Experimentally increased brood size accelerates actuarial senescence and increases subsequent reproductive effort in a wild bird population

Boonekamp, J. J. , Bauch, C., Verhulst, S. and Richardson, D. (2020) Experimentally increased brood size accelerates actuarial senescence and increases subsequent reproductive effort in a wild bird population. Journal of Animal Ecology, 89(6), pp. 1395-1407. (doi: 10.1111/1365-2656.13186) (PMID:32037534) (PMCID:PMC7317873)

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Abstract

The assumption that reproductive effort decreases somatic state, accelerating ageing, is central to our understanding of life‐history variation. Maximal reproductive effort early in life is predicted to be maladaptive by accelerating ageing disproportionally, decreasing fitness. Optimality theory predicts that reproductive effort is restrained early in life to balance the fitness contribution of reproduction against the survival cost induced by the reproductive effort. When adaptive, the level of reproductive restraint is predicted to be inversely linked to the remaining life expectancy, potentially resulting in a terminal effort in the last period of reproduction. Experimental tests of the reproductive restraint hypothesis require manipulation of somatic state and subsequent investigation of reproductive effort and residual life span. To our knowledge the available evidence remains inconclusive, and hence reproductive restraint remains to be demonstrated. We modulated somatic state through a lifelong brood size manipulation in wild jackdaws and measured its consequences for age‐dependent mortality and reproductive success. The assumption that lifelong increased brood size reduced somatic state was supported: Birds rearing enlarged broods showed subsequent increased rate of actuarial senescence, resulting in reduced residual life span. The treatment induced a reproductive response in later seasons: Egg volume and nestling survival were higher in subsequent seasons in the increased versus reduced broods' treatment group. We detected these increases in egg volume and nestling survival despite the expectation that in the absence of a change in reproductive effort, the reduced somatic state indicated by the increased mortality rate would result in lower reproductive output. This leads us to conclude that the higher reproductive success we observed was the result of higher reproductive effort. Our findings show that reproductive effort negatively covaries with remaining life expectancy, supporting optimality theory and confirming reproductive restraint as a key factor underpinning life‐history variation.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Boonekamp, Dr Jelle
Authors: Boonekamp, J. J., Bauch, C., Verhulst, S., and Richardson, D.
College/School:College of Medical Veterinary and Life Sciences > Institute of Biodiversity Animal Health and Comparative Medicine
Journal Name:Journal of Animal Ecology
Publisher:Wiley for British Ecological Society
ISSN:0021-8790
ISSN (Online):1365-2656
Published Online:12 March 2020
Copyright Holders:Copyright 2020 The Authors
First Published:First published in Journal of Animal Ecology 89(6):1395-1407
Publisher Policy:Reproduced under a Creative Commons licence

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