The Relation between Capacity for Growth and Length of Growing Season: Evidence for and Implications of Countergradient Variation

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Abstract
Evidence suggests that the capacity for growth (i.e., maximum growth potential) within a species may vary inversely with the length of the growing season across a latitudinal gradient. I evaluated this hypothesis with data on three species—American shad Alosa sapidissima, striped bass Morone saxatilis, and mummichog Fundulus heteroclitus—having wide latitudinal ranges (≈29–46°N) along the east coast of North America. For each of these species, the length of the first growing season decreases by a factor of about 2.5 with increasing latitude within the species' range, yet body size at the end of the first growing season is independent of latitude. Northern fish must, therefore, grow substantially faster within the growing season than do southern fish. This “countergradient variation” in growth rate may be more widespread than has been recognized. A similar latitudinal pattern in growth rate has a genetic basis in the Atlantic silverside Menidia menidia, and data on Atlantic salmon Salmo salar, lar...