Cane toad
| Cane Toad | |
|---|---|
| File:Bufo marinus.JPG | |
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Class: | |
| Order: | |
| Family: | |
| Genus: | |
| Species: | B. marinus
|
| Binomial name | |
| Bufo marinus Linnaeus, 1758
| |
The Cane Toad (Bufo marinus), also known as the Giant Neotropical Toad or Marine Toad, is a large terrestrial "true toad" native to Central and South America. A member of the genus Bufo, which includes hundreds of different true toad species in different habitats throughout the world, the dark-brown-colored Cane Toad is a fecund breeder — females lay single-clump spawns with large numbers of eggs. Its reproductive success is partly due to "opportunistic feeding", and among frogs it has a unique diet of both dead and living matter. Adults average 10 to 15 centimetres (4–6 in) in length; the largest recorded specimen weighed 2.65 kilograms (5.8 lb) and measured 38 centimetres (15 in) from snout to vent.
The Cane Toad has large poison glands, and adults and tadpoles are highly toxic to most animals if ingested. Because of its voracious diet, the Cane Toad has been introduced to many parts of the world as a method of agricultural pest control, notably in the case of Australia in 1935, and derives its common name from its use against sugar cane pests.
Taxonomy
The common name of "Cane Toad" is derived from the original purpose of using it to eradicate pests in sugar cane crops. The Cane Toad has many other common names, including "Giant Toad" and "Marine Toad"; the former refers to their size, and the latter to the binomial name, Bufo marinus. Other common names include "Giant Neotropical Toad," "Dominican Toad," "Giant Marine Toad," "Giant Toad," "Marine Toad, and "South American Cane Toad."
The Cane Toad is morphologically similar to many of the species in the Bufo genus. It shares a strong similarity with three species: the Southern toad (Bufo terrestris), the Oak Toad (Bufo quercicus), and Fowler's toad (Bufo fowleri), which is very similar to the American toad (Bufo americanus). The Southern Toad can be distinguished by the presence of two bulbs in front of the parotoid glands, and the Oak Toad by the presence of an orange line down the centre of its back, and by smaller, round parotoid glands. The Fowler's and American Toads both have a pale, cream-white stripe that runs down the dorsal surface; the Cane Toad lacks this stripe.
In Australia, the adults may be confused with species of the Limnodynastes, Neobatrachus, Mixophyes, and Notaden genera. These species can be readily distinguished from the Cane Toad by the lack of large parotoid glands behind their eyes. Cane toads have been confused with the Giant Burrowing Frog (Heleioporus australiacus), because both are large and warty in appearance; however, the Giant Burrowing Frog can be readily distinguished from the Cane Toad by its vertical pupils. Juvenile Cane Toads may be confused with species of the Uperoleia genus, because they all have large parotoid glands; juvenile Cane Toads can be distinguished from these species by the ridging around their eyes and the lack of bright colouring on their thighs.
Physical description
The Cane Toad is a very large frog, reaching an average length of 10 to 15 centimetres (4–6 in), and much longer in some cases. "Prinsen", a specimen kept as a pet in Sweden, is listed by the Guinness Book of Records as the largest recorded specimen, which weighed 2.65 kilograms (5.8 lb) and measured 38 centimetres (15 in) from snout to vent, or 53.9 centimetres when fully extended.[1] A preserved specimen in the museum of Queensland was 24.1 centimetres (9.4 in) long 16.5 centimetres (6.5 in) wide and weighed 1.36 kg (3 lb).[2] They have a life expectancy of 10 to 15 years in the wild, and as long as 20 years in captivity.
The skin of the Cane Toad is dry and warty. It has distinct ridges above the eyes, which run down the snout. Cane Toads can be grey, brown, red-brown or olive in colour, with varying patterning. A large parotoid gland lies behind each eye. The ventral surface is cream and may have blotches in shades of black or brown. The pupils are horizontal and the irises golden. The toes have a fleshy webbing at their base, and the fingers are free of webbing .
Cane Toad morphlings are much smaller than adults—only 5 to 10 millimetres (0.2–0.4 in) long; typically, they have smooth, dark skin, although some specimens have a red wash. Morphlings lack the adults' large parotoid glands, so they are usually less poisonous. Because they lack this key defence mechanism, it is estimated that only 0.5% of metamorph toads reach adulthood.[3] The tadpoles are small and uniformly black. They are bottom-dwellers and group together, creating a school, and congregate around plants. Tadpoles reach up to 27 millimetres (1 in) in length, or up to 22 millimetres (0.9 in) during overcrowding.
