Abstract
Whether the persistence of natural plant populations is limited by genetic diversity, gene flow, or other ecological and evolutionary factors is an important question in plant population genetics. An assessment of the distribution of genetic variation within and among populations is thus useful for understanding broad-scale gene flow patterns in plants with diverse pollination syndromes. We studied Pogonia ophioglossoides (L.) Ker Gawl., which is self-compatible but a primarily outcrossing species in the Tribe Pogonieae in the family Orchidaceae. Using three self-developed, highly polymorphic nuclear microsatellite (simple sequence repeat, or SSR) markers and two chloroplast microsatellites, we assessed genetic variation in eight populations representing its natural distribution. Relatively high within-population genetic variation (mean An = 9.08, Ho = 0.44, and He = 0.71) was detected in P. ophioglossoides. Eleven different alleles and 13 unique haplotypes were detected for two cpDNA microsatellites. Genetic differentiation based on the hierarchical AMOVA showed that 21% (ФPT = 0.21, P = 0.000) and 63% (ФPT = 0.63, P = 0.000) of the nuclear and cpDNA microsatellite allelic diversity, respectively, was distributed among populations. Pairwise FST values ranged from 0.041 to 0.224 and each was statistically significant at P ≤ 0.05. The isolation by distance estimate did not show an association between genetic differentiation and geographic distance indicating that populations were diverging independently. We documented fine-scale spatial genetic structure (FSGS) up to 40 m distance in Texas. Overall, gene flow across the sampled populations of P. ophioglossoides appears restricted, and the short-distance SGS suggests localized seed dispersal in this locally common North American terrestrial orchid.
Highlights
The Orchidaceae represents approximately 10% of the angiosperm flora on the planet [1], and a majority of the species is considered rare and uncommon in their natural habitats
We studied eight disjunct populations of Pogonia ophioglossoides that ranged in pair-wise geographic distances from 116 km to 2603 km to: 1) quantify genetic diversity within and among populations, and 2) assess spatial distribution of genetic variation within a single population
A total of 60 alleles at three nuclear SSRs (nSSRs) loci were observed across eight populations of P. ophioglossoides
Summary
The Orchidaceae represents approximately 10% of the angiosperm flora on the planet [1], and a majority of the species is considered rare and uncommon in their natural habitats. The family is represented in almost all of the ecosystems across earth and displays a wide variety of ecological and biological strategies. Allogamy appears to be the primary mode of sexual reproduction within the Orchidaceae, though many taxa exhibit autogamy and/or geitonogamy. Regardless of the reproductive mode, low fruit-to-flower ratios are prevalent. The low reproductive success of orchids is implicated in inducing high genetic drift, which when combined with episodic selection may explain the exceptional diversification of species within the family [3]. Considering that the Orchidaceae represents complex and highly specialized ecological strategies, is represented globally, and represents a large proportion and diversity of flowering plants. It is of great interest to evolutionary biologists, biodiversity conservationists, and horticulturists alike
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