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Abstract Detail

Evolutionary insights from studies of geographic variation: Establishing a baseline and looking ahead to future change

Herlihy , Chris R [1], Busch, Jeremiah [2].

What explains the geographic pattern of flower color in the narrow endemic Leavenworthia stylosa?.

Examples of conspicuous polymorphisms in fitness related traits within narrowly endemic species provide unique opportunities to examine evolutionary processes at the local scale. Leavenworthia stylosa (Brassicaceae) is a small, early-flowering winter annual endemic to the limestone cedar glades of central Tennessee.  Individual plants produce either yellow or white petals, and most populations contain only a single flower color morph. Across the very small geographic range of this species there a strong spatial pattern of flower color variation. Here we present the results of several experiments aiming to explain the evolutionary maintenance of this flower color polymorphism and its geographic distribution.  We sampled a large number of populations throughout the species range, and performed reciprocal transplants between yellow-flowered and white-flowered areas of the range. We show that there is limited genetic differentiation and substantial gene flow among populations, suggesting that the polymorphism may be maintained by local variation in natural selection. We found only weak evidence for local adaptation to abiotic conditions by the two color morphs.  Across the range, there was variation in the abundance of pollinators and their preference for yellow or white flowers, however this did not occur in a way that could maintain the flower color polymorphism. White flowers are often larger than yellow flowers, and they frequently produce more seeds.  However, fruits produced by white flowers suffer greater damage from a weevil seed predator.  This tradeoff between fecundity and protection from seed predation may help explain the maintenance of the polymorphism, but does not explain the geographic distribution of flower color. Leavenworthia stylosa competes for pollinators with several co-flowering white-flowered Leavenworthia species.  When in sympatry with congeneric species, L. stylosa often has yellow flowers.  We planted arrays containing both flower color morphs of L. stylosa and the white-flowered Leavenworthia exigua.  We found that pollinators tended to move among flowers of the same color, including moving between the two species. Movement of pollen from L. exigua to L. stylosa results in the production of sterile offspring.  The shift to yellow flowers in populations of L. stylosa where its range overlaps with congeners may represent a case of reproductive character displacement, and may help explain both the maintenance of the flower color polymorphism and its geographic pattern.

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1 - Middle Tennessee State University, Department Of Biology, 1301 E Main St, PO Box 60, Murfreesboro, TN, 37132, USA
2 - Washington State Univsity, School of Biological Sciences, PO Box 644236, Pullman, WA, 99164, USA

flower color
Geographic variation
character displacement.

Presentation Type: Symposium or Colloquium Presentation
Session: SY08
Location: Firs North/Boise Centre
Date: Wednesday, July 30th, 2014
Time: 8:45 AM
Number: SY08003
Abstract ID:562
Candidate for Awards:None

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