Emydura subglobosa

Geographic Range

Emydura subglobosa is found on islands and rivers in coastal Australia and New Guinea, such as Fraser Island, the Jardine River, Daru, Cape York, Stradbroke Islands, and the islands in Torres Strait (Legler and Georges, 1993). These turtles also occur in lowland swamps, which cover large areas of the tropical, open plains in western Papua New Guinea (Georges Guarino and Bito, 2006).

• Biogeographic Regions
• australian australian
  • native native

• Other Geographic Terms
• island endemic island endemic

Habitat

Preferred habitat of red-bellied short-necked turtles are rivers, swamps, and ponds of Papua New Guinea and Australia (Georges et al. 2008). In the lower Kikori and Omati rivers they inhabit slow-moving waters, swamps, and seasonal wetlands (PNG Gas Project, 2005). Like other freshwater turtles, red-bellied short-necked turtles alternate periods in the water with time basking to raise body temperature (Webb, 1978). Most of their life is spent in water, where they forage for food. If there is a water scarcity in hotter months, they move to flooded areas (Georges, Guarino and Bito, 2006).

• Habitat Regions
• temperate temperate
• terrestrial terrestrial
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• temporary pools

• Wetlands
• marsh marsh
• swamp swamp

• Other Habitat Features
• riparian riparian

Physical Description

Red-bellied short-necked turtles have olive-colored heads with a yellow-cream stripe running from the tip of the nose through the eye and into the iris (Georges et al. 2008). A black spot is always present in front of and behind the pupil in Emydura victoriae and variable in Emydura tanybaraga (Thomson, 2003). They have a prominent upper jaw and two yellow whiskers on the chin; the same yellow coloration runs along the light-colored jaw line. The upper neck region is dark gray and the lower, light gray with red streaks running along it. This same coloration appears on the bottom jaw and belly of the turtle, although the color can vary among bright orange, yellow, or pink (Legler and Georges, 1993; Ernst and Barbour, 1989). The limbs, tail, plastron, and abdominal regions are all marked with red (Ernst and Barbour, 1989). Young red-bellied short-necked turtles generally have brighter markings that fade as they grow, with their red color turning pinkish with time (Ernst and Barbour, 1989). Females are larger in carapace length, but have shorter tails. Male carapaces range from 13.3 to 17.3 cm, female carapaces range from 15.2 to 25.5 cm.

Red-bellied short-necked turtles are members of the family of side-necked freshwater turtles, Chelidae . They can be characterized by how they extend and retract their necks. They lay their neck and head sideways, underneath the upper edge of the shell (Werneburg et al., 2009).

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger
• sexes shaped differently

Development

In many marine, freshwater, and terrestrial turtles, the gender of the embryo is influenced by incubation temperature. However, this is not the case with Australian chelids studied to date, which lack temperature dependent sex determination (Georges and Legler, 1993).

Following pipping (breaking of the shell), hatchlings remain for a day or so in the eggshell, where they survive on the remains of the yolk sac (Georges et al., 2007).

Research suggests that these turtles grow at a faster rate prior to maturity, when growth rates drop abruptly to provide sufficient resources for reproduction (Georges, 1995). The estimated age at sexual maturity is 14 years for males and 9 years for females The greatest expected lifespan for chelid turtles is estimated at about 100 years for both sexes (Martins and Souza, 2008). In Emydura and Chelodina species, females tend to grow faster, reaching larger carapace lengths than males. The shells of females have a tendency to be deeper and more spacious than the males to facilitate the storage of eggs (Georges and Legler, 1993).

• Development - Life Cycle
• indeterminate growth indeterminate growth

Reproduction

Emydura species mate year-round, with peaks in the spring and fall. Males of Emydura species have sperm all year in the epididymides. Females of Emydura species accumulate yolk in the ovaries in late summer through winter. During the breeding season, males communicate with females with a series of signaling postures, including a combination of simultaneous stroking, eye blinking, and head bobbing. The female may be stationary or swimming; when she stops the encounter and surfaces, the male quickly assumes a nose-to-nose position, performing nose squirts. Males and females continue bobbing their heads in alternating sequence as they align their bodies. Once this maneuver is complete the mating begins (Georges & Legler, 1993). During mating, the cloacas touch. They remain together for many hours, although copulation may only occur for a short time. This mating process may occur more than once for up to several days, and may involve multiple partners at any given time. Red-bellied short-necked turtles have scent glands in their carapace that produce odors used during competition between males during breeding season.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

