Striped mouse

Striped mouse

Striped mouse (Rhabdomys pumilio) on the cover of the August edition of Behaviour

Striped mouse (Rhabdomys pumilio) on the cover of the August edition of Behaviour
My photo and the accompanying paper (see List of publications) were published in this issue.

Wednesday, November 20, 2019

Male fawn-footed mosaic-tailed rat reproductive biology

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.

Thursday, October 17, 2019

Identifying resilience

Dear friends,

I thought you would be interested in this project.

My research project, “Identifying Resilience”, was chosen to be part of JCU’s crowdfunding pilot and it is now LIVE at

You will find more information about the fawn-footed mosaic-tailed rats and my project on the Pozible platform:

As this is an All-Or-Nothing crowdfunding campaign, I have to reach my target of $4,975 by the end of October, or it won’t get funded at all!

That is why I rely on all of you to support me: Please pledge and share my project with your networks – internally and externally.

The more people who know about my project, the better. Also, please don’t hesitate to get in touch with me:

Facebook: Tasmin Rymer
Twitter: @dr_rymer
LinkedIn: Tasmin Rymer
ResearchGate: Dr Tasmin Rymer
Google Scholar: Tasmin Rymer
JCU Research Portfolio: Dr Tasmin Rymer JCU Research Portfolio

Thank you very much!


Monday, September 23, 2019

Even MORE information on fawn-footed mosaic-tailed rats…

So were’ well into September and I bet you thought I’d forgotten about Blog 9. Pretty soon, we’ll be talking about Christmas! Nearly off on another big adventure tomorrow to visit North America again, this time to the intriguing city of Montreal (Figure 1).

Fig. 1. Montreal, Canada (Photo:DAVID ILIFF. License: CC BY-SA 3.0;;
Fig. 2. Fawn-footed mosaic-tailed rat M. cervinipes
But, more importantly, let’s carry on with our discussion on the native Australian fawn-footed mosaic-tailed rat Melomys cervinipes (Figure 2). Still pretty general at this point, but you have to start with the basic biology. 

So, I started talking about the form and function of these animals in the last blog, specifically talking about their skulls and dentition. If we keep with the head region, the brain weights about 1.9g, which accounts for about 2.7% of the overall mass of the animal. Now that’s pretty intriguing, because human brain mass is also around 2-3% of body weight, so their brains are definitely not small if we’re relating this to body size. Maybe this says something about their cognitive ability?

Fig. 3. General rodent stomach (Adapted from John DeSosso)
If we move away from the head, we know a little bit about their stomachs too. Like most rodents, they have two stomach regions that are clearly demarcated: the corpus, or forestomach, and the antrum, or the hindgut (Figure 3). The forestomach is larger than the hindgut, and Breed & Ford(2007) noted an extended fundic diverticulum, suggesting the potential that they may be able to store plant material. The small intestine is pretty long too, contributing about 50% of the length of the alimentary canal.

Moving even further away from the head, a very large amount of work has been done on the reproductive anatomy of this species, with general similarities to brown rats Rattus norvegicus (Figure 4) being observed. So, let’s focus on females first. Females have two pairs of inguinal teats. They have two uterine horns, which is typical of murid rodents. The ovaries of juveniles are characterised by naked peripheral ova, small- and medium-sized follicles, and extensive atresia.
Fig. 4. Brown rat Rattus norvegicus (Photo: Jean-Jacques Boujot. License:;

Similarly, typical of murids, the ovary of non-pregnant females often shows degeneration of follicles in different developmental stages, but in comparison to juveniles, mature, non-pregnant females also show healthy mature follicles of varying sizes. Ripe follicles are smaller than newly formed corpora lutea, being only 75-80% in size in comparison. Females average 3.25 follicles per oestrus, and activity in the ovary is evenly distributed between the two ovaries. Pregnant females bear considerably larger corpora lutea, being about 170% larger, than non-pregnant females during the early stages of pregnancy. As embryo size increases, the size of the corpus luteum decreases, corresponding to a decrease in function.

In the next blog, I’ll start off with male reproductive anatomy to keep the story going.

You can read more about my research in my publications, listed on my blog. You can also find me on ResearchGate, the James CookUniversity website, Twitter and Facebook.