Evol Ecol Res 5: 53-68 (2003)     Full PDF if your library subscribes.

The use of fluctuating asymmetry and phenotypic variability as indicators of developmental instability: a test of a new method employing clonal organisms and high temperature stress

Torsten Nygaard Kristensen,1,2* Cino Pertoldi,1,3 Ditte Holm Andersen1,3,4 and Volker Loeschcke1,5

1Department of Ecology and Genetics, University of Aarhus, Aarhus, Denmark, 2Department of Animal Breeding and Genetics, Danish Institute of Agricultural Sciences, Tjele, Denmark, 3Department of Landscape Ecology, National Environmental Research Institute, Rønde, Denmark, 4Dipartimento di Biologia Evoluzionistica Sperimentale, Bologna, Italy and 5Institute for Advanced Study, La Trobe University, Bundoora, Victoria, Australia

Address all correspondence to Torsten Nygaard Kristensen, Department of Ecology and Genetics, University of Aarhus, Building 540, Ny Munkegade, DK-8000 Aarhus C, Denmark.
e-mail: torsten.kristensen@biology.au.dk


Developmental instability, as estimated by two measures – fluctuating asymmetry and phenotypic variability – was examined using sternopleural bristle number and two wing traits in a clonal strain of Drosophila mercatorum. Eggs were exposed to short-term (30 min) heat stress in water baths at different temperatures (35–40°C in 0.5°C steps) or to a control temperature regime at 25°C. Fluctuating asymmetry and phenotypic variability in sternopleural bristle number were not affected to a significant extent by heat stress, whereas the fluctuating asymmetry and phenotypic variability of both wing measures were significantly higher in adults developed from heat-stressed eggs than in adults developed from eggs kept at 25°C. For both wing measures, there was a tendency for the highest fluctuating asymmetry and phenotypic variability to be observed at temperatures of 37–39°C, suggesting that individuals who experienced the greatest developmental instability at very high temperatures (39.5–40°C) did not survive the heat stress. For the two wing measures, the fluctuating asymmetry and phenotypic variability were significantly correlated, but this was not the case for sternopleural bristle number. Based on a new method, we quantified the effect that environmental variability had on fluctuating asymmetry and phenotypic variability, but found no correlation with the temperatures at which the eggs were stressed. This shows the unpredictability or the impossibility of controlling environmental variability, even in laboratory experiments. We suggest that the method introduced here may in part explain why non-reproducible results have been obtained in developmental instability studies.

Keywords: clonal organism, developmental instability, Drosophila mercatorum, environmental variation, short-term heat stress.

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