The endocrine basis of phenotypic plasticity in a predator-prey system.

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Why are there so many patterns in colouration, morphology, life history and behaviour within a particular species? Recently, developmental biologists and ecologists have begun to join forces to answer this question in the field of ecological developmental biology (ECO-DEVO). They are asking how phenotypic plasticity (the variation in colour, morphology etc.) emerges from the interplay between a changing environment and the physiological machinery that regulates an organisms development. From an ecological standpoint, identifying the developmental basis of phenotypic plasticity is the identification of the mechanism giving rise to the variation we see in organisms behaviour, morphology and life history. From an evolutionary perspective, this developmental definition brings the study of phenotypic plasticity closer to the molecular and physiological basis of development, which is emerging as the foundation of evolutionary research. Here, I propose to investigate the developmental (e.g. hormonal) basis of inducible defences in a classic water-flea (Daphnia pulex) - phantom midge (Chaoborous spp.) predator-prey system. In this system, predator based chemical signals induce striking adaptive morphological and life history defences in the prey. These include protuberances and spikes on juvenile heads and delayed maturity at a larger size - fundamental, sub-lethal shifts in morphology and development that confer increased survival. The interplay between invertebrate hormones such as ecdysteroids, juvenile hormone and other peptides is known to regulate just these types of developmental changes: the moult cycle and the timing of and variation in morphology, growth and development. The proposed research will test the hypothesis that the chemical signal that predators do emit actually triggers an adaptive shift in the endocrine system, leading to adaptive changes in prey growth and development. This research aims to a) identify the hormones and peptides that underpin the induction of these adaptive, developmental changes; b) identify predator induced change in the time sequence of hormone concentration; and c) test among four hypothesis for the developmental control of the induced phenotype.