Download Isoodon obesulus (Peramelemorphia

Mammalian Species 47(929):112–123
Isoodon obesulus (Peramelemorphia: Peramelidae)
Michael M. Driessen and Robert K. Rose
Biodiversity Conservation Branch, Department of Primary Industries, Parks, Water and Environment, P.O. Box 44, Hobart, Tasmania
7001, Australia; [email protected] (MMD)
Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529-0266, USA; [email protected] (RKR)
Key words: Australia, bandicoot, marsupial, peramelid, red fox
© 2015 by American Society of Mammalogists
Synonymies completed 1 April 2014
DOI:10.1093/mspecisev012
Nomenclatural statement.—A life science identifier (LSID)
number was obtained for this publication: urn:lsid:zoobank.org:
pub:68880F84-0246-4403-B39A-EE02E5ECF59Awww.mammalogy.org
Isoodon DESMAREST, 1817
to Sydney, New South Wales; across northern Australia to
the Kimberley Range; in southern and eastern New Guinea
…….……………….……………….… Isoodon macrourus
Ramus angle ≥ 111° and ramus width < 11 mm
……………………….…………………………………... 2
Didelphis: Shaw, 1797:298. Part, not Didelphis Linnaeus, 1758.
Perameles É. Geoffroy Saint-Hilaire, 1804:56. Part.
Thylacis Illiger, 1811:76. Part.
Didelphys: Illiger, 1811:76. Incorrect subsequent spelling of, but
not Didelphis Linnaeus, 1758.
Isoodon Desmarest, 1817:409. Type species Didelphis obesula
Shaw, 1797 by monotypy.
Perameles: Gray, 1841:407. Part, not Perameles É. Geoffroy
Saint-Hilaire, 1804.
Delphinus: Sherborn, 1902:677. Error for Didelphis, not
Delphinus Linnaeus, 1758 or Didelphis Linnaeus, 1758.
Thylacis Haltenorth, 1958:24. Not Thylacis Illiger, 1811
(= Perameles).
2.Skull length 2.2–2.4 times skull width; tail relatively
shorter, 25–30% of head and body length; dorsum
Context and Content. Order Peramelemorphia, Family
Peramelidae, Subfamily Peramelinae. The genus Isoodon has
3 living species (Groves 2005). A key to species of Isoodon,
derived from Le Souef et al. (1926), Lyne and Mort (1981), and
Menkhorst and Knight (2001), follows:
1.Ramus angle of mandible 103–107° and ramus width >
12 mm; tail long, 27–45% of head and body length; historical distribution mostly coastal from Cape York, Queensland
Fig. 1.—An adult male Isoodon obesulus from Tinderbox, Tasmania, in
May 1979. Used with permission of the photographer, Hans Wapstra.
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Abstract: The southern brown bandicoot, Isoodon obesulus, is a plump grayish-brown generalized omnivorous marsupial, mostly
restricted to southern coastal regions of mainland Australia and to the island state of Tasmania. Two subspecies are recognized, with
I. o. nauticus restricted to the islands off the South Australia coast. I. obesulus lives in a range of habitats, especially those providing
some vegetative cover and with soils yielding earthworms, grubs, insects, and roots. Shrinking distributions toward coastlines and
water courses suggest that I. obesulus may be less tolerant of drought than many marsupials. The illegal introduction of the red fox
(Vulpes vulpes) into Tasmania in 2001 or 2002 and its potential establishment could lead to a decline in bandicoot populations similar
to those seen in the past century on mainland Australia following fox introductions there.
47(929)—Isoodon obesulus
mammalian species113
brindled brown, buff, and black; distribution: Cape York,
Queensland; coastal fringe from the Hawkesbury River to
the Victorian border, New South Wales; coastal Victoria,
South Australia, and Western Australia; all of Tasmania
…………………...……………………… Isoodon obesulus
Skull length ≤ 2.05 times skull width; dorsum golden brown
streaked with black; historical distribution across mainland
Australia, except perhaps Victoria; restricted to northern
Western Australia, including several islands; Marchinton
Island, Northern Territory ………………...… Isoodon auratus
Isoodon obesulus (SHAW, 1797)
Southern Brown Bandicoot
Context and Content. Context as for genus. Isoodon obesulus
has 2 extant subspecies (Groves 2005):
I. o. nauticus O. Thomas 1922:678. See above.
I. o. obesulus (Shaw 1797:298). See above; affinis (Waterhouse),
fusciventer (Gray), and peninsulae (Thomas) are synonyms.
Nomenclatural Notes. Isoodon is derived from the Latin, “iso”
meaning equal and odon referring to teeth. All teeth in Isoodon are
peg-like and about similar in form. The Latin word obesus means
plump or fat, whereas ulus is a diminutive suffix (Strahan 1981).
Thus, the specific name refers to its plump appearance. Other common names include short-nosed bandicoot, southern short-nosed
bandicoot and, in Western Australia, quenda (Kirsch 1968). Although
considered as a synonym in Groves (2005), peninsulae may eventually be regarded as a form of I. auratus (Gordon et al. 1990).
DIAGNOSIS
Isoodon obesulus has a thick-set body with a short conical
muzzle, small ears, short tail, and a grizzled brownish-gray dorsum streaked with black to give an agouti appearance. Digits 2
GENERAL CHARACTERS
Isoodon obesulus is compact and robust, with a pelage of
fine, short, and bristly hairs that is glossy, almost sleek, in living
animals (Fig. 1). Most hairs are banded (hispid), being light at the
roots, blackish in the middle sections, and yellowish at the tips,
producing a grizzled look to the pelage (Wood Jones 1924). The
hairs of the underfur are dark gray, but lighter at their tips. The
yellowish-gray venter results from grayish bristle hairs and nearly
white underfur. The comparatively short tail (ca. 25–30% of the
head and body length in specimens from Tasmania) is brownish
above and white below. In high density populations in Western
Australia, the tail is often bitten off and reduced to a stub (C.
