Phenotypic Plasticity and Adaptation in a Holometabolous Insect: The Chironomid Midge

Attention is currently shifting from a gene-centred view of evolution to a more phenotype-focussed one. Here, I attempt to test this new paradigm against a diverse and ecologically prominent taxon, the chironomid midge. I conclude that putting phenotypic and developmental flexibility at the forefront helps resolve some persistent difficulties in understanding the process of adaptation. 1. Introduction One of the most interesting recent conceptual developments in ecology and evolutionary theory is the renewed emphasis on phenotypic plasticity, conditional alternative phenotypes, and development [1–4]. This is a notable departure from the gene-centred thinking which has dominated evolutionary biology from the rediscovery of Mendel’s laws, through the modern synthesis, and up until the present day [4]. In the words of West-Eberhard, the chief proponent and architect of this emerging paradigm, the “theoretical incorporation of developmental plasticity calls for changes in thinking about virtually every major question of evolutionary biology, and resolves some of its most persistent controversies.” Morris [5, page 238] expresses the same opinion “Claims for the primacy of the gene have distorted the whole of biology.” These contrasting views of evolution and some of their profound consequences are summarised below. The Gene-Centred View Mutation → Genome change → Selection → Loss of genetical variability → New genotype → New phenotype → Evolution. Environmentally Lead Evolution Environmental induction → Change in gene expression → New phenotype → Selection → Increased variability → Evolution. Although it has long been appreciated that the phenotypic expression of a gene or combination of genes is heavily influenced by the developmental environment, this fact has recently taken on far greater significance with the realization that inherited variation in phenotypic responses may play an important role in driving evolutionary change. Thus, in contrast to the gene-centred view of evolution (exemplified most notably by Dawkins and by Wilson [6, 7]), where phenotypes change through the slow accumulation of advantageous mutations, the newly emerging paradigm suggests that significant phenotypic reorganization can occur through altered responses to the developmental environment such as the duplication of body parts, cross-sexual transfer of traits, or heterochrony. Such a view of adaptive evolution is by no means mutually exclusive with more traditional models of adaptation and can be considered as a broadening of our understanding of potential mechanisms of