Why are dasyurids (carnivorous marsupials) so interesting? In my view, it’s because they are carnivorous and so are more alert in order to hunt, catch, and devour their prey. Some of their prey – the invertebrates, insects and spiders for example – would be relatively easy to find and eat once the dasyurid learned to avoid any stings. However, some of the vertebrates, lizards and rodents would be more of a challenge.
We were trapping once near Kinglake, and someone found a trap that seemed to be full of blood and long black hair. When we emptied the trap, we found a very feisty female brushtail phascogale, the tuan, with six fairly new young in the pouch, and a headless bush rat, which looked heavier than her. And lots of blood. It looked like the tuan had chased the rat into the trap and then dispatched him. When released, the tuan bolted up the nearest tree.
It’s not just the violence… dasyurids also have interesting and varied sex lives. Many marsupial herbivores, like kangaroos and wallabies, use variation in the length of gestation to expand the length of pregnancy by intervals of embryonic arrest. Whereas some dasyurids play a double game. For example, the agile antechinus has “developmental arrests” – a temporary period of reversible, suspended development – to delay birth until after all the aggressive males are dead, giving the mother a hassle-free lactation period. The stripe-faced dunnart, which lives in semi-arid locations, can shorten the gestation period by decreasing the length of the arrest or deleting an arrest to take advantage of a good season.
Female dasyurids also have the capacity to store sperm in the lower oviduct, which remain viable for variable periods. In the agile antechinus, sperm can be stored for up to 13 days and still result in 88 to 92% of the oocytes successfully fertilised. After this the fertility rate falls dramatically to zero by 20 days.
Another interesting fact about the dasyurids is that some of them, like the northern quoll, squirt (eject under pressure) their newborns into the pouch together with their birth membranes. In the pouch the membranes drop off the newborn as the young move towards and onto a teat. My laboratory found evidence that this happens in the stripe-faced dunnart as well. What a feat for the mother, what a colossal squeeze and what amazing accuracy? Of course, dasyurids usually have more new-born young than teats, so if one squirt goes over the shoulder instead of into the pouch, they can afford to be cavalier about it!
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Lynne Selwood is a zoologist specialising in the embryology of marsupials and how the fertilised egg forms the cells that make an embryo and a placenta. She has applied this to marsupial conservation and control of fertility.
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