Patterns of integrated growth of body parts in Rook (Corvus frugilegus) ontogeny

The early period of ontogeny is key to understanding the patterns of body plan formation in birds. Most studies of avian development have focused on the development of individual avian characters, leaving their developmental integration understudied. We explored the dynamics and integration of relative percentage increments in body mass, lengths of head, skeletal elements of wing and leg, and primary flight feathers in the embryonic and postnatal development of the Rook (Corvus frugilegus). The relative percentage increments were calculated according to Brody's equation. Groups of similar growing traits (modules) were determined using hierarchical cluster analysis, and the degree of correlation between modules was estimated by PLS analysis. The embryonic and postnatal periods demonstrate significant consistency both in the dynamics of changes in relative percentage increments of studied traits as well as in the clustering of individual modules. The modules mainly include the body mass and head length, as well as the elements that form the fore- and hind limbs. Differences were revealed in the combination of modules into clusters in embryonic and postnatal periods. Hind limb elements clustered together with wing elements in the embryonic period but with body mass and the head in the postnatal period. The strongest modularity was noted for the leg in embryogenesis, and for the wing in postnatal development. The forelimb and especially the primary feathers had more distinctive growth patterns. We suggest the changes in the degree of integration between locomotor modules in ontogenesis are connected with the earlier functioning of the legs in the postnatal period and with the preparation of the wings for functioning after a chick leaves the nest.