Fig. 1.

Outcomes of adaptation to seasonality. (A) Selective gradients on life history traits fluctuate seasonally. (B) For species with short generation times relative to season length, these fluctuating selective gradients can result in cyclic fluctuations in both phenotype (solid line) and allele frequency (broken line) at polymorphic loci, leading to maintenance of genetic polymorphisms within populations under certain conditions. (C) Seasonal fluctuations can also be accommodated through phenotypic plasticity, whereby a single genotype produces multiple phenotypes in response to environmental variation. (D) Unpredictable fluctuations will favor the evolution of bet-hedging, whereby a single genotype either produces multiple variable phenotypes whose fitness varies across the season (solid lines), or a single generalist phenotype whose fitness in summer is decreased but which has higher cumulative fitness across the year than a specialist phenotype.