CONOVER, D.O.; Stony Brook University: Countergradient variation and the evolution of growth rate: lessons from silverside fishes

Recent findings are fundamentally changing our view of the evolution of juvenile growth rate, related physiological traits, and their thermal reaction norms. Countergradient variation in growth appears to be a widespread means of adapting to climate change. An emerging variety of trade-offs with growth have been identified, indicating that selection optimizes rather than maximizes growth rate in response to local environmental factors. Here I synthesize our knowledge of the evolution of growth rate among wild and captive populations of the Atlantic silverside, Menidia menidia, and I discuss the strengths and weaknesses of this species as a general model. Studies of the silverside have demonstrated clearly that growth rate and the underlying suite of physiological traits that support growth are finely tuned to selection gradients in the wild. The costs of growth are an accelerating function of growth rate, thus fulfilling a crucial theoretical necessity. Selection experiments on captive populations have shown that these traits evolve rapidly in response to size-dependent mortality and that selection acting on one life stage (e.g., on adults) affects traits in all other life stages (e.g. larvae). Such knowledge has extremely important applied value for harvested organisms: since mortality caused by fishing is a highly non-random process, the evolutionary consequences of fishing need serious attention by fishery managers.