Platypus Genome Complete

We've talked before about the platypus and all it's strangeness. The platypus genome has has just been sequenced, revealing some things we already suspected: the platypus shares features with birds, reptiles and mammals. Follow the link for the Nature News story, podcast and video interview with the authors behind the project.

Bayblab podcast Episode10

Have you ever wondered who doctor B is? Are you interested in using wikis, podcasts and blogs in teaching? Well you're out of luck because we managed to screw up our first interview. But fear not, we have 3 random guys sitting on the next table in crystal clear audio quality thanks to our new mic (thanks invitrogen!). Nevertheless, we talk about some of the most poisonous animals on earth, the list may surprise you, and ponder whether science can help to make jury duty a more reproducible experience...

A duck designed by committee

"we would like to mention the Platypus, estranged relative of the mammal, which has a duck-bill, otter's tail, webbed feet, lays eggs, detects its aquatic prey in the same way as the electric eel, and has venomous barbs attached to its hind legs, thus combining all 'typical' Australian attributes into a single improbable creature." - Douglas Adams

As the above quote illustrates, the platypus is a bizarre beast. Belonging to the order Monotremata (literally, 'single hole'), all urinary, defecatory and reproductive systems open into a single duct, the cloaca (literally, 'sewer') and as most people know is one of the few mammals to lay eggs (the few species of echidna being the others). Platypus eggs more closely resemble those of reptiles than birds and are incubated in utero for the majority of the incubation period. The female has 2 ovaries, but only one is functional. It is also rare amongst mammals in that the male of the species has spurs on the hind legs that can produce venom toxic enough to kill a dog, or cause a great deal of pain to a human.

As if being a cross between a bird and a reptile wasn't enough, the platypus bill is packed with nerves that can be used for electrolocation, more commonly found in fish species, to aid in foraging in the riverbed.

But ultimately, the platypus is mammalian, meaning it has mammary glands, produces milk and nurses its young. Even in this aspect of its physiology, the platypus is unique. Unlike other mammals, the platypus has no nipples. Instead, the mammary glands are more like sweat glands, secreting milk directly onto the fur where it is licked off by its young.

Genetically, the platypus has other interesting features including a strange quirk in visual pigment evolution and in its sex chromosomes. The platypus has 5 pairs of sex chromosomes (making up ~15% of the genome) lacking the classic sex-determining SRY gene, which in some ways resemble the reptile/bird ZW sex determination system.

Because of its shared characteristics between mammal and reptile, some people view the platypus as an evolutionary link between the two. Because of their unique phylogenetic position, the platypus genome is currently being sequenced to answer some questions about evolutionary biology and mammalian gene organization.

Venomous mammals

Until recently, I was completely unaware that some mammals are venomous. This discovery dates from over 50 years ago, yet it is a neglected area of research considering how much attention is given to other venomous phyla for their medicinal properties. I had seen the spurs on the hind legs of platypoda, but most monotremes (other than the platypus) have spurs without functional venom glands.

Yet shrews actually have a venomous bite: the bottom canines have deep grooves which deliver the venom produced by specialized salivary glands. These insectivores use the venom to paralyse their preys for up to 16 days, so that they can store them for a later snack. The active component of the venom, called blarinasin (BLTX), shares about 50% identity with human tissue kallikreins. This mode of action is the same employed by other venomous species such as the rattlesnake: "BLTX converted kininogens to kinins, which may be one of the toxic pathogens, and had dilatory effects on the blood vessel walls. The acute toxicity and proteolytic activity of BLTX were strongly inhibited by aprotinin, a kallikrein inhibitor, suggesting that its toxicity is due to a kallikrein-like activity of the venom". A bioprospecting company based in the maritime, at Mt Allison University, is looking to develop this toxin for neuropathic pain applications.

Solenodon are also venomous. They are possibly one of the funniest looking mammals (shown above), like the lovechild of a shrew and an elephant, measuring about 30cm, grunting like a pig, with tits on its ass, and glands in the armpits that make it smell like a goat. As a note to intelligent design believers, they are susceptible to their own venom (better not bite your tongue), they freeze when they sense danger, and they have difficulty running, often stumbling and tripping over their own toes and tumbling over, making them easy targets. Originally from the Caribbean, they are all but extinct due to pets. I guess the bite didn't pack enough punch.

Finally, I was surprised to learn that there is a venomous primate on the island of Borneo and much of South-East Asia. The slow loris is a nocturnal animal which secretes a toxin in its saliva, and mothers lick their offspring before letting them forage for protection.