Wednesday, March 15, 2006
Evolution Of Morphological Integration: Developmental Accommodation Of Stress-induced Variation
1) Press Release
Stress is a major factor in evolution, but for stress-induced modifications to have evolutionary importance they have to be inherited and persist in a sufficient number of individuals within a population. This requires an organism to survive stress and reproduce at least once; thus stress-induced variation has to be accommodated by an organism without much reduction in its functionality. How is such accommodation accomplished?
In an article in the September issue of The American Naturalist, Alexander V. Badyaev (University of Arizona) and colleagues show that complexity and cohesiveness of foraging structures of shrews enables accommodation of stress-induced developmental abnormalities in individual components of morphological complexes. Such developmental compensation and accommodation not only allow shrews growing under stressful environments to maintain locally adaptive foraging morphology, but also provide a mechanism for stress-induced evolutionary change.
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[Badyaev et al, The American Naturalist, Sept '05]
Extreme environmental change during growth often results in an increase in developmental abnormalities in the morphology of an organism. The evolutionary significance of such stress-induced variation depends on the recurrence of a stressor and on the degree to which developmental errors can be accommodated by an organism's ontogeny without significant loss of function. We subjected populations of four species of soricid shrews to an extreme environment during growth and measured changes in the patterns of integration and accommodation of stress-induced developmental errors in a complex of mandibular traits. Adults that grew under an extreme environment had lower integration of morphological variation among mandibular traits and highly elevated fluctuating asymmetry in these traits, compared to individuals that grew under the control conditions. However, traits differed strongly in the magnitude of response to a stressor--traits within attachments of the same muscle (functionally integrated traits) had lower response and changed their integration less than other traits. Cohesiveness in functionally integrated complexes of traits under stress was maintained by close covariation of their developmental variation. Such developmental accommodation of stress-induced variation might enable the individual's functioning and persistence under extreme environmental conditions and thus provides a link between individual adaptation to stress and the evolution of stress resistance.
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