Sexual dimorphism in body shape of Chiasognathus grantii ( Coleoptera: Lucanidae)

Chiasognathus grantii, endemic species of temperate forests in Chile and Argentina, has a pronounced sexual dimorphism observed in the jaw shape and size, besides the shape of the pronotum and the last abdominal segment. Also, differences in the size of individuals have also been recorded for this species throughout its distribution in Chile and part of Argentina; this has been used as evidence for some authors to consider the name 'pygmaeus', although this variety has not been quantitatively assessed from the genetic or morphologic point of view. Shape variation of C. grantii was quantitatively assessed according to its geographic distribution and sexual dimorphism. A morphometric analysis was conducted on 283 individuals to determine variations exclusively attributed to body shape by means of a photographic record of the ventral area in the insect. There were significant interpopulation differences for the symmetric component of body shape ( individual variation) between sex, mainly expressed as an expansion of the third abdomen segment in females and its contraction in males. However, there is not enough statistical evidence to differentiate subspecies. There is a discussion about these interpopulation differences, if they are attributed only to sexual dimorphism or if they may also be a response to selective stress due to intrasexual competition for feed resources or due to environmental variations during the ontogenetic development.