Fluctuating and directional asymmetry in natural bird populations exposed to different levels of habitat disturbance, as revealed by mixture analysis

Authors

  • L. Lens,

    1. Laboratory of Animal Ecology, Department of Biology, University of Antwerp (UIA), Universiteitsplein 1, B-2610 Wilrijk, Belgium, and, Department of Ornithology, National Museums of Kenya, PO Box 40658, Nairobi, Kenya.
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  • S. Van Dongen

    1. Laboratory of Animal Ecology, Department of Biology, University of Antwerp (UIA), Universiteitsplein 1, B-2610 Wilrijk, Belgium.
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Luc Lens E-mail: llens@uia.ua.ac.be

Abstract

While bilateral trait asymmetry is widely recognized to estimate developmental instability, much controversy exists over which types of asymmetry (fluctuating, directional, and/or antisymmetry) to use. Recently it has been hypothesized that the three types are strongly interrelated, and that increased developmental instability may be reflected in a transition from fluctuating to directional asymmetry and/or antisymmetry. Alternatively, habitat disturbance might change the genetic expression of directional asymmetry. We present herein the first empirical evidence for stress-mediated shifts in types of asymmetry in natural populations, by using mixture analysis to model tarsus asymmetry in bird populations exposed to different levels of habitat disturbance. Observed asymmetry patterns almost exclusively consisted of true fluctuating asymmetry in the least disturbed populations, but became progressively mixed with directional asymmetry under increasing disturbance. Failing to unravel these mixtures of different forms of asymmetry may have critical implications for the analysis and interpretation of asymmetry data.

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