Gambling on grandchildren: do aphids hedge their bets?

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All organisms live in an uncertain world, and must prepare their offspring for survival in the face of this variation. In order to ensure that at least some offspring survive to reproduce, several tactics are available to mothers. (i) Pessimism: mothers may invest more resources than are normally required, just in case times are hard. (ii) Plasticity: mothers may provide offspring with the ability to change phenotype according to the prevailing environmental conditions. (iii) Bet hedging (or risk spreading): mothers may produce offspring with a variety of phenotypes, in the hopes that at least some of them survive to reproduce. The concept of bet hedging has received a great deal of support in organisms whose offspring emerge in different seasons: in this scenario, the non-intuitive outcome is that increasing the variability of ones offspring can reduce the variance in their future success, thus benefitting fitness and causing heritable bet hedging behaviour to spread through populations. This glamorous explanation has also been applied to organisms whose offspring experience unpredictable spatial variation within a season. However, such WITHIN generation bet hedging is actually very difficult to evolve. Between generation bet hedging works because offspring of a certain phenotype all experience the same environment. Within generation bet hedging only works in VERY small populations, because there is no correlation between environment and phenotype. Aphids have been promoted as a classic example of within-generation bet hedging. When aphid mothers produce unwinged offspring, they give them a uniform number of ovarioles (reproductive investment) because their environment is predictable (the same plant on which the mother lives). However, when mothers make winged offspring, who must fly away into an unpredictable environment, they give them variable reproductive potential. I aim to demonstrate that this can only be considered within generation bet hedging, and can only be favoured by natural selection, if offspring with different reproductive potential also have different dispersal propensities and dispersal distances. In this way, a correlation between phenotype and environment is created that satisfies the assumption of bet hedging as an adaptive response to heterogeneity. A better understanding of bet hedging in aphids will provide us with clearer information on optimal tactics for living in a changing, and extremely variable, environment. This may guide tactics for pest control in a changing climate, and may even suggest optimal tactics for human resource use in the face of an unpredictable and resource-limited future.