In red-bellied short-necked turtles, females have a large area inside their carapace to store eggs, whereas males have a larger tail. Ovulation and nesting begins in early spring. Only female turtles leave the water during the night or early morning to deposit eggs in hollow cavities constructed in sand or soil. Females lay eggs within about an hour. Emydura subglobosa , Elseya novaeguineae , and Carettochelys insculpta lay their eggs in the soil of the forest floor, often near the base of trees or in the sandy soil of freshwater swamps during the late, dry season between August and October (Georges, 2007; Georges et al., 2006). Emydura subglobosa individuals lay white, calcareous, ellipsoid eggs averaging 35.0 ±0.05 mm long and 19.0 ±0.02 mm wide. Estimated mean egg weight of eggs is 7.68 ±0.20 g. These turtles can produce two to four clutches a year, laying from four to eleven eggs each time, with an average of 7 eggs in each clutch (Georges et al., 2006). Eggs incubate and hatch the following dry season in July through August. Many factors can impact the incubation and hatching period: ambient temperatures, cloud cover, river levels and flow, tides, and the phase of the moon. High temperatures promote early hatching and cold temperatures promote later hatching times. Hatchlings make their journey to freshwater without parental guidance or protection (Georgeset al., 1993). Red-bellied short-necked turtles typically mature between 7 and 12 years old with both males and females maturing at carapace lengths of 14 to 15 cm (Georges et al., 2006).

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

After digging a cavity and depositing eggs, female red-bellied short-necked turtles immediately return to freshwater, leaving the eggs uncovered. In contrast, other turtles painstakingly cover a cavity after depositing eggs. Emydura macquarii drops its shell hard onto the ground to compact the soil in the filled nest. This tamping of the soil has been observed also in Chelodina longicollis , Chelodina oblonga , Chelodina expansa and Pseudemydura umbrina as a way of protection against predators. Red-bellied short-necked turtles abandon their eggs once they are laid and do not protect the hatchlings (Georges, Limpus & Parmenter, 1993).

• Parental Investment
• no parental involvement
• pre-fertilization
  • provisioning

Lifespan/Longevity

Red-bellied short-necked turtles have been reported to live 15 to 20 years in captivity.

Behavior

Red-bellied short-necked turtles swim and bask to control internal body temperatures. During the basking process, tears run down the side of the turtle’s head and into the mouth while the mouth opens and closes, known as gular movements. Panting and frothing at the mouth has been observed, although it is more common in Emydura macquarii than in the other Emydura species. Wetting of the head or limbs, removing the extremities from direst exposure to heat, and changes to breathing patterns are all mechanisms that prevent over-heating (Webb, 1978).

Red-bellied short-necked turtles, like other short-neck turtles, snap and bite when threatened, delivering painful wounds. They tuck in their head while tilting their shell towards the predators to reduce damage to soft body parts (Legler and Georges, 1993).

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• motile motile
• sedentary sedentary
• aestivation
• solitary solitary

Home Range

Red-bellied short-necked turtles do not actively defend a territory.

Communication and Perception

Red-bellied short-necked turtles have highly developed senses necessary for communication and perception. These senses assist them in locating food, avoiding predators, and finding mates during the breeding season. Studies have shown that these freshwater turtles can communicate with each other via a wide range of vocalizations that are too soft for humans to hear. Evidence also suggests that echolocation may be developed for finding prey as well as used to get a three-dimensional image of the turtle’s pond (Latta & Craig, 2009). Red-bellied short-necked turtles, like other freshwater turtles have a nictitating membrane (transparent third eyelid) for underwater vision. Their sense of smell is achieved through the nose and through a specialized Jacobsen’s organ, which identifies chemical debris floating in the air and water. Although turtles do not have an external ear opening, they do have a tympanum (eardrum) that is covered with skin and can detect low-frequency vibrations under water and on land. Red-bellied short-necked turtles have four scent glands in the carapace. These glands produce an odor as defense against predators and among competing males during breeding season. They communicate with potential mates through extensive courtship ceremonies that include the bobbing of their heads as they align their bodies (Legler and Georges, 1993).

