Osteohistological variations in the Antarctic penguin Pygoscelis adeliae (Aves, Sphenisciformes)

Abstract To analyze the osteohistological variations between adult individuals of Pygoscelis adeliae , histological sections of the mid-level of the shaft of different bones (humerus, radius, ulna, carpometacarpus, femur, tibiotarsus, tarsometatarsus and ribs) of a female and a male, were compared. The results indicate that, at the microanatomical level, the sections present a compact tissue with a reduced (or null) medullary cavity and a high bone density resulting from the internal compaction of the tissues. At the histological level, three tissue regions, defined by their bone matrix, level of organization of the vascular channels, and the degree of compaction, can be identified. However, sexual differences and variations in the microstructure and histology along the skeleton were found in the penguin Pygoscelis adeliae . A medullary cavity defined by an inner circumferential system appears in the male, whereas in the female, a remaining medullary cavity without the development of an inner circumferential layer, a lower degree of bone compaction, the presence of medullary tissue, and intertrabecular spaces, was observed. These results are consistent with reports of medullary bone in females from other groups of birds and provided an assistant criterion for the differentiation of sexes.