Abstract Detail

Ecological Section

Haggerty, Brian [1], Mazer, Susan [2].

Natural selection on phenological traits across the biogeographic range of a California annual wildflower: independent effects on fitness of first flowering date and flowering synchrony.

There is a rich history in ecology and evolution of assessing the adaptive significance of life history traits. For plant phenology, a large body of research has demonstrated that, within populations, early flowering individuals tend to achieve higher fitness than later flowering individuals (i.e., natural selection favors early flowering). Much of this work, however, has focused on the date that an individual produces its first flower, and relatively little attention has been given to an individual’s flowering time relative to the flowering of co-occurring individuals. As a result, we know little about the adaptive significance of flowering synchrony (the overlap in flowering among individuals). To help fill this gap, we investigated the strength of natural selection on first flowering date and flowering synchrony in a California annual wildflower, Clarkia unguiculata (elegant Clarkia). Field surveys conducted in nine populations distributed along a 1525m elevation gradient in the Sierra Nevada Mountains revealed clinal variation in first flowering date (higher elevations flowered later), whereas mid-elevation populations showed the highest levels of flowering synchrony, with low and high-elevation populations showing similar lower levels of synchrony. Phenotypic selection gradient analyses in these populations detected consistent selection favoring earlier flowering in most populations. In addition, we detected significant positive linear selection and negative quadratic selection on flowering synchrony – plants that flower synchronously with their population achieve higher relative fitness than less synchronous individuals, but there are often decreasing gains in fitness associated with flowering synchronously. Although the strength of selection on these traits varied among populations, on average the strength of selection on flowering synchrony was as strong as, or stronger than, selection on first flowering date, with selection on synchrony occurring independently of selection on first flowering date. To assess the genetic basis of flowering synchrony, we grew these populations in a common garden along with 20 additional populations collected from low, mid, and high elevations at each of 7 latitudes representing the geographic range of the species. This experiment revealed that, across all sampled populations, flowering synchrony increases with latitude and elevation. A significant Latitude x Elevation effect, however, indicated that elevation clines in synchrony vary by latitude. Taken together, the field and common garden studies suggest not only an adaptive basis to geographic variation in flowering synchrony, but that selection on flowering time in the context of the flowering schedules of co-occurring individuals is a trait subject to natural selection.

Broader Impacts:

1 - University of California, Santa Barbara, Ecology, Evolution, and Marine Biology, Santa Barbara, CA, 93106, USA
2 - University of California Santa Barbara, Department of Ecology & Marine Biology, 4119 Life Sciences Building, Santa Barbara, CA, 93106, USA

Keywords:
phenology
synchrony
biogeography
selection
adaptation.

Presentation Type: Oral Paper:Papers for Sections
Session: 32
Location: Marlborough B/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 2:30 PM
Number: 32005
Abstract ID:457
Candidate for Awards:None