What drives selection on flowering time? An experimental manipulation of the inherent correlation between genotype and environment

Abstract

The optimal timing of the seasonal switch from somatic growth to reproduction can depend on an individual's condition at reproduction, the quality of the environment in which it will reproduce, or both. In annual plants, vegetative size (a function of age at flowering) affects resources available for seed production, whereas exposure to mutualists, antagonists, and abiotic stresses in the environment (functions of Julian date of flowering) influences success in converting resources into offspring. The inherent tight correlation between age, size, and environment obscures their independent fitness contributions. We isolated the fitness effects of these factors by experimentally manipulating the correlation between age at flowering and date of flowering in Brassica rapa. We staggered the planting dates of families with differing ages at flowering to produce experimental populations in which age at flowering and date of flowering were positively, negatively, or uncorrelated. In all populations, plants with an early date of flowering produced more seed than those flowering late, regardless of age or size at flowering onset. The temporal environment was thus the principal driver of selection on flowering time, but its importance relative to that of age and size varied with the presence/absence of herbivores and seed predators.

Selection and plasticity both account for interannual variation in life‐history phenology in an annual prairie legume

“…Similar to a previous study in Brassica rapa (Austen & Weis, 2015), we find a stable relationship between fitness and flowering date, with earlier flowering resulting in higher fitness. Similar to a previous study in Brassica rapa (Austen & Weis, 2015), we find a stable relationship between fitness and flowering date, with earlier flowering resulting in higher fitness.…”

Phenological responses to multiple environmental drivers under climate change: insights from a long‐term observational study and a manipulative field experiment

“…Whether more rapid phenological shifts relative to the rate of environmental change would enhance fitness awaits experimental manipulation of the timing of flowering relative to the timing of snowmelt. Nevertheless, empirical studies almost universally document directional selection for earlier flowering under contemporary conditions (Munguía‐Rosas et al ., ; Austen et al ., ; Wadgymar et al ., ), even when accounting for plant size and age (Austen & Weis, ). One might expect stabilizing selection on flowering time, as individuals that flower too early in the season may lack sufficient resources to maximize fecundity (Anderson et al ., ; Austen et al ., ).…”

Estimating selection through male fitness: three complementary methods illuminate the nature and causes of selection on flowering time

“…In the uncorrelated treatment, AAF varied independently of JDF (electronic supplementary material, figure S1a-c). Temperature and photoperiod decreased over the course of the experiment, indicating that JDF was a reasonable proxy for the environment experienced during reproduction [24]. The field experiment is described in full elsewhere [24]; we provide essential details here.…”

“…We recorded AAF as days between seed planting and flowering. Although two replicate populations per treatment were established during 2011 [24], only one replicate could be evaluated for male fitness given available resources.…”