Abstract
Stochastic environments shape life‐history traits and can promote selection for risk‐spreading strategies, such as bet‐hedging. Although the strategy has often been hypothesized to exist for various species, empirical tests providing firm evidence have been rare, mainly due to the challenge in tracking fitness across generations. Here, we take a ‘proof of principle’ approach to explore whether the reproductive strategy of multiple‐batch spawning constitutes a bet‐hedging. We used Atlantic cod (Gadus morhua) as the study species and parameterized an eco‐evolutionary model, using empirical data on size‐related reproductive and survival traits. To evaluate the fitness benefits of multiple‐batch spawning (within a single breeding period), the mechanistic model separately simulated multiple‐batch and single‐batch spawning populations under temporally varying environments. We followed the arithmetic and geometric mean fitness associated with both strategies and quantified the mean changes in fitness under several environmental stochasticity levels. We found that, by spreading the environmental risk among batches, multiple‐batch spawning increases fitness under fluctuating environmental conditions. The multiple‐batch spawning trait is, thus, advantageous and acts as a bet‐hedging strategy when the environment is exceptionally unpredictable. Our research identifies an analytically flexible, stochastic, life‐history modelling approach to explore the fitness consequences of a risk‐spreading strategy and elucidates the importance of evolutionary applications to life‐history diversity.
Highlights
Natural environmental conditions change continuously across multiple spatial and temporal scales
To explore whether multiple-batch spawning is a bet-hedging strategy of Atlantic cod, we looked into across-generational fitness elements of multiple-batch spawning populations under simulated environmentally stochastic scenarios and compared them to a single-batch spawning population
It has been hypothesized that multiple-batch spawning in fishes might comprise a bet-hedging strategy and yield high fitness returns (e.g. Hutchings & Rangeley, 2011)
Summary
Natural environmental conditions change continuously across multiple spatial and temporal scales. Bet-hedging life histories have been reported for a variety of species and hypothesized for even more, from bacteria (Beaumont et al, 2009) to vertebrates (Lips, 2001; Mahony & Thumm, 2002), the strength of the evidence for most has been limited or, as Simons (2011) put it, the evidence has been elusive He proposed six, ranked evidence conditions that need to be met: (I) recognize a bet-hedging trait; (II) monitor the unpredictable environment; (III) observe differences in the trait among populations; (IV) demonstrate differences in fitness dynamics; (V) validate whether the trait is favoured under relevant varying environments; and (VI) test the optimality of the trait under a range of conditions of fluctuating selection (Simons, 2011). Our primary objectives are to (i) observe how multiple-batch spawning affects populational dynamics; (ii) evaluate the fitness consequences of multiple-batch spawning within a spawning season, under different levels of environmental stochasticity; (iii) inspect the variance in reproductive output within generations; and (iv) analyse the proportion of successful spawning seasons
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