WALL, DENNIS P. Dennis P. Wall, Department of Integrative Biology &, University and Jepson Herbaria, University of California, Berkeley, Berkeley, CA 94720, Phone: (510) 643-9556, Fax: (510) 643-5390, email:email@example.com. - Population structure and diversfication patterns in the paleotropic endemic moss, Mitthyridium.
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. The present study uses biogeographic, ecological and
biological data within one phylogeny of a paleotropic endemic moss,
Mitthyridium to dissect causal factors driving its relatively recent
radiation. Mitthyridium, a monophyletic and distinct group, has a
relatively narrow geographic distribution including several island
endemics and may represent a model radiation. Relationships of
lineages below the traditional species level in the group were
discovered through phylogenetic analysis of faster evolving regions in
the nucleus (Glyceraldehyde-3 phosphate dehydrogenase (GPD)), and
chloroplast (3’ spacer regions of rbcL and rps4) using samples from
across most of the distribution of Mitthyridium. GPD is a single copy
nuclear gene that provides appropriate variation for phylogeography.
The present study introduces this gylocolytic gene as new to studies
of moss systematics and demonstrates its utility for phylogenetic
reconstruction, with special emphasis on the population structure of
Mitthyridium. Results show that subspecific lineages are biologically
distinct and island specific. A particular biological feature
distinguishing the lineages--variability in sexual expression (from
fully sexual to vegetative)--was mapped to the phylogeographic
structure to test the influence of reproductive mode on rate shifts.
Preliminary results indicate trends towards increasing asexuality
among island populations of Mitthyridium that are correlated with
geography. The shifts in reproductive mode, when localized along the
phylogeny, are significantly concentrated with changes in rates of
diversification, both in anagenetic and cladogenetic contexts. These
results allow for a rigorous examination of causal mechanisms driving
rapid evolutionary radiation on oceanic islands.
Key words: diversification rate shifts, Glyceraldehyde-3 phosphate dehydrogenase, Mitthyridium, phylogeography