Saturday, 25 December 2010

Platypus: The duck-billed, egg-laying mammal

Just a guy holding a platypus
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Monotremata
Family: Ornithorhynchidae
Genus: Ornithorhynchus
Species: Ornithorhynchus anatinus
Conservation Status: Least Concern (Not threatened)
Common Name(s): Platypus


If you have never heard of the Platypus you are probably thinking that the creature depicted above is a weird duck species or something. Well.. you can't be more wrong than that!

The platypus is actually a mammal. A very strange one that is, and not just for the way it looks, which on close inspection looks like a crazy hybrid of a duck, a beaver and an otter. For instance, other than the closely-related echidna, it’s the only surviving mammal that lays eggs!

Want more? Platypuses are again one of the very few known mammals with the sense of electroreception, (or electrolocation), meaning that they can sense the electrical fields produced by other organisms, much like sharks can. The only other known mammals with electroreception are the echidna and the Guiana dolphin (Sotalia guianensis).

Still, that's not all. Platypuses have one more trait that is rare in the mammalian world. But let's keep something out of the introduction!

Now, lets start with the basics about this truly bizarre animal.

Distribution & Habitat
Platypuses are semi-aquatic animals, occurring in small streams and rivers over an extensive area, from the cold highlands of Tasmania and the Australian Alps to the tropical rainforests of coastal Queensland and as far north as the base of the Cape York Peninsula.

Along the coastal river systems, their distribution is really unpredictable, as they are absent from many healthy rivers whereas they have a well established presence in some really degraded and polluted rivers, like the lower Maribyrnong.

Image showing the distribution of Platypus
Platypus Distribution

Description
Weight varies from 0.7 to 2.4 kg (~1.5 to 5.3 lb), with males being slightly larger than females. Males have an average length of 50 cm (~20 in) and females have an average length of 43 cm (~17 in). There is a significant variation in average size from region to region, and this pattern does not seem to follow any particular climatic rule. It has been hypothesized that it may be the result of other factors, like predation and human encroachment.

They have a flat tail, covered with dense, brown fur that can trap a layer of insulating air. The tail is also used for storing fat tissue.



Platypuses swimming at the Sydney Aquarium, Sydney, Australia


They have webbed feet and a large rubbery snout, giving them a duck-like appearance.  Unlike birds, the snout doesn't open and acts as a sensory organ, with two types of receptors, electroreceptors and mechanoreceptors.. The electroreceptors are located in rostrocaudal rows inside the skin of the bill, whereas the mechanoreceptors (touch-sensing receptors) are uniformly distributed across the bill. The electroreception ability is explained later in the article.

The nostrils are found on the snout's dorsal surface, whereas the eyes and ears are placed in a groove set, just back from it. This groove closes when they swim. Unlike other mammals, they use an alternate rowing motion using only their front feet to propel themselves while swimming. The hind feet (which are held against the body) and the tail are used for steering.

Unlike placental animals that have an average body temperature close to 37°C (99°F), the platypus has a body temperature of only 32 °C (90 °F). Studies suggest that this is a gradual adaptation to the harsh environmental conditions they are commonly exposed to, rather than an evolutionary trait of the monotreme order.

It takes them 2 years to reach sexual maturity. In captivity, platypuses have survived to be up to 17 years old whereas in the wild, there have been reports of  up to 11 years old individuals.


A platypus swimming in a Tasmanian creek
Platypus swimming in a creek , somewhere in Tasmania
Credit: Claus

What makes them so unique?
The species has many particularly strange traits, considering its mammalian nature:
  • Electrolocation
  • It lays eggs, instead of giving birth to youngs
  • Produces venom

Now let's see these three traits in more detail.

Electrolocation
Platypuses belong to the monotreme order, which is the only known order containing mammals with the ability of electrolocation, with the exception of at least one species of dolphin (Sotalia guianensis). In simple words, the sense of electrolocation allows these strange animals to sense the electrical fields produced by the muscular contractions of other animals. Electrolocation is primarily used to detect prey.

It is believed that the platypus is able to determine the direction of an electric source by comparing differences in signal strength across the sheet of electroreceptors. This also explains the characteristic side-to-side motion of the platypus's head when it hunts. The cortical convergence of electrosensory and tactile inputs suggests a mechanism for determining the distance of prey items which, when they move, emit both electrical signals and mechanical pressure pulses; the difference between the times of arrival of the two signals would allow computation of distance.

When underwater, the animal closes its eyes, ears, and nose. Electrolocation is the only sense they are essentially left with. Surviving without it would be practically impossible, as they would not be able to prey at all.

