Adaptive Significance of Tracheal Elongation in Manucodes (Paradisaeidae)

Abstract

The five species of manucode Manucodia (including Phonygammus) (Diamond 1972, Beehler and Finch 1985) are monogamous and sexually monomorphic, glossy blue-black, and are medium-to-large passerines of the family Paradisaeidae. They are confined to forests of New Guinea, certain satellite islands and tropical northeastern Australia (Cooper and Forshaw 1977, Beehler et al. 1986, Coates 1990). Of the 37 other, conspicuously sexually dimorphic, birds-of-paradise (two monomorphic Paradigalla spp. excepted), 35 are known or presumed to reproduce polygamously. In the latter 35 species, males are promiscuous, and females attend the nest, egg(s) and young alone and unaided (Gilliard 1969, Cooper and Forshaw 1977, Coates 1990, Frith 1992, Frith and Frith 1990, 1992, 1993a, 1993b and unpubl. data). The remaining two species constitute the little-known monotypic, sexually monomorphic and monogamous genera Macgregoria and Lycocorax. Manucodes are of considerable interest within the Paradisaeidae because the two species that have been studied are monogamous and non-territorial, range widely, and are gregarious, fig-eating specialists (Beehler 1983, 1985, Beehler and Pruett-Jones 1983). In contrast, most monogamous passerines are territorial. The rare avian phenomenon of an elongated and looped trachea has been long-known in Manucodia spp. (Lesson 1826 [cited in Forbes 1882a], Pavesi 1874 [cited in Forbes 1882a1, Forbes 1882a, Beddard 189 1). This adaptation in Manucodia is well-described (Clench 1978). Clench noted that vouna male M. keraudrenii have’a simple, straight trachea‘ihat develops with increasing age into an elongate, coiled and looped trachea that lies subcutaneously upon the pectoral muscle(s). Trachea elongation is far greater in males than in females (which have a shorter looped trachea that bends laterally across the pectoral muscles but may not form