Stress and developmental stability: Vegetation removal causes increased fluctuating asymmetry in shrews

Environmental stress can increase phenotypic variation in populations by af fecting developmental stability of individuals. While such increase in vari ation results from individual differences in ability to buffer stress, grou ps of individuals and different traits may have different sensitivity to st ressful conditions. For example, the sex that is under stronger directional selection for faster growth may be more sensitive to stressful conditions during development. On an individual level, stress-induced variation in a t rait may be related to the strength of stabilizing selection that acts on t he trait. We experimentally examined sensitivity of mandibular development to stress in a free-living population of common shrews (Sorex cinereus), a short-lived insectivore mammal with very limited dispersal and nearly conti nuous foraging activity. We found a strong increase in asymmetry in shrews born under stressful conditions. Increased asymmetry was associated with lo wer physiological condition in both control and stressed populations, altho ugh the effect of asymmetry on fitness was more pronounced under stressful conditions. Males' developmental stability was more sensitive to stressful conditions than developmental stability of females, suggesting that their a pparently faster and more variable growth is more sensitive to stress than is growth of females. Mandible traits differed in their sensitivity to envi ronmental changes. Preliminary results suggest that this differential sensi tivity is proportional to the degree of developmental and functional morpho logical integration among mandibular traits.