Geographic patterns of microsatellite variation inBoechera stricta, a close relative ofArabidopsis

Abstract

The genus Boechera is a widespread North American group with great potential for studies of ecology and evolution: Boechera is closely related to Arabidopsis and exhibits different ecological and reproductive strategies. Boechera stricta (previously Arabis drummondii) is a morphologically and genetically well-defined, perennial crucifer species. Fifteen natural populations of diploid individuals from the Rocky Mountains were analysed using 21 microsatellite loci. In accordance with our expectation for this predominately inbreeding species, a high F IS value (0.89) was observed. Furthermore, populations of B. stricta were highly differentiated, as indicated by F ST = 0.56. Three clusters were identified using structure- the majority of populations belonged to either the Northern or Southern cluster. Together, the north-south partitioning and evenness of genetic variation across the two clusters suggested multiple refugia for this perennial herb in the Rocky Mountains. Pleistocene glaciation, together with the topographically and climatologically heterogeneous cordillera, has profoundly influenced the genetic architecture of B. stricta. Genetic population structure was also influenced by relatively recent genome admixture at two levels: within species (involving individuals from the Northern and Southern clusters) and between species (with the hybridization of B. stricta and Boechera holboellii). This complexity of population structure at presumably neutral microsatellite loci located throughout the genome in B. stricta provides a baseline against which to test whether functional genetic variation is undergoing local adaptive evolution throughout the natural species range.

Multilocus Patterns of Nucleotide Diversity, Population Structure and Linkage Disequilibrium inBoechera stricta, a Wild Relative of Arabidopsis

“…The NORTHERN group is geographically located in the northern Rocky Mountains, while the SOUTHERN group is centered in Colorado. The WESTERN group corresponds to the Monida group found previously (Song et al 2006), which is now seen to extend westward to the Cascades and Sierra Nevada. Three individuals from Utah (UT02, UT05, and UT07) and one accession from Arizona (AZ01) showed admixture between NORTH and SOUTH, and one accession from Idaho (ID89) showed admixture between NORTH and WEST.…”

“…Although asexual hybrids between B. stricta and B. holboellii are found in some populations (Schranz et al 2005;Kantama et al 2007), these are readily identified by their divergent morphology and high levels of heterozygosity, and are not included in this study. Average F IS and F IT in B. stricta are $0.90 and 0.95, respectively (Song et al 2006), and these studied genotypes had been propagated by self-pollination in the laboratory for one generation; hence, levels of residual heterozygosity were very low.…”

“…B. stricta (previously Arabis drummondii) is a morphologically and genetically well-defined, monophyletic, short-lived perennial crucifer species (Dobes et al 2004). Genetic and molecular analyses indicate that B. stricta is predominantly diploid, sexual, and inbreeding (F IS ¼ 0.9 and F IT ¼ 0.95) (Schranz et al 2005;Song et al 2006). B. stricta populations are distributed in diverse habitats across much of western North America, providing opportunities to study evolutionary and ecological functional genomics in undisturbed natural environments.…”

Ecological genomics: understanding gene and genome function in the natural environment

“…At this stage, both approaches have yielded interesting results (Roberts and Feder, 2000;Weinig et al, 2002;Kessler et al, 2004). Some have taken to using a combined approach, as is being done in the study of the genetic structure of Bochera stricta populations (Song et al, 2006). By taking the best of both worlds, the latter, compromise approach promises to be extremely fruitful.…”

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

“…Molecular data from B. crandallii (Roy 1995), B. stricta (Song et al. 2006), and B. spatifolia (Lovell et al. 2014) indicate that self‐pollination is the dominant reproductive mode for each species.…”