Abstract Detail

Reproductive Processes

Brunet, Johanne [1], Flick, Andrew [2], Bauer, Austin [3].

Phenotypic selection on flower color and floral display size by three bee species.

Measuring phenotypic selection exerted by pollinators and by individual pollinator species presents various challenges. We introduce an approach to calculate relative fitness within each pollinator species, based on differential flower visits to plants in a population. The approach eliminates the potential impact of differences in seed set among pollinator species on phenotypic selection. We quantify phenotypic selection on flower color and floral display size overall and within each of three distinct bee species, the European honey bee, Apis mellifera, the common eastern bumble bee, Bombus impatiens, and the alfalfa leafcutting bee, Megachile rotundata. These pollinators are the major visitors to Medicago sativa in this study. To minimize the impact of resource availability and environmental factors on reproductive success, plants were grown in a common garden. For flower color, we examined the chroma, hue and reflectivity of flowers. For floral display size, we estimated the number of open flowers per raceme, the number of racemes per stem and the number of stems per plant. We used the total number of seeds produced per plant as a measure of female reproductive success. We estimated the overall relative fitness of a plant by dividing the absolute fitness of a plant (number of seeds set) by the mean absolute fitness over all plants. Each floral trait examined was scaled such that its mean was 0 and its variance was 1: (trait value – trait mean)/trait standard deviation. We performed regression analyses between relative fitness and scaled plant traits to detect the presence of linear and quadratic selection differentials and selection gradients together with the presence of correlational selection. We determined overall phenotypic selection and phenotypic selection by each pollinator species. Overall, positive directional selection was detected on components of floral display size but not on flower color. We observed an overall positive correlational selection on the number of open flowers per raceme and chroma or darkness of flowers. However, this pattern of selection was only detected with bumble bee and not with honey bee or leafcutting bee. Bumble bee favored plants with more racemes per stem while a negative selection gradient was detected for honey bee and leafcutting bee. Phenotypic selection differed among bee species but the overall phenotypic selection patterns, at least via female function, could be explained by the phenotypic selection observed over the three bee species. 

Related Links:
Brunet laboratory website

1 - USDA-ARS VCRU, 1575 Linden Drive , Madison, WI, 53706, United States
2 - Agricultural Research Service-Oak Ridge Institute for Science and Educ, 455 Science Drive , Suite 170, Madison, WI, 53706, USA
3 - University of Wisconsin-Madison, Entomology, 1630 Linden Drive, Madison, Wisconsin, 53706, US

Flower color
Floral display
bumble bee
Honey bee
Leafcutting bee
Phenotypic selection.

Presentation Type: Oral Paper
Session: REP4, Reproductive Processes 4
Location: Virtual/Virtual
Date: Thursday, July 30th, 2020
Time: 3:00 PM
Number: REP4001
Abstract ID:568
Candidate for Awards:None

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