Chelodina expansa

Broad-shelled long-necked turtle
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Order: Testudines
Suborder: Pleurodira
Family: Chelidae
Subfamily: Chelodininae
Genus: Chelodina
Subgenus: Macrochelodina
Species: C. (M.) expansa
Binomial name
Chelodina expansa
(Gray, 1857)
Synonyms [1]
  • Chelodina expansa Gray, 1857
  • Chelodina expansas Goode, 1967 (ex errore)
  • Chelodina oblonga expansa Blackmore, 1969
  • Macrochelodina expansa Wells & Wellington, 1985

Chelodina (Macrochelodina) Expansa, commonly known as the broad-shelled river turtle or the broad-shelled snake-necked turtle [2], is a pleurodire freshwater turtle and is the biggest of the long-necked turtles. [3] The broad-shelled river turtle is one of the oldest maturing and longest living species of freshwater turtles in existence[4] and occurs in wide sympatry with Emydura macquarii and Chelodina longicollis. C. expansa is listed as ‘vulnerable’ in South Australia and ‘threatened’ in Victoria.[3]

Distribution and habitat

Broad-shelled river turtles are found throughout the Murray-Darling River system of South-Eastern Australia. A number of distinctive populations have been located across central and coastal Queensland areas. [2]

C. expansa is mostly found in turbid waters at depths of which are greater than three metres. [3] The turtle generally inhabits permanent streams [2] and may occur in rivers, oxbows, ponds in floodplains, backwater, and swamps [3] across its distributed region, however is mostly a river turtle. [2] The broad-shelled river turtle will tend to inhabit environments that are undisturbed and have moderate vegetation cover for nest construction. The turtle has shown a preference of aquatic habitats in structured environments, where submerged logs, root systems and dead trees occur. Factors such as shelter from predators, and food availability may influence the habitat preference of e. Expansa. Seasonal changes including the water levels and flow may also influence the selected the habitat. [3]

Description

The broad-shelled river turtle has a broad, oval and flattened shell with a length of around 50cm. [2]The carapace length is often longer in females then males. [3] The turtle has a rich brown to blackish-brown above, typically displaying fine dark flecks or reticulations. The turtle has a whitish or creamy coloured underneath. The plastron is narrow and the shell does not display any noticeable expansion anteriorly. The shell is usually twice as long as wide and is broadest at the level of the bridge. The head is broad and highly depressed and the eyes are directly dorsolateral. [2] When extended, the neck may surpass the measurement of the carapace. [3]

Behaviour

The broad-shelled river turtle is mostly active from the Australian spring season (October) through to early autumn (April). The species tends to decrease in movement and feeding over the cooler winter months.[3] C. expansa is described to also show head bobbing and self-grooming actions. [5]

Chelodina expansa spends most of its time in water.[4] During periods when water levels are low, C. expansa will traverse over land to find other water sources. The turtle may also bury itself into mud and enter extended periods of aestivation until rain occurs and water levels increase.[4] The broad-shelled river turtle has shown a ‘body-slamming’ type behaviour when compacting nests [6]The turtle is not typically found to nest after dark and is generally observed to nest during daylight. This is assumed to be a strategy to select more thermally appropriate nest sites, where both areas of sun and shade exposure can be identified. They will tend to select sites that have higher sun coverage to construct their nests. Due to the extended incubation period, the selection of nest sites is commonly a long way from the waters edge and is seen to be a behavioural strategy to minimise the risk of nest flooding. Hatchlings are however exposed to a number of challenges during their travels to the water. [6]

Reproduction

C.expansa habitually constructs its nest throughout the Australian autumn season[2] or in early winter when soils decrease in temperature. [7] The female broad-shelled river turtle will generally travel up to one kilometre away from the bank to lay her eggs and it is common to find nests at the top of ridges. [3] Nest temperatures will decrease after initial construction, remain low during the winter period and slowly increase during spring to a maximum temperature during summer. [8]

Clutches usually contain between 5-28 eggs and the incubation period is exceptionally long due to inherently slow embryonic development[7], averaging between 324 and 360 days.[3] The development of the embryo also slows the process as it enters a two distinct diapause stages[3][7]. The primary diapause stage occurs inside the female, the secondary diapause is triggered through a drop in temperature and occurs after the egg is laid and once a small period of growth has occurred.[3] The young will generally hatch during Spring [2], Asynchronous hatching is most likely maladaptive in the natural environment [7]

Diet

The broad-shelled river turtle is highly specialised and entirely carnivorous. [3] C. expansa primarily preys upon frogs, [9] crustaceans, aquatic insects, and small fish. [3]

Predators

The red fox (Vulpes vulpes) and ravens (Corvus spp.) are the major threat for the nests of the broad-shelled river turtle. Predation on nests is the main challenge for C. expansa, however it is thought that the turtle becomes aware of predators, mostly from olfactory and visual signs. The main predator for hatchlings is the spotted barramundi. [3]

Threats

The broad-shelled river turtle is infected with parasitic adult worms (D. pearsoni and D. megapharynx). The worms appear to be host specific and live in the intestines of C. expansa. [10]

For photographs and distribution maps of Chelodina Expansa please see: https://commons.wikimedia.org/wiki/Category:Chelodina_expansa.

References

  1. ↑ Fritz Uwe; Peter Havaš (2007). "Checklist of Chelonians of the World" (PDF). Vertebrate Zoology. 57 (2): 335–336. ISSN 1864-5755. Archived from the original (PDF) on 2010-12-17. Retrieved 29 May 2012.
  2. 1 2 3 4 5 6 7 8 Cogger, Harold (2014). Reptiles and amphibians of Australia. CSIRO Publishing.
  3. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Ercolano, Ellyn (2008). "Aquatic and terrestrial habitat use of the Australian freshwater turtle, Chelodina expansa".
  4. 1 2 3 Loudon, F.K.; Spencer, R.J. (2012). Applying theories of life history and ageing to predict the adaptive response of Murray River turtles to climate change and habitat. Wildlife and Climate Change: Towards robust conservation strategies for Australian fauna.
  5. ↑ Legler, J.M. (1978). "Observations on behavior and ecology in an Australian turtle, Chelodina expansa (Testudines: Chelidae).". Canadian Journal of Zoology. 56(11),: 2449–2453.
  6. 1 2 Booth, D.T. (2010). "The natural history of nesting in two Australian freshwater turtles.". Australian Zoologist,: 198–203.
  7. 1 2 3 4 Booth, D (2002). "The breaking of diapause in embryonic broad-shell river turtles (Chelodina expansa).". Journal of Herpetology,: 304–307.
  8. ↑ Booth, D.T. (1998). "Nest temperature and respiratory gases during natural incubation in the broad-shelled river turtle, Chelodina expansa (Testudinata: Chelidae).". Australian Journal of Zoology: 183–191.
  9. ↑ Chessman, B.C. (1983). "Observations on the Diet of the Broad-Shelled Turtle, Chelodina Expansa Gray (Testudines: Chelidae).". Wildlife Research: 169–172.
  10. ↑ Jue Sue, L; Platt, T.R. (1999). "Description and life-cycle of three new species of Dingularis ng (Digena: Plagiorchiida), parasites of Australian freshwater turtles.". Systematic Parasitology,: 175–207.
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