuals infected by trematodes. This lack of correlation was reconfirmed in a retrospective power analysis. In a period of 9 years, male frequencies decreased but infection levels increased. These results do not support the Red Queen hypothesis. In samples with high male frequency the number of embryos was low, perhaps indicating that males may have a negative effect on embryo numbers. This effect of males on fitness could perhaps suggest that the cost of sex is fewer embryos. The reduction in embryo numbers may also represent a trade‐off between mating and egg production costs.

Geographic parthenogenesis and plant-enemy interactions in the common dandelion

“…Better support for this hypothesis could come from observing the same correlation between antagonists and host sex-asex variation in randomly selected populations, not in populations sampled along the north–south transect of geographic parthenogenesis (because of possible confounding effects of other factors that might cause geographic parthenogenesis). Population surveys in different species have previously explored a correlation between host sex-asex variation and antagonist prevalence, confirming RQ predictions in some systems [42,43,47] but not in others [44,45,48]. If we look at the populations only in the southern part of the dandelion transect, where sexuals and asexuals coexist, the association between infection rate and the proportion of asexuals also showed a negative trend across populations (β = −0.16 for the asexual-rust association, n = 10 population; β = −0.26 for the asexual-weevil association, n = 7 populations).…”

“…For instance, similar surveys in other systems demonstrated the same pattern using larger numbers of populations [42,43]. A positive correlation between pest/pathogen prevalence and host sexual reproduction has been found in some but not in all systems that have been comprehensively studied [44,45]. …”

Sex is a ubiquitous, ancient, and inherent attribute of eukaryotic life

“…Indeed, there is no consensus on a single major advantage for sex, and prevailing opinion is shifting toward a combination of advantages (71). That sex creates genetic variation, repairs DNA breaks, restores methylation patterns, and prevents accumulation of disadvantageous mutations is well accepted (72,73). These features have varying importance in different eukaryotic lineages, yet it is likely that the advantages of sex, elaborated in detail for multicellular organisms (71,74), either apply also for unicells or that there are some other advantages.…”

Geographic variation in sterilizing parasite species and the Red Queen

“…Many empirical studies in a variety of hostÁparasite systems have supported this basic prediction of the Red Queen (Glesener and Tilman 1978, Lively et al 1990, Moritz et al 1991, Schrag et al 1993, Busch et al 2004), although a handful of studies have not (Ben-Ami andHeller 2005, Tobler andSchlupp 2005). Some of the field evidence favouring the Red Queen hypothesis stems from research on the frequency of males (i.e.…”