Synergism between mutational meltdown and Red Queen in parthenogenetic biotypes of the freshwater planarian Schmidtea polychroa

Abstract

Do parasites and accumulation of deleterious mutations act synergistically in balancing the costs of sex? We addressed this possibility in the freshwater planarian flatworm Schmidtea polychroa . Sexual and parthenogenetic forms of this species sometimes coexist but show no ecological separation. Previous studies indicate that in a mixed sexual/ parthenogenetic population in Lago di Caldonazzo (N. Italy) parthenogens get more frequently infected with parasites. At the same time, they suffer from higher embryo mortality, which has been interpreted as a sign of accumulation of deleterious mutations. In the present study, we test whether these two factors are correlated, by focusing on the differences among the clonal lineages of a predominantly parthenogenetic subpopulation. Our results suggest that, for two out of three parasite types found, the infections are positively associated with the indirect measure of host mutation load.

Role of parasite load and differential habitat preferences in maintaining the coexistence of sexual and asexual competitors in fish of theCobitis taeniahybrid complex

“…() and Bruvo et al . () for such an effect). However, this is an unlikely explanation in Cobitis because all triploids from site C belong to clonal lineages, which are widespread in the large Odra River basin and their spread throughout the river basin in the early Holocene has been supported by microsatellite analysis (Janko et al ., ).…”

Correlations between sex rate estimates and fitness across predominantly parthenogenetic flatworm populations

“…Moreover, parthenogenetic lineages show significant correlation between mutation and parasite load giving evidence to the so‐called pluralistic approach (West et al. , 1999; West‐Eberhard, 2005), which combines both mutational and environmental models (Bruvo et al. , 2007).…”

“…Reduction in fertility most likely results from developmental problems and increased embryo mortality which in turn was used as an indicator for the accumulation of deleterious mutations in previous studies (Storhas et al. , 2000; Bruvo et al. , 2007).…”

Why Are Sex and Recombination So Common?

“…In finite populations, the coevolution of hosts and parasites can result in a combination of factors that might favor the evolution of sex in addition to fluctuating epistasis: strong selection, beneficial mutations, and a significant increase in drift as different genotypes go through bottlenecks, severely reducing N e . The synergistic interaction of the different factors (e.g., drift, selection, and mutation) can result in a further increased advantage for sex and recombination and calls for pluralistic models (West et al 1999; Cooper et al 2005; Bruvo et al 2007).…”