Dickman, pers. comm.). The small rounded ears are covered with
fine yellowish-gray hairs. The eye is black. The brown rhinarium
is naked with a midline groove and laterally cleft nostrils.
The vibrissae are numerous and well developed. The mystacial set lies in 5 rows with hairs dark at the base and pale at the
tips. The genal set contains 6 long vibrissae and there are > 12
others on each side. The manus has a digital formula of 3 > 2 >
4 > 5 > 1; the latter is rudimentary and the smallish 5 is without
a claw. Digits 2, 3, and 4 have ill-defined pads, are fusiform and
well developed, with strong claws. The sole of the pes, like that
of the manus, is coarsely granular and naked. The digital formula
of the pes is 4 > 5 > 2 = 3 > 1; the 1st digit is rudimentary and
clawless. Digits 2 and 3 are joined except at their clawed tips
(= syndactyly) and the well-developed and strongly clawed digits
4 and 5 also are more or less conjoined.
The rear-opening abdominal pouch has 8 nipples arranged in
an incomplete circle. Mean external measurements (mm; ranges
in parenthesis) of male and female I. o. obesulus, respectively
(n = 23, 12; measurement obtained from museum specimens
by RKR), from Tasmania were: total length, 500.2 (325–612),
406.1 (340–428); length of tail, 132.0 (120–157), 125.1 (110–
195); length of hind foot, 69.8 (57–78), 59.0 (45–67); length of
ear, 33.4 (27–38), 30.7 (25–36). Measurements of males (n = 38)
and females (n = 27), respectively, from Victoria were: total
length, 411.3 (310–575), 381.2 (255–460); length of tail, 118.9
(94–149), 113.0 (85–145); length of hind foot, 56.9 (44–75),
53.6 (38–64); length of ear, 29.9 (24–36), 29.7 (20–37).
The “fairly massive” skull of I. obesulus (Wood Jones 1924),
with prominent ridges and elongated bullae, has a shortened rostrum compared to other bandicoots and cheek teeth are reduced
in size, giving the appearance of a dentition of equal-sized teeth
(= isoodon; Fig. 2). Cranial measurements (means; mm) for
males (n = 11) and females (n = 8), respectively, from Tasmania
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Didelphis obesula Shaw, 1797:298. Type locality unknown;
restricted to Ku-ring-gai Chase National Park, N of Sydney,
N. S. W. [New South Wales, Australia], 33o 36’ S, 151o 16’
E, 1.5 km S of Hawkesbury River, 7.5 km from Coal and
Candle Creek Road turnoff on West Head Road, based on
Neotype designation by Dixon (1981:132–133).
Perameles obesula: É. Geoffroy Saint-Hilaire, 1804:64. Name
combination.
Perameles fusciventer Gray, 1841:407. Type locality “King
George Sound,” Western Australia.
Perameles affinis Waterhouse, 1846:373. Type locality “Kangaroo
Point near Hobart, Van Diemen’s Land [Tasmania].”
Isoodon nauticus O. Thomas, 1922:678. Type locality “Franklin’s
Island, Nuyts Archipelago, S. Australia.”
Isoodon obesulus O. Thomas, 1922:678. First use of current
name combination.
Isoodon peninsulae O. Thomas, 1922:679. Type locality “Utingu,
Northern Cape York,” Queensland.
and 3 of the pes are joined (syndactylous) except at the clawed
tips, and claws, if present, are strong. Among the bandicoots
(Isoodon, Perameles, Peroryctes, Echymipera, Microperoryctes,
and Rhynchomeles), Isoodon and Perameles are the most similar
in appearance. Isoodon is larger and heavier than Perameles and
has shorter more rounded ears that when laid forward barely reach
the eye. The ears of Perameles cover the eye when laid forward.
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mammalian species47(929)—Isoodon obesulus
120°
140°
Northern
Territory
20°
20°
Queensland
Western Australia
South
Australia
New South
Wales
Victoria
1000 km
Tasmania
120°
40°
140°
Fig. 3.—Geographic distribution of Isoodon obesulus. Subspecies are:
1, I. o. nauticus; 2, I. o. obesulus (others). Distributions are becoming
increasingly coastal on mainland Australia.
an asymptote at about 600 (n = 7—Lobert and Lee 1990). In
I. o. nauticus from Franklin Island, South Australia, 139 adult
males weighed 595 g and 143 females 527 g (Copley et al. 1990).
DISTRIBUTION
Fig. 2.—Dorsal, ventral, and lateral views of skull and lateral view of
mandible of an adult female Isoodon obesulus (Tasmanian Museum and
Art Gallery, Accession Number A705) from Lymington, Tasmania, 9
June 1965; A. Halton. Greatest length of skull is 63.9 mm.
were: greatest length of skull, 74.9, 67.5; width of cranium,
15.6, 14.5; width of zygomatic, 31.8, 28.5; length of maxillary
toothrow, 24.3, 23.2; length of molariform teeth in mandibular
toothrow, 25.7, 24.3. During tooth development, the replacing
premolar develops terminally on a dental lamina lingual to the
deciduous premolar in both jaws (Fosse and Risnes 1972). In
the upper jaw this lamina is isolated, whereas in the mandible it
remains connected to P2.
Sexual size dimorphism in I. obesulus becomes apparent by
the 1st breeding season, and by the time they are 2 years old males
may be 40–50% heavier than females. I. obesulus in Tasmania
grows faster and weighs more than those from Victoria. In northern Tasmania (Heinsohn 1966), 8 males weighed 1,166 g and
5 females 947 g, whereas in southern Tasmania (Mallick et al.