Platypus skeleton  at Melbourne Museum
Platypus skeleton  at Melbourne Museum


Venom
Another interesting fact is that they are one of they very few venomous mammals. Some other notable mammalian examples are:
  • The Cuban solenodon (Solenodon cubanus) and the Hispaniolan solenodon (Solenodon paradoxus)
  • Several shrew species like the American short-tailed shrew (Blarina brevicauda) and the Mediterranean water shrew (Neomys anomalus)
  • The common vampire bat (Desmodus rotundus)

Both male and female platypuses are born with ankle spurs which produce a venom containing many different toxic proteins. The venom is primarily composed of defensin-like proteins (DLPs), three of which are unique to the species. The venom is produced by the male's crural, kidney-shaped alveolar glands, connected by a thin-walled duct to a calcaneus spur on each hind limb. Females have rudimentary spur buds that do not develop, instead they drop off  before they reach the age of 1 years old  and lack any functional crural glands. In most females, the spurs are dropped before they reach the age of three months.

The venom is powerful enough to paralyze or kill small animals, like dogs and cats but not humans. Although non lethal to humans, it can be extremely painful, many times leaving the victim incapacitated. Typically, an edema develops very rapidly around the wound and slowly but steadily spreads throughout the rest of the limb.

According to a few sources, the venom may cause a long-lasting hyper-algesia (heightened pain sensitivity), that may persist for days, months, perhaps even years. In 1991, Keith Payne, a former member of the Australian Army and recipient of the Victoria Cross, was struck on his hand by a stranded platypus, while he was trying to rescue it. Payne described the pain to be worse than that of grenade shrapnel. One month later he was still experiencing pain in that hand. More than a decade later, in 2006, Payne reported discomfort and stiffness when carrying out certain physical activities, like using a hammer.

As aforementioned, the venom is exclusively produced by males, with production levels rising during mating. This is why it is speculated that it may be used as a means of asserting dominance between males.

Image showing the venom-delivering spur in a male platypus
The venom-delivering spur is found only on the
hind limbs of males

Egg-laying & Reproduction
Finally, the last strange thing about platypuses is that they lay eggs. The only other surviving mammals that lay eggs are the four extant Echidna species.

The species breeds once every year, with mating occurring sometime between June and October. Most studies indicate a polygamous mating system.

During the non-mating period, individuals live in a simple ground burrow, with an entrance that is about 30 cm (12 in) above water level, however after mating has occurred, the female platypus constructs a deeper and more complex burrow, with a length of up to 20 m (66 feet). The burrow is blocked at intervals with plugs, a safeguard against rising waters, predators and possibly as a means of regulating humidity and temperature. The female  also uses fallen leaves and reeds at the end of the burrow, to create a soft nest where she will later lay her eggs. The female drags the required building materials by tucking them underneath her curled tail As for males, they simply return to their year-long burrows and take no participation in "child-raising".

Female platypuses lay 1-3 (2 in average) small and leathery eggs, with a diameter of 11 mm (~0.4 in). They develop inside the utero for 28 to 30 days and are incubated for 10 days. The newborn hatchlings are very vulnerable, blind and hairless and suck milk from the mother's porous milk patches (platypuses have no nipples) ,taking them about 4-5 months to wean. Hatchlings are born with teeth that quickly fall of, leaving only the horny plates with which they grind their food.

During the first month after hatching, the mother leaves the burrow for very small periods, only to forage. When she does so, she first creates many thin soil plugs along the burrow, most probably to protect the offsprings from predators. When she returns and pushes herself through them, the water on her fur stays on these plugs and as a result the burrow remains dry. After the first month, she starts spending less and less time with her youngs, until they are completely weaned.

Platypus in Broken River, Queensland, Australia
Platypus swimming in Broken River, Queensland


Behavior
Platypuses are nocturnal and crepuscular animals (mainly active during dawn and dusk), although they do show some activity during the day, especially when the sky is overcast. Each individual's "home" range is thought to be up to 7 km (4.3 miles), with a male's range overlapping those of 3-4 females.

Platypuses are excellent swimmers, spending much of their time in the water, searching for prey using their electroreception. Each dive lasts for about 30 seconds, while recovery at surface, anywhere from 10 to 20 seconds. Very rarely does a dive last for more than 30 seconds. Dives of more than 40 seconds are extremely rare.

When not in the water, the platypus returns to its small resting burrow. The burrow is usually built near the riverbank and not far above water level. These burrows are typically hidden under a protective tangle of roots.

Platypuses in the wild have been observed to emit a low growl when disturbed. In captivity, researchers have observed a wide range of other vocalizations.

