Morphological reflections of evolutionary adaptations in the tongue of the white-headed duck
During an organism’s evolution, functional adaptations help species to become better suited to their ecological niches. From the morphological aspect, these adaptations are reflected in the anatomical specializations of different organs. Specializations of the lingual organ is a critical adaptation of birds, such as the white-headed duck (Oxyura leucocephala), that enables their nutritional requirements to be met. For optimal use of the available food resources, the white-headed duck utilizes three methods of food collection, namely pecking, grazing and filter-feeding. Since this species is classified as endangered, we conducted the present study on two carcasses of the white-headed duck (death due to natural causes) employing routine histological methods, light microscopy and scanning electron microscopy. Our results show that the tongue of this bird shares some similarities and some differences with the tongue of other members of the family Anatidae. The results confirm that it is better adapted to the filter-feeding method rather than to other types of food intake. This adaptation is reflected by anatomical specializations of its lingual structures, including the stair-like outline shape, bi-sectional lingual body, a deep median sulcus, lateral conical papillae, mucus secreting glands, lack of serous secreting glands, cartilaginous skeleton and the triangular fibromuscular structure of the lingual body. The so-called triangular structure and cartilaginous skeleton are the major structures involved in the lingual motions during the filter-feeding method. The presence of the triangular structure and its connection with the cartilaginous skeleton and lingual mucosa have not previously been reported in any species of birds.
KeywordsAnseriformes Anatidae Filter-feeding method Lingual organ Triangular structure
This work was financially supported by research council of University of Tabriz (project number 3379).
Compliance with ethical standards
Conflict of interest
All authors declare that they have no conflict of interest.
- Atiénzar F, Antón-Pardo M, Armengol X, Barba E (2012) Distribution of the white-headed duck Oxyura leucocephala is affected by environmental factors in a Mediterranean wetland. Zool Stud 51:783–792Google Scholar
- del Hoyo J, Collar NJ, Christie DA, Elliott A, Fishpool LDC (2014) HBW and BirdLife illustrated checklist of the birds of the world. Vol 1: non-passerines. Lynx Edicions/BirdLife International, Barcelona/BrusselsGoogle Scholar
- Green AJ, Hughes B (1996) Action plan for the white headed duck (Oxyura leucocephala) in Europe. In: Heredia B, Rose L, Painter M (eds) Globally threatened birds in Europe. Council of Europe Publishing, Strasbourg, pp 119–146Google Scholar
- Hutchinson GE (1965) The ecological theater and the evolutionary play. Yale University Press, 1965Google Scholar
- Igwebuike UM, Anagor TA (2013) The morphology of the oropharynx and tongue of the muscovy duck (Cairina moschata). Vet Arhiv 83:685–693Google Scholar
- Mayr E (1966) Animal species and evolution. Belknap Press of Harvard University Press, CambridgeGoogle Scholar
- Nickel R, Schummer A, Seiferle E (1977) Anatomy of the domestic birds. Verlag Paul Parey, BerlinGoogle Scholar
- Parchami A, Dehkordi RAF, Bahadoran S (2010a) Fine structure of the dorsal lingual epithelium of the common quail (Coturnix coturnix). World Appl Sci J 10:1185–1189Google Scholar
- Parchami A, Dehkordi RAF, Bahadoran S (2010b) Scanning electron microscopy of the tongue in the golden eagle Aquila chrysaetos (Aves: Falconiformes: Accip-itridae). World J Zool 5:257–263Google Scholar