FUSELIER, LINDA C.* and D. NICHOLAS MCLETCHIE. University of Kentucky, Department of Biological Sciences, 101 Morgan Bldg., Lexington, KY 40506. - Sex-specific and environment-dependent phenotypic selection on pre-adult traits in Marchantia inflexa.
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