They sleep for up to 14 hours per day.

Predators
The species has many natural predators, including:
  • Eagles
  • Goannas ( large lizards of the genus Varanus)
  • Hawks
  • Owls
  • Red foxes
  • Snakes
  • Water Rats
Despite having many natural predators, the species mortality rate in the wild is quite low. Even introduced animals, like the red fox, have had only a minor impact on their numbers.



Video about platypuses by National Geographic

Diet
They are carnivorous animals, mainly feeding on:
  • Annelid worms ( segmented worms of the phylum Annelida)
  • Freshwater shrimps
  • Insect larvae
  • Yabbies freshwater crayfish

The platypus either uses the snout to dig out prey, or directly catches it while it swims. Next, it will use the cheek-pouches to carry it on the surface, where it is consumed. To retain their body mass, platypuses need to eat about 20% of their own weight on a daily basis. This is why they sometimes spend up to 12 hours of the day foraging.


Another short-video about platypuses by National Geographic


Conservation status & Threats
The European settlement in Australia resulted in many species going extinct or having their numbers greatly reduced. Fortunately, this is not the case with the Platypus. Other than its loss from the state of South Australia, the species now has about the same distribution as it did some hundred years ago. In South Australia, the species extinction was most probably the result of declining water quality due to extensive land clearing and irrigation schemes. Recently, a small population was introduced on the Kangaroo Island in South Australia, along with other animals,  including Koalas and Cape Barren Geese (a large goose species).

Today, most populations are stable and healthy, with platypuses being a very common sight in most places within their distribution. However, this was a very different story 50 years ago. Deforestation, dams, irrigation projects and other human related activities like hunting, threatened the survival of the species. The introduction of red foxes in 1845 for hunting, also had a minor impact on their numbers. However, thanks to the combined efforts of the Australian government and other organizations, the populations have greatly recovered and even returned to areas from where they had gone extinct.

Recently a new threat has appeared, a disease called mucormycosis, caused by the Mucor amphibiorum fungus. For now, only Tasmanian platypuses have been affected. There have been no sighs of the disease in mainland Australia. Diseased animals develop skin lesions or ulcers in many areas of their body, including the back, tail and legs. The disease affects the animal's capacity to retain body temperature and to hunt effectively. The disease is many-times lethal, with most individuals dying from secondary infections and/or starvation.

Today, the species is listed by the IUCN as of least concern and has a presumably bright future, with no immediate threats on the horizon.


A guy playing with a young platypus at Healesville Sanctuary, near Melbourne.
Such a lucky guy

In captivity
In Australia, Platypuses are exhibited in numerous aquariums, at the following wildlife sanctuaries:

1) Queensland
  • Platypus House at Lone Pine Koala Sanctuary in Brisbane
  • David Fleay Wildlife Park, Gold Coast
  • Lone Pine Koala Sanctuary, Brisbane
  • Walkabout Creek Wildlife Centre, Brisbane

2) New South Wales
  • Taronga Zoo, Sydney
  • Sydney Aquarium, Sydney
  • Australian Reptile Park, Foster

3) Victoria
  • Healesville Sanctuary, near Melbourne, Victoria

4) South Australia
  • Warrawong Sanctuary near Mylor in the Adelaide Hills (near Adelaide), South Australia.

As of 2013, no zoo outside of Australia exhibits these strange animals. In the past, there were three attempts to bring a few individuals to the Bronx Zoo, in 1922, 1947, and 1958. The first platypus, a male, arrived on 14th July 1922 but died less than two months later, on 30th August 1922. On 28th April 1947, one male (Cecil) and two females (Betty & Penelope) went on exhibit in Bronx Zoo. Betty died of pneumonia on 6th September 1948. The other two lived much longer, but Penelope "went missing" on 1st August 1957 whereas Cecil died on 18th September 1957. Three more platypuses, a male and two females, arrived on 7th June 1958. This bunch didn't do well, with the longest living of them dying less than 2 years later, on 25th March 1959.

Breeding in captivity has proven to be possible, but not easy. The first successful attempt was made by David Fleay, an Australian naturalist, who also established the first platypusary, a simulated stream in a tank that is capable of sustaining one or more platypuses. The first platypusary was established at the Healesville Sanctuary, where breeding first took place in 1943. Since then, there have been at least four more succesfull attempts, all at the Taronga Zoo, Sydney in 1998, 2000, 2003 and 2006. Furthermore, 1972, Fleay discovered a dead young of about 50 days old, which had presumably been born in captivity, at his wildlife park at Burleigh Heads on the Gold Coast, Queensland.

