Sex as a strategy against rapidly evolving parasites

Abstract

Why is sex ubiquitous when asexual reproduction is much less costly? Sex disrupts coadapted gene complexes; it also causes costs associated with mate finding and the production of males who do not themselves bear offspring. Theory predicts parasites select for host sex, because genetically variable offspring can escape infection from parasites adapted to infect the previous generations. We examine this using a facultative sexual crustacean, Daphnia magna, and its sterilizing bacterial parasite, Pasteuria ramosa. We obtained sexually and asexually produced offspring from wild-caught hosts and exposed them to contemporary parasites or parasites isolated from the same population one year later. We found rapid parasite adaptation to replicate within asexual but not sexual offspring. Moreover, sexually produced offspring were twice as resistant to infection as asexuals when exposed to parasites that had coevolved alongside their parents (i.e. the year two parasite). This fulfils the requirement that the benefits of sex must be both large and rapid for sex to be favoured by selection.

Simulated climate change, epidemic size, and host evolution across host–parasite populations

“…However, this relies on the assumption that host genes that confer resistance to current parasites also confer resistance to future parasites (this is sometimes, though not always the case in this system: (Little & Ebert, 2001;Auld, Tinkler, & Tinsley, 2016 (Anderson et al, 1986;King & Lively, 2012). However, this relies on the assumption that host genes that confer resistance to current parasites also confer resistance to future parasites (this is sometimes, though not always the case in this system: (Little & Ebert, 2001;Auld, Tinkler, & Tinsley, 2016 (Anderson et al, 1986;King & Lively, 2012).…”

“…year. However, this relies on the assumption that host genes that confer resistance to current parasites also confer resistance to future parasites (this is sometimes, though not always the case in this system: (Little & Ebert, 2001;Auld, Tinkler, & Tinsley, 2016 (Anderson et al, 1986;King & Lively, 2012). Moreover, a decline in genetic diversity reduces a population's capacity to respond to further selection more generally, because diversity is the currency with which a population pays for adaptation (Lande & Shannon, 1996).…”

Bridging the gap between theory and data: the Red Queen Hypothesis for sex

“…Through decades of work, Lively et al have demonstrated that the population satisfies necessary conditions for the host-parasite coevolutionary dynamics and provides support for the hypothesis (e.g., Lively (1987Lively ( , 1989; Lively (1995b, 1998); Jokela et al (2009);Vergara et al (2014b); Gibson et al (2016)). While field studies often provide only indirect evidence for the hypothesis, experimental systems can be used to directly test the hypothesis (Auld et al, 2016;Slowinski et al, 2016;Lynch et al, 2018;Zilio et al, 2018).…”

Digest: The Red Queen hypothesis demonstrated by the Daphnia -Caullerya host-parasite system†

“…Therefore, Daphnia provides a powerful model to study the importance of parasitism as a driver of evolution and disease; in fact, it has been used to understand the link between sex and parasites (Auld et al. ), multihost parasitism (Auld et al. ), and the virulence of human pathogens (Le Coadic et al.…”

“…In particular, the short generation times of Daphnia (one to three weeks) coupled with the availability of isolated populations (with lakes representing closed study systems) facilitated the reconstruction of rapid coevolutionary dynamics. Therefore, Daphnia provides a powerful model to study the importance of parasitism as a driver of evolution and disease; in fact, it has been used to understand the link between sex and parasites (Auld et al 2016), multihost parasitism (Auld et al 2017), and the virulence of human pathogens (Le Coadic et al 2012). Using long-term, high-resolution records, Turko et al (2018) have shown that interactions between parasites and their hosts are not fixed in time but result from a dynamic battle of adaptation and counter-adaptation, as predicted by the Red Queen hypothesis.…”