1998a), males weighed 1,245 g (n = 49) and females 1,001 g
(n = 78). By contrast, in southern Victoria, both the heaviest
male (1,150 g) and female (730 g) were smaller than averagesized Tasmanian I. obesulus and growth of females reached
At the time of settlement by Europeans, Isoodon obesulus was
common throughout much of peripheral mainland Australia, from
the Sydney region southward and westward to Adelaide, with isolated populations in the extreme northeastern section of the Cape
York Peninsula in Queensland (Gordon et al. 1990), southwestern Western Australia (Friend 1990), and on the island state of
Tasmania (Hocking 1990). Since then, distributions have been
shrinking, in response to loss of habitat, introduced predators, and
other factors (Fig. 3). The destructive role of introduced predators is seen in the selective predation by red foxes (Vulpes vulpes)
on I. obesulus in Western Australia (Dickman 1988) and by the
increases in sizes of I. obesulus populations after fox control programs were initiated in the west (Kinnear et al. 2002). In New
South Wales, so few post-1970s records exist (except for some in
the Sydney region, all near the Victoria border) that I. obesulus is
considered to be rare (Ashby et al. 1990). In New South Wales, it
occurs primarily in Ku-ring-gai Chase and Garigal National parks
just north of Sydney and in the far southeast corner including Ben
Boyd National Park and Nadgee Nature Reserve (Department of
Environment and Conservation [NSW] 2005). In between these
areas, the species has been found in a small number of national
parks and state forests. Except for populations in the Grampian
and Dandenong ranges, I. obesulus is restricted to coastal or fluviatile plains across the width of Victoria (Menkhorst and Seebeck
1990). In the Grampians, populations exist at elevations up to
1,000 m. The species is absent from Victorian islands despite large
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40°
47(929)—Isoodon obesulus
mammalian species115
FOSSIL RECORD
The recent ancestry of Isoodon obesulus can be traced to
fossils from several late Pleistocene and Holocene localities,
including Victoria Cave in southeastern South Australia, dated
more than 50,000 years ago (Archer and Hand 1984) and Black’s
Point Sinkhole, a 4,000-year-old record from Venus Bay, South
Australia (McDowell 1997). Two local faunas from southwestern Western Australia include fossils of I. obesulus: Mammoth
Cave (70,000–37,000 years ago) and Devil’s Lair (35,000–
12,000 years ago). I. obesulus fossils are known from 3 caves
in south-central Tasmania, all of late Pleistocene age and 1 cave
with specimens dated to 2,500 years ago (Cosgrove et al. 1990).
Fossil remains, including those from Pleistocene deposits of
Darling Downs, southeastern Queensland (Price 2004), indicate
that I. obesulus formerly lived throughout southeastern, central, and northwestern Queensland (Archer 1978; Muirhead and
Godthelp 1996), far more widely than at present.
Holocene fossils dated < 4,000 years ago are from the
Fromm’s Landing local fauna in South Australia (Archer and
Hand 1984). Although extant only on West Sister Island of the
Furneaux Island group and absent from Ranga Cave (8,000 years
ago) deposits on Flinders Island, subfossils are known from
sand dunes on Flinders, Cape Barren, and Passage Islands of
Tasmania (Hope 1973). Subfossils are known from 6 of 7 sites
on the basalt plains of western Victoria, including both cave and
aboriginal (beach midden) localities, Pyramids Cave deposits in
eastern Victoria, and from McEachern’s Cave in extreme southwestern Victoria (Wakefield 1964, 1967a, 1967b).
Based on 12S rRNA sequence data, Isoodon diverged
from Perameles in the late Miocene, about 8 million years ago
(Westerman and Krajewski 2000).
FORM AND FUNCTION
The skull of Isoodon obesulus is notable for its slender rostrum. The dental formula is i 5/3, c 1/1, p 3/3, m 4/4, total 48.
Although the name Isoodon, meaning “teeth of equal size,” is
not literally true, the canines and cheek teeth are smallish, giving
that appearance. All teeth have roots; hence, these bandicoots
can be aged by degree of tooth wear.
Comparisons of variation in size and shape of skulls from
5 recent (< 100 years) and 5 subfossil (“a few thousand years”)
sites in southwest Western Australia reveal skulls of modern
I. obesulus to be larger, with relatively longer snouts, and showing greater geographic variation than subfossil representatives
(Cooper 2000).
The caecum is capacious and descending, and both upturned
and pointed at the tip. The large intestine is short and wide (Hill
and Rewell 1955).
Basal metabolic rates (BMRs) for I. obesulus held at 5°C
increments of ambient temperatures (Ta) from 10–35°C showed
the typical mammalian responses of increasing basal metabolic
rate from its low point in the thermal neutral zone (TNZ: 25–35°C)
to more than double (2.4 times) that value at 10°C (Larcombe
2002). Basal metabolic rate is 64.6% of that predicted for a placental mammal of comparable size, near the 70% value typical
of all marsupials (Dawson and Hulbert 1970). The increase in
oxygen consumption between 30 and 10°C was achieved by a
2.3-fold increase in tidal volume and a 30% increase in breathing
rate. By contrast, the efficiency in the uptake of oxygen (26–
27%) did not change over this range of temperatures.
Maximal running speed of 2 adult I. obesulus (mean body
mass = 718 g) was 14.3 km/h (Garland et al. 1988). When undisturbed and seemingly undetected, I. obesulus sometimes hops in
a manner similar to rabbits. Galloping, 1 of 4 gaits recorded on
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tracts of apparently suitable habitat. I. obesulus is widespread in
Tasmania, having been recorded either as road-killed or trapped
specimens virtually across the state except in the central plateau
(Hocking 1990). The greatest concentrations seem to be in the
southeastern quarter and the northern tier (Rounsevell et al. 1991),
areas with rich soils and moderate rainfall. Although persisting on
only 1 island (West Sister Island) in the Furneaux group of Bass
Strait islands, subfossils are known on at least 3 other islands;
some survived to the 20th century on the largest, Flinders Island
(Hope 1973). Subfossil remains also are known from 2 of the
western Bass Strait islands (Hope 1973; Bowdler 1984), but not
from the largest, King Island, the most distant among all islands
off the north coast of Tasmania.
