Morphometric Analysis of Coptotermes spp. Soldier Caste (Blattodea: Rhinotermitidae) in Indonesia and Evidence of Coptotermes gestroi Extreme Head-Capsule Shapes

Simple Summary The morphological characteristics of the soldier caste in termites provide valuable taxonomic information at the species level. Head-shape variation in soldiers was often used as an indicative characteristic in some genera. While species with egg-shaped and waterdrop-shaped head capsule (HC), Coptotermes gestroi and C. curvignathus, respectively, are familiar in Indonesia, neither a measurement nor head index may avoid the subjectivity of shape interpretation. We conducted linear and geometric morphometrics analyses of soldiers' HC of Coptotermes spp. obtained from various locations in Indonesia. Although subtle differences were observed, the posterior parts of the HC laterally expanded in a gradual manner in C. gestroi, C. sepangensis, and C. curvignathus in that order. Furthermore, three extreme head-shape variations of C. gestroi were found to exist in nature. Overall, we explicitly vocalized the complexity of utilizing HC morphometric measurement and shape for species determination in Coptotermes spp. Linear and geometric morphometrics approaches were conducted to analyze the head capsule (HC) shape of collected soldier caste specimens of Coptotermes from various locations in Indonesia. The soldiers' morphology was observed and measured. The results of the principal component analysis of the group of all species showed two important groups of variables, i.e., the body size and setae characteristics of the pronotum and head. The multicollinearity of the morphometric variables showed the importance of body measurements as well as important alternative characteristics such as the pronotum setae (PrS) and HC setae. Four trends of HC shape were observed across the species. Interestingly, three extreme shapes were depicted by geometric morphometrics of the C. gestroi HC. The phylogenetic tree inferred from 12S and 16S mitochondrial gene fragments showed high confidence for C. gestroi populations. The lateral expansion of the posterior part of the HC across the species was in accordance with the increasing of the number of hairlike setae on the pronotum and HC. These differences among species might be associated with mandible-force-related defensive labor and sensitivity to environmental stressors.

Automated summary

The morphological characteristics of soldier caste in termites provide taxonomic information at the species level. The study conducted linear and geometric morphometrics analyses to analyze head capsule shape of soldier caste specimens of Coptotermes from Indonesia. Different head-shape variations were observed, with three extreme shapes found in C. gestroi. The lateral expansion of the posterior part of the head capsule across species was correlated with the number of hairlike setae on the pronotum and head.