Ecology and behaviour
Adult Cane Toads possess enlarged parotoid glands behind the eyes, and other glands across the back. When threatened, the Cane Toad secretes a milky-white fluid known as bufotoxin from these glands. Bufotoxin contains components that are toxic to many animals. There are many reported deaths of animals, and even reported deaths of humans,[4] after consumption of Cane Toads. A Cane Toad is capable of inflating its lungs, puffing up and lifting its body off the ground to appear taller and larger to a predator.
Most frogs identify prey by their movements; Cane Toads can also locate food using their sense of smell. They are not therefore limited to living prey and can eat plants, carrion, dog food and other household refuse, as well as the normal frog prey of small vertebrates and a wide range of invertebrates. They are active primarily at night, ranging far from water.
The common name of "Marine Toad", and the scientific name Bufo marinus, suggest a link to marine life; however, there is no such link. Adult Cane Toads are entirely terrestrial, venturing to fresh water to breed, and tadpoles have been found to only tolerate salt concentrations equivalent to that of 15% of sea water.[5] Both eggs and tadpoles are toxic to many animals. This toxic protection is lost for a period after metamorphosis until the parotoid glands develop. Cane Toads inhabit open grassland, generally avoiding forested areas; this inhibits their spread in many of the regions in which they were introduced.
Many species prey on the Cane Toad in its native distribution. These include the Broad-snouted Caiman (Caiman latirostris), the Banded Cat-eyed Snake (Leptodeira annulata), the eel (family: Anguillidae), various species of killifish, the Jungle Perch (Kuhila rubestris), some species of catfish (order: Siluriformes) and some species of ibis (subfamily: Threskiornithinae). Predators outside the Cane Toad's native range include the Tawny Frogmouth (Podargus strigoides), the Whistling Kite (Haliastur sphenurus), the Water Rat (Hydromys chrysogaster), the Black Rat (Rattus rattus) and the Water Monitor (Varanus salvator). These predators require either a tolerance to the Cane Toad's toxins, or behavioural adaptations that allow them to avoid the most poisonous areas of the frog as they hunt and consume it.
Reproduction
The males of the Cane Toad will call near a still water source to attract females. The call is a loud, long trill; likened to the sound of a small engine or "pur". As with all true toads, the male and female undergo inguinal amplexus, in which the male is behind the female, and grips her around the waist. The female will then release her eggs, which the male covers with sperm.
Females lay from 4,000 to 36,000 eggs per clutch, and breed at least twice per year. They are opportunistic breeders, breeding whenever enough water is available. As a result, they have no breeding season. The eggs are laid in still or slow flowing water, where the males congregate and call as a chorus. Eggs are laid in long strands, usually tangled around plants or submerged objects. The eggs are black, and surrounded in a clear jelly 4-5mm in diameter. The duration until the eggs hatch is dependent upon the water temperature — lasting from 25 hours at 34 degrees Celsius (93.2 Fahrenheit) to 155 hours at 14 degrees Celsius (57.2 Fahrenheit). The development of tadpoles also varies, from 12 to 60 days.
Distribution
The Cane Toad is native to the Americas, from the Rio Grande Valley in southern Texas to central Amazon and south-eastern Peru. This range includes both tropical and semi-arid environments. The density of the Cane Toad within its native distribution is significantly lower than that of its introduced distribution. In South America, it is recorded at densities of 20 adults per 100 square metres, but in Australia the density reaches 1000-2000 adults over the same area.[6]
Introductions
The Cane Toad has been introduced to many regions of the world, particularly the Pacific, for reasons of biological control of agricultural pests. Prior to 1844, Cane Toads were introduced into Martinique, Barbados and Jamaica. They were introduced into Jamaica to control the rat population, however this was unsuccessful.