In South Australia, I. obesulus is now found in forest and
woodland habitats on Eyre Peninsula, in the Mt. Lofty Ranges,
and on the Fleurieu Peninsula, in the extreme southeastern section of the state, and on Kangaroo Island (Kemper 1990; Paull
1995), where it is most secure, in the absence of red foxes. I. obesulus also is known as subfossils from several sites in coastal
South Australia. I. o. nauticus is known from Franklin and St.
Francis Islands and as subfossil material from Flinders Island,
all in South Australia (Kemper 1990). In Western Australia, the
pattern is similar: shrinking distributions, surviving populations
ever more coastal, and subfossil locations indicating broader distributions in the past (Friend 1990). Populations currently are
found in areas of high rainfall in the southwest and south coasts
of Western Australia. In Western Australia at least, its disappearance is directly linked to habitat loss; where I. obesulus survives,
it is common where wetlands and waterways provide adequate
cover, areas which lie almost entirely within the 1,000 mm isohyet (Friend 1990; Cooper 1998).
Isoodon obesulus in Queensland is poorly understood, but its
known locations (slated for preservation in a national park) overlap with the distributional range of Isoodon macrourus (northern
brown bandicoot—Gordon et al. 1990). The only other location
where 2 species of Isoodon are sympatric is in the poorly surveyed Kimberley Range of Western Australia, where I. macrourus and I. auratus, the golden bandicoot, potentially overlap in
large areas (Friend et al. 1991). A recent discovery in the Lamb
Range extends the distribution of I. obesulus 350 km from the
nearest contiguous populations (Pope et al. 2001).
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mammalian species47(929)—Isoodon obesulus
ONTOGENY AND REPRODUCTION
In Isoodon obesulus, each testis has 6 single loops and one
3-limbed loop in the seminiferous tubule, with 15 connections
between the tubules and the duct draining the testis (deBurlet
1921; Woolley 1990). An 1,155 g male had a combined testes
mass of 4.4 g, or 0.38% of body mass (Tyndale-Biscoe and
Renfree 1987). A 790 g male had an estimated 48 million sperm
per epididymis, or 25 million per gram of testis (Bedford et al.
1984). Scrotal diameter (mm) reached an asymptote beyond
500 g, indicating fertility by that body size (Reese 2001).
All peramelids are polyestrous, with spontaneous ovulation;
the mean ovulation rate is 20–21 days in I. obesulus. After ovulation, the granulosa cells of the follicle are penetrated by cells
of the theca interna, which fill the central cavity of the developing corpus luteum (O’Donoghue 1916). After 4 days, growth of
the corpus luteum is due entirely to hypertrophy of luteal cells
(Tyndale-Biscoe and Renfree 1987).
In I. obesulus, gestation is short (< 15 days by most accounts
but as few as 12 days in Ullmann [1981]) and parturition occurs
during the peak of the luteal phase. If lactation follows, the
corpora lutea remain large and seemingly functional for about
40 days of the 60-day lactation period. The follicular phase is
suppressed by lactation. After day 45, the corpora lutea decline
rapidly in size, coincidental with declining progesterone levels,
and new follicles grow; ovulation occurs soon after (TyndaleBiscoe and Renfree 1987).
The 1st endoderm cells appear in I. obesulus blastocysts
1.0–1.5 mm in diameter and the blastocysts are fully bilaminar
by 1.5–1.9 mm (Hollis and Lyne 1977), estimated at day 6 (Lyne
and Hollis 1977). Like other peramelids (but not other families
of marsupials, except the Phascolarctidae [koala]), I. obesulus has both yolk sac (choriovitelline) and allantoic placentae.
During the later stage of gestation, the chorioallantois forms a
discoidal placenta with a long, thick umbilical cord (TyndaleBiscoe and Renfree 1987).
The mean number of pouch young is variable and always
many fewer than the 8 teats can accommodate: 2.1 on both
Franklin Island and Belair National Park, South Australia
(Copley et al. 1990; Reese 2001), 1.57 and 2.58 in 2 years of
study in Victoria (Lobert and Lee 1990), 3.0 in another study
in Victoria (Stoddart and Braithwaite 1979), 2.8 in northern
Tasmania (Heinsohn 1966), and 3.05 for 23 litters in southern Tasmania (Mallick et al. 1998a). Although litters of 2–3
are most common, as many as 5 have been reported (Mallick
et al. 1998a). Because females can have up to 4 litters per year
and can live for nearly 4 years, a long-lived female could produce up to 32 young during her lifetime (Lobert and Lee 1990).
Litter size decreases (by unknown mechanisms) as the pouch
young age, although handling during study may contribute to
this pattern. In one study, litter size increased linearly with
female body mass (Stoddart and Braithwaite 1979). An analysis
of growth patterns of I. obesulus, using the Gompertz growth
model (Cockburn and Johnson 1988), revealed a decelerating
growth rate throughout ontogeny. However, this deceleration
is mitigated by its indeterminate growth. Instantaneous relative growth rates calculated during the final 42 days of lactation
revealed a decrease in overall growth rates from 14.0% increase
in body mass per day in early-phase, to 7.8% per day during
mid-phase, to 3.5% daily increase during late-phase lactation
(Duffy and Rose 2007).
