Hard and soft selection on phenology through seasonal shifts in the general and social environments: A study on plant emergence time.
The timing of transition out of one life-history phase determines where in the seasonal succession of environments the next phase is spent. Shifts in the general environment (e.g., seasonal climate) affect the expected fitness for particular transition dates. Variation in transition date also leads to temporal variation in the social environment. For instance, early transition may confer a competitive advantage over later individuals. If so, the social environment will impose frequency- and density-dependent selection components. In effect, the general environment imposes hard selection, whereas the social environment imposes soft selection on phenology. We examined hard and soft selection on seedling emergence time in an experiment on Brassica rapa. In monoculture (uniform social environment), early emergence results in up to a 1.5-fold increase in seed production. In bicultures (heterogeneous social environment), early-emerging plants capitalized on their head start, suppressing their late neighbors and increasing their fitness advantage to as much as 38-fold, depending on density. We devised a novel adaptation of contextual analysis to partition total selection (i.e., cov(ω, z)) into the hard and soft components. Hard and soft components had similar strengths at low density, whereas soft selection was five times stronger than hard at high density.
Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada.|Koffler Scientific Reserve at Jokers Hill, University of Toronto, King Township, Ontario, Canada.
Arthur E
AE
Weis
Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada.|Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts.
Kyle M
KM
Turner
Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada.
Bergita
B
Petro
Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada.
Emily J
EJ
Austen
Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada.
Susana M
SM
Wadgymar
D029741:Brassica rapa / Q000235:genetics / Q000254:growth & development*; D004777:Environment; D018525:Germination; D010641:Phenotype; D012621:Seasons; D036226:Seedlings / Q000235:genetics / Q000254:growth & development; D012641:Selection, Genetic; D013997:Time Factors
Competition; constant yield; contextual analysis; frequency-dependent selection; germination; multilevel selection; phenotypic manipulation; social environment; social selection