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