Meeting Abstract
Although behavior may often be a fairly direct target of natural or sexual selection, it cannot evolve without changes in subordinate traits that cause or permit its expression. In principle, changes in endocrine function could be a common mechanism underlying behavioral evolution and, if so, then correlated responses in other aspects of behavior, life history, and organismal performance (e.g., locomotor abilities) should commonly occur because any cell with appropriate receptors could be affected. At the same time, because hormones are likely to affect multiple traits, including through early-life parental effects, they might be “used” routinely by selection to achieve (adaptively) correlated changes. Nevertheless, the seminal papers in modern evolutionary physiology scarcely mentioned the endocrine system. Ways in which behavior coadapts with other aspects of the phenotype can be studied directly through artificial selection and experimental evolution. Several studies have targeted rodent behavior for selective breeding and reported changes in other aspects of behavior, life history, and lower-level effectors of these organismal traits, including endocrine function. One example involves selection for high levels of voluntary wheel running in four replicate High Runner lines of mice. Circulating levels of several hormones (including insulin, testosterone, thyroxine, triiodothyronine) have been characterized, three of which – corticosterone, leptin, and adiponectin – differ between HR and control lines, depending on sex, age, and generation. Potential changes in circulating levels of other behaviorally and metabolically related hormones, as well as in other components of the endocrine system (e.g. receptors), have yet to be examined. Overall, results to date identify promising avenues for further studies on the endocrine basis of activity levels.
