Developmental instability in fragmented populations of prairie phlox: A cautionary tale

Considerable attention has recently been focused on using levels of develop mental instability among members of a population to detect environmental or genetic stresses on animals or plants. It is not yet clear, however, that high developmental instability in a sample of individuals always indicates environmental stress or poor genetic quality. We studied 13 fragmented popu lations of prairie phlox (Phlox pilosa L.) to test the hypothesis that deve lopmental instability should decrease with increasing population size - as expected if small populations suffer genetic problems associated with inbre eding or are exposed to more environmental stress than larger populations. We used two different measures of developmental instability, each calculate d for two different traits: radial asymmetry of flowers (for petal width an d petal length) and modular fluctuating asymmetry of leaves (for leaf width s at two points along the leaf). There were weak but significant correlatio ns among individuals for four of six pairwise combinations of these measure s. Surprisingly, three of our four measures of developmental instability sh owed strong population size effects that were opposite to those expected: d evelopmental instability increased with population size. We conclude that m easures of developmental instability cannot be applied uncritically for bio monitoring without considerable knowledge of developmental mechanisms, natu ral history, and population biology of the species in question.