Application of geometric morphometrics to analyse allometry in two species of the genus Myrmica (Hymenoptera: Formicidae)

Abstract

Allometric changes in shape were analyzed in two species of the genus Myrmica using geometric morphometics. The pattern of allometry was visualized by thin plate splines (TPS) analysis. In 291 worker ants, 41 landmarks and 252 semilandmarks were fixed in images from four aspects: dorsal head, frontodorsal clypeus, dorsal mesosoma and lateral petiole. To explore how shape varies with size, a multivariate regression on centroid size was performed using the scores of all partial warps (PWs) from all four aspects. Multivariate analysis of covariance (MANCOVA) was used to compare the pattern of allometry between species, using all PWs from pooled coordinates of the two species as varieties, centroid size as the covariate and species as the grouping factor. For all four aspects in each species, the null hypothesis of isometry was rejected (i.e., allometry was present) since the multivariate regressions were statistically significant. The amount of shape variation accounted for by the regressions differed considerably between the species studied and among the four aspects, ranging from 2.62 % for the petiole of M. vandeli to 13.95 % for the mesosoma of M. scabrinodis. There were no significant differences between the two species in the allometric patterns of head and clypeus aspects (MANCOVA test). In a multivariate ordination, removing the allometric effects reduced overlap between species only a little or not at all. Geometric morphometrics allows the visualization of the allometries of particular shape components that would probably remain undetected by a conventional morphometric analysis.