Insights into the morphological evolution of Psittaciformes: skeletogenesis and sequence heterochronies of Myiopsitta monachus (Arini, Psittacidae)

TAMBUSSI CLAUDIA P.; CARRIL JULIETA

Diamante, Entre Rios

Congreso; 9th International Meeting of the Society of Avian Paleontology and Evolution; 2016

Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción (CICYTTP-CONICET).

Heterochronies involves changes in time or event rates and/or developmental processes underlying the formation of morphological characters. They are of great importance in the evolutionary developmental biology (Evo-Devo) and can be studied seeking for changes in the order of occurrence of the events between taxa, known as sequence heterochrony. Psittaciformes is one of the most homogeneous avian orders, characterized by their colourful feathers, robust and recurved beaks, zygodactyl feet, advanced cognitive abilities, highly developed locomotor system and feeding behaviours, and by their altriciality. By the using of the differential staining of cartilage and bone plus clearing technique, the complete ossification sequence of the monk parakeet Myiopsitta monachus was determined. Results show a general pattern similar to that described for other birds: lower ossification degree and delayed skeletons relative to precocial birds, some elements are not ossified at hatching, and hindlimbs ossify before forelimbs, condition that could be linked to altriciality. To establish the conservation degree of the sequences, different species of Aves were selected and event-pairing method and character mapping on a phylogeny were applied. Approximately 80% of the character states exhibits an homogeneous distribution, reaffirming largely preserved ossification sequences of Aves. Event-pair cracking phylogenetic method was also applied. Results reveal a high number of heterochronies within Aves and shows that limbs long bones may behave as modules. In the sequence of Myiopsitta monachus the early appearance of some hyoid apparatus elements occurs and could be related to the development of tongue in Psittaciformes and its role in handling food. This is in concordance with functional hypothesis (suggesting that the functionally important bones ossify earlier in the sequence) and size hypothesis (suggesting that the time of onset of an organ formation in the embryo is related to its adult size). In addition, the ossa ectethmoidale and mesethmoidale ossify early. These bones provide the origin site of the Psittaciformes´ novel adductor m. ethmomandibularis associated with strong bite forces, and its acceleration in the sequence may correspond to the forementioned functional hypothesis. This work is the first dedicated to establish the ossification sequence of the whole skeleton for any Psittaciformes and means an important step in the study of morphological evolution by increasing the data on the development of a wild non-model Aves.