Proximate Composition, Reproductive Development, and a Test for Trade-Offs in Captive Sockeye Salmon

Abstract

—Energy limitations during reproduction should lead to the evolution of adaptive patterns of energy use and should cause trade-offs in the expression of different traits. We addressed these issues by measuring secondary sexual development, gonad investment, and proximate composition for sockeye salmon Oncorhynchus nerka maturing in captivity. Each of the last 3 months before maturity was characterized by a different pattern of reproductive development and energy use. From June to July, gonad mass increased (1.1% to 5.2% of male body mass; from 1.3% to 2.7% of female body mass), muscle fat decreased (15.1% to 8.6% sex-specific values averaged), and viscera fat decreased (23.9% to 16.7%). From July to August, male gonad mass did not change appreciably, but female gonad mass nearly doubled (to 5.5% of body mass). Muscle fat and viscera fat continued to decrease (to 6.0% and 8.8%, respectively), but muscle protein remained relatively constant. From August to maturity (September–October), female gonad mass more than tripled (to 18.6% of body mass) and secondary sexual characters increased in linear dimension by as much as 20.0% (male snout length). Viscera fat continued to decline (to 3.3%), but muscle fat did not decrease appreciably. The conservation of muscle protein until after fat was depleted may postpone reductions in performance that would accompany muscle degeneration. Mass-specific energy decreased between June and maturity in muscle (9.5–5.6 kJ · g21) and viscera (11.2–4.9 kJ · g21). We found no evidence for trade-offs in allocation between stored somatic energy, the size of secondary sexual characters, and gonad investment. An important area requiring further research is the effect of variation in energy stores prior to maturity on reproductive development at maturity. This prebreeding energy variation may obscure phenotypic trade-offs. Animals can obtain only a limited amount of energy from their environment, and this energy must then be allocated among competing physiological processes, including metabolism, somatic growth, and reproductive development (Calow 1985; Sibly and Calow 1986). To compensate for these inevitable resource-based constraints, many animals store energy when food is plentiful and mobilize that energy during less productive periods (Reznick and Braun 1987; Sandberg and * Corresponding author: ahendry@bio.umass.edu 1 Present address: Organismic and Evolutionary Biology Program, University of Massachusetts Amherst, 319 Morrill Science Center, Amherst, Massachusetts 01003-5810, USA. 2 Present address: Department of Molecular and Cell Biology, Division of Neurobiology, University of California, Berkeley, California 94720, USA. 3 Present address: University of Idaho, Hagerman Fish Culture Experiment Station, 3059F National Fish Hatchery Road, Hagerman, Idaho 83332, USA. Received May 17, 1999; accepted March 14, 2000 Moore 1996; Doughty and Shine 1997; Jönsson 1997). Energy reserves are often taxed most severely during breeding, when time and energy are diverted from procuring food and into tasks associated with successful reproduction (Wootton 1985). Because reproductive investment has important consequences for fitness, natural selection should favor optimization of energy storage, allocation, and use (Calow 1985; Sibly and Calow

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Cite this paper

@inproceedings{HendryProximateCR, title={Proximate Composition, Reproductive Development, and a Test for Trade-Offs in Captive Sockeye Salmon}, author={Andrew P. Hendry and Andrew H. Dittman and Ronald W. Hardy} }