Presentation Detail

Selection, Natural

Austen, Emily [1], Weis, Arthur E. [1].

Selection for early flowering through male fitness: three complementary analyses of a phenotypic manipulation.

The form and intensity of natural selection on flowering time has been the subject of extensive investigation for at least five decades, with the body of evidence indicating that selection on flowering time is typically negative. However, most flowering time studies have estimated plant fitness through female function (seed production) alone, whereas most flowering plant species are hermaphroditic. Since hermaphrodites achieve reproductive success both by producing and by siring seeds, a full understanding of selection on flowering time requires examination of male function, too. Moreover, few studies have discriminated between selection on an individual's flowering day-of-year (calendar time), its days from emergence to flowering onset (developmental time), and its timing of flowering relative to neighbors (relative time), obscuring our understanding of the causal relationship between flowering time and fitness. The intrinsic correlation between these three flowering time axes poses a challenge to isolating their independent effects. We performed phenotypic manipulations to maintain, break, and reverse the correlation between developmental time and relative time in experimental populations of the self-incompatible annual, Brassica rapa. We estimated selection through male fitness in these populations by: (1) an analysis of mating opportunity based on flower production schedules, (2) a full probability genetic paternity analysis, and (3) a novel experimental evolution analysis. Agreement among the three analyses was strong, though in one instance, experimental evolution did not detect a response to selection predicted by methods 1 and 2. Collectively,our analyses reveal that relative time is a more important determinant of male fitness than developmental time, with relatively early individuals achieving greater male fitness than relatively late individuals in all populations. In contrast, selection on developmental time varied in magnitude and direction across populations. We suggest that the observed negative selection on relative time may be driven in part by declining fruit set probability within plants: plants that flower relatively early can sire on the first flowers produced by their neighbors, which have a higher probability of maturing into fruit than do last-produced flowers. Flowering time shapes a plant's interactions with its pollinators, seed predators, and overall environment, and can evolve rapidly in the course of species invasion and in response to climate change. Our work provides new insight into the relationship between this critical trait and male fitness.

1 - University of Toronto, Department of Ecology and Evolutionary Biology, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada

Keywords:
phenology
Experimental Evolution
male fitness
paternity analysis
hermaphrodite
plants.

Presentation Type: Regular Oral Presentation
Session: 55
Location: Rendezvous A/Snowbird Center
Date: Sunday, June 23rd, 2013
Time: 8:45 AM
Number: 55002
Abstract ID:467
Candidate for Awards:W.D. Hamilton Award for Outstanding Student Presentation