Evol Ecol Res 8: 149-167 (2006) Full PDF if your library subscribes.
Phenotypic and genetic variability of sternopleural bristle number in Drosophila melanogaster under daily thermal stress: developmental instability and anti-asymmetry
G. Pétavy,1 J.R. David,1 V. Debat,1‡ C. Pertoldi2,3 and B. Moreteau1*
1Laboratoire Populations, Génétique et Evolution, CNRS, 91198 Gif-sur-Yvette cedex, France, 2Department of Ecology and Genetics, Aarhus University, Aarhus and 3Department of Wildlife Ecology and Biodiversity, National Environmental Research Institute, Rønde, Denmark
Author to whom all correspondence should be addressed.
Question: Daily thermal cycles are the rule under natural conditions, and may be very stressful. Are there specific effects of such cycling regimes upon a phenotypic bilateral trait, sternopleural bristle number?
Organism: Experiments were performed on two temperate natural populations of Drosophila melanogaster, collected in the vicinity of Paris (France).
Methods: Altogether, 33 isofemale lines were investigated in their second laboratory generation. Four thermal regimes were used: two constant non-stressful temperatures (17 and 25°C) and two stressful, alternating regimes, one applying a daily cold stress (8–25°C, average 17.5°C), the other applying a daily heat stress (18–33°C, average 25.5°C).
Conclusion: Both alternating regimes increased the within-line (environmental) variance but not the genetic variance. These results are at odds with what was observed, on the same set of lines, for body size traits. Fluctuating asymmetry of bristle number was increased by stress. This was accompanied by the induction of a bimodal shape of the right minus left difference. Such anti-symmetry implies a negative, random interaction between sides of the thorax.
Keywords: bilateral symmetry, bimodality, canalization, cold stress, fluctuating asymmetry, heat stress, intraclass correlation, isofemale lines.
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