Sugar glider

Sugar glider[1]
Illustration by Neville Cayley
Conservation status
Least Concern  (IUCN 3.1)[2]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Infraclass:	Marsupialia
Order:	Diprotodontia
Family:	Petauridae
Genus:	Petaurus
Species:	P. breviceps
Binomial name
Petaurus breviceps Waterhouse, 1839[3]
Range map of the formerly recognized subspecies of sugar glider:[note 1]    P. b. breviceps (introduced in Tasmania)    P. b. longicaudatus    P. b. ariel[note 2]    P. b. flavidus[note 3]    P. b. tafa[note 4]    P. b. papuanus    P. b. biacensis[note 5]
Synonyms
P. (Belideus) breviceps,  Waterhouse 1839 P. kohlsi,  Troughton 1945[7]

The sugar glider (Petaurus breviceps) is a small,

The sugar glider, as strictly defined in a recent analysis, is only native to a small portion of southeastern Australia, corresponding to southern Queensland and most of New South Wales east of the Great Dividing Range; the extended species group, including populations which may or may not belong to P. breviceps, occupies a larger range covering much of coastal eastern and northern Australia, New Guinea, and nearby islands.^[4][5] Members of Petaurus are popular exotic pets; these pet animals are also frequently referred to as "sugar gliders", but recent research indicates, at least for American pets, that they are not P. breviceps but a closely related species, ultimately originating from a single source near Sorong in West Papua.^[12] This would possibly make them members of the Krefft's glider (P. notatus), but the taxonomy of Papuan Petaurus populations is still poorly resolved.^[13]

Taxonomy and evolution

The genus Petaurus is believed to have originated in New Guinea during the mid Miocene epoch, approximately 18 to 24 million years ago. The modern Australian Petaurus, along with New Guinean members of what were formerly considered P. breviceps, diverged from their closest living New Guinean relatives ~9-12 mya. They probably dispersed from New Guinea to Australia between 4.8 and ~8.4 mya, with the oldest Petaurus fossils in Australia being dated to 4.46 million years.^[14] This may have been possible due to sea level lowering from about 7 to 10 mya, resulting in land bridges between New Guinea and Australia.

The taxonomy of the species is complex, and is still not fully resolved. It was formerly understood to have a wide range across Australia and New Guinea, being the only glider to have this distribution, and to be divided into seven subspecies, with three occurring in Australia and four in New Guinea.^[15] This traditional subspecific division was based on small morphological differences, such as colour and body size.^[14] However, a 2010 genetic analysis using mitochondrial DNA indicates that these morphologically-defined subspecies may not represent genetically unique populations.^[15]

Further studies have found significant genetic variation within populations traditionally classified in P. breviceps, sufficient to warrant splitting the species into multiple. The subspecies P. b. biacensis, from Biak Island off of New Guinea, was reclassified as a separate species, the Biak glider (Petaurus biacensis).^{[note 5]} In 2020, a landmark study suggested that P. breviceps actually comprised three cryptic species: the Krefft's glider (Petaurus notatus), found throughout most of eastern Australia and introduced to Tasmania, the savanna glider (Petaurus ariel), native to northern Australia, and a more narrowly defined P. breviceps, restricted to a small section of coastal forest in southern Queensland and most of New South Wales. In addition, other sugar glider populations throughout this range (such as those on New Guinea and the Cape York Peninsula) may represent undescribed species or be conspecific with previously described species. This indicates that contrary to previous findings of a large range (which in fact applied to P. notatus and, to a lesser extent, to P. ariel), P. breviceps is a range-restricted species that is sensitive to ecological disasters, such as the 2019-20 Australian bushfires, which significantly affected large portions of its habitat.^[4][5][16]

P. breviceps and P. notatus are estimated to have diverged ~1 million years ago, and may have originated from long term geographic isolation. The early-mid Pleistocene saw an uplifting of the Great Dividing Range, contributing to and coinciding with aridification of the interior of Australia, including on the western side of the range.^[15] This, as well as other climactic and geographic factors, may have isolated the ancestors of P. breviceps to refugia on the eastern, coastal side of the Great Dividing Range.^[4] This would be an example of allopatric speciation.

Distribution and habitat

Sugar gliders are distributed in the coastal forests of southeastern Queensland and most of New South Wales. Their distribution extends to altitudes of 2000m in the eastern ranges. In parts of its range, it may overlap with Krefft's glider (P. notatus).^[5][17]

The sugar glider occurs in

Like all arboreal, nocturnal marsupials, sugar gliders are active at night, and they shelter during the day in tree hollows lined with leafy twigs.[19]

The average home range of sugar gliders is 0.5 hectares (1.2 acres), and is largely related to the abundance of food sources;^[20] density ranges from two to six individuals per hectare (0.8–2.4 per acre).

