Early is better: seasonal egg fitness and timing of reproduction in a zooplankton life-history model

Varpe, Øystein; Jørgensen, Christian; Tarling, Geraint A. ORCID:; Fiksen, Øyvind. 2007 Early is better: seasonal egg fitness and timing of reproduction in a zooplankton life-history model. Oikos, 116 (8). 1331-1342.

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Timing of reproduction influences future prospects of offspring and therefore the reproductive value of parents. Early offspring are often more valuable than later ones when food availability and predation risk fluctuate seasonally. Marine zooplankton have evolved a diversity of life history strategies in response to seasonality. We present a state-dependent life history model for the annual and herbivorous high-latitude copepod Calanoides acutus. Individuals are characterised by four states; developmental stage, structural size, energy reserves and vertical location. There are two habitats, a surface habitat with seasonal predation risk and food availability, and a safer deep habitat with no food and low metabolism (diapause). Optimal life histories (diapause and energy allocation strategies) are found by dynamic programming. Seasonal egg fitness (reproductive value) emerges from the model and peak values are typically before the feeding season. Disentangling the fitness components, we conclude that seasonality in egg fitness is caused both by environmental seasonality in food and predation risk and by time-constraints on development and diapause preparation. Realised egg production, as predicted from population simulations, does not match the seasonal peak in offspring fitness but is delayed relative to peak egg fitness. We term this an 'internal life history mismatch' as constraints and tradeoffs cause sub-optimal bird dates for most eggs whereas mothers maximise their reproductive value by high number of eggs rather than few and optimally timed eggs. The earliest eggs have a disproportionately high contribution to population recruitment, emphasising the importance of early eggs and the need to understand seasonal patterns in offspring fitness.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: BAS Programmes > Global Science in the Antarctic Context (2005-2009) > DISCOVERY 2010 - Integrating Southern Ocean Ecosystems into the Earth System
ISSN: 0030-1299
NORA Subject Terms: Marine Sciences
Biology and Microbiology
Ecology and Environment
Date made live: 26 Oct 2011 09:11 +0 (UTC)

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