QUANTITATIVE DESIGN OF THE SKELETON IN BIRD HATCHLINGS - DOES TISSUE COMPARTMENTALIZATION LIMIT POSTHATCHING GROWTH-RATES

Based on a detailed description of hatchling skeletons of the precocia l buttonquail (Turnix suscitator) and the altricial budgerigar (Melops ittacus undulatus), this report presents the hypothesis that the rate of avian posthatching growth is limited by the quantitative design (i. e., relative volumes of cartilage, bone, and marrow) of the hatchling skeletons. A large portion of bone in the skeletal elements and fast g rowth are hypothesized to be mutually exclusive. This hypothesis is te sted by morphometric techniques and by statistical comparison of morph ometric and growth data. All predictions are met by the data, and the design of hatchling skeletons is described as determined by a tradeoff between tissue composition of skeletal elements and maximum rates of posthatching growth. The precocial design shows large bony areas that supposedly resist mechanical stress of locomotion; however, the relati vely small cartilaginous areas exclude high growth rates. The altricia l design shows the reverse relationship with small bony areas and a la ck of locomotion on the one side but large cartilaginous areas and fas t posthatching growth on the other side. (C) 1994 Wiley-Liss, Inc.