Tupaia palawanensis

Geographic Range

The Palawan treeshrew ( Tupaia palawanensis ) is endemic to the Palawan island region of the Philippines (Esselstyn et al., 2004) and the nearby islands of Culion, Busuanga, and Cuyo (Sargis et al., 2014).

• Biogeographic Regions
• oriental oriental
  • native native

• Other Geographic Terms
• island endemic island endemic

Habitat

Palawan treeshrews mainly inhabit low-elevation forests but are occasionally found in montane forests or agricultural areas (Esselstyn et al., 2004). Palawan's forests are diverse and include tropical and coniferous rainforests, casuarina forests, and scrub forests (Ventura, 2000).

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest
• rainforest rainforest
• scrub forest scrub forest

• Other Habitat Features
• agricultural agricultural

Physical Description

As with all treeshrews, the Palawan treeshrew has a squirrel-like appearance, with fur covering the body and tail. The dorsum of Tupaia palawanensis is an ochre color with a darker midline and reddish tones towards the posterior. The legs and feet are of similar coloration to the body, except black-colored 5 toes. They typically do not have long vibrissae (Lyon, 1913).

All treeshrews have dilambdodont molars and a dental formula of I 2/3, C 1/1, P 3/3, M 3/3 (Lyon, 1913). The middle four the lower incisors form a tooth comb similar to that of lemurs. However, treeshrew tooth combs do not include the canines (Rose et al., 1981).

A distinguishing feature of treeshrew skulls is a complete post-orbital bar (Clark, 1925). An elongate nose (Merritt, 2010) and forward-facing eyes (Fuchs and Corbach-Söhle, 2010) are also characteristic of treeshrews. Small lateral ridges of hardened tissues are found along the palate of treeshrews. They are complete in adults and may aid in eating fruits (Emmons, 2000). Palatal ridges of developing young are incomplete due to a depression along the midline. This may be a way to more efficiently channel milk down the throat when nursing (Martin, 1968).

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

Reproduction

Most treeshrew species are monogamous, although this is unknown for T. palawanensis (Fuchs and Corbach-Söhle, 2010; Merritt, 2010).

• Mating System
• monogamous monogamous

The natal nest is made by the male in most treeshrew species (Merritt, 2010). There is some evidence that delayed implantation may occur in Tupaia (Hayssen et al., 1993). In T. palawanensis , females have two pairs of mammary glands. Males have a permanent sac for the testes, which are anterior to the penis, and an ampullary gland (Hayssen et al., 1993; Merritt, 2010).

Although unknown for the Palawan treeshrew, other treeshrews go about 45 weeks between births in captivity. Near the end of the 41- to 55-day gestation, the male is especially attracted to the female and attempts frequent copulation. Only after giving birth will the female allow mating to occur (Martin, 1968; Fuchs and Corbach-Söhle, 2010). Breeding season is unknown for the Palawan treeshrew. Other treeshrew species appear to breed year round (Nowak, 1999).

Typically, treeshrews have 1 to 3 offspring per litter that are born without fur and with eyes closed (Hayssen et al., 1993). Newborn treeshrews weigh from 6 to 10 g and are weaned within 30 days (Fuchs and Corbach-Söhle, 2010). Both males and females reach sexual maturity in 2 to 4 months (Fuchs and Corbach-Söhle, 2010; Merritt, 2010; Nowak, 1999).

• Key Reproductive Features
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous viviparous

Treeshrews are unique for their system of absentee maternal care. The female gives birth in a natal nest (which is separate from the parental nest), nurses the newborns, and then leaves. She returns every two days and delivers 5 to 15 g of milk to her young in short bouts of nursing lasting 5 to 15 minutes. The milk is approximately 10% protein, 25% fat, and 2% sugar. The young remain inactive between nursings, possibly because of the milk's low sugar content. The high fat content most likely helps the young maintain a high body temperature while the mother is gone (Merritt, 2010). The young treeshrews groom themselves from birth, not interacting with the mother other than during nursing (Martin, 1968). After about 1 month the young follow the mother to the parental nest and remain there until sexual maturity (Merritt, 2010).

• Parental Investment
• altricial altricial
• female parental care female parental care
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
• pre-independence
  • provisioning
    • female
• post-independence association with parents

Lifespan/Longevity

The lifespan of T. palawanensis is unknown. The longest lifespan in captivity for a Tupaia treeshrew was a T. glis that lived for 12 years and 5 months (Nowak, 1999). The expected lifespan in captivity for a treeshrew is 9 to 12 years (Fuchs and Corbach-Söhle, 2010).

Behavior

Most treeshrews are diurnal and forage almost constantly during the day, taking short breaks between searches (Emmons, 1991; Nowak, 1999). Both sexes are territorial. At night, the monogamous pair will sleep in the same nest along with any weaned, sexually immature offspring. Unweaned offspring sleep in a separate nest (Martin, 1968). Nests are usually made in fallen trees or tree roots (Nowak, 1999).

• Key Behaviors
• terricolous
• diurnal diurnal
• motile motile
• territorial territorial

Home Range

The approximate home ranges for males and females are 2,300 m^2 and 2,000 m^2, respectively. Male territories are 1 to 5 ha, and about 1 ha in females (Dimalibot, 2010).

Communication and Perception

Treeshrews do not appear to use vocalizations to communicate (Benson et al., 1992). Although vocalization in Tupaia palawanensis has not been studied, T. belangeri has been shown to have 8 distinct calls that could be categorized as contact, attention/alarm, or aggressive/defensive. All sounds were made between 0.4 to 15 kHz.

