IS FLUCTUATING ASYMMETRY A RELIABLE BIOMONITOR OF STRESS - A TEST USING LIFE-HISTORY PARAMETERS IN SOYBEAN

Deviations from a symmetrical state (developmental instability) are of ten used as biomonitors of stress and are reportedly impacted at conce ntrations less than those required to impact life history features. He re. we evaluate the use of fluctuating asymmetry (deviations from bila teral symmetry) of soybean leaves across a gradient of salinity rangin g from 0 to 9 g NaCl/L. We used a broad gradient to determine if measu res of fluctuating asymmetry were more sensitive than survivorship, gr owth, and reproduction. All plants receiving less than 3 g NaCl/L surv ived, and reproduced. with no differences among these treatments for a ny life history feature. In contrast, all plants receiving more than 3 g NaCl/L produced no offspring and died. Thus, we clearly examined th e response of plants subjected to sublethal doses. Estimates of fluctu ating asymmetry did not differ among the 0 to 900 mg NaCl/L treatments . However the standard error about the regression coefficients of the cumulative internode length vs. node number, an alternative measure of developmental instability, increased significantly under stress. Leaf shape also changed; however, this is not a measure of developmental i nstability because it does not represent deviations from a development al invariant. Thus, fluctuating asymmetry failed to identify stress be fore life history parameters were affected, although alternative measu res of developmental instability proved more sensitive in soybean.