Abstract Detail

Population Genetics/Genomics

Hersh, Evan [1], Whitton, Jeannette [2].

Population genomics of diploid-sexual and polyploid-apomictic Easter daisies (Townsendia hookeri – Asteraceae) shed light on the origins and spread of asexuality. .

We know that asexuality has arisen repeatedly from sexual backgrounds, but the conditions under which asexuals establish and spread (while sexuals persist) in nature are poorly understood. Species (or close relatives) with sexual and asexual forms often show range divergence, with asexual populations showing greater geographic, latitudinal, or elevational spread – a pattern commonly termed “geographical parthenogenesis” (GP). Hypothesized mechanisms for GP relate to genetic, ecological, and/or demographic differences between sexuals and asexuals, but no single explanation has yet emerged. For example, there may be a small set of widespread clones with high ecological amplitude, or a series of ecologically specialized clones that partition the available niche space. Understanding the origins of asexual lineages and how they are arranged on the landscape is key to sifting through these hypotheses, and can shed light on their success in nature. Townsendia hookeri is a perennial flowering plant with diploid sexual and polyploid apomictic (reproducing asexually through seeds) populations that show a classic pattern of GP. In order to investigate the population genetic structure of both sexual and apomictic T. hookeri populations, we used a genotyping by sequencing approach (reduced representation ddRAD library) to generate over 250 million paired-end reads. De novo assembly, mapping, and SNP-calling were performed using the dDocent bioinformatic pipeline. After stringent filtering, several thousand shared SNPs were identified and imported into R for population genomic analysis and visualization. While most apomictic populations are composed of the same genotype (indicating strict clonality), some populations show signs of admixture in their population structure. In addition, two apomictic populations do not indicate clonal structure at all, which suggests that they may be recently formed (or transitional) asexual lineages. Our data provides evidence for multiple origins of apomixis in T. hookeri, with both widespread clonal lineages in some regions and a diverse array of clones in others. These results do not fit perfectly into any one model of GP, which highlights how unique dynamics can shape the relationships between reproductive modes in different systems.

1 - University Of British Columbia, 215-1075 West 14th Avenue, Vancouver, BC, V6H1P4, Canada
2 - Department Of Botany, University Of British Columbia, 3529-6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada

Keywords:
Apomixis
ddRAD-seq
polyploidy
phylogeography
Population genomics
geographical parthenogenesis
Townsendia.

Presentation Type: Oral Paper
Session: POPGEN2, Population Genetics/Genomics II
Location: Tucson H/Starr Pass
Date: Wednesday, July 31st, 2019
Time: 1:45 PM
Number: POPGEN2002
Abstract ID:903
Candidate for Awards:Margaret Menzel Award