Project description:PREMISE OF THE STUDY:Microsatellite primers were designed for Calochortus gunnisonii (Liliaceae), a montane lily species of the central and southern Rocky Mountains, using next-generation DNA sequencing. The markers will be used to investigate population structure, genetic diversity, and demographic history. METHODS AND RESULTS:Thirteen polymorphic microsatellite loci were isolated from C. gunnisonii using Illumina MiSeq next-generation DNA sequencing and bioinformatic screening. The mean number of alleles per locus ranged from 4.15 to 5.92 (avg. = 4.97). Observed and expected heterozygosity ranged from 0.077 to 0.871 and 0.213 to 0.782, respectively. The primers were also tested for cross-species amplification value with C. flexuosus, C. nuttallii, C. kennedyi var. kennedyi, and C. subalpinus. CONCLUSIONS:These primers will be useful for genetic and evolutionary studies across C. gunnisonii's range within the southern and central Rocky Mountains. Furthermore, these markers have proven valuable for cross-species amplifications within Calochortus.
Project description:We used nuclear genomic data and statistical models to evaluate the ecological and evolutionary processes shaping spatial variation in species richness in Calochortus (Liliaceae, 74 spp.). Calochortus occupies diverse habitats in the western United States and Mexico and has a center of diversity in the California Floristic Province, marked by multiple orogenies, winter rainfall, and highly divergent climates and substrates (including serpentine). We used sequences of 294 low-copy nuclear loci to produce a time-calibrated phylogeny, estimate historical biogeography, and test hypotheses regarding drivers of present-day spatial patterns in species number. Speciation and species coexistence require reproductive isolation and ecological divergence, so we examined the roles of chromosome number, environmental heterogeneity, and migration in shaping local species richness. Six major clades-inhabiting different geographic/climatic areas, and often marked by different base chromosome numbers (n = 6 to 10)-began diverging from each other ~10.3 Mya. As predicted, local species number increased significantly with local heterogeneity in chromosome number, elevation, soil characteristics, and serpentine presence. Species richness is greatest in the Transverse/Peninsular Ranges where clades with different chromosome numbers overlap, topographic complexity provides diverse conditions over short distances, and several physiographic provinces meet allowing immigration by several clades. Recently diverged sister-species pairs generally have peri-patric distributions, and maximum geographic overlap between species increases over the first million years since divergence, suggesting that chromosomal evolution, genetic divergence leading to gametic isolation or hybrid inviability/sterility, and/or ecological divergence over small spatial scales may permit species co-occurrence.
