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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Experimental determination of the photoperiodic basis for geographic variation in avian seasonality
Auteurs :	Timothy Coppack, Auteur
Type de document :	Article
Dans :	Journal of Ornithology (148 DEC 2007)
Article en page(s) :	S459-S467
Langues:	Anglais
Résumé :	Geographic variation in the timing of breeding, moult and migration of birds reflects adjustment of their annual cycles to regional differences in environmental conditions. Understanding to what degree this variation results from phenotypic plasticity or from genetic adaptation is important both as a goal of primary research and especially because we need to understand the potential for species to adapt to global environmental change. The annual change in day-length remains invariant, year after year, and birds depend primarily on this environmental information to match breeding and migration schedules with the changing seasons. Here, I review what is known about the role of photoperiodic responses in shaping geographic variation in avian life cycles, focussing on intra-specific comparative studies in passerine birds. Experiments with hand-raised individuals from different populations kept under identical conditions (common-garden experiments) suggest that differences in the timing of events are not photoperiodically determined when trait differences persist. A single common-garden experiment has no neutral testing ground, however. Thus, if birds breeding at different latitudes have evolved (or retained) non-parallel reaction norms, a single test environment is not sufficient to quantify genetic and environmental influences. While reciprocal transplantation may control for this problem, such an extended experimental design has only rarely been considered. More recently, population-specific reaction norms have been studied by assigning full siblings to various photoperiodic regimes. Through this approach, the extent of genotype-by-environment interaction can be estimated, which is essential information when interpreting trait differences among populations under natural conditions and predicting how species or populations will respond to photoperiodic conditions outside present-day geographical ranges.

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