In Tasmania, young are born from July to February, and
females can have up to 4 litters per year (Heinsohn 1966). In
Victoria, where breeding ends in December, females can have
as many as 3 litters in a year (Lobert and Lee 1990). In a study
spanning 10 years in Western Australia, litters were recorded in
every month (Thomas 1990). Females of I. o. nauticus likewise
lactate year-round and at least 4 litters are produced annually
by some females (Copley et al. 1990). Importantly, young born
early in the year can mature and breed in the year of their birth,
an unusual feature for marsupials. Thus, with rapid maturation
and up to 4 litters per year, I. obesulus has a high reproductive
potential, rivaling that of some rodents.
Neonates weigh 350 mg, develop quickly, permanently exit
the pouch at about 53 days, and are weaned a week later (Lobert
and Lee 1990). Probably as a result of more efficient transfer in
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film, occurred at 3.73 m/s or 14.4 km/h). At this speed, the length
of a stride approaches 1 m, or 3–4 body lengths (Moloney 1982).
Field metabolic rates were 644 kJ/day for a 1.23 kg I. obesulus in autumn and 459 kJ/day for a 517 g individual in spring.
The rates of water flux for these 2 bandicoots were 109 and
40 ml/day, respectively (Nagy et al. 1991).
The pH of I. obesulus blood, 7.36–7.58, was in the range of
5 other marsupials, as were levels of 5 blood gases. The values of
5 serum electrolytes (Na+, K+, Ca2+, Mg2+, and Cl−) likewise were
similar to values for 9 other marsupials. Levels of organic constituents in the blood and of serum proteins were comparable to
those of the 11 other examined marsupials (Parsons et al. 1971).
A body temperature (Tb) of 32.4°C was recorded for captive I. obesulus using deep rectal thermistors (Guiler and Heddle
1970). Results by Larcombe (2002), who held animals for ≥ 3 h
at different temperatures before recording body temperature,
suggest that I. obesulus is slightly (by as much as 2.6°C) hypothermic at ambient temperatures of 10, 15, 20, and 25°C. At 30
and 35°C, at the upper end of the thermal neutral zone, body
temperature was 35.0 and 36.0°C, respectively. The temperature of the scrotum (24.5°C) in an anesthetized male was 4.9°C
below body temperature (Setchell 1977), but less temperature
differential was detected when a thermistor was used directly on
testicular vessels (Guiler and Heddle 1970).
Studies of visual pathways in I. obesulus have revealed that
retinal projections to the lateral geniculate nucleus (LGd), an
important processing center linking retina to visual cortex, differ from those of other polyprotodont marsupials (Haight and
Sanderson 1990). One difference is the proportionately smaller
volume of the lateral geniculate nucleus, compared to other marsupials, suggesting that binocular vision is poorly developed in
I. obesulus.
47(929)—Isoodon obesulus
mammalian species117
Differential survival is evident even during pouch life. In I. obesulus nauticus from Franklin Islands, South Australia, sex ratios
of pouch young favored females (1:1.41) but were near parity
or favored males as adults (Copley et al. 1990). This pattern can
be explained if the 50% higher survival of males during the first
8 months of life (Lobert and Lee 1990) applies to the Franklin
Island population. In the Franklin Island population, only 45 of
167 marked pouch young were trapped as juveniles, representing
either mortality or trap avoidance of 73%; 22% were lost before
weaning so the greater disappearance occurs during the 1st weeks
of independence (Copley et al. 1990). Seasonal survival in this
island population was highest in winter, the period of greatest
rainfall. Life span in the wild is 3.5–4.0 years (Lobert and Lee
1990), and in Tasmania 1 individual was at least 3.75 years old
based on the time between its first and last capture (Mallick et al.
1998a).
ECOLOGY
Isoodon obesulus is a generalist omnivore, eating adult
and immature insects of several orders, spiders, isopods, earthworms, fungal sporocarps, a range of monocot and dicot roots,
and ferns in Tasmania (Mallick et al. 1998b). Common foods
were eaten in proportion to their availability, except that crickets
and blackberries were selected preferentially in season (Mallick
et al. 1998b). In a study in northern Tasmania, I. obesulus consumed mainly invertebrates; the only plant material eaten was
the fruit of boxthorn (Heinsohn 1966). However, in another
dietary study in southern Tasmania (Quin 1988), I. obesulus
consumed many plant items, such as grasses, seeds, clover root
nodules, plus fungi and a range of invertebrate foods. In Western
Australia, where 77% of invertebrate prey items were > 5 mm
long, insects comprised 52% of the diet by volume, arachnids
and oligochaetes 6% each, and myriapods and crustaceans 5%
each (Broughton and Dickman 1991). In Queensland, invertebrates were a major component of the diet of I. obesulus, contributing 35–56% of fecal contents; roots represented the most
important plant food, with grasses, forbs, fruits, and hypogeous
fungi also eaten but in small quantities (Keiper and Johnson
2004). The substantial activity of trehalase and cellobiase in the
mucosa of the small intestine suggests that both insects (trehalose is a disaccharide found only in insects) and plant material
(cellobiose is formed during cellulose breakdown) are digestible
by I. obesulus (Kerry 1969).
Isoodon obesulus is preyed upon by a range of predators.
On Franklin Island, South Australia, barn owl (Tyto alba) and
tiger snake (Notechis scutatus) are major predators (Copley et al.
1990), as are cats (Felis catus), red foxes, eastern quolls, and
feral dogs elsewhere (Godsell 1983; Dickman 1988; Mallick
et al. 1997). In the jarrah forests of Western Australia, I. obesulus was present more frequently than expected compared to other
medium-sized mammals in the diet of the chuditch (Dasyurus
geoffroii), indicating its susceptibility to predation (Glen et al.
