Phenotypic plasticity is the ability of a given genotype to produce different phenotypes in different environments. Although this phenomenon is well described, the mechanisms responsible for phenotypic plasticity are still poorly understood. Abdominal pigmentation in D. melanogaster is one particularly well studied example of phenotypic plasticity: cold temperature induces a dark pigmentation in the tergites, in particular in posterior segments, while higher temperature has the opposite effect. Using a genetic analysis we show that phenotypic plasticity of abdominal pigmentation is caused by the temperature sensitivity of a network of chromatin regulators, normally buffered by chaperones. This affects in particular two genes Abd-B and bab, which are haploinsufficient and have well characterised roles on abdominal pigmentation. We show that Abd-B expression and bab interaction with chromatin regulators are modulated by temperature. Remarkably, a large portion of this chromatin regulator network also controls the development of the sex comb along the proximo-distal axis of the leg in D. melanogaster males. We show that temperature also induces phenotypic plasticity in the sex comb phentoype. Thus, we argue that phenotypic plasticity of pigmentation in Drosophila is a side effect of a global impact of temperature on epigenetic mechanisms. We suggest that the thermosensitivity of this network is related to the high variability and evolvability of abdominal pigmentation and sex comb morphology in the genus Drosophila.
Jean-Michel Guibert (b. Cherbourg, France, in 1972) has been a Post-Doc in the group of Prof. Christian Schlötterer at the Institute of Animal Breeding and Genetics, University of Veterinary Medicine, Vienna. From 1996 to 2000 he worked on his PhD thesis ("The Engrailed Genes and the Body Plan of Barnacles (cirripedia)") in the EvoDevo group at the Laboratoire de Biologie Moléculaire et Cellulaire du Développement" (UMR 7622 CNRS-UPMC, Paris), where Prof. Jean S. Deutsch was his supervisor. From 2000 to 2003 Dr. Guibert was a Post-Doc in the group of Pat Simpson in the Department of Zoology at Cambridge University, where he studied the evolution and development of bristle pattern in dipterans.