Ecological genetics of range size variation in Boechera spp. (Brassicaceae)

Abstract

Many taxonomic groups contain both rare and widespread species, which indicates that range size can evolve quickly. Many studies have compared molecular genetic diversity, plasticity, or phenotypic traits between rare and widespread species; however, a suite of genetic attributes that unites rare species remains elusive. Here, using two rare and two widespread Boechera (Brassicaceae) species, we conduct a simultaneous comparison of quantitative trait diversity, genetic diversity, and population structure among species with highly divergent range sizes. Consistent with previous studies, we do not find strong associations between range size and within‐population genetic diversity. In contrast, we find that both the degree of phenotypic plasticity and quantitative trait structure (Q ST) were positively correlated with range size. We also found higher F ST: Q ST ratios in rare species, indicative of either a greater response to stabilizing selection or a lack of additive genetic variation. While widespread species occupy more ecological and climactic space and have diverged at both traits and markers, rare species display constrained levels of population differentiation and phenotypic plasticity. Combined, our results provide evidence for a specialization–generalization trade‐off across three orders of magnitude of range size variation in the ecological model genus, Boechera.

Mutation Accumulation in an Asexual Relative of Arabidopsis

“…lyrata reference). Sexual Boechera spatifolia are self-compatible and highly inbred ( F IS = 0.75, ~85% selfing, [21]), while apomicts are typically hybrids. Therefore, it is not surprising that across all sites and populations, apomicts displayed much greater observed heterozygosity ( H 0 = 0.23, Fig 2A) than sexuals ( H 0 = 0.15).…”

Determinants of geographic range size in plants

“…flowering time, specific leaf area) varies across environments at the genotypic level (Sexton et al , ). This may explain the lack of strong support for a positive relationship between phenotypic plasticity and range size, especially since studies differ drastically in focal traits used for quantifying plasticity (e.g., Sheth & Angert, ; Lovell & McKay, ; Hirst et al , ) and are often unable to determine whether plasticity is adaptive (Dostál et al , ).…”

“…Thus, most studies that have compared quantitative genetic variation in widespread and restricted species have had limited sample sizes for making robust inferences, often 1–2 species pairs with contrasting range sizes (e.g. Lovell & McKay, ), and we are unaware of any study involving more than 10 species (Kellermann et al , ; Sheth & Angert, ). Third, genetic variation may change across space (Pujol & Pannell, ) and time (Leigh et al , ), so including multiple populations per species at multiple time points would further increase the sample sizes needed to test this hypothesis.…”

The Boechera Genus as a Resource for Apomixis Research

“…Earlier work on the population dynamics of the sexual species B. fecunda (Song and Mitchell-Olds, 2007) and B. stricta (Song et al, 2009), using sequence data from several nuclear loci and microsatellites, revealed similar levels of polymorphism and population differentiation in both species, regardless of the marked difference between the widespread B. stricta and the endangered B. fecunda with a reduced range. Similarly, studies comparing the widespread species B. stricta and B. latifolia with the rare species B. crandallii and B. vivariensis did not find strong associations between species size range and within-population genetic diversity (Lovell and McKay, 2015). However, the more widespread species exhibited higher phenotypic plasticity and quantitative trait structure (Qst), while the rare species contained stronger signatures of selection evidenced by higher Qst: Fst ratios, with Fst referring to the fixation index (Lovell and McKay, 2015).…”

“…Similarly, studies comparing the widespread species B. stricta and B. latifolia with the rare species B. crandallii and B. vivariensis did not find strong associations between species size range and within-population genetic diversity (Lovell and McKay, 2015). However, the more widespread species exhibited higher phenotypic plasticity and quantitative trait structure (Qst), while the rare species contained stronger signatures of selection evidenced by higher Qst: Fst ratios, with Fst referring to the fixation index (Lovell and McKay, 2015). Extending the work of Song and Mitchell-Olds (2011) on B. fecunda , Leamy et al (2014) found regional adaptation through extensive quantitative characterization of populations in Montana (United States) using microsatellite markers.…”