Mating Systems in Sphagnum

Sphagnum capillifolium expressing maleSynopsis: This research is the first to characterize the diversity of mating patterns in natural populations of Sphagnum. In peat mosses, sexual condition is a species-level trait: most species produce only one type of gamete (unisexual) while a minority of species are bisexual, producing both egg and sperm in the same plant. This will have a major effect on mating patterns, because the bisexual species can produce completely homozygous offspring with a single round of mating! We sampled maternal gametophytes and all attached sporophyte offspring in 19 populations of 14 species in North America, including both unisexual and bisexual species from every section of the genus. We were also interested in the role of microhabitat preference in shaping mating patterns. For instance, species that tend to occur only in “hummocks” high above the water table are more likely to have trouble dispersing sperm (which needs water to swim to the egg) than species that prefer completely aquatic habitats. We showed that sexual condition is a primary driving factor behind both mating patterns and genetic diversity of populations; populations of bisexual species tended to have lower genetic diversity and a high rate of inbreeding.

Microhabitat preference played a more complex role: populations o hummock-preferring bisexual species were more likely to have high inbreeding than hollow-preferring bisexual species. But in populations of unisexual species, the reverse was true! Considering the results from our study of the evolution of niche preferences, this means that both biology and phylogenetic history likely play large roles in determining the mating patterns in populations of peat mosses.

My role: This research was part of my PhD dissertation, so I designed the research, collected nearly all of the samples in Maine, North Carolina, and Alaska, and conducted the analyses! I also developed several scripts for assigning individuals to genets and improved on previous scripts for calculating FIS in populations of moss sporophytes.

Johnson, M. G., and A. J. Shaw. 2015. Genetic diversity, sexual condition, and microhabitat preference determine mating patterns in Sphagnum (Sphagnaceae) peat‐mosses. Biological Journal of the Linnean Society. 115(1): 96-113.

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