Platypus House at Lone Pine Koala Sanctuary in Brisbane, Queensland, Australia
Platypus House at Lone Pine Koala Sanctuary in Brisbane, Queensland


Other Interesting Facts about the Platupus
- Recent studies indicate that the eyes of the platypus may be more similar to those of the Pacific hagfish (Eptatretus stoutii) than to those of most tetrapods. Their eyes also feature double cones, something very rare in mammals.
- When the platypus was first discovered by European naturalists, it created great dispute on whether females laid eggs or not. Many even believed the animal was a hoax! The dispute was finally cleared in 1884, when William Hay Caldwell (1859-1941), a Scottish zoologist was sent to Australia, where he and his team of 150 Aborigines, managed to discover a few eggs. Due to the high cost per word, Caldwell famously wired London, "Monotremes oviparous, ovum meroblastic."  meaning that platypuses are "monotremes, egg-laying with the eggs being similar to those of reptiles in that only part of the egg divides as it develops."
-  On average, each platypus has about 40,000 electroreceptors on its bill. In contrast, the long-billed echidna (Tachyglossus bruijni) has only 2,000.
- The species scientific name Ornithorhynchus anatinus is derived from the Greek word "ορνιθόρυνχος" (ornithorhynkhos), which roughly translates to "bird snout"; and anatinus, which means "duck-like" in Latin.
- There is no universally agreed plural for the word platypus. Most scientists prefer the term "platypuses" or just "platypus". Sometimes, the term "platypi" is used instead, although it is technically incorrect and a form of pseudo-latin. If we were to remain true to the Greek spirit, we would use the word "platypodes".
- Early British settlers used many names for the animal, including "watermole", "duckbill", and "duckmole".
- The platypus is an iconic symbol of Australia, appearing as the main mascot of national events, teams etc. It is also featured on the reverse of the Australian 20-cent coin and is the animal emblem of the state of New South Wales.

You may also like
  • EchidnaEchidnas are animals of the family Tachyglossidae. Along with the platypus, they are the only surviving monotreme members. Similarly, they lay eggs and have electroreception.



Selected References & Further Reading
- Hall, B. (1999). The Paradoxical Platypus BioScience, 49 (3) DOI: 10.2307/1313511
- Dawson, T., Grant, T., & Fanning, D. (1979). Standard Metabolism of Monotremes and the Evolution of Homeothermy. Australian Journal of Zoology, 27 (4) DOI: 10.1071/ZO9790511
- Bethge, P., Munks, S., Otley, H., & Nicol, S. (2003). Diving behaviour, dive cycles and aerobic dive limit in the platypus Ornithorhynchus anatinus Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 136 (4), 799-809 DOI: 10.1016/S1095-6433(03)00198-3
- Leon Hughes, R., & Hall, L. (1998). Early development and embryology of the platypus Philosophical Transactions of the Royal Society B: Biological Sciences, 353 (1372), 1101-1114 DOI: 10.1098/rstb.1998.0269
- Manger PR, Hall LS, & Pettigrew JD (1998). The development of the external features of the platypus (Ornithorhynchus anatinus). Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 353 (1372), 1115-25 PMID: 9720109
- Hawkins, M., & Battaglia, A. (2009). Breeding behaviour of the platypus (Ornithorhynchus anatinus) in captivity Australian Journal of Zoology, 57 (4) DOI: 10.1071/ZO09090
- Connolly, J. (2009). A review of mucormycosis in the platypus (Ornithorhynchus anatinus) Australian Journal of Zoology, 57 (4) DOI: 10.1071/ZO09043
- Furlan E, Stoklosa J, Griffiths J, Gust N, Ellis R, Huggins RM, & Weeks AR (2012). Small population size and extremely low levels of genetic diversity in island populations of the platypus, Ornithorhynchus anatinus. Ecology and evolution, 2 (4), 844-57 PMID: 22837830
- de Plater, G., Martin, R., & Milburn, P. (1995). A pharmacological and biochemical investigation of the venom from the platypus (Ornithorhynchus anatinus) Toxicon, 33 (2), 157-169 DOI: 10.1016/0041-0101(94)00150-7
- Lee S. Crandall, The Management of Wild Mammals in Captivity. University of Chicago Press, 1964.

4 comments:

  1. I toughtthis was a very intresting animal

    ReplyDelete
  2. dude ive never heaerd off a platapus
    well i have but not much

    ReplyDelete
  3. anniled worms what the heck that is a weird diet

    ReplyDelete
  4. How did a duck and beaver have a baby

    ReplyDelete