Morphological integration of head capsule in millipede Megaphyllum unilineatum (C. L. Koch, 1838) (Diplopoda: Julida) during ontogeny

      Morphological integration is defined as covariation of multiple parts of the morphological traits. Modularity is characterized by the presence of subunites (modules), which have high level of integration within themselves, but weak between themselves. In this respect, differences in function, anatomical structure and embrionical origin of modules can influence development and function of organism. The aim of our study was to test the hypothesis that the distal region of the head capsule is a modul in Megaphyllum unilineatum using geometric morphometrics. Millipedes belonging to postembryonic stadia VI to XI were collected from Krnjača, Belgrade. The ontogenetic stadia were determined by counting the number of rows of ocelli, the total number of ocelli and rings, and the number of rings with and without walking legs. In data processing, the following statistical programs were used: MakeFan, TpsDig, CoordGen, MorphoJ, and R program. Procrustes ANOVA showed that individual × side interaction was significant. Allometry was significant for the symmetric component (SC), but not for the asymmetric component (FA). Since covariance coefficients (RV) for SC and FA had lower values than 10.4% and 13.8% (respectively) of other RV coefficients obtained by a random contiguous partition of dorsal part of the head capsule, modularity hypothesis is rejected. Further, the scaled variance of the eigenvalues of the SC (EV) was significantly lower before than after allometry removal. These results indicate that distal and proximal regions of the head capsule, due to their strongly morphological integration, develop and function as a module during ontogeny in this species.