Sexual dimorphisms may evolve through sex-specific and/or environment-dependent selection that results in different phenotypic optima for the sexes. Sexual dimorphisms in clonal expansion traits have recently been documented in Marchantia inflexa, a dioecious thallose liverwort. To uncover possible mechanisms for the maintenance and evolution of these pre-adult sexually dimorphic characters we used selection analyses to measure the magnitude and direction of selection on traits associated with asexual fitness and tested for sex-specific and environment-dependent selection regimes. We planted replicate genotypes of male and female M. inflexa in two different light environments in a greenhouse and measured morphological and phenological characters associated with growth and asexual reproduction. Timing to cupule onset and plant size early in development were under sex-specific selection in a low light environment. Disruptive selection acted on timing to cupule onset in females in low light and on male size in high light. Females exhibited environment-dependent selection and a sex-specific cost of plasticity in cupule onset. Both females and males displayed maladaptive phenotypes in low light with respect to timing of cupule onset but males also displayed a maladaptive size phenotype in low light. The presence of sex-specific and environment-dependent selection acting on pre-adult traits in M. inflexa may drive different phenotypic optima in the sexes and maintain sexual dimorphisms in traits associated with asexual reproduction.

Key words: asexual reproduction, Marchantia inflexa, selection, sexual dimorphism