Connecting the Embryo: Anatomical Network Analysis of the Skeletal Development of the Altricial Monk Parakeet (Aves: Psittaciformes)

Abstract

We used for the first time the powerful quantitative tool AnNA toprovide new insights on the sequence of bone to bone connection,loss, and fusion events leading to the adult skeletal organization duringthe development of a bird. Connections (physical junctions) of thebones (nodes) of the skeleton of 36 specimens of the altricial monkparakeet Myiopsitta monuchus were documented through the ontogenetictrajectory, from embryonic stage 34 to adult. Besides node andwhole-network parameters, we also assessed changes in modularityand complexity during ontogeny. Results showed that: (1) during development,31 of a total of 163 bones lose independence due to fusions (reduction of nodes), the majority in the skull between day 22 afterhatching (AH) and adult, (2) 12% of the total connections (338 in adult)are present prior to hatching (of some bones of the skull, mandible andmetatarsals), (3) the largest increase in connections is between days15 and 18 AH, (4) the skull connects with the column at day six AH,(5) vertebral connections do not follow a distinguished pattern, (6) girdlesconnect to the column AH, (7) the pelvic girdle connects with thecolumn earlier than the pectoral girdle, and (8) pelvic girdle and hindlimb connections begin and ends before those of the pectoral girdleand the forelimbs. These connectivity patterns match well with theknown skeletogenesis process in this species. Particularly, connectionsof the girdles could be linked to the altriciality due to requirements foractive movement in the use of the hind limbs inside the nest, but notthe need to use forelimbs to fly until much later. DRG funded by grantBFU2015-70927-R. CPT funded by grant PICT2330.