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Other Communication Modes
• scent marks scent marks

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• echolocation echolocation
• vibrations vibrations
• chemical chemical

Food Habits

Red-bellied short-necked turtles are omnivorous, feeding on filamentous algae, periphyton, sponges, aquatic macrophytes, aquatic macro-invertebrates, terrestrial insects that fall into the water, and carrion. These turtles also rely heavily on crushing mollusks, fish, insects, worms, aquatic plants, vegetable matter and seeds as a part of daily living (PNG Gas Project, 2005). They rely on their broad, sharp, horny jaws and front feet to tear food, their tongue serves to direct food down the gullet. Many freshwater, short-necked turtles, such as Emydura subglobosa and Chelodina species, ingest large quantities of water that contain their prey by gaping and sucking in prey in the water (Legler & Georges, 2007).

The combination of an elongated digestive tract and slow passage rate ensures maximum nutritional benefit from the large amounts of fiber ingested. Food intake is temperature dependent; an increase in the ambient temperature will cause an increase in the heart rate, in turn increasing the metabolism of the turtle, breaking down the food much faster. Commensal bacteria and other microorganisms help with the task of breaking down cellulose during its passage through the digestive tract. Fat is stored in the abdomen so will not affect thermo-regulation.

Turtle malformations can exist due to diet restrictions, including disfigurement of mouthparts caused by excessive keratin and megacephaly, a disorder where turtles, eating and crushing hard food like mollusks, grow a severely enlarged head, up to 20% of the carapace length (Legler & Georges, 1993).

• Primary Diet
• omnivore omnivore

• Animal Foods
• fish
• carrion carrion
• insects
• terrestrial non-insect arthropods
• mollusks
• terrestrial worms
• aquatic crustaceans

• Plant Foods
• leaves
• flowers
• algae
• macroalgae macroalgae
• phytoplankton phytoplankton

Predation

Predators include introduced red foxes ( Vulpes vulpes ) and domestic cats ( Felis catus ). Water rats ( Hydromys chrysogaster ), goannas ( Varanus gouldii ),and crows ( Corvus tristis ) prey on nests of Emydura macquarii and may prey on Emydura subglobosa . Much predation occurs in coastal areas, where predators include large marine turtles ( Cheloniidae ), tiger sharks ( Galeocerdo cuvier ), crocodiles ( Crocodylus species), and humans (Georges et al., 1993). Human predation includes taking of eggs and adults as a local food source. Emydura subglobosa has four scent glands as a defense mechanism against predators. The odor usually is only released when threatened. Although, the use of the musk is unknown, recent data suggest that once the powerful odor is released, nearby predators leave the surrounding area (Legler and Georges, 1993; Latta, 2009).

Ecosystem Roles

Red-bellied short-necked turtles feed on insects and plants. While digging in the soil during egg-laying or while searching for food they allow for better aeration of the soil by permitting nutrients to reinvigorate the soil, allowing for improved water holding capacity (Georges, 2007). They serve as sustenance for local people but also for large predators (Legler and Georges, 1993).

Commensal bacteria and other microorganisms, such as Polystomoides australiensis , live in bladders of Emydura subglobosa . Notopronocephalus peekayi live in the digestive tract of this species and other freshwater river turtles of New Guinea. This species helps to break down cellulose (Alderton, 1988; Ferguson & Smales, 2006).

• Ecosystem Impact
• creates habitat
• soil aeration soil aeration

Economic Importance for Humans: Positive

The production of turtle meat and turtle products are important for cash economies in New Guinea (Georges, 2007). Freshwater turtles and their eggs are an important source of protein for some peoples (Rhoden and Genorupa, 2000).

• Positive Impacts
• pet trade pet trade
• food food
• body parts are source of valuable material

Economic Importance for Humans: Negative

There are no known adverse effects of Emydura subglobosa on humans.

Conservation Status

Red-bellied short-necked turtles are listed as a species of least concern by the IUCN. However, there may be isolated populations in arid regions throughout their range and have extended times to sexual maturity. This combination leads some to believe that a pre-emptive conservation program should be implemented (Martins and Souza, 2008; Georges 1995). Increasing anthropogenic threats also pose a threat (Rhodin and Genorupa, 2000).

Additional Links

Encyclopedia of Life

Contributors

Melissa Whistleman (author), Radford University, Karen Powers (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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