Abstract Detail

Reproductive Processes

Leventhal, Laura [1], Weis, Arthur [2], Bai, Karen [3], Peters, Madeline [3], Ison, Jennifer [4].

Selection on phenological traits changes over the flowering season in a self-incompatible annual: Implications for the formation of adaptive temporal clines.

Plants mate repeatedly as they open and close successive flowers over the course of the season. This raises the possibility that selection—i.e., the covariance between phenotype and mating success—is stronger during some intervals but weaker at others. Many studies have documented selection pressures changing between breeding seasons; however, few studies have observed pressures changing within a breeding season. It has been suggested that when selection on a focal trait shifts over the course of a season, temporal genetic structure can facilitate the formation of adaptive temporal clines. Our study provides a method for evaluating the changing strength and direction of selection gradients in the annual self-incompatible, Brassica rapa. We used a novel field manipulation to sample and genetically characterize the pool of successful pollen over consecutive intervals in four open pollinated B. rapa plots. All potential pollen donors were genotyped at ten microsatellite loci. We then genotyped 1,885 resulting offspring and used a full probability maximum likelihood framework to calculate donor siring success, and thus selection via male fitness. To gain insight on how small-scale spatial distribution impacted pollen movement, donors were aggregated into dense clusters in two plots, but uniformly distributed in the others. We reconstructed the paternity of offspring from a large field experiment using a Bayesian maximum likelihood paternity analysis. After assigning paternity, we evaluated the strength and direction of selection via selection gradients on start date, total number of flowers, and skew at seven points within a breeding season. We also calculated pairwise spatial distance between father-offspring pairs. We found directional selection via male fitness towards a late start date and hypothesis that this could be a mechanism for the maintenance of flowering time variation. Additionally, we found directional selection towards more total flowers during peak and late season. These results, as well as the distance pollen moved, were dependent on the spatial distribution of the plants. Together, our results suggest that with limited gene flow and the right selective pressures, an adaptive temporal cline is possible in plants with heritable flowering times.

1 - The College of Wooster, The College of Wooster (Biology Dept), 1189 Beall Ave, Wooster, OH, 44691, United States
2 - University of Toronto, Department of Ecology and Evolutionary Biology, 25 Willcocks Street, Toronto, Ontario, M5S , Canada
3 - University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada
4 - The College Of Wooster, Biology Department, 1189 Beall Ave., Wooster, OH, 44691, United States

temporal genetic structure
assortative mating
Brassica rapa
adaptive cline
pollen pool
selection gradient
isolation by time
isolation by distance.

Presentation Type: Poster
Session: P, Reproductive Processes
Location: Grand Ballroom - Exhibit Hall/Mayo Civic Center
Date: Monday, July 23rd, 2018
Time: 5:30 PM
Number: PRP018
Abstract ID:861
Candidate for Awards:None

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