Experimentally manipulated growth rate in threespine sticklebacks: Assessing trade offs with developmental stability

The evolution of 'adaptive' growth rate and its influence on how other life history traits evolve is a neglected topic in biology. Growth rate influences life history because size strongly influences age-specific survival and fecundity, and because growth rate defines the relationship between age and size. Improved predictions about the evolution of life history traits may be possible with a greater understanding of the factors that influence the evolution of growth rate. We experimentally tested the hypothesis that a trade off may exist between growth rate and developmental stability in freshwater threespine sticklebacks, Gasterosteus aculeatus. We compared the degree of developmental instability (measured as fluctuating asymmetry = FA) in four lateral plate and two fin traits of fish reared under a high vs. low growth regime in response to food ration and temperature. We found evidence that symmetry was reduced (FA increased) in fast growing compared to slow growing fish, suggesting that a trade off between developmental stability and growth is possible. FA plausibly reflected developmental instability because of significant associations between rank FA levels across traits in individuals. These results are preliminary because of the possible confounding effects of temperature and food ration on asymmetry, and because we do not know if this trade off has fitness or other life history consequences. Our results also do not support the hypothesis of honest signaling sometimes invoked in studies of sexual selection because greater symmetry was found under poorer rather than better resource levels.