Friday 29 May 2015

Muntjac: a deer with fangs

There is a possibility that, next year at The Institute, I will be asked to teach Molecular Biology and Immunology to our 4th Year Biologists. I had my annual timetable meeting with the new HoD and was boasting about my research record discovering genes of immunological interest in chickens Gallus gallus and cows Bos taurus.  Suddenly I twigged that my roomie has been kicked upstairs to a part-time admin position and was looking to shed her 4hrs/wk MolBol&Imm lectures!  Bottling out and back-pedalling, I stoutly asserted I was a) old and b) hoping to coast quietly down-river to retirement and that c) it would be better taught by some young person more up to date with his/her MolBio. After I thought a bit and acquired a backbone, I e-mailed the HoD to say that I'd be happy to teach MolBolImmunol if that would help the cause. We'll see and you'll hear how that turns out in due course. Then over the w/e El Asturiano sent me a link about the Indian Muntjac and I was kick-started to think that I could do whole chunks of the 4th Year course just talking about cetartiodactyls, a word I find I used without definition [shame] a couple of weeks ago. For starters I could tell them a war story from the battle with morphologists by which molecular evolutionists defined a new mammalian order Cetartiodactyla to include cows, sheep, goats, antelopes, pigs, hippos, llamas, camels and . . . whales.
Mais revenons nous a nos muntjacs. The genus Muntiacus consists of about a dozen species of small deer.  Fossils that can fit into this genus have been found in Miocene [7-24mya] deposits in Central Europe, making it one of the oldest extant types of deer. M. reevesi the Chinese muntjac has been introduced into England through the ineptitude of the Duke of Bedford who allowed these exotics to escape from his estate at Woburn in 1925.  Since then the species has spread to pretty much every county. Munjacs are small, but you can differentiate an adult muntjac from a juvenile some-other-deer by the presence of its tusks - enlarged upper canines most clearly seen on the stripped skull [L above].  That's not so surprising as pigs are cetartiodactyls also although they tend to develop the lower canines into formidable weapons. The most extreme example of canine development is in Babyrousa babyrussa known in English as . . . the babirusa. Their upper canines start development pointing downwards and then, in males, do an extraordinary and elaborate curve upwards to punch through the maxilla to create a fearsome curlicue in front of the eyes.  What are the developmental signals that drive that?  Dunno, but my students next year are going to find out!

Muntiacus reevesi has a more or less normal number of chromosomes at 2N=46, which happens to be the same number as we have but it has a sister species Muntiacus muntjak which is only distinguishable from M. reevesi through very careful scrutiny by an expert 'deerologist'. M. muntjak, in contrast to Bedford's Folly, has the distinction of having the smallest number of chromosomes of any mammal at 2N=6,7.  The 6,7 indicates another bizarre trait: females have 6 chromosomes (2 pairs of 'autosomes' + XX), males in this species have 7 (2 pairs of 'autosomes' + X+Y1+Y2).  Somewhere along the way, their Y chromosome has gotten split into two unequal halves.  Despite this absurd difference in chromosome count, the two species are interfertile, sort of, the cross yields viable offspring but they are sterile in  the same way as crosses between horses Equus caballus and donkeys Equus africanus asinus are called mules or hinnies (depending on which species is the jumper and which the jumpee).

Everybode kno that mules are sterile at least partly because they cannot sort out the discrepancy in chromosome number of their parents 2N=64 for horse and 2N=62 for donkeys and the hybrids have an odd number at 2N=63 presumably with two short chromosomes from horse trying to pair up with a single long one from the donkey parent. In fact not all female mules are sterile and there have been numerous (but still proportionately rare) examples since the time of Herodotus. The Muntiacus hybrid must be a real mess at meiosis when the pairs of chromosomes line up to halve their number to produce the gametes: sperm and egg. Lest you think that the USA has a corner on gun-nuts, you can shoot a muntjak in England if you have a gun and £75.  The deer which I illustrate [R] to show they are but little (and not fierce) are neither sleeping nor smiling, they are venison.

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