Evolutionary negative allometry of orthopteran hind femur length is a general phenomenon

Abstract

1. Body size influences the way that organisms both perform their locomotor activities and perceive their environment. Allometry of insect legs with respect to body size is affected by many factors such as ontogenetic constraints and natural selection. Negative allometry, positive allometry, or isometry could result from different mechanisms influencing leg length and locomotion performance. 2. We tested three main models of hind femur length allometry (natural selection for jumping performance, ontogenetic constraint, and the size-grain model) in Orthoptera, a Polyneopteran order with large size range and high habitat and lifestyle diversification. We used a data set of 1549 species including members of both suborders, Ensifera and Caelifera, and many representative families using a Linear Mixed Model approach, and Reduced Major Axis and Ordinary Least Squares regression to explore evolutionary interspecific allometry in this order. 3. Our results showed a generalized trend of negative allometry (leg length decreases with body size increase) at the ordinal, subordinal, and familial levels, contrary to the expectations of the size-grain model and supporting our main hypothesis of a common ancestral developmental pattern regulating leg negative allometry in Orthoptera. 4. The conservation of a common hind leg allometric pattern in Orthoptera provides a basic framework to study adaptation of hind limbs to different habitats and lifestyles, and has important implications for the analysis of ecogeographic and evolutionary rules.