What does the geography of parthenogenesis teach us about sex?

Abstract

One contribution of 15 to a theme issue 'Weird sex: the underappreciated diversity of sexual reproduction'. Theory predicts that sexual reproduction is difficult to maintain if asexuality is an option, yet sex is very common. To understand why, it is important to pay attention to repeatably occurring conditions that favour transitions to, or persistence of, asexuality. Geographic parthenogenesis is a term that has been applied to describe a large variety of patterns where sexual and related asexual forms differ in their geographic distribution. Often asexuality is stated to occur in a habitat that is, in some sense, marginal, but the interpretation differs across studies: parthenogens might not only predominate near the margin of the sexuals' distribution, but might also extend far beyond the sexual range; they may be disproportionately found in newly colonizable areas (e.g. areas previously glaciated), or in habitats where abiotic selection pressures are relatively stronger than biotic ones (e.g. cold, dry). Here, we review the various patterns proposed in the literature, the hypotheses put forward to explain them, and the assumptions they rely on. Surprisingly, few mathematical models consider geographic parthenogenesis as their focal question, but all models for the evolution of sex could be evaluated in this framework if the (often ecological) causal factors vary predictably with geography. We also recommend broadening the taxa studied beyond the traditional favourites.This article is part of the themed issue 'Weird sex: the underappreciated diversity of sexual reproduction'.

Condition-dependent sex: who does it, when and why?

“…temperature or drought, proximity to the boundary of the species' range), it might result in both low population density and poor individual condition. Switching to sexual reproduction precisely when the condition is bad-and the density low-might be detrimental, and reproducing asexually, while 'waiting out' for better conditions could be a favourable strategy (see also [70]). …”

Sexual conflict and the evolution of asexuality at low population densities

“…Feedbacks between population density and sexually antagonistic male-female interactions could play a role in explaining patterns of geographical parthenogenesis, i.e. the finding that the absence of males, as a derived trait, is often associated with marginal environments that are potentially of low population density [26]. In plants, this is often considered to support ideas of reproductive assurance when mate availability is low [27,28].…”

The genomic basis of eco‐evolutionary dynamics

“…) and discussed possible drivers of spatial variation in reproductive strategies and how such variation can shape the evolutionary dynamics of populations (e.g. Tilquin & Kokko ). The influence of spatial variation in reproductive strategies on evolution was also considered by Yvonne Willi.…”