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Physiological Basis of Latitudinal Growth Differences in Menidia menidia: Variation in Consumption or Efficiency?

T. M. C. Present and D. O. Conover
Functional Ecology
Vol. 6, No. 1 (1992), pp. 23-31
DOI: 10.2307/2389767
Stable URL: http://www.jstor.org/stable/2389767
Page Count: 9
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Physiological Basis of Latitudinal Growth Differences in Menidia menidia: Variation in Consumption or Efficiency?
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Abstract

Growth rate increases with latitude in the Atlantic silverside, Menidia menidia, and the population differences have a genetic basis. Understanding the evolution of this latitudinal gradient in somatic growth requires knowledge of the physiological basis of the growth-rate variation. In theory, the faster growth of northern fish must be achieved by higher consumption rates and/or higher somatic growth efficiencies. If, as is frequently assumed, physiological efficiencies are often maximized by natural selection, the faster growth of higher-latitude silversides should result solely from higher consumption rates. We compared the consumption rates and gross growth efficiencies of fish from laboratory-reared stocks that were originated with fish from Nova Scotia (NS) and South Carolina (SC). Experiments were conducted on young, immature fish at a variety of excess ration levels under conditions of controlled fish density at low (17C) and high (28C) experimental temperatures. NS fish consumed more food (1.7 times) than SC fish and also had significantly higher (1.8-2.2 times) growth efficiencies. Genetic variation in both consumption rate and growth efficiency is therefore responsible for the interpopulation variation in growth rate. This suggests that costs and trade-offs associated with both high consumption rates and high growth efficiency may be the reason why low-latitude populations have submaximal growth rates. The assumption that growth efficiencies are generally at the maximum level that a species is physiologically and genetically capable of achieving should be viewed with caution.

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