Sex versus parasitism versus density

Abstract

The Red Queen hypothesis predicts that sexual reproduction should be favoured when the risk of infection by parasites is high. However, this prediction may also be achieved independently by means of the reproductive assurance and the density-dependent transmission hypotheses because higher densities increase the chances of fertilization (i.e. mates are easier to find) and increase the risk of infection. Additionally, the Red Queen hypothesis makes a long-term prediction that infection should be genotype-specific, with time-lagged dynamics. In the present study, we attempt to consolidate these two predictions by investigating whether sexuality and parasitism alternate in a time-lagged fashion on an ecological time-scale. In a 3-year study, we examined the time-lagged dynamics between male frequencies, infection levels (by Centrocestus sp.), and snail densities of four natural populations of sexual and asexual Melanoides tuberculata snails. The results obtained provide no evidence of either prediction of the Red Queen hypothesis. We found partial support for reproductive assurance in a single population, and could not discriminate between the three hypotheses in another population. The remaining two populations did not support any of the hypotheses in question.

Clonal diversity driven by parasitism in a freshwater snail

“…We indeed found that infection prevalence is significantly correlated with the observed variation in clonal diversity of M. tuberculata populations. Consistent with previous work (Heller & Farstey, ; Ben‐Ami & Heller, , , ), we found no relationship between infection prevalence and male frequency. Furthermore, snail density could neither explain the variation in host clonal diversity nor explain the variation in male frequency.…”

“…Moreover, sex in M. tuberculata plays a crucial role in its ability to invade new ecosystems, because it amplifies the effect of multiple introductions of the snail by generating novel trait combinations (Facon et al ., , ). The frequency of fertile males can reach up to 66% particularly in Israel (Livshits & Fishelson, ; Heller & Farstey, ; Hodgson & Heller, ; Ben‐Ami & Heller, , , ).…”

Cost of resistance to trematodes in freshwater snail populations with low clonal diversity

“…Female M. tuberculata usually reproduce parthenogenetically (obligate apomixis) [ 23 – 25 ], but also via sporadic sexual reproduction in the presence of males [ 26 ]. In Israel, the frequency of fertile males can reach up to 66% [ 21 , 27 – 30 ]. Furthermore, sex plays a crucial role in the ability of M. tuberculata to invade new ecosystems, because it amplifies the effect of multiple introductions of the snail by generating novel trait combinations [ 31 , 32 ].…”

The Maintenance of Sex and David Lack’s Principle

“…This, however, only challenges the universality of the red-queen theory. (See Brown et al (1995); Hanley et al (1995); Vernon et al (1996); Weeks (1996); Ben-Ami & Heller (2005; 2008); Tobler & Schlupp (2005); Killick et al (2008); Kotusz et al (2014) for evidence on exceptions to red-queen predictions. )…”