Unpredictability of maternal environment shapes offspring behaviour without affecting stress-induced cortisol in an annual vertebrate.

Exposure of females to stressful conditions during pregnancy or oogenesis has a profound effect on the phenotype of their offspring. For example, offspring behavioural phenotype may show altered patterns in terms of the consistency of behavioural patterns and their average level of performance. Maternal stress can also affect the development of the stress axis in offspring leading to alterations in their physiological stress response. However, the majority of evidence comes from studies utilising acute stressors or exogenous glucocorticoids, and little is known about the effect of chronic maternal stress, particularly in the context of stress lasting throughout entire reproductive lifespan. To bridge this knowledge gap, we exposed female sticklebacks to stressful and unpredictable environmental conditions throughout the breeding season. We quantified the activity, sheltering and anxiety-like behaviour of offspring from three successive clutches of these females, and calculated Intra-class Correlation Coefficients for these behaviours in siblings and half-siblings. We also exposed offspring to an acute stressor and measured their peak cortisol levels. An unpredictable maternal environment had no modifying effect on inter-clutch acute stress responsivity, but resulted in diversification of offspring behaviour, indicated by an increased between-individual variability within families. This may represent a bet-hedging strategy, whereby females produce offspring differing in behavioural phenotype, to increase the chance that some of these offspring will be better at coping with the anticipated conditions.