gabbywild

Global adventures of a windblown, thrill-driven aspiring veterinarian

Wacky Wednesday: The Phalangerids January 18, 2012

Phalangerids are a family of marsupials from Australia & New Guinea and include species such as brushtail possums and cuscuses.  Supposedly 26 phalangerid species exist, but most of them remain very elusive due to their clandestine behavior hidden in dense rain forests. The most common phalangerid is the common brushtail possum, and thus it is the one we know most about. Scarily, though, we know very little about the more threatened cuscus. 

Although these Down Under babies can be found from the outback boondocks to the suburbs of Australian cities, these Australian creatures are thought to have originated in rain forests from mainland Australia. They can now be found in Australia, New Guinea, and in adjacent islands as far west as Sulawesi and as far east as the Solomon Islands. The common brushtail poosum was introduced to New Zealand. They are predominantly nocturnal creatures (except for the bear cuscus of Sulawesi), and they are arboreal.

The two “poster children” of phalangerids we will discuss are the cuscuses and brushtail possums.

Cuscuses and brushtail possums are different from one another in several ways (other than obvious genetic and physical characteristics- please see the photos):

1) The cecum of some subspecies of cuscus is actually able to sort particles, providing its leafy diet with a sense of being more specialized.

2) They are distributed differently geographically. Cuscuses live mainly on smaller islands or in the highlands of mountains. Thus there are more subspecies of cuscus than there are of the common brushtail possum.

3) They express their glands differently. For example, in addition to expressing secretions from their sternal and paracloacal glands, cuscuses release a reddish brown secretion from their faces when they are distressed, especially around their eyes.

4) Different subspecies eat different proportions of food and even totally different diets, such as some being almost entirely leaf-eaters while some subspecies of cascus eating exclusively fruits.

5) The brushtail possums, and not the cuscuses or the scaly-tailed possum, posses a cartilaginous laryngeal resonance chamber to boom out sound.

What do phalangerids have for dinner? Mostly they just consume leaves, but according to their skull anatomy, dentition patterns, and some scientific observation, they also can eat fruits, invertebrates, eggs, and a small vertebrate here and there. In some areas, the common brushtail possum eats 95% eucalyptus leaves. In the tropical woodlands, up to 53% of the diet can consists of Cooktown ironwood, which is actually extremely toxic to cattle. With such a leafy diet rich in cellulose & hemicellulose, obviously a little bit of microbial digestion is needed. Thus these guys actually use a great deal of hingut fermentation to digest their food. Thus they have a larger colon and cecum so that they retain food for longer.

Do phalangerids chemically text message? Well, sort of- just without a phone, of course. Because they are so solitary, they commonly use four types of scent glands to get each other’s attention.

In the common brushtail possum, mainly it is the males that wipe their secretions from their mouthes and chest glands on branches of trees. They also deposit sinuous urine trails that cells from their paracloacal glands onto branches. The reason for doing so is to let all the other bros around know that he’s there. It allows for a phalangerid to declare his/her presence and attempt to mark his/her territory. Females mainly produce a very sticky, jelly-like secretion from their cloaca that is purposefully smeared onto branches during their estrous cycle. They smear this out in order to tell males, “I’m ready to mate. Come and get me.” And trust me, they do.

And they are chitty chatty, too! The brushtail possums are one of the most vocal of the marsupials with humans able to hear their calls from up to 1,000 ft. away. They have 7 basic calls: the buccal click, the agonistic grunt, the hiss, the loud screech, the alarm chatter, the soft “appeasement call” of the male, and the young brushtail possum “contact call”. What helps augment their sound is the presence of a cartilaginous laryngeal resonance chamber that is unique to this genus.

Common brushtails are loners except when breeding or rearing young, which usually leave at the end of their 3rd or 4th year to create their own little “home” that encloses from 1-2 den trees within their home range that they mark and defend against others of the same sex. Individuals of the opposite sex or of “lower social rank” are “tolerated” within one of those areas that they mark. How they determine social rank remains elusive.

Females will defend themselves 1 m from a male, but during the breeding season (even though the female still gets a little peeved), the male sends her very soft calls to appease her until he becomes her “consort male”. If there is no “consort male” present, several males may try to take over a female at the same time while she is in estrus. Agonistic behavior, which is behavior that involves both threatening and submissive behavior between competitors or mates, that follows mating.

After mating, males from the lower-elevation and tropical more climes become completely disinterested in the female, gets up and leaves without even asking for a eucalyptus sandwich! These males play no role in rearing the young. Unfortunately, I have heard of similar social problems in our species.

Common brushtails from the mountains actually tend to form long-term pair-bonds and remain monogamous. Males even take great care for their young. It is hypothesized that the more stable environment may be the cause for this. At this time it seems that only bear cuscuses, the largest and most diurnal phalangerid, maintain long-term pair-bonding.

Unfortunately, these creatures are threatened. Between 1923-1959, over 1,000,000 pelts of common brushtails were exported from Tasmania. Recently this has slowed down, especially in eastern Australia, but still cuscuses have been experiencing poaching difficulties, as unfortunately they sleep openly on branches. Another problem that the common brushtails experience is that they can be infected with bovine tuberculosis- a discovery of 1970. This led to the fear that the common brushtail could re-infect cattle, so a very costly poisoning program was established with the hope to exterminate all infected common brushtails in New Zealand.

The situation has dulled down a little bit, but loss in population size, especially for the endangered Telefomin and Black-spotted cuscuses are frightening. We need all you readers to stay wild for them!

Stay Wild,

Gabby Wild

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