Evolution of mating systems in Sphagnum peatmosses

Bryophytes, by their haploid dominant life cycle, possess several unique qualities ideal for study of mating patterns. In particular, the possibility of intragametophytic selfing in some species, and the vegetative propagation of gametes allow for a unique window into the haploid stage that is intractable in other groups. Despite these advantages, there have been relatively few studies on mating patterns bryophytes in natural populations. Sphagnum (peatmoss) is an excellent case study in the interactions between sexual condition, ecology, and mating patterns. In the first Chapter, we use microsatellites to characterize the genetic diversity and mating patterns in fourteen species of Sphagnum, diverse in sexual condition (separate vs combined sexes in the haploid stage) and ecology (microhabitat variance along the water table). We find that genetic diversity and mating patterns are related only in species with separate sexes, that sexual condition and ecology have interacting effects on inbreeding coefficients, and that inbreeding depression is not a common phenomenon in Sphagnum. In the second Chapter, we conduct an intensive survey of one population of Sphagnum macrophyllum, to detect whether variance in haploid fecundity and mating success is related to diploid fitness. We find a relationship between mating success and fecundity (a signal of sexual selection), and fitness of the diploid generation is connected to the parentage of the haploid generation. Finally, in Chapter 3 we use phylogenetic comparative methods to track the phylogenetic signal in microhabitat preference in Sphagnum. We find extremely fast rates of evolution along the micronutrient gradient, but high phylogenetic signal along a hydrological gradient. Given that Sphagnum species living high above the water table have reduced water availability, phylogenetic signal in the hydrological gradient has macroevolutionary implications for mating systems in Sphagnum.