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the chorioallantoic placenta, I. obesulus releases from the teat
and its eyes open at one-half (or less) the age of marsupials of
comparable size: 135–140 days in the carnivorous eastern quoll
(Dasyurus viverrinus) and 147 days in the herbivorous longnosed potoroo (Potorous tridactylus). These features contribute
to the rapid maturity (3–4 months) in I. obesulus.
The peramelid lactational strategy is a contributing factor to
the exceptionally rapid rates of preweaning growth and development. In early-phase milk of I. obesulus (before day 30), the
levels of protein, lipids, and solids (100/ml) were 10.5, 10.4, and
27.3 g, respectively, but by late-phase (days 46–60), the respective values were 11.3, 26.4, and 52.3 g. Thus, although lipid levels comprise about 65% of total energy (kJ/ml) early, by late
lactation this proportion has increased to > 80%, the protein levels having remained almost constant from week to week (Duffy
and Rose 2007).
Although earlier studies yielded no reports of breeding in
Tasmania during the months of January to April, 2 of 4 females
had pouch young in March of 1 year and 4 of 6 in March of
another year (Mallick et al. 1998a). In Tasmania, females
mature in 4–5 months (but females as young as 3–4 months with
≥ 50 mm pes length had pouch young—Mallick et al. 1998a)
and males in 6 months, so both sexes can breed in the year of
their birth (Heinsohn 1966). In Victoria, maturity is not reached
until 7 months (Lobert and Lee 1990). The pattern of continued growth in adult life is best recorded in populations from
Cranbourne, Victoria (Lobert and Lee 1990). Measurements of
body mass and length of pes indicate that although females seem
to reach an asymptote at about 600 g (aged 18–24 months), they
do continue to grow throughout life (a maximum of 3.5 years in
that population). Likewise, many males continue the progression
of slow growth throughout adult life.
Although not found in I. obesulus nauticus from Franklin
Island, South Australia (Copley et al. 1990) or in small samples
from Victoria (Lobert and Lee 1990), the positive correlation
between maternal body mass and litter size suggests that female
condition (due to seasonal changes in food availability) can have
important population consequences. Breeding may cease when
females have lost mass (Heinsohn 1966) or during drought periods (Mallick et al. 1998a), but photoperiod may be important too
in determining the onset of breeding (Heinsohn 1966; Stoddart
and Braithwaite 1979). I. obesulus in temperate locations (as
in Victoria and Tasmania, 37–42°S) or at > 1,000 m elevations
breeds seasonally, whereas populations from Queensland (29°S)
breed year-round, perhaps in response to adequate food supplies.
Several authors speculate that both number and size of litters
are related to food abundance (Heinsohn 1966; Lobert and Lee
1990; Mallick et al. 1998a).
Minimum survival rates of males are always higher than of
females, the greatest difference being in the 1st breeding season
(60% versus 40%—Lobert and Lee 1990). Only 2 young were
recruited at 2 study populations during a 3-year drought period
in Tasmania (Mallick et al. 1998a), suggesting reduced levels of
reproduction or poor survival of young under these conditions.
118
mammalian species47(929)—Isoodon obesulus
for production of plant and animal biomass. In brief, I. obesulus
might be much less tolerant of drought than many marsupials.
Home ranges of I. obesulus vary depending on method of
analysis and population density. Home ranges mostly in the 1–5
ha range (Lobert 1990) and population densities of 1–5 per ha
(Lobert and Lee 1990) support Moloney’s (1982) speculation
that territories, if they exist at all, are in the form of spatiotemporal systems based on avoidance. At Cranbourne, Victoria, both
male and female I. obesulus were solitary and occupied home
ranges of 0.8–3.0 ha at densities up to 5 per hectare (Lobert and
Lee 1990). In southern Tasmania, nonoverlapping home ranges
were reported for both sexes (Mallick et al. 1998a). Home
ranges of 6.95 ha for males and 3.28 ha for females in southern
Tasmania (Mallick et al. 1998a) are similar to those from northern Tasmania, 6.6 and 2.3 ha, respectively (Heinsohn 1966).
By contrast, on Franklin Island, South Australia, the values for
males and females were 2.1–2.2 and 1.5–1.6 ha, respectively
(Copley et al. 1990). In Western Australia, where home ranges
for males averaged 2.34 ha and those of females 1.83 ha, supplemental food led to a 35% increase in home range (Broughton and
Dickman 1991).
Six species of ectoparasitic mites from 2 families and 5
genera are reported by Green (1989): Gymnolaelaps annectans,
Haemolaelaps flagellatus, H. marsupialis, Mesolaelaps antipodianus, Myonyssus decumani, and Neotrombicula novaehollandiae. An intraerythrocytic protozoan parasite, Hepatozoon,
is known from I. obesulus in Western Australia (Wicks et al.
2006). Recently, a novel virus, named bandicoot papillomatosis
carcinomatosis virus type 2, was obtained from an I. obesulus in
Western Australia; it caused multicentric papillomatous lesions
which responded to treatment during rehabilitation (Bennett
et al. 2008).
BEHAVIOR
There are conflicting reports on when Isoodon obesulus is
active within the 24-h day. Radio-tracking studies conducted
over the winter in southern Victoria revealed a diurnal pattern
(Lobert 1990), which conflicts with Heinsohn (1966), Moloney
(1982), and others, who found I. obesulus to be strictly nocturnal
in Tasmania. In one study, I. obesulus emerged 52.2 min after
sundown and remained active for 6.26 h (with 1 exception—
Moloney 1982).
In the laboratory, I. obesulus becomes active at dusk and
has a single period of activity lasting 6–8 h (Armstrong et al.
1990). Continuous video recordings confirmed that I. obesulus
was almost entirely nocturnal, emerging about 30 min after sundown and staying active for about 7 h (Larcombe 2003). Little
time was spent grooming (8 min) or drinking (2 min) each day.
