SPERMATOZOAL ULTRASTRUCTURE IN 3 SPECIES OF PARROTS (AVES, PSITTACIFORMES) AND ITS PHYLOGENETIC IMPLICATIONS

Background: DNA-DNA hybridization studies suggest that Psittaciformes are highly, but not the most, derived nonpasserines. Multilocus protei n electrophoresis indicates that cockatoos (Cacatuinae) form a monophy letic lineage distant from the other Australo-Papuan psittacids (Psitt acinae). Methods: Transmission electron microscope procedures are appl ied to the spermatozoa of three parrots, in the Cacatuninae and Psitta cinae, to investigate these relationships. Results: Psittaciform sperm have the following characteristics: (1) conical acrosome vesicle; rod like perforatorium; cylindrical, highly condensed nucleus; proximal an d distal centriole embedded in dense material; elongate periaxonemal m itochondrial midpiece, (2) nine dense peripheral axonemal fibers (coar se fibers), (3) no fibrous sheath around the axoneme, (4) mitochondria with linear cristae, lacking intra- (or inter-) mitochondrial dense b odies, (5) restriction of the endonuclear perforatorial canal to the a nterior region of the nucleus, (6) a short distal centriole, and (7) n ucleus abutting on but not penetrating the acrosome. Conclusions: (1) These features are tetrapod symplesiomorphies, (2) is an amniote synap omorphy; the fibers differ from those of reptiles in being uniform in size, (3) loss of the fibrous sheath is an apomorphy known elsewhere o nly in columbiforms, (4) are apomorphies relative to basal aminiotes ( Chelonia, Sphenodon, and Crocodilia), (5) is an apomorphic condition s hared with other nonpasserines (galliforms and the white-naped crane) and crocodilians, (6) the latter taxa differ from parrots in a plesiom orphic elongation of the distal centriole, and (7) is a unique apomorp hy of parrot sperm relative to other nonpasserines and reptiles. The s hort midpiece of N. hollandicus distinguishes this cacatuine from the two psittacines. (C) 1995 Wiley-Liss, Inc.