Multiple‐batch spawning as a bet‐hedging strategy in highly stochastic environments: An exploratory analysis of Atlantic cod

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.

Global decline in ocean memory over the 21st century

“…Some species with relatively constant reproductive effort, species with so-called K-selected life histories ( 62 , 63 ), are best suited for persistent environmental conditions and may flourish during periods of low variability. In contrast, the so-called r-selected species may “hedge their bets” and demonstrate multiple major reproductive efforts during years of rarely occurring optimal conditions ( 64 ). This fundamental dichotomy in species’ life history attributes may be useful for understanding and predicting which populations may be negatively or positively affected by future changes in ocean memory.…”

Multiple-batch spawning: a risk-spreading strategy disarmed by highly intensive size-selective fishing rate

“…[ 22 ] age-specific fecundity ( N eggs ) Hutchings [ 28 ] batch number ( N batches ) derived in Hočevar et al . [ 21 ] based on empirical data from Roney et al . [ 29 ] multiple-batch spawning costs ( Costs MBS ) derived in Hočevar et al .…”

“…[ 29 ] multiple-batch spawning costs ( Costs MBS ) derived in Hočevar et al . [ 21 ] based on empirical data from Roney et al . [ 29 ] size-based fishing selectivity ( L(t) is the length of an individual at the time of fishing) Kuparinen & Hutchings [ 30 ] …”

“…The number of spawned batches is positively correlated to female body size [ 19 ] and the relation is derived from the fitted data on the number of batches and female fork length L fork( t ) ( table 1 ) gathered on cod from coastal Skagerrak (fig. 2 in [ 21 ]). We implemented batch spawning costs to the model because we consider multiple-batch spawning a bet-hedging trait [ 21 ] which acts with associated costs to mean arithmetic fitness [ 31 – 33 ].…”

“…The spawning dynamics of cod, in which fish shed eggs in multiple batches within every spawning season [ 18 ], grant a spatial and temporal risk-spreading effect [ 20 ]. This diverse distribution of egg batches contributes to higher across-generational fitness and can act as a bet-hedging strategy under environmental conditions when odds of survival are low and hard to predict [ 21 ].…”