Fitness dependence preserves selection for recombination across diverse mixed mating strategies

A Numerical Model Supports the Evolutionary Advantage of Recombination Plasticity in Shifting Environments

AbstractNumerous empirical studies have witnessed an increase in meiotic recombination rate in response to physiological stress imposed by unfavorable environmental conditions. Thus, inherited plasticity in recombination rate is hypothesized to be evolutionarily advantageous in changing environments. Previous theoretical models proceeded from the assumption that organisms increase their recombination rate when the environment becomes more stressful and demonstrated the evolutionary advantage of such a form of plasticity. Here, we numerically explore a complementary scenario-when the plastic increase in recombination rate is triggered by the environmental shifts. Specifically, we assume increased recombination in individuals developing in a different environment than their parents and, optionally, also in offspring of such individuals. We show that such shift-inducible recombination is always superior when the optimal constant recombination implies an intermediate rate. Moreover, under certain conditions, plastic recombination may also appear beneficial when the optimal constant recombination is either zero or free. The advantage of plastic recombination was better predicted by the range of the population's mean fitness over the period of environmental fluctuations, compared with the geometric mean fitness. These results hold for both panmixia and partial selfing, with faster dynamics of recombination modifier alleles under selfing. We think that recombination plasticity can be acquired under the control of environmentally responsive mechanisms, such as chromatin epigenetics remodeling.

Modeling the evolution of recombination plasticity: A prospective review

Meiotic recombination is one of the main sources of genetic variation, a fundamental factor in the evolutionary adaptation of sexual eukaryotes. Yet, the role of variation in recombination rate and other recombination features remains underexplored. In this review, we focus on the sensitivity of recombination rates to different extrinsic and intrinsic factors. We briefly present the empirical evidence for recombination plasticity in response to environmental perturbations and/or poor genetic background and discuss theoretical models developed to explain how such plasticity could have evolved and how it can affect important population characteristics. We highlight a gap between the evidence, which comes mostly from experiments with diploids, and theory, which typically assumes haploid selection. Finally, we formulate open questions whose solving would help to outline conditions favoring recombination plasticity. This will contribute to answering the long-standing question of why sexual recombination exists despite its costs, since plastic recombination may be evolutionary advantageous even in selection regimes rejecting any non-zero constant recombination.

Wild sunflower goes viral: citizen science and comparative genomics allow tracking the origin and establishment of invasive sunflower in the Levant

Globalization and intensified volume of trade and transport around the world are accelerating the rate of biological invasions. It is therefore increasingly important to understand the processes through which invasive species colonize new habitats, often to the detriment of native flora. The initial steps of an invasion are particularly critical, as the introduced species relies on limited genetic diversity to adapt to a new environment. However, our understanding of this critical stage of the invasion is currently limited. We used a citizen science approach and social media to survey the distribution of invasive sunflower in Israel. We then sampled and sequenced a representative collection and compared it with available genomic data sets of North American wild sunflower, landraces and cultivars. We show that invasive wild sunflower is rapidly establishing throughout Israel, probably from a single, recent introduction from Texas, while maintaining high genetic diversity through ongoing gene flow. Since its introduction, invasive sunflower has spread quickly to most regions, and differentiation was detected despite extensive gene flow between clusters. Our findings suggest that rapid spread followed by continuous gene flow between diverging populations can serve as an efficient mechanism for maintaining sufficient genetic diversity at the early stages of invasion, promoting rapid adaptation and establishment in the new territory.

Selection for Plastic, Pathogen-Inducible Recombination in a Red Queen Model with Diploid Antagonists

Antagonistic interactions and co-evolution between a host and its parasite are known to cause oscillations in the population genetic structure of both species (Red Queen dynamics). Potentially, such oscillations may select for increased sex and recombination in the host, although theoretical models suggest that this happens under rather restricted values of selection intensity, epistasis, and other parameters. Here, we explore a model in which the diploid parasite succeeds to infect the diploid host only if their phenotypes at the interaction-mediating loci match. Whenever regular oscillations emerge in this system, we test whether plastic, pathogen-inducible recombination in the host can be favored over the optimal constant recombination. Two forms of the host recombination dependence on the parasite pressure were considered: either proportionally to the risk of infection (prevention strategy) or upon the fact of infection (remediation strategy). We show that both forms of plastic recombination can be favored, although relatively infrequently (up to 11% of all regimes with regular oscillations, and up to 20% of regimes with obligate parasitism). This happens under either strong overall selection and high recombination rate in the host, or weak overall selection and low recombination rate in the host. In the latter case, the system’s dynamics are considerably more complex. The prevention strategy is favored more often than the remediation one. It is noteworthy that plastic recombination can be favored even when any constant recombination is rejected, making plasticity an evolutionary mechanism for the rescue of host recombination.