With the reversal of light-dark (LD) cycles, most animals reentrained within 8–15 days (Armstrong et al. 1990). However,
1 or 2 did not entrain, and persisted with their original cycle in
this unstable entrainment for 50 days in the reversed light-dark
cycles, indicating (as suggested by Lyne’s [1981] studies of 2
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2010). Bones of I. obesulus were found in 7 of 72 red fox
scats collected at the Royal Botanic Garden-Cranbourne near
Melbourne, Victoria, and constituted 5.5% of diet items (Coates
and Wright 2003). Recent field studies have shown that I. obesulus does not respond to the odors of either native or introduced predators, further indicating its vulnerability to predation
(Russell and Banks 2005; Valentina et al. 2010).
Potential competitors include the eastern barred bandicoot
(Perameles gunnii) in Tasmania (Heinsohn 1966; Mallick et al.
1998a). The only area of mainland Australia where a congener
of I. obesulus is present is in northeastern Queensland, where
I. macrourus is sympatric.
In Victoria, I. obesulus inhabits heathlands, shrubland, and
open forest and woodland, where it is associated with welldrained soils and “dry” heath communities (Menkhorst and
Seebeck 1990). Although older heath communities seem to be
preferred (18-year-old—Braithwaite and Gullan 1978; 12-yearold—Opie 1980), sufficient ground cover may be more important than species or age of dominant plants (Lobert 1985). Fire
interval also may be important in determining the quality and
availability of suitable habitat (Stoddart and Braithwaite 1979).
In high rainfall areas of northeastern Queensland, I. obesulus
prefers relatively dry sclerophyll woodlands characterized by
high abundance of grass tree (Xanthorrhoea johnstonii) and
high shrub cover in the understory (Keiper and Johnson 2004).
In Western Australia, I. obesulus living in the jarrah (Eucalyptus
marginata) forests is significantly larger in body mass than those
inhabiting reed swamps (Cooper 1998). Factors controlling
these size differences were demonstrated to be genetic, based on
breeding and growth studies conducted in the laboratory (Hale
2000).
Its widespread distribution within Tasmania suggests
that I. obesulus has broad habitat tolerances. Hocking (1990)
describes it as primarily occupying dry sclerophyll forest, scrub,
and healthland communities, especially those with dense ground
cover of shrubs (Leptospermum and Melaleuca), in long matrush (Lomandra longifolia), or in agricultural areas dominated
by such introduced plants as brambles (Rubus), gorse (Ulex
europaeus), or boxthorn (Lycium ferrocissimum). High population densities also are associated with pastures near dense cover
(Heinsohn 1966) but in southern Tasmania, most captures were
recorded in forests or at their edges and few (< 10%) in pasture
(Mallick et al. 1998a). The I. obesulus apparently quickly colonizes recently logged and burnt forest patches, benefiting from
the dense ground cover and food resources in early seral stages
(Green 1982).
It is likely that production of invertebrate prey, made possible by abundant rainfall, affects the distribution as well as
abundance of I. obesulus. Trapping results in Gippsland (southeastern Victoria) reveal that I. obesulus is found in lowland sites
< 50 km from the coast, sites near watercourses with moist soils,
and in association with heath or woodland vegetation (Opie et al.
1990). In Western Australia, I. obesulus distribution corresponds
to the 1,000 mm isohyet, and its historic distribution (primarily
near coastlines) suggests an association with adequate rainfall
47(929)—Isoodon obesulus
mammalian species119
ears, chest, neck, shoulders, dorsum, and flanks, movements
interspersed with gnawing and licking the syndactylous claws,
are most common. Face-washing behavior, wiping the muzzle
with forepaws which are then licked as if to clean, never extends
posterior to the ears and frequently follows eating. A 3rd behavior, one that frequently increases in association with rainfall, is
gnawing and licking all accessible parts of the pelage (Moloney
1982).
Subauricular cephalic skin glands in both sexes of I. obesulus expand enormously during the breeding season, especially
in males, causing the upper surface to bulge outwards, become
rugose, and form pits at the bases of hair follicles (Stoddart
1980). When an animal is handled or frightened, the gland complex weeps profusely, suggesting a role in communication, perhaps useful at courtship.
The aggression of captive animals toward one another frequently is accompanied by grunts and squeaks (Wood Jones
1924). When disturbed, I. obesulus emits sneezing and spitting
noises and immediately seeks cover (Heinsohn 1966).
In intraspecific encounters, a grunting and squeaking dominant I. obesulus pursues and eventually overtakes its equally vocal
subordinate and jumps on its back, striking with its claws and
removing patches of hair. Subsequent scratching by the pursuer
using its forefeet removes additional hair (Wood Jones 1924).
Although the hair is readily scratched off, the skin of I. obesulus
is exceedingly tough (R. K. Rose, in litt.) and hence is impossible
to open with the clawed feet of aggressors. In this way, dominance
is established without killing or maiming the subordinate animal.
Other evidence of aggression is seen in the scarred, shortened,
and missing tails of some I. obesulus. The size of defurred areas
is positively correlated with population density and body mass,
and males have significantly more fur loss than females (Thomas
1990). In the laboratory, hair grows back partially in 4 weeks and
more fully in 8 weeks (Wood Jones 1924).
GENETICS
In Isoodon obesulus, the diploid number (2n) = 14.
Autosomes consist of 3 pairs of large metacentric or submetacentric chromosomes, 1 pair of medium-sized metacentric chromosomes, and 2 pairs of small chromosomes, one of which may
have a satellited short arm (Sharman 1961). Chromosomes are
similar in both subspecies, with the X chromosome showing the
greatest morphological variation (Hayman and Martin 1974).
