Abstract
Calochortus (Liliaceae) displays high species richness, restriction of many individual taxa to narrow ranges, geographic coherence of individual clades, and parallel adaptive radiations in different regions. Here we test the first part of a hypothesis that all of these patterns may reflect gene flow at small geographic scales. We use amplified fragment length polymorphism variation to quantify the geographic scales of spatial genetic structure and apparent gene flow in Calochortus albus, a widespread member of the genus, at Henry Coe State Park in the Coast Ranges south of San Francisco Bay. Analyses of 254 mapped individuals spaced 0.001–14.4 km apart show a highly significant decline in genetic identity with ln distance, implying a root-mean-square distance of gene flow σ of 5–43 m. STRUCTURE analysis implies the existence of 2–4 clusters over the study area, with frequent reversals among clusters over short distances (<200 m) and a relatively high frequency of admixture within individuals at most sampling sites. While the intensity of spatial genetic structure in C. albus is weak, as measured by the Sp statistic, that appears to reflect low genetic identity of adjacent plants, which might reflect repeated colonizations at small spatial scales or density-dependent mortality of individual genotypes by natural enemies. Small spatial scales of gene flow and spatial genetic structure should permit, under a variety of conditions, genetic differentiation within species at such scales, setting the stage ultimately for speciation and adaptive radiation as such scales as well.
Highlights
Calochortus (Liliaceae sensu APG 2009) is a large genus of bulbous geophytes, ranging from British Columbia east to the Dakotas and south to Guatemala, with a center of diversity in California (Ownbey 1940; Gerritsen and Parson 2007; Fiedler and Zebell 2012)
Patterson and Givnish (2004) used plastid sequence data to show that Calochortus includes seven major clades centered in different geographic regions; that individual floral syndromes, habitat preference, and serpentine tolerance have each evolved independently several times; and that closely related species are often nearest neighbors geographically. They proposed that narrow endemism, geographic coherence of individual clades, and parallel adaptive radiations in different areas might all have resulted from limited gene flow via seed dispersal over small spatial scales, resulting in spatial genetic structure (SGS) within species at small spatial scales, and in some cases resulting in speciation and endemism over limited scales as well
Ecology and Evolution published by John Wiley & Sons Ltd
Summary
Calochortus (Liliaceae sensu APG 2009) is a large genus (ca. 70 spp.) of bulbous geophytes, ranging from British Columbia east to the Dakotas and south to Guatemala, with a center of diversity in California (Ownbey 1940; Gerritsen and Parson 2007; Fiedler and Zebell 2012). Patterson and Givnish (2004) used plastid sequence data to show that Calochortus includes seven major clades centered in different geographic regions; that individual floral syndromes, habitat preference, and serpentine tolerance have each evolved independently several times; and that closely related species are often nearest neighbors geographically. They proposed that narrow endemism, geographic coherence of individual clades, and parallel adaptive radiations in different areas might all have resulted from limited gene flow via seed dispersal over small spatial scales, resulting in spatial genetic structure (SGS) within species at small spatial scales, and in some cases resulting in speciation and endemism over limited scales as well
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