WALL, DENNIS P. University of California, Berkeley. - Population structure and patterns of island radiation in the paleotropic endemic moss, Mitthyridium: insights from a rapidly evolving nuclear gene, glyceraldehyde 3-phosphate dehydrogenase (gpd).
Studies of diversification rate shifts require knowledge of both
phylogeny and time. Yet, even with these components, the picture
remains incomplete if the goal is to determine causal factors driving
such shifts. In the present analysis I optimize biogeographic data and
data on reproductive strategy to a large phylogeny of Mitthyridium,
consisting of 140 population exemplars, in order to comprehend causal
factors driving its relatively recent radiation. To reconstruct
adequately this shallow level of phylogenetic divergence, I employ a
single copy nuclear gene Glyceraldehyde-3 phosphate dehydrogenase
(gpd). The gene’s utility for plant systematics is poorly known, and
this represents the first study to use gpd for moss phylogeography.
Using gpd, I reconstruct the relationships among 140 populations
distributed across the known geographic range Mitthyridium. I
optimized to this phylogeny the variation in reproductive strategy
(Mitthyridium has a range of reproductive expression from fully sexual
to vegetative) to test the influence of island isolation on
reproductive mode and the consequent influence of reproductive
strategy on diversification rate shifts. Results show a trend towards
increased loss of sexual reproduction among island populations. These
island groups were found sister to mainland populations that show
significantly higher frequencies of sexual reproduction. This finding
suggests a general evolutionary trend towards loss of sex on islands.
Furthermore, the shift in reproductive mode is correlated with a shift
in diversification rate. This correlation suggests a plausible cause
of the rapid lineage radiation among island members of Mitthyridium.
Key words: diversification, Glyceraldehyde-3 phosphate dehydrogenase, Phylogeography