Native owls (

The sugar glider has a squirrel-like body with a long, partially (weakly)^[22] prehensile tail. The length from the nose to the tip of the tail is about 24–30 cm (9–12 in), and males and females weigh 140 and 115 grams (5 and 4 oz) respectively.^[23] Heart rate range is 200–300 beats per minute, and respiratory rate is 16–40 breaths per minute.^[24] The sugar glider is a sexually dimorphic species, with males typically larger than females. Sexual dimorphism has likely evolved due to increased mate competition arising through social group structure; and is more pronounced in regions of higher latitude, where mate competition is greater due to increased food availability.^[25]

The fur coat on the sugar glider is thick, soft, and is usually blue-grey; although some have been known to be yellow, tan or (rarely)

Each foot on the sugar glider has five digits, with an opposable toe on each hind foot. These opposable toes are clawless, and bend such that they can touch all the other digits, like a human thumb, allowing it to firmly grasp branches. The second and third digits of the hind foot are partially syndactylous (fused together), forming a grooming comb.^[22] The fourth digit of the forefoot is sharp and elongated, aiding in extraction of insects under the bark of trees.^[17]

The gliding membrane extends from the outside of the fifth digit of each forefoot to the first digit of each hind foot. When the legs are stretched out, this membrane allows the sugar glider to glide a considerable distance. The membrane is supported by well developed tibiocarpalis, humerodorsalis and tibioabdominalis muscles, and its movement is controlled by these supporting muscles in conjunction with trunk, limb and tail movement.^[11]

Lifespan in the wild is up to 9 years; is typically up to 12 years in captivity,^[10] and the maximum reported lifespan is 17.8 years.^[27]

Biology and behaviour

Gliding

The sugar glider is one of a number of

This form of arboreal locomotion is typically used to travel from tree to tree; the species rarely descends to the ground. Gliding provides three dimensional avoidance of arboreal predators, and minimal contact with ground dwelling predators; as well as possible benefits in decreasing time and energy consumption^[29] spent foraging for nutrient poor foods that are irregularly distributed.^[30] Young carried in the pouch of females are protected from landing forces by the septum that separates them within the pouch.^[26]

Torpor

Sugar gliders can tolerate ambient air temperatures of up to 40 °C (104 °F) through behavioural strategies such as licking their coat and exposing the wet area, as well as drinking small quantities of water.^[17] In cold weather, sugar gliders will huddle together to avoid heat loss, and will enter torpor to conserve energy.^[31] Huddling as an energy conserving mechanism is not as efficient as torpor.^[31] Before entering torpor, a sugar glider will reduce activity and body temperature normally in order to lower energy expenditure and avoid torpor.^[32][33] With energetic constraints, the sugar glider will enter into daily torpor for 2–23 hours while in rest phase.^[31] Torpor differs from hibernation in that torpor is usually a short-term daily cycle. Entering torpor saves energy for the animal by allowing its body temperature to fall to a minimum of 10.4 °C (50.7 °F)^[31] to 19.6 °C (67.3 °F).^[34] When food is scarce, as in winter, heat production is lowered in order to reduce energy expenditure.^[35] With low energy and heat production, it is important for the sugar glider to peak its body mass by fat content in the autumn (May/June) in order to survive the following cold season. In the wild, sugar gliders enter into daily torpor more often than sugar gliders in captivity.^[33][34] The use of torpor is most frequent during winter, likely in response to low ambient temperature, rainfall, and seasonal fluctuation in food sources.^[31]

Diet and nutrition

Sugar gliders are seasonally adaptive omnivores with a wide variety of foods in their diet, and mainly forage in the lower layers of the forest canopy.

To obtain sap or gum from plants, sugar gliders will strip the bark off trees or open bore holes with their teeth to access stored liquid.[36] Little time is spent foraging for insects, as it is an energetically expensive process, and sugar gliders will wait until insects fly into their habitat, or stop to feed on flowers.^[36] Gliders consume approximately 11 g of dry food matter per day.^[29] This equates to roughly 8% and 9.5% of body weight for males and females, respectively.

They are

The age of sexual maturity in sugar gliders varies slightly between the males and females. Males reach maturity at 4 to 12 months of age, while females require from 8 to 12 months. In the wild, sugar gliders breed once or twice a year depending on the climate and habitat conditions, while they can breed multiple times a year in captivity as a result of consistent living conditions and proper diet.[22]

A sugar glider female gives birth to one (19%) or two (81%) babies (joeys) per litter.

