Bet-hedging across generations can affect the evolution of variance-sensitive strategies within generations

Abstract

In order to understand how organisms cope with ongoing changes in environmental variability, it is necessary to consider multiple adaptations to environmental uncertainty on different time scales. Conservative bet-hedging (CBH) represents a long-term genotype-level strategy maximizing lineage geometric mean fitness in stochastic environments by decreasing individual fitness variance, despite also lowering arithmetic mean fitness. Meanwhile, variance-prone (aka risk-prone) strategies produce greater variance in short-term payoffs, because this increases expected arithmetic mean fitness if the relationship between payoffs and fitness is accelerating. Using evolutionary simulation models, we investigate whether selection for such variance-prone strategies is counteracted by selection for bet-hedging that works to adaptively reduce fitness variance. In our model, variance proneness evolves in fine-grained environments (lower correlations among individuals in energetic state and/or payoffs), and with larger numbers of independent decision events over which resources accumulate prior to selection. Conversely, multiplicative fitness accumulation, caused by coarser environmental grain and fewer decision events selection, favours CBH via greater variance aversion. We discuss examples of variance-sensitive strategies in optimal foraging, migration, life histories and cooperative breeding using this bet-hedging perspective. By linking disparate fields of research studying adaptations to variable environments, we should be better able to understand effects of human-induced rapid environmental change.

Individual reversible plasticity as a genotype-level bet-hedging strategy

“…When fitness accumulates multiplicatively, as occurs in coarse-grained environments for traits that are expressed only once or a few times per lifetime (Starrfelt and Kokko 2012;Haaland et al 2019a), adaptive bet-hedging at the genotype level can cause individuals to invest more in phenotypic plasticity than they would do otherwise. This is because although this additional plasticity comes at a cost to their expected reproductive output, it also lowers their variance in fitness, and is therefore selected for at the genotype level.…”

“…This is because although this additional plasticity comes at a cost to their expected reproductive output, it also lowers their variance in fitness, and is therefore selected for at the genotype level. This increased investment in phenotypic plasticity represents a type of what has been termed conservative bet-hedging (see Haaland et al 2019a), since it lowers genotype fitness variance by lowering fitness variance at the individual level. Essentially, the genotype benefits from individuals 'playing it safe'…”

“…The main result here that traits contributing to fitness fewer times within a lifetime show more plasticity (due to conservative bet-hedging) may explain certain among-species patterns in plastic adjustment in breeding phenology in response to recent climate change (Radchuk et al 2019). Across generations, traits directly related to reproductive decisions contribute purely multiplicatively to fitness in semelparous species (that reproduce only once), but also additively in iteroparous species, reducing the importance of bet-hedging as the expected number of breeding opportunities per lifetime increases (Haaland et al 2019a).…”

“…Another factor modifying the extent to which a given trait is subject to selection for bet-hedging is how often the trait is expressed within an individual's lifetime (see Haaland et al 2019a), and this is especially relevant in the case of reversible plasticity. If the trait is only expressed once per lifetime, fitness accumulation across distinct events only occurs among individuals.…”

“…Such traits should therefore be subject to evolution of adaptive bet-hedging strategies (Haaland et al 2019a). On the other hand, traits expressed several times under a series of different environmental conditions within a lifetime can accumulate fitness additively across events.…”