Interactions between genetic and ecological effects on the evolution of life cycles

Abstract

Sexual reproduction leads to an alternation between hap-loid and diploid phases, whose relative length varies widely across taxa. Previous genetical models showed that diploid or haploid life cycles may be favored, depending on dominance interactions and on effective recombination rates. By contrast, niche differentiation between haploids and diploids may favor biphasic life cycles, in which develop-ment occurs in both phases. In this article, we explore the interplay be-tween genetical and ecological factors, assuming that deleterious muta-tions affect the competitivity of individuals within their ecological niche and allowing different effects of mutations in haploids and diploids (in-cluding antagonistic selection). We show that selection on a modifier gene affecting the relative length of both phases can be decomposed into a direct selection term favoring the phase with the highest mean fitness (due to either ecological differences or differential effects of mutations) and an indirect selection term favoring the phase in which selection is more efficient. When deleterious alleles occur at many loci and in the presence of ecological differentiation between haploids and diploids, evolutionary branching often occurs and leads to the stable coexistence of alleles coding for haploid and diploid cycles, while temporal varia-tions in niche sizes may stabilize biphasic cycles.