Hana Thompson MSc Candidate, Eckert lab A shift from sexual to asexual reproduction in a wetland plant: implications for range edge dynamics All species have limits to their geographic distributions, and these limits are thought to reflect a failure of adaptation to conditions beyond the range. The adaptive capacity of populations at range limits could be strongly influenced by the amount and distribution of genetic variation, which in turn is strongly affected by variability in reproductive system, particularly in plants which exhibit diverse reproductive modes. Plants can reproduce sexually, either through outcrossing (exchanging pollen with other individuals) or self-fertilization. Many plants have the capacity for some form of asexual reproduction as well, by producing parthenogenic seeds or clonal reproduction via vegetative propagation. Sexual and asexual reproduction have different ecological requirements, meaning that a species with both methods of reproduction can have separate sexual and asexual niches. In some species, the sexual niche is narrower than the asexual niche, thus shifts to asexuality might allow these species to thrive in environments where sexual reproduction is inhibited. Decodon verticillatus is a wetland plant that reproduces sexually through most of its range and exhibits a shift to asexual clonal reproduction at the northern range margin. For my master’s research I am investigating the evolutionary causes and consequences of this shift to asexuality, and the implications for range edge dynamics in Decodon verticillatus using a transcriptomic analysis of RNA-seq data. I found that the range-edge populations show genetic signatures of long-term asexuality, such as increased heterozygosity and a breakdown of isolation by distance. This suggests that the asexual populations are long-lived and well-established, and that shifting to asexuality may have allowed range expansion beyond the sexual niche of D. verticillatus. Understanding the factors that influence range limits and range expansion is becoming increasingly important to better anticipate the capacity of species to adapt, and potentially shift their ranges in response to anthropogenic environmental changes.
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