Endocrine regulation of predator-induced phenotypic plasticity.

Stuart R. Dennis,Gerald A. LeBlanc,Andrew P. Beckerman

doi:10.1007/s00442-014-3102-8

Stuart R. Dennis, Gerald A. LeBlanc + Show 1 more

Open Access

https://doi.org/10.1007/s00442-014-3102-8

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Abstract

Elucidating the developmental and genetic control of phenotypic plasticity remains a central agenda in evolutionary ecology. Here, we investigate the physiological regulation of phenotypic plasticity induced by another organism, specifically predator-induced phenotypic plasticity in the model ecological and evolutionary organism Daphnia pulex. Our research centres on using molecular tools to test among alternative mechanisms of developmental control tied to hormone titres, receptors and their timing in the life cycle. First, we synthesize detail about predator-induced defenses and the physiological regulation of arthropod somatic growth and morphology, leading to a clear prediction that morphological defences are regulated by juvenile hormone and life-history plasticity by ecdysone and juvenile hormone. We then show how a small network of genes can differentiate phenotype expression between the two primary developmental control pathways in arthropods: juvenoid and ecdysteroid hormone signalling. Then, by applying an experimental gradient of predation risk, we show dose-dependent gene expression linking predator-induced plasticity to the juvenoid hormone pathway. Our data support three conclusions: (1) the juvenoid signalling pathway regulates predator-induced phenotypic plasticity; (2) the hormone titre (ligand), rather than receptor, regulates predator-induced developmental plasticity; (3) evolution has favoured the harnessing of a major, highly conserved endocrine pathway in arthropod development to regulate the response to cues about changing environments (risk) from another organism (predator).

Highlights

Phenotypic plasticity—the expression of different phenotypes in different environments by single genotypes—can alter the mean and variance of traits on which selection can act
There are several independent lines of published evidence that, when combined, predict that predator-induced phenotypic plasticity in morphology and life history is under endocrine regulation by juvenoid and ecdysteroid signalling
The evidence comes from detailed information on why development matters under predation risk and how the endocrine system regulates growth, development and morphology in arthropods

Summary

Introduction

Phenotypic plasticity—the expression of different phenotypes in different environments by single genotypes—can alter the mean and variance of traits on which selection can act. This topic draws the attention of ecologists interested in the origins and consequences of trait variation, of evolutionary biologists interested in plasticity as a source of selectable variation, and of developmental biologists interested in genes, hormones and the developmental control of traits such as morphology and life history (Nijhout 2003b; Pigliucci 2001; Sultan 2007; Tollrian and Harvell 1999). Strong links between phenotypic plasticity and developmental biology are established in plants, where it is understood how endocrine physiology mediates environmental signals to produce phenotypes.

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