Computer Modelling the Origins of Sexual Reproduction: Testing the Red Queen and Court Jester

Abstract

What drives the maintenance of sexual reproduction in Eukaryota is a key question in evolutionary biology. Modelling and empirical studies investigating this seemingly disadvantageous reproductive method are widespread. To date, there are no definitive answers regarding the ecological conditions which may lead to the retention of sexual breeding. Sex originated prior to the Last Eukaryote Common Ancestor (LECA). The time since this innovation, coupled with the diversity of sexual traits and ecologies in living organisms, makes it hard to identify mechanisms underlying its origin and subsequent maintenance. Unisexuality is the likely ancestral state of eukaryotic sex. Traits such as isogamy and selfing are yet to be explored in conjunction with changing environments. Here, I use the eco-evolutionary model REvoSim to assess how biotic Red Queen, abiotic Court Jester and pluralistic conditions impact the prevalence of sex over macroevolutionary timescales in a single unisexual digital ecosystem. My results indicate antagonistic relationships (pathogens/ predators), high rates of abiotic change, and limited environmental resources all elicit higher proclivity of sex in evolutionary agents sharing traits of LECA. Increased sex also helps organisms evade faster-evolving antagonists; this suggests pathogenic relationships, in particular, may increase the propensity to elicit unisexual sex. Pluralistic investigations show increased sexual breeding in response to antagonists and dynamic abiotic environments. I argue that Abandon-Ship mechanisms allow sexual life cycles to break down maladapted epistatic relationships in stressful conditions, regardless of their ecological origin, in digital populations. My findings support multiple mechanisms driving sex within early eukaryotes. I highlight the need to investigate Abandon-Ship dynamics further in living systems experiencing stress from multiple ecological sources. Further work can be completed within REvoSim to address the Tangled Bank theories of sex maintenance, and in addition, secondary sexual transitions such as post-mating isolation can be explored.

Date of Award	31 Dec 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Russell Garwood (Supervisor) & Robert Sansom (Supervisor)