A shared mechanism of defense against predators and parasites: chitin regulation and its implications for life-history theory.
Defenses against predators and parasites offer excellent illustrations of adaptive phenotypic plasticity. Despite vast knowledge about such induced defenses, they have been studied largely in isolation, which is surprising, given that predation and parasitism are ubiquitous and act simultaneously in the wild. This raises the possibility that victims must trade-off responses to predation versus parasitism. Here, we propose that arthropod responses to predators and parasites will commonly be based on the endocrine regulation of chitin synthesis and degradation. The proposal is compelling because many inducible defenses are centered on temporal or spatial modifications of chitin-rich structures. Moreover, we show how the chitin synthesis pathway ends in a split to carapace or gut chitin, and how this form of molecular regulation can be incorporated into theory on life-history trade-offs, specifically the Y-model. Our hypothesis thus spans several biological scales to address advice from Stearns that "Endocrine mechanisms may prove to be only the tip of an iceberg of physiological mechanisms that modulate the expression of genetic covariance".
Department of Animal and Plant Sciences, University of Sheffield, Western Bank Sheffield, S10 2TN, U.K.
Andrew P
AP
Beckerman
Ashworth Laboratories, Institute of Evolutionary Biology, University of Edinburgh Kings Buildings, Edinburgh, EH9 3JT, U.K.
Job
J
de Roij
Department of Animal and Plant Sciences, University of Sheffield, Western Bank Sheffield, S10 2TN, U.K.
Stuart R
SR
Dennis
Ashworth Laboratories, Institute of Evolutionary Biology, University of Edinburgh Kings Buildings, Edinburgh, EH9 3JT, U.K.
Tom J
TJ
Little
Chitin; disease; endocrine physiology; inducible defenses; parasites; predation; trade-offs