ON THE ONTOGENY OF DEVELOPMENTAL STABILITY IN A STABILIZED TRAIT

Developmental stability is most accurately assessed by measuring the s mall asymmetries between left and right elements of bilateral traits, i.e. fluctuating asymmetry. Although there has been much recent intere st in fluctuating asymmetry, as low asymmetry may reflect high fitness , relatively little is known concerning the developmental origins of t hese minor discrepancies. Understanding the mechanisms that determine fluctuating asymmetry is crucial to interpreting much of the recent li terature, for example, it has often been claimed that asymmetry reflec ts properties of an individual's genome. Therefore, in this study, we have examined the ontogeny of fluctuating asymmetry in the primary fea thers of European starlings (Sturnus vulgaris) and compared our data w ith six published hypotheses of the mechanisms of asymmetry developmen t. We found that signed asymmetries were not consistently biased towar d either the left or the right side among feathers on the same individ ual; growth increments (measured every two days) were also not sided; and both absolute and relative asymmetry decrease as the feathers deve lop. These data are most consistent with a developmental regulatory sy stem that involves some elements of feedback between left and right si des and episodes of compensational growth to correct large asymmetries . We discuss the possible differences in developmental mechanisms that determine asymmetry in traits of varying functional importance.