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; https://creativecommons.org/licenses/by-sa/3.0/deed.en; https://en.wikipedia.org/wiki/File:Montreal_Twilight_Panorama_2006.jpg)

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: https://creativecommons.org/licenses/by-sa/2.0/; https://www.flickr.com/photos/jean-jacquesboujot/4241977404)

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.