Does asexuality confer a short term advantage? A case study in the fern myriopteris gracilis (pteridaceae)
Asexual taxa are generally seen as evolutionary dead ends, relegated to the tips of phylogenies due to elevated extinction rates. Despite this macroevolutionary disadvantage, there is evidence in some cases that asexual reproduction may provide a short-term benefit. This is particularly evident in asexual species that display a wider distribution than their sexual relatives. Alternatively, it is possible that such broad distributions are an illusion created by multiple asexual lineages, each occupying a relatively small area. Myriopteris gracilis Fée (Pteridaceae) is a North American asexual fern species with a particularly large range. In this study we investigate, first, if M. gracilis is exclusively asexual throughout its range and second, whether M. gracilis comprises a single wide-ranging lineage, or multiple, more geographically restricted lineages. Sexuality was assessed by counting spores/sporangium in 502 herbarium specimens from 28 states and provinces in the USA, Canada and Mexico, revealing no cryptic sexual populations. Lineage structure was then assessed with both plastid DNA sequence and Genotyping By Sequencing (GBS) SNP datasets. The plastid data identified two large, roughly eastern and western, groups. Each group was further subdivided by the GBS data, to reveal a complex distribution of asexual lineages of varying geographic range sizes none of which accounted for the total size of the M. gracilis range. Thus, viewed as a single, continuous distribution, they tend to overstate the success of any one lineage in M. gracilis and by extension, asexuality's contribution to short-term success in other species.
Thesis (M.S.)--Wichita State University, Fairmount College of Liberal Arts and Sciences, Dept. of Biological Sciences