Jamieson, B.G.M., Koehler, L. and
Todd, B.J. 1995a.
Spermatozoal ultrastructure in three species of parrots (Aves,
Psittaciformes) and its phylogenetic implications. The Anatomical
Record 241, 461-468.
Background: DNA-DNA hybridization studies
suggest that Psittaciformes are highly, but not the most, derived
nonpasserines. Multilocus protein electrophoresis indicates that
cockatoos
(Cacatuinae) form a monophyletic lineage distant from the other
Australo-Papuan
psittacids (Psittacinae). Methods: Transmission electron microscope
procedures
are applied to the spermatozoa of three parrots, in the Cacatuninae and
Psittacinae, to investigate these relationships. Results. Psittaciform
sperm
have the following characteristics: (1) conical acrosome vesicle;
rodlike
perforatorium; cylindrical, highly condensed nucleus; proximal and
distal
centriole embedded in dense material; elongate periaxonemal
mitochondrial
midpiece, (2) nine dense peripheral axonemal fibers (coarse fibers),
(3) no fibrous
sheath around the axoneme, (4) mitochondria with linear cristae,
lacking intra-
(or inter-) mitochondrial dense bodies, (5) restriction of the
endonuclear
perforatorial canal to the anterior region of the nucleus, (6) a short
distal
centriole, and (7) nucleus abutting on but not penetrating the
acrosome.
Conclusions: (1) These features are tetrapod symplesiomorphies, (2) is
an
amniote synapomorphy; the fibers differ from those of reptiles in being
uniform
in size, (3) loss of the fibrous sheath is an apomorphy known elsewhere
only in
columbiforms, (4) are apomorphies relative to basal aminiotes
(Chelonia,
Sphenodon, and Crocodilia),
(5) is an apomorphic condition shared with
other
nonpasserines (galliforms and the white-naped crane) and crocodilians,
(6) the
latter taxa differ from parrots in a plesiomorphic elongation of the
distal
centriole, and (7) is a unique apomorphy of parrot sperm relative to
other
nonpasserines and reptiles. The short midpiece of N. hollandicus
distinguishes
this cacatuine from the two psittacines.