Breeding is seasonal in southeast Australia, with young only born in winter and spring (June to November).[20] Unlike animals that move along the ground, the sugar glider and other gliding species produce fewer, but heavier, offspring per litter. This allows female sugar gliders to retain the ability to glide when pregnant.^[49]

Socialisation

Sugar gliders are highly social animals. They live in family groups or colonies consisting of up to seven adults, plus the current season's young. Up to four age classes may exist within each group, although some sugar gliders are solitary, not belonging to a group.^[20] They engage in social grooming, which in addition to improving hygiene and health, helps bond the colony and establish group identity.

Within social communities, there are two codominant males who suppress subordinate males, but show no aggression towards each other. These co-dominant pairs are more related to each other than to subordinates within the group; and share food, nests, mates, and responsibility for scent marking of community members and territories.^[50]

Territory and members of the group are marked with saliva and a scent produced by separate glands on the forehead and chest of male gliders. Intruders who lack the appropriate scent marking are expelled violently.^[8] Rank is established through scent marking; and fighting does not occur within groups, but does occur when communities come into contact with each other.^[17] Within the colony, no fighting typically takes place beyond threatening behaviour.^[51] Each colony defends a territory of about 1 hectare (2.5 acres) where eucalyptus trees provide a staple food source.^{[citation needed]}

Sugar gliders are one of the few species of mammals that exhibit male parental care.^[52] The oldest codominant male in a social community shows a high level of parental care, as he is the probable father of any offspring due to his social status. This paternal care evolved in sugar gliders as young are more likely to survive when parental investment is provided by both parents.^[52] In the sugar glider, biparental care allows one adult to huddle with the young and prevent hypothermia while the other parent is out foraging, as young sugar gliders aren't able to thermoregulate until they are 100 days old (3.5 months).^[52]

Communication in sugar gliders is achieved through vocalisations, visual signals and complex chemical odours.^[17] Chemical odours account for a large part of communication in sugar gliders, similar to many other nocturnal animals. Odours may be used to mark territory, convey health status of an individual, and mark rank of community members. Gliders produce a number of vocalisations including barking and hissing.^{[citation needed]}

Human relations

Conservation

Under the prior taxonomy, the sugar glider was not considered endangered, and its conservation rank was "Least Concern (LC)" on the IUCN Red List.^[2] However, with newer taxonomic studies indicating that it has a small and restricted range, it is now thought to be far more sensitive to potential threats. For example, the species' native range was hit hard by the 2019-20 Australian bushfires, which occurred just a few months prior to the publishing of the study indicating the true extent of its range. Sugar gliders use tree hollows, making them especially sensitive to intense fires.^[53] However, despite the loss of natural habitat in Australia over the last 200 years, it is adaptable and capable of living in small patches of remnant bush, particularly if it does not have to cross large expanses of cleared land to reach them. Sugar gliders may persist in areas that have undergone mild-moderate selective logging, as long as three to five hollow bearing trees are retained per hectare.^[54] Although not currently threatened by habitat loss, the ability of sugar gliders to forage and avoid predators successfully may be decreased in areas of high light pollution.^[55]

In captivity, the sugar glider can suffer from calcium deficiencies if not fed an adequate diet. A lack of calcium in the diet causes the body to leach calcium from the bones, with the hind legs first to show noticeable dysfunction.^[58] Calcium to phosphorus ratios should be 2:1 to prevent hypocalcemia, sometimes known as hind leg paralysis (HLP).^[59] Their diet should be 50% insects (gut-loaded) or other sources of protein, 25% fruit and 25% vegetables.^[60] Some of the more recognised diets are Bourbon's Modified Leadbeaters (BML),^[61] High Protein Wombaroo (HPW)^[62] and various calcium rich diets with Leadbeaters Mixture (LBM).^[63] Iron storage disease (hemochromatosis) is another dietary problem that has been reported in captive gliders and can lead to fatal complications if not diagnosed and treated early.^[64]

A large amount of attention and environmental enrichment may be required for the highly social species, especially for those kept as individuals. Inadequate social interaction can lead to depression and behavioural disorders such as loss of appetite, irritability and self-mutilation.^[65]

As a pet

In several countries, the sugar glider (or what was formerly considered to be the sugar glider) is popular as an

DNA analysis indicates that "the USA (sugar) glider population originates from West Papua, Indonesia with no illegal harvesting from other native areas such as Papua New Guinea or Australia".^[12] Given that the West Papuan gliders have been tentatively classified as Krefft's gliders (albeit to be changed in the future),^[13] this indicates that at least the captive gliders kept in the United States are Krefft's gliders, not sugar gliders.

Notes

Species notes