Phenotype images of Gryllus personatus and five resulting morphological measurements

Sexual size dimorphism (SSD) and sexual shape dimorphism (SShD) are of
interest to evolutionary ecology, but the two phenomena can very easily be
conflated by not taking a multivariate approach to measuring size. In our
study we draw attention to this problem by measuring four body size
dimensions (maxillae span, head width, pronotum length and mean hind femur
length) in lab-reared individuals of the badlands cricket (Orthoptera,
Gryllinae, Gryllus personatus) and conducting a variety of multivariate
analyses to test whether there is SSD and/or SShD. We found that males had
wider heads and maxillae than females, and females had longer pronota and
hind femora than males. This difference in the direction of sexual
dimorphism indicates SShD. However, multivariate methods failed to detect
SSD, instead confirming that the sexes primarily differ in body shape. We
suggest that orthopterists studying sexual dimorphism minimally measure
head width, pronotum length and hind femur length as a standard that will
allow a more repeatable and generalizable assessment of the prevalence and
direction of both SSD and SShD.