The maintenance of sexual reproduction in a structured population

Abstract

We present the results of a computer simulation model in which a sexual population produces an asexual mutant. We estimate the probability that the new asexual lineage will go extinct. We ¢nd that whenever the asexual lineage does not go extinct the sexual population is out-competed, and only asexual individuals remain after a su¤ciently long period of time has elapsed. We call this type of outcome an asexual takeover. Our results suggest that, given repeated mutations to asexuality, asexual takeover is likely in an unstructured environment. However, if the environment is subdivided into demes that are connected by migration, then asexual takeover becomes less likely. The probability of asexual takeover declines towards zero as the number of demes increases and as the rate of migration decreases. The reason for this is that asexuality leads to a greater loss of ¢tness due to mutation and genetic drift, in comparison to what occurs under sexual reproduction. Population subdivision slows the spread of asexual lineages, which allows more time for the genetic degeneration caused by asexuality to take place.

Sexual selection and its effect on the fixation of an asexual clone

“…More research is needed to address its role on the problem of sex, specifically when it acts together with a combination of mutation accumulation and other forces, e.g. parasites (Howard & Lively 1994) or limited dispersal (Peck et al 1999;Salathé et al 2006 Figure 1. The maintenance of sexual reproduction in a population with or without sexual selection.…”

An Evolving Genetic Architecture Interacts with Hill–Robertson Interference to Determine the Benefit of Sex

“…The magnitudes of both the long-and short-term advantages of sex are likely to be affected additionally by many factors we have not considered here, such as deviations from random mating (Shields 1982;Jaffe 2000;Agrawal 2001;Siller 2001;Blachford and Agrawal 2006), population structure (Peck et al 1999;Agrawal and Chasnov 2001;Salathé et al 2006;Roze 2009;Hartfield et al 2012), ploidy (Kirkpatrick and Jenkins 1989;Kondrashov and Crow 1991;Agrawal and Chasnov 2001;Otto 2003;Haag and Roze 2007;Roze 2009), number of loci (Iles et al 2003), and environmental change (Charlesworth 1993;Barton 1995;Otto and Nuismer 2004;Carja et al 2014;Nowak et al 2014), leaving many questions yet to be answered.…”

Inevitable evolution: back toThe Originand beyond the 20th Century paradigm of contingent evolution by historical natural selection

“…Most of the genetic models will provide only a long-term advantage to the sexual population over the asexual population, and this advantage cannot generally explain the evolutionary transition from asexual to sexual reproduction, nor the evolutionary maintenance of sexual reproduction should asexual variants arise in sexual populations (for exceptions see Kondrashov 1982Kondrashov , 1993Peck et al 1999). Another limitation to most of the genetic models is that they do not consider why asexual reproduction is more common in negligible-sized organisms than in larger organisms, nor why the sexual unit is a single male per female with the average offspring receiving half of the genes from the father and the other half from the mother.…”

“…Sexual reproduction is currently seen as a contingent character that evolves from a historical selection imposed by genetic recombination. So far at least twenty different hypotheses have been proposed (for reviews see Bulmer 1994;Kondrashov 1994;Ebert and Hamilton 1996;Hurst and Peck 1996;Otto and Lenormand 2002;Agrawal 2006;Otto and Gerstein 2006), and according to these sexual recombination may protect against the accumulation of deleterious mutations, for example, by Muller's ratchet where recombination breaks up genetic associations between loci allowing for selective elimination of deleterious mutations (Fisher 1930;Muller 1932Muller , 1964Crow and Kimura 1965;Kondrashov 1982Kondrashov , 1993Manning and Thompson 1984;Wagner and Gabriel 1990;Charlesworth et al 1993;Lynch et al 1993;Peck 1994;Lynch et al 1995;Peck et al 1997;Peck et al 1999), by segregation that breaks up genetic associations within a locus (Otto 2003;Dolgin and Otto 2003), by evolutionary traction where deleterious mutations in asexual organisms hitchhike to fixation owing to selection for rare beneficial mutations (Manning and Thompson 1984;Rice 1987;Hadany and Feldman 2005), or by Hill-Robertson interference that reduces the effective population size making Muller's ratchet more effective (Hill and Robertson 1966;Felsenstein and Yokoyama 1976;Palsson 2002;Keightley and Otto 2006). Recombination has also been seen to favour sexual reproduction because it brings together favourable alleles from different chromosomes, which may increase the rate of adaptation …”