In 1920, Cane Toads were introduced into Puerto Rico to control the populations of white-grub (genus: Phyllophaga), which was a pest of sugar cane. By 1932, the Cane Toad was widespread throughout the island, and the populations of white-grubs were dramatically decreased. The decrease in the white-grub population was attributed to the Cane Toad, however there may have been other factors. The six year period after 1931 (when the Cane Toad was most prolific, and the white-grub saw dramatic decline) recorded the highest ever rainfall for Peurto Rico. However, the assumption of the Cane Toad's involvement in the decrease in white-grub populations led to the large scale introductions throughout many parts of the Pacific.
Introduced populations now occur in Australia, Florida, Papua New Guinea, the Philippines, the Ogasawara Islands and Ryukyu Islands of Japan, most Caribbean islands and many Pacific islands including Hawaii and Fiji. The introductions were generally a failure, and most of the pests the Cane Toad was originally introduced to kill were wiped out with the use of insecticides. Since the introductions, the Cane Toad has become a pest in most countries to which it was introduced, and poses a serious threat to native animals of the regions. The introduction of the Cane Toad has had a particularly large impact on Australian biodiversity. This is probably due to the large number of species that the Cane Toad successfully competes with, and the large areas of open grassland.
Introduction to Australia
In attempts to control the native Cane Beetle, 102 Cane Toads were introduced to Australia from Hawaii in June 1935. They bred immediately in captivity and by August 1935 over 3000 young toads were released in areas around Cairns, Gordonvale and Innisfail in northern Queensland. After successes in these areas more Toads were released around Ingram, Ayr, Mackay and Bundaberg. Releases were temporarily limited due to environmental concerns, but resumed in other areas after September 1936. Since their release, toads have steadily expanded their range through Queensland, reaching the border with New South Wales in 1978 and the Northern Territory in 1984. The toads on the western frontier of their advance have evolved larger legs.[7] It is thought to be related to their ability to travel further. It is estimated that the Cane Toad migrates at an average of 40 kilometres (25 mi) per year.[8]
The long-term impact of toads on the Australian environment is difficult to determine. Precipitous declines in populations of the Northern Quoll have been observed after toads have invaded an area. There are also a number of reports of goanna and snake populations declining after the arrival of toads.[9] The preliminary risk assessment of Cane Toads in Kakadu National Park stated that the predation of the Cane Toad by native wildlife to be the greatest risk to biodiversity. The other factors, such as competition with native wildlife for similar resources, and predation of the Cane Toad on native wildlife, were considered much lower risk.[10]
A number of native species have been reported as successfully preying on toads. Some birds, such as the Black Kite (Milvus migrans),[11] have learned to attack a toad's belly, avoiding the venom-producing glands on the back of the head. Reports by researchers in the Northern Territory indicate that a native frog, Dahl's Tree Frog (Litoria dahlii), is apparently able to eat the tadpoles and live young of the toad without being affected by the poison that often kills other predators.[12] This is believed to account for slower than expected infestations of toads in certain areas of the Northern Territory. Some snakes have been reported to have evolved smaller jaws so that they are unable to swallow large Cane Toads and survive a smaller dose of poison. [13]
As of 2005, some success is being had using dark ultraviolet lights to lure and capture Cane Toads for extermination.[14]
Cane Toads in popular culture
The introduction and migration of the Cane toad in Australia was popularized by the film Cane Toads: An Unnatural History (1987) which tells the tale with a humorous edge and is often shown in Environmental Science courses. It was also referenced in Simpsons episode Bart vs. Australia.
Notes
- ^ Wyse, E. (editor) (1997). Guinness Book of Records 1998. Guinness Publishing. p. 249. ISBN 085112044X.
{{cite book}}:|first=has generic name (help) - ^ Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books. p. 108. ISBN 0730104680.
- ^ Anstis, M. (2002). Tadpoles of South-Eastern Australia: A Guide with Keys. Reed New Holland. p. 274. ISBN 1876334630.
- ^ "issg Database: Ecology of Bufo marinus". Retrieved 2006-05-16.
- ^ Ely, C.A. (1944). "Development of Bufo marinus larvae in dilute sea water". Copeia. 56(4): 256.
- ^ Lampo, M. (1998). "The Invasion Ecology of the Toad Bufo marinus: from South America to Australia". Ecological Applications. 8(2): 288–296.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ "Toxic Toads Evolve Longer Legs, Study Says. 15/02/06. National Geographic News". Retrieved 2006-05-19.
- ^