Abstract Detail

Population Genetics/Genomics

Wallace, Lisa [1], Bowles, Marlin [2].

Does habitat variation drive floral and genetic divergence in Platanthera dilatata, with moderation by inter-population gene flow? Evidence from Southeast Alaska.

Platanthera (Orchidaceae) is a phenotypically diverse genus whose floral variation has been attributed to differences in pollinator-mediated selection among species. Intraspecific phenotypic variation is also commonly reported in Platanthera and provides opportunities to study evolutionary divergence as it is occurring and to understand how different factors ultimately influence phenotypic variation. In this study, we compared floral variation, genetic variation, and habitat characteristics of 26 populations of Platanthera dilatata (Orchidaceae) in coastal Southeast Alaska to gain a deeper understanding of the phenotypic variation in floral traits that characterizes this species in that region. We addressed the following questions: 1) Are phenotypic and genetic variation structured spatially and by environmental variation, 2) Is there an association between phenotypic and genetic variation and if so, do vegetation and edaphic factors explain these patterns, 3) To what extent are populations at this scale exchanging genes. We identified two morphological groups that vary in flower size. Importantly, these forms occur in divergent habitats, with small-flowered forms restricted to more acidic muskeg bogs, whereas large-flowered forms occur across an edaphic gradient, including anthropogenic roadsides, meadows, and poor to rich fens. Genetic data also indicate the presence of two groups that largely correspond to the phenotypic divisions but with some exceptions that may indicate unidirectional gene flow. This may be pollinator-facilitated, as the large-flowered form appears to have greater pollinator diversity, including long- and short-tongued moths and butterflies, while the small-flowered form may be more restricted to short-tongued moths. The opposing forces of pollinator-mediated selection driving populations towards different floral phenotypes and gene flow uniting them could account for the complex floral variation commonly reported for this species yet lack of strong genetic divergence observed in previous studies.

1 - Old Dominion University, Biological Sciences, Mills Godwin Building Rm. 110, Norfolk, VA, 23529, United States
2 - The Morton Arboretum, 4100 IL 53, Lisle, IL, 60532, USA

Phenotypic variation
intraspecific variation
GeneticĀ  variation.

Presentation Type: Oral Paper
Number: PGG1004
Abstract ID:178
Candidate for Awards:None

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