Individual variation in age-dependent reproduction: Fast explorers live fast but senesce young?


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Abstract

Adaptive integration of life history and behaviour is expected to result in variation in the pace-of-life. Previous work focused on whether ‘risky’ phenotypes live fast but die young, but reported conflicting support. We posit that individuals exhibiting risky phenotypes may alternatively invest heavily in early-life reproduction but consequently suffer greater reproductive senescence.We used a 7-year longitudinal dataset with >1,200 breeding records of >800 female great tits assayed annually for exploratory behaviour to test whether within-individual age dependency of reproduction varied with exploratory behaviour. We controlled for biasing effects of selective (dis)appearance and within-individual behavioural plasticity.Slower and faster explorers produced moderate-sized clutches when young; faster explorers subsequently showed an increase in clutch size that diminished with age (with moderate support for declines when old), whereas slower explorers produced moderate-sized clutches throughout their lives. There was some evidence that the same pattern characterized annual fledgling success, if so, unpredictable environmental effects diluted personality-related differences in this downstream reproductive trait.Support for age-related selective appearance was apparent, but only when failing to appreciate within-individual plasticity in reproduction and behaviour.Our study identifies within-individual age-dependent reproduction, and reproductive senescence, as key components of life-history strategies that vary between individuals differing in risky behaviour. Future research should thus incorporate age-dependent reproduction in pace-of-life studies.Great tits differ in patterns of age-dependent reproduction as a component of pace-of-life. Slow explorers produce stable clutch sizes throughout their reproductive lives. Fast explorers by contrast show age-related increases followed by reproductive senescence. Age-related reproduction therefore constitutes a key component of personality-related life-history variation.

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