ECOLOGY AND THE EVOLUTION OF BIPHASIC LIFE CYCLES

abstract: Sexual eukaryotes undergo an alternation between haploid and diploid nuclear phases. In some organisms, both the haploid and diploid phases undergo somatic development and exist as independent entities. Despite recent attention, the mechanisms by which such biphasic life cycles evolve and persist remain obscure. One explanation that has received little theoretical attention is that haploid‐diploid organisms may exploit their environments more efficiently through niche differentiation of the two ploidy phases. Even in isomorphic species, in which adults are morphologically similar, slight differences in the adult phase or among juveniles may play an important ecological role and help maintain haploid‐diploidy. We develop a genetic model for the evolution of life cycles that incorporates density‐dependent growth. We find that ecological differences between haploid and diploid phases can lead to the evolution and maintenance of biphasic life cycles under a broad range of conditions. Parameter estim...