It’s November, and time for Blog 11. I can’t believe that
it’s nearly the end of the year already! Last time I wrote, I was asking for
your help with crowd funding a project to continue studying the awesome
Australian rodent, the fawn-footed mosaic-tailed rats Melomys cervinipes (Figure 1). And I left you waiting patiently to
learn all about the reproductive anatomy and biology of male mosaic-tailed rats.
So, here you are. The information you’ve been waiting for. There may be some
confusing terms, but I’ll provide some information to help make it easier to
understand.
Fig. 1. Juvenile fawn-footed mosaic-tailed rat M. cervinipes |
Adult breeding males have scrotal or inguinal testes. In
layman’s terms, that’s the groin area. The testes are quite large in relation
to the body size, being about 2% of the body mass. This is even big for a murid
rodent! Regression of the testes can be seen when males are not breeding. This
makes sense – if you’re not going to breeding, why waste a heap of time
producing sperm that you’re not going to use?
While morphologically similar to other rodents, the glans penis is quite long and wide in comparison to other Australian rodents. In
anatomical terms, this is really referring to the rounded head or tip of the
penis itself. In M. cervinipes, it is
longer and wider than the glans penis of the grassland mosaic-tailed rat M.
burtoni (Figure 2), but is actually also a little narrower too. The glans penis
has small spines near the tip that disappear towards the base, and there is
epidermal folding. The proximal baculum is short and wide. Okay, so what is
this “baculum”? Basically, it’s a little isolated bone derived from connective
tissue. What does it do? Well, believe it or not, but it aids reproduction by
maintaining stiffness during copulation.
Fig. 2. Grassland mosaic-tailed rat M. burtoni. Photo: Russell Best, QPWS, 2009 |
The seminal vesicles are saccular and well-developed, and
have coagulating glands on the inner curves. Their function is to produce the
seminal fluid that carries the sperm. The seminal vesicles are bound to the
prostate at the base. Active spermatogenic seminiferous tubules are much wider
than inactive ones. The sperm averages about 107 μm in length, and is more
complex in structure than is seen in Australasian Rattus. The falciform (meaning “curved like a sickle” or hooked)
head has two additional elaborate ventral F-actin processes extending from the
upper concave surface, joining at the base. The apical hook ultrastructural
organization resembles the sperm of Rattus,
but there are two ridges of subacrosomal material along the upper convex
nuclear margin. Males have lots of types of accessory glands. In juvenile
males (Figure 1), pretty much everything is smaller in size, although similar in structure.
In addition, while spermatogenesis may occur, it generally doesn’t fully
progress past the primary spermatocyte stage.
In the next blog, I’ll move on to looking at the ontogeny
and reproduction of mosaic-tailed rats.
You can read more about my research in my publications,
listed on my blog. You can also find me on ResearchGate, the James Cook University website, Twitter and Facebook.