Using Parthenogenetic Lineages to Identify Advantages of Sex

Abstract

The overwhelming predominance of sexual reproduction in nature is surprising given that sex is expected to confer profound costs in terms of production of males and the breakup of beneficial allele combinations. Recognition of these theoretical costs was the inspiration for a large body of empirical research-typically focused on comparing sexual and asexual organisms, lineages, or genomes-dedicated to identifying the advantages and maintenance of sex in natural populations. Despite these efforts, why sex is so common remains unclear. Here, we argue that we can generate general insights into the advantages of sex by taking advantage of parthenogenetic taxa that differ in such characteristics as meiotic versus mitotic offspring production, ploidy level, and single versus multiple and hybrid versus non-hybrid origin. We begin by evaluating benefits that sex can confer via its effects on genetic linkage, diversity, and heterozygosity and outline how the three classes of benefits make different predictions for which type of parthenogenetic lineage would be favored over others. Next, we describe the type of parthenogenetic model system (if any) suitable for testing whether the hypothesized benefit might contribute to the maintenance of sex in natural populations, and suggest groups of organisms that fit the specifications. We conclude by discussing how empirical estimates of characteristics such as time since derivation and number of independent origins of asexual lineages from sexual ancestors, ploidy levels, and patterns of molecular evolution from representatives of these groups can be used to better understand which mechanisms maintain sex in natural populations.

Can resource costs of polyploidy provide an advantage to sex?

“…Other systems that allow at least partial decoupling of sex and ploidy level include Potamopyrgus antipodarum (sexual 2 Â , asexual 3-4 Â ; and the cockroach genus Pycnoscelus (2 Â sexuals, 2 Â and 3 Â asexuals; Gade and Parker, 1997). Thorough surveys of many additional polyploid taxa that vary in mating system can be found in Suomalainen et al (1987); Otto and Whitton (2000); Lundmark and Saura (2006);and Neiman and Schwander (2011).…”

Niche differentiation and colonization of a novel environment by an asexual parasitic wasp

“…Another important determinant of the diversity of asexual populations is the mechanism by which the asexual females produce eggs (recently reviewed in Neiman & Schwander, ). Although our study was not aimed at directly evaluating the mode of reproduction used by asexual D. muliebre , the microsatellite data do permit some initial speculation.…”

“…Because standing levels of genetic variation in an asexual assemblage will depend largely on the number of transitions from the asexual ancestor (reviewed in Neiman & Schwander, ), we here evaluate whether different D. muliebre lineages appear to have evolved from a single sexual ancestor or instead arose from different independent transitions from sexuality. We used variation at the mitochondrial gene cytochrome oxidase I (COI) as a coarse proxy for lineage membership, and a panel of five microsatellite loci to evaluate patterns of allelic variation within and between lineages and compare variation with their closest sexual relative, D. ferrugineum .…”

Evolutionary mysteries in meiosis

“…This raises two connected mysteries: why are some types of modifications much more frequent than others, and how can mitotic (or mitosis-like) asexual reproduction ('apomixis' or 'clonal parthenogenesis' in animals, 'mitotic apomixis' in plants) evolve from meiosis? Examples of meiosis-derived modes of asexual reproduction include chromosome doubling prior to meiosis ('endomitosis' or 'pre-meiotic doubling'), fusion of two of the four products of a single meiosis ('automixis' in animals, 'within-tetrad mating' in fungi), and suppression of one of the two meiotic divisions (included under 'automixis' or 'meiotic apomixis', depending on the author; see [68][69][70][71][72][73][74] for detailed descriptions of these processes).…”