Johnston,
S.D., Daddow, L., Carrick, F.N. and Jamieson, B. 2004. Observations
of
spermiogenesis and epididymal sperm maturation in the rufous hare wallaby,
Lagorchestes hirsutus (Metatheria, Mammalia). — Acta Zoologica (Stockholm)
85: 53 – 58
Acrosomal
development in the early spermatid of the rufous hare wallaby
shows
evidence of formation of an acrosomal granule, similar to that found in
eutherian
mammals, the Phascolarctidae and Vombatidae. Unlike the other
members
of the Macropodidae so far examined, the acrosome of this species
appears
to be fully compacted at spermiation and extends evenly over 90% of
the
dorsal aspect of the nucleus. During spermiogenesis, the nucleus of the
rufous
hare wallaby spermatid showed evidence of uneven condensation of
chromatin;
this may also be related to the appearance of unusual nucleoplasm
evaginations
from the surface of the fully condensed spermatid. This study was
unable
to find evidence of the presence of Sertoli cell spurs or nuclear rotation
during
spermiogenesis in the rufous hare wallaby. The majority of spermatozoa
immediately
before spermiation had a nucleus that was essentially perpendicular
to
the long axis of the sperm tail. Nuclei of spermatozoa found in the process
of
being released or isolated in the lumen of the seminiferous tubule were
rotated
almost parallel to the long axis of the flagellum; complete parallel
alignment
occurred during epididymal maturation. At spermiation spermatozoa
have
characteristically small cytoplasmic remnants compared to those of other
macropods.
Unlike the majority of macropodid spermatozoa so far described,
the
spermatozoa of the rufous hare wallaby showed little evidence of
morphological
change during epididymal transit. There was no formation of a
fibre
network around the midpiece or of plasma membrane specializations in
this
region; the only notable change was a distinctive flattening of midpiece
mitochondria
and scalloping of the anterior mitochondrial sheath to accom-modate
the
sperm head. Preliminary evidence from spermiogenesis and
epididymal
sperm maturation supports the classification of the rufous hare
wallaby
as a separate genus but also indicates that its higher taxonomic position
may
need to be re-evaluated.
Dr
S. D. Johnston, School of Animal Studies, The University of Queensland,
Gatton,
4343, Australia. E-mail: s.johnston@mailbox.uq.edu.au
Queensland,
Gatton, 4343; 2 Department
of
Zoology and Entomology, The University
of
Queensland, 4072, Australia
Keywords:
acrosomal
granule, epididymal sperm
maturation,
Lagochestes hirsutus,
phylogeny,
rufous
hare wallaby, spermiogenesis, sperm
ultrastructure