Bet-hedging as an evolutionary game: the trade-off between egg size and number

摘要

In a recent paper, Olofsson et al. (2009) explore the evolution of egg mass in a temporally variable environment using an individual-based simulation model. The model includes realistic assumptions such as density-dependent population growth and a fluctuating minimum size for survival. Their main focus was on the evolution of variation in egg mass both within and between clutches, and they explore whether this variation is adaptive, and if it is, how it should be distributed within and between clutches. Much of their discussion is couched in terms of evolutionary bet-hedging, the idea that a reduction in mean fitness can be selected for provided there is a corresponding decreases in the temporal variance in fitness (Seger & Brockmann 1987). Olofsson et al. (2009) identify three possible bet-hedging strategies: (i) conservative bet-hedging (large eggs with little variation in egg mass), (ii) diversified bet-hedging (medium egg mass and large within-clutch egg mass variation), and (iii) coin flipping (medium egg mass and large betweenclutch variation in mean egg mass but little withinclutch variation). Olofsson et al. (2009) therefore use changes in the mean and variance in egg mass to identify different types of bet-hedging strategies. In this commentary we wish to make three points; (i) in order to be a useful concept, bet-hedging must be defined in terms of the mean and variance in fitness, not trait values, and using trait variation to identify bet-hedging strategies can be very misleading, (ii) the precise way that variation is added to a model is critical, and (iii) diversified strategiescan only be understood from the point of view of the genotype (or strategy).