RICHARDSON, CHARLES R.*, D. NICHOLAS MC LETCHIE, and PHILIP H. CROWLEY. Center for Ecology, Evolution and Behavior and the T.H. Morgan School of Biological Sciences, University of Kentucky, Lexington Ky, 40506-0225. - Life-history tradeoffs and genotypic variation in the dioecious liverwort Marchantia inflexa.
Tradeoffs among growth, asexual and sexual reproduction have not been
extensively documented despite the vast number of organisms that can
reproduce through asexual and sexual methods. This experiment
characterizes life-history variation among genotypes and tests for
tradeoffs among life-history traits in the dioecious bryophyte
Marchantia inflexa. Marchantia inflexa can reproduce
asexually from gemmae produced in cupules or sexually through spores.
Genotypes were collected from populations in Trinidad that were
classified as either Sex Expressing (SE) or Non Sex-Expressing (NSE)
based upon the presence or absence of sex expression in the population
at the time of collection. Sixty-four genotypes, sixteen males and
sixteen females from both SE and NSE populations were grown in a
greenhouse in either high or low light conditions. The plants were
censused thrice weekly and the dates of first asexual and sexual
reproduction were recorded. Plant size and the number of cupules and
sex structures were quantified bi-weekly. MANOVA's were used to assess
the variation for two growth, asexual and sexual characters (i.e. 6
parameters) and repeated measure analysis was used to compare the
amount and pattern of cupule and sexual production. Genotype identity
was nested within sex for all analyses. The MANOVA detected a
significant genotype (Wilk's Lambda=0.1 F=1.3 p < 0.05) and sex
(Wilk's Lambda=0.32 F=3.6 p < 0.0001) effect on M. inflexa
life-histories. Genotypes displayed clonal heritability estimates
between 0.74 and 0.017. The repeated measures analysis detected
significant interactions between time and sex (Wilk's Lambda=0.9 F=1.6
p< 0.01), genotype (Wilk's Lambda=0.2 F=1.3 p< 0.0001) and the
combination of light and sex (Wilk's Lambda=0.9 F=1.3 p < 0.05) on
cupule production. Pearson's correlations did not find evidence of
negative tradeoffs as early cup production was positively correlated
with early sex expression (r =0.21 p< 0.01) and high growth rates (r =
0.17 p< 0.01).
Key words: Marchantia inflexa, bryophyte, clonal heritability, cost of reproduction, life-history tradeoffs