All Peramelines have XX:XY sex-determining mechanisms
but in I. obesulus, no somatic cell has the full chromosome number due to the loss of an X chromosome in females and the Y
chromosome in males, leaving all somatic cells XO (Hayman
and Martin 1965).
Discriminant function analyses and a phylogeny of Isoodon
based on mtDNA control region sequences reveal 2 groups,
I. macrourus and I. obesulus/auratus (Pope et al. 2001). The latter is not distinct for mtDNA, the phylogenetic divergence being
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other peramelids) that bandicoots may have different circadian
pacemakers than other mammals.
Isoodon obesulus makes a nest of shredded vegetation, usually set in a slight depression but always in a well-hidden and
camouflaged location (Stodart 1977). In dense vegetation and
with no obvious entrance, such nests are difficult to detect.
Isoodon obesulus spends most of its active period feeding.
Feeding activity consists of “nosing” the ground to detect subterranean food items by olfaction (Stodart 1977; Moloney 1982; Quin
1985). Using its forepaws, it then scratches conical depressions in
the soil, up to 8 cm deep (Mallick et al. 1998b). Based on a survey
of 196 excavations, I. obesulus diggings averaged 48 mm deep and
35 mm in diameter (Moloney 1982). The role of olfaction in detecting subterranean prey was examined by pulverizing cockroaches
and then burying them (and controls) in cups placed at different
depths (Quin 1985). Although olfaction was important in prey
detection, auditory trials revealed that hearing was not.
Studies of prey-killing behavior in an arena revealed that
frogs were universally avoided but lizards were approached
and attacked within 5 s and killed 2 s later, with ingestion completed within 30 s (Moloney 1982). Lab mice were investigated
and sniffed immediately; the 1st attempts to pin with the forepaws usually were unsuccessful but the average I. obesulus
pursued and administered a killing bite to the head within 53 s.
Consumption followed while I. obesulus was in a crouched position. Newly hatched domestic chicks were approached, pursued,
and killed in a similar manner but the average time was 2 min
57 s. Laboratory rats and 19-day old chicks were pursued but
rarely killed. Vertebrates usually were eaten head first. The forepaws never conveyed food to the mouth but sometimes were
used to hold down (stabilize) prey (Moloney 1982). Although I.
obesulus can drink water with rapid thrusts of the tongue, drinking is rare because dew, water in their prey, and metabolic water
usually fulfill their needs. Even in the lab, I. obesulus spends
little time drinking (Larcombe 2003).
Isoodon obesulus moves about independently, although
areas of use tend to be restricted, probably due to the distribution
of food resources. In studies of spatial discrimination, I. obesulus performs as well as laboratory rats (Rattus norvegicus—
Buchmann and Grecian 1974), perhaps indicating a rapid ability
to learn under specific conditions. Mutual avoidance among
individuals, except when breeding, was observed by Moloney
(1982). After a testing period of approaches, contacts by 2 male
I. obesulus always led to aggression, naso-nasal sniffing, retreating, and naso-anal sniffing, followed by the assumption of the
agonistic posture position by the dominant male. The aggressor
then relentlessly pursued the subordinate, striking with forepaws
and biting, usually on the rump (Moloney 1982). Female–female
interactions and heterosexual pairings were characterized by
mutual avoidance. Estimates of home range size and population
density support the view that I. obesulus is intolerant of its kind
except at breeding time.
Of the 3 types of autogrooming activities (Moloney 1982),
the rapid raking movements of the hind feet to scratch the snout,
120
mammalian species47(929)—Isoodon obesulus
CONSERVATION
Like those of other peramelids, the distribution of Isoodon
obesulus has shrunk substantially since European settlement of
Australia. Populations in New South Wales and South Australia
are listed as endangered and vulnerable under respective State
legislations, and I. o. obesulus is listed as “Endangered” under the
Federal Environment Protection and Biodiversity Conservation
Act of 1999 (Australian Government Web site: www.deh.gov.
au/biodiversity/threatened/species). Threats include changed fire
regimes, predation by introduced predators (especially foxes and
cats), habitat fragmentation, and land clearing. The application
of population viability analysis (PVA), used to evaluate the most
effective management/conservation methods of the endangered
I. obesulus in Victoria, revealed the importance of including
multiple habitats when developing population viability analysis
models (Southwell et al. 2008). I. obesulus is considered secure
in Queensland, Tasmania, Victoria, and Western Australia as the
species is not listed in these states. However, the illegal introduction of the red fox to Tasmania in 2001 or 2002 and its potential
establishment could lead to a decline in I. obesulus populations
similar to those seen in the past century on mainland Australia
following red fox introductions. Poison campaigns using sodium
monofluoroacetate (Compound 1080) to kill red foxes have
enabled I. obesulus populations to rebound in several places on
mainland Australia, an indication of the efficiency of these predators (Kinnear et al. 2002; Murray et al. 2006). Underpasses,
intended to connect fragmented populations of I. obesulus separated by new highways, can lead to declines when red foxes
use the same underpasses (Harris et al. 2010). In April 2015,
the International Union for Conservation of Nature and Natural
Resources status for the species was listed as “Least Concern,”
with a “Decreasing” population trend.
ACKNOWLEDGMENTS
We gratefully acknowledge the assistance of J. Rainbird and
B. Smith of the Queen Victoria Museum in Launceston for access
to and measurements of specimens in the collection, K. Medlock
and D. Robertson of the Tasmanian Museum and Art Gallery
in Hobart for access to specimens, R. O’Brien of Museum
Victoria for providing measurements of Victorian bandicoots,
and J. Walch for assistance with skull photography and processing. Thanks also to H. Wapstra of Tasmania Parks and Wildlife
for the photograph of the live bandicoot and, for their courtesies
to the junior author, to Tasmania Parks and Wildlife, where the
draft of this account was written during a study leave.
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