“What kind of maternal effects can be selected for in fluctuating environments?”

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Stephen R. Proulx and Henrique Teotónio

Should mothers play dice with their babies’ future? Only when the stakes are really high!

Panel showing how Hybrid Maternal Effect (HME) can increase fitness over the other maternal effect strategies. The dashed yellow lines show the boundary of the region where HME has a strictly higher fitness than Randomizing Maternal Effect or Deterministic Maternal Effect, and still produces a strategy where some offspring randomization occurs. The yellow regions indicate that HME has an advantage of at least 0.001 over the next best strategy.
(Credit: Proulx and Teotónio 2017)

How should parents act to improve the fitness of their offspring in an uncertain world? While much attention has been paid to “diversifying bet-hedging” (where offspring phenotypes are randomized), Proulx and Teotónio find that bet-hedging is unlikely to evolve de novo. Rather, most ecological conditions lead to the initial evolution of maternal strategies that base offspring phenotype on the maternal environment itself. This is because parents almost always have some direct probabilistic information about their offspring’s environment simply because environments are correlated in time (positively or negatively).

To study the evolution of maternal effects, the researchers considered scenarios where offspring phenotype determines fitness in an environmentally dependent way and where total maternal fecundity depends on the suite of offspring phenotypes, owing to the costs of offspring production. This allows an “apples to apples” comparison between bet-hedging strategies and informed maternal effect strategies with the same phenotypic capabilities. The authors found a simple relationship between the fitness parameters and the frequency of environmental change that shows that informed maternal effects are favored when there is more information available. But fitness comparisons of alternative strategies do not get at the question of the evolutionary dynamics governing the origin of novel strategies.

After modeling the micro-evolution of maternal effect strategies, Proulx and Teotónio found that even when the environment contains little information, informed maternal effect strategies are much more likely to evolve than bet-hedging type strategies. However, once phenotypes with extreme differences in environment-dependent fitness evolve, bet-hedging strategies may evolve and come to dominate the population. Read the Article