The origins of allometry: size and shape polymorphism in the common waterstrider, Gerris remigis Say (Heteroptera, Gerridae)

Abstract

Changes in size, whether ontogenetic or phylogenetic, tend to be associated with changes in shape. This allometry can arise through two different evolutionary mechanisms: (1) selection acting primarily on overall size may be associated with changes in shape because of physiological and mechanical constraints or differential responses of different body components; or (2) selection acting primarily on shape (on the size of specific body components) may be associated with changes in overall size because of genetic correlations, and thus correlated responses, of other body components. To assess the relative importance of these two mechanisms, shape polymorphism is examined along two axes of size dimorphism (sex and wing morphology) in the common waterstrider, Gerris remigis Say. Eight measurements were made of body and appendage qomponents of 234 adults, from three independent populations. Univariate and multivariate analyses reveal that both sexes and wing morphs differ significantly in size and shape. Shape differentiation along the two axes of size dimorphism is found to be dissimilar, partially independent of size, and strongly correlated with the ecological specialization of the various morphs. These observations suggest that selection is acting directly on shape, and thus that allometry in this species primarily reflects shape-mediated changes in size (mechanism 2), rather than size-mediated changes in shape. The role of developmental processes in facilitating this shape differentiation is discussed.

Ontogenetic trajectories and hind tibia geometric morphometrics of Holymenia clavigera (Herbst) and Anisoscelis foliacea marginella (Dallas) (Hemiptera: Coreidae)

“…We did not find any study that used similar method to detect ontogenetic allometry in insects. For Hemiptera, current works have used multivariate methods as principal components analysis to evaluate shape and size polymorphisms (Fairbain 1992), as well as to compare the three kinds of allometry (static, ontogenetic and evolutionary) in some Gerridae (Klingenberg & Zimmermann 1992b). Thus, it is difficult to discuss our findings in conjunction with other allometric studies.…”

“…Within Insecta, previous studies of hemipterans have investigated static allometry in the hind tibia of Acanthocephala declivis guatemalana Distant, and their role in sexual selection (Eberhard 1998, also see Mitchell 1980), as well as studies concerning immature multivariate growth patterns (e.g. Klingenberg & Zimmermann 1992a, b), and size and shape dimorphism in gerrids (Fairbain 1992).…”

The effect of past condition on a multicomponent sexual signal

“…In insects, the development of the extremities takes place in the late larval stages, mediated by separate clusters of imaginal cells. Growth of legs and wings is therefore decoupled from growth of overall body size (Fairbairn 1990;Milan et al 1996;Nijhout & Emlen 1998). The scaling relationship that relates trait expression to variation in body size commonly has a genetic basis, reflecting condition-sensitive mechanisms of trait expression that have been shaped by natural and sexual selection (Emlen & Nijhout 2000).…”

The evolution of shape in the wing dimorphic cricket, Allonemobius socius

“…1). Fairbairn (1992) examined size and shape differences between morphs and sexes of the waterstrider Aquarius (formally Gerris) remigis and showed that macropters have relatively larger thoraxes which also differ in shape from the micropters. These differences presumably reflect constraints caused by the large size of the flight muscles and possibly the mechanical requirements for muscle attachment and strength to sustain the stresses of flight.…”