title: Exaggerated trait growth in insects.
abstract: Animal structures occasionally attain extreme proportions, eclipsing in size the surrounding body parts. We review insect examples of exaggerated traits, such as the mandibles of stag beetles (Lucanidae), the claspers of praying mantids (Mantidae), the elongated hindlimbs of grasshoppers (Orthoptera: Caelifera), and the giant heads of soldier ants (Formicidae) and termites (Isoptera). Developmentally, disproportionate growth can arise through trait-specific modifications to the activity of at least four pathways: the sex determination pathway, the appendage patterning pathway, the insulin/IGF signaling pathway, and the juvenile hormone/ecdysteroid pathway. Although most exaggerated traits have not been studied mechanistically, it is already apparent that distinct developmental mechanisms underlie the evolution of the different types of exaggerated traits. We suggest this reflects the nature of selection in each instance, revealing an exciting link between mechanism, form, and function. We use this information to make explicit predictions for the types of regulatory pathways likely to underlie each type of exaggerated trait.
authors.affiliation: Department of Entomology, Washington State University, Pullman, Washington 99164; email: lavine@wsu.edu , hiroki.goto@wsu.edu.
authors.forename: Laura
authors.initials: L
authors.lastname: Lavine
authors.forename: Hiroki
authors.initials: H
authors.lastname: Gotoh
authors.forename: Colin S
authors.initials: CS
authors.lastname: Brent
authors.forename: Ian
authors.initials: I
authors.lastname: Dworkin
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Emlen
mesh_terms: D000818:Animals; D005075:Biological Evolution; D007313:Insecta / Q000033:anatomy & histology / Q000235:genetics* / Q000254:growth & development*; D010641:Phenotype; D012641:Selection, Genetic
keywords: extreme growth; extreme size; growth mechanisms; insulin signaling pathway; juvenile hormone; sexual selection; soldier castes