Phenotypic variation and sexual size dimorphism in Dichroplus elongatus (Orthoptera: Acrididae)

Abstract

Patterns of body size evolution are of particular interest because body size can affect virtually all the physiological and life-history traits of an organism. Sexual size dimorphism (SSD), a difference in body size between males and females, is a widespread phenomenon in insects. Much of the variation in SSD is genetically based and likely due to differential selection acting on males and females. The importance of environmental variables and evolutionary processes affecting phenotypeic variation in both sexes may be useful to gain insights into insect ecology and evolution. Dichroplus elongatus is a South American grasshopper widely distributed throughout Argentina, Uruguay, most of Chile and southern Brazil. In this study we analyzed 122 adult females of D. elongatus collected in eight natural populations from Central-East Argentina. Females show large body size variation among the analyzed populations and this variation exhibits a strong relationship with fecundity. Our results have shown that larger females were more fecund than smaller ones. We found that ovariole number varied along a latitudinal gradient, with higher ovariole numbers in populations from warmer locations. A considerable female biased SSD was detected. SSD for three analyzed morphometric traits scaled isometrically. However, SSD for thorax length displayed a considerable variation across the studied area indicating a larger relative increase in female size than in male size in warmer environmental conditions.