Contact calls in T. belangeri include rhythmic clucks and whistles that are only made by males during mating. Attention/alarm calls are short (40 to 70 ms) up-down frequency call made when the animal is disturbed and is nearly always accompanied with a tail flick. A short (40 to 70 ms) whistle is made when the animal is startled, but only causes the tip of the tail to move. Chatter appears to be the most frequently used alarm call and is made with the mouth closed. A screech-like sound is made when a treeshrew is being chased or attacked by an aggressor, and lasts 130 to 490 ms. A snort sound is used when treeshrews are in close proximity to on another and during fights. It is also used when something approaches the nest (Binz and Zimmermann, 1989).

Young treeshrews in the natal nest typically do not make much sound other than occasional squeaks and clicks when startled. Purring-like sounds are made during suckling (Benson et al., 1992).

As in most mammals, the retinas of treeshrews are composed of two types of photoreceptors: rods, responsible for vision in low-light conditions, and cones, which allow color vision and high spatial acuity. Treeshrews have the highest proportion of cones--approximately 96%--of any mammal known, which presumably gives them excellent color vision (Jacobs and Neitz, 1986). The exact purpose for their high color vision in unknown. Tupaia treeshrews also have very good senses of smell and hearing, both of which aid in prey capture. They also use scent markings (Emmons, 2000).

• Communication Channels
• visual visual
• acoustic acoustic

• Other Communication Modes
• scent marks scent marks

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

The food habits of the Palawan treeshrew have not been studied. Treeshrews in genral are primarily insectivorous but will also eat fruit and flowers. They eat the pulp of the fruit and spit out the seed and any fibrous outer covering. The passage of food through the body ranges from 13 to 38 minutes in treeshrews (Emmons, 1991; Emmons, 2000).

• Primary Diet
• carnivore carnivore
  • insectivore insectivore
  • eats non-insect arthropods
  • vermivore
• herbivore herbivore
  • frugivore frugivore
  • eats sap or other plant foods

• Animal Foods
• insects
• terrestrial non-insect arthropods
• terrestrial worms

• Plant Foods
• fruit
• sap or other plant fluids

Predation

Although there has been no observation of predation on the Palawan treeshrew in the wild, there are species on Palawan that eat small mammals. These include Palawan pit vipers ( Trimeresurus schultzei ), ospreys ( Pandion haliaetus ), Palawan scops owls ( Otus fuliginosus ), leopard cats ( Prionailurus bengalensis ), binturongs ( Arctictis binturong ), Asian palm civets ( Paradoxurus hermaphroditus ), Malayan civets ( Viverra tangalunga ), and several species of hawks (Brown et al., 2009; Esselstyn et al., 2004).

The practice of absentee maternal care is suggested to be an anti-predator behavior. Since the mother only visits her young every 2 days, there is less of a chance that a predator will follow her to the nest (Merritt, 2010; Nowak, 1999). The mother often takes different paths to the nest each time and appears to be very cautious when approaching (Emmons, 2000). Newborn treeshrews stay in their nest for nearly one month, urinating and defecating in the same spot in the nest. The young typically return to that same spot, showing that this may be a behavior to keep them in the nest, away from predators (Martin, 1968).

Ecosystem Roles

Any insectivore has an impact on the invertebrate population where it lives (Hayward and Phillipson, 1979). The specific impact T. palawanensis has on insect populations is unknown.

Tupaia montana has a mutualistic relationships with Bornean giant pitcher plants ( Nepenthes sp.). The pitcher plants produce nectar, which treeshrews lick off. The treeshrew then defecates in the bowl of the plant, providing it with nitrogen and phosphorus (Greenwood et al., 2011). Though this mutualism has not been observed with T. palawanensis , there are species of pitcher plants on Palawan (Robinson et al., 2009).

Economic Importance for Humans: Positive

Treeshrews are used in biomedical research to study human diseases and conditions such as depression, myopia, hepatitis, liver cancer (Cao et al., 2003), the H1N1 virus (Yang et al., 2013), and even chronic alcohol consumption (Fu et al., 2014). They have also been kept as house pets (Lyon, 1913).

• Positive Impacts
• research and education

Economic Importance for Humans: Negative

The Palawan treeshrew has no known negative effects on humans.

Conservation Status

The Palawan treeshrew is listed as Least Concern by the IUCN because it can live in a wide range of habitats and appears to have a relatively stable population (Gonzalez et al., 2008).

All treeshrews are listed on Appendix II of CITES, a holdover from when treeshrews were classified as primates.

Other Comments

Treeshrews were originally classified in the order Insectivora, then Menotyphla, and then Primates before finally being placed in their own order, Scandentia (reviewed in Sargis, 2004). Their squirrel-like appearance lead to the misleading name of treeshrew (Martin et al., 2011). Tupaia palawanensis was formerly classified as a subspecies of Tupaia glis but is now considered a distinct species. Tupaia moellendorffi from the adjacent islands of Culion, Busuanga, and Cuyo was previously recognized as distinct from Tupaia palawanensis , but recent research suggests the two are not differentiable morphologically and are minimally divergent genetically (Sargis et al., 2014).

Additional Links

Encyclopedia of Life

Contributors

Micah Bador (author), University of Alaska Fairbanks, Link Olson (editor), University of Alaska Fairbanks, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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Yang, Z., J. Zhao, Y. Zhu, Y. Wang, R. Liu, S. Zhao, R. Li, C. Yang, J. Li, N. Zhong. 2013. The tree shrew provides a useful alternative model for the study of influenza H1N1 virus. Virology Journal , 10/111: 1-9.