Stress and Developmental Stability: Vegetation Removal Causes Increased Fluctuating Asymmetry in Shrews

Abstract

Environmental stress can increase phenotypic variation in populations by affecting developmental stability of individuals. While such increase in variation results from individual differences in ability to buffer stress, groups of individuals and different traits may have different sensitivity to stressful 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 trait may be related to the strength of stabilizing selection that acts on the 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 continuous foraging activity. We found a strong increase in asymmetry in shrews born under stressful conditions. Increased asymmetry was associated with lower physiological condition in both control and stressed populations, although 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 apparently faster and more variable growth is more sensitive to stress than is growth of females. Mandible traits differed in their sensitivity to environmental changes. Preliminary results suggest that this differential sensitivity is proportional to the degree of developmental and functional morphological integration among mandibular traits.