Interspecific Variation of Testis Size and Epididymal Sperm Numbers in Australasian Rodents with Special Reference to the Genus Notomys
Date
1997
Authors
Breed, W.
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Journal article
Citation
Australian Journal of Zoology, 1997; 45(6):651-669
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Abstract
<jats:p>
When testis mass is plotted against body mass for Australasian rodents, an
allometric relationship is found to occur. Nevertheless, considerable
interspecific variability in testis mass as a percentage of body mass is
evident for the different species, with the smallest relative size of testes
in the Australian rodents being present in most Notomys
and several Pseudomys species. In other
Pseudomys, and nearly all species of the other genera,
the relative size of testes is considerably greater.
Notomys and Pseudomys with small
testes tend to have a lower relative volume of seminiferous tubules to the
total testicular mass than species with relatively large testes. These species
also generally have small cauda epididymides and a less dense sperm population
in this region. The data thus clearly indicate far fewer sperm are produced,
and stored, in the male reproductive tract of these animals. The causative
reason(s) for the differences in relative testis size are discussed and the
possibility that it relates to variation in breeding system, and hence
potential intermale sperm competition, is considered. However, the scant data
available do not indicate an obvious association among these parameters. It is
thus suggested that, in Notomys at least, the relatively
small testes may relate to the other divergent features of the reproductive
tract one of the consequences of which may be a highly efficient
sperm-transport system.</jats:p>