The roles of plasticity versus dominance in maintaining polymorphism in mating strategies

Abstract

Although natural selection is expected to reduce variability, polymorphism is common in nature even under strong selective regimes. Discrete polymorphisms in mating strategies are widespread and offer a good opportunity to understand the genetic processes that allow the maintenance of polymorphism in relatively simple systems. Here we explored the genetic mechanism underlying the expression of discrete mating strategies in the rock-paper-scissors (RPS) game. Heterozygotes carry the genetic information for two different strategies, yet little attention has been devoted to the mechanisms underpinning heterozygote phenotype and its consequences for allele frequency dynamics. We explored the maintenance of polymorphism under 1) genetic dominance or 2) plasticity, as mechanisms driving the expression of alternative strategies in males. We developed an alternative mating strategy model and analysed allele frequency dynamics using time series analyses. Our results show that both genetic mechanisms can maintain polymorphism depending on population demographic characteristics but that plasticity can enhance the likelihood that polymorphism is maintained relative to dominance. Time series analysis on simulation outcomes show that the RPS game is mostly driven by a single strategy, but the importance of this strategy on long term dynamics is stronger when gene expression shows dominance rather than plasticity.

Social Games and Genic Selection Drive Mammalian Mating System Evolution and Speciation

“…We modeled frequency-dependent social competition among three genetically determined strategies using a game theoretic approach (Maynard Smith 1982). We assumed that fitness is determined by additive effects of alleles at a single locus in a diploid sexual organism (table S1; tables S1-S7 are available online; Alonzo and Sinervo 2001;Sinervo et al 2007;Friedman and Sinervo 2016;Barreto et al 2017;Moulherat et al 2017). The single gene we model has effects on a number of behaviors and is similar to empirical findings in systems with a supergene (e.g., ruffs [Küpper et al 2016;Lamichhaney et al 2016]), pleiotropic effects on multiple behaviors (e.g., slime molds [Queller et al 2003;Foster et al 2004]), or both (e.g., lizards ).…”

“…We assume fitness intransitivity for competition (F M matrix) among the three alternative alleles (polygyny 1 monogamy 1 sneak 1 polygyny; table S1A), which holds when expanded to all genotype pairs (table S1D). Such intransitivity is critical for a stable trimorphism (Bomze 1983;Sinervo and Lively 1996;Sinervo et al 2007;Friedman and Sinervo 2016;Moulherat et al 2017) and has been described in a number of species with very broad taxonomic coverage ranging from bacteria to plants to vertebrates chap. 7 in Friedman and Sinervo 2016).…”

“…These models focused on the influence of extrinsic factors on mating system evolution. In contrast to these phenotypic models, a handful of studies examined how genetic systems might influence mating system evolution; these models yield surprising results (Ptak and Lachmann 2003;Sinervo et al 2007;Moulherat et al 2017). For example, Ptak and Lachmann (2003) showed that specific attention to allelic inheritance leads to a much broader state space where polygyny is stable based on a polygyny threshold scenario (i.e., resource defense polygyny).…”

“…For example, Ptak and Lachmann (2003) showed that specific attention to allelic inheritance leads to a much broader state space where polygyny is stable based on a polygyny threshold scenario (i.e., resource defense polygyny). Likewise, Moulherat et al (2017) showed that differences in gene expression (dominance vs. plasticity) alters the likelihood that a set of alternative male strategies is maintained within a population. Moreover, recent game theoretic models have suggested that social interactions can have important effects on model outcomes (Alonzo 2010;Dillard and Westneat 2016).…”

“…Specifically, we add two new elements to past models. First, we model three alternative strategies as in past studies on the maintenance of alternative mating strategies (e.g., Sinervo et al 2007;Moulherat et al 2017), but with a focus on mating system state when alternative strategies are not maintained as well as cases when multiple strategies are maintained. Second, we model two social behaviors (neighborhood choice and paternal care) driven by genic recognition of others, as suggested in recent empirical work (Bester-Meredith et al 1999;Mateo 2004;Holmes and Mateo 2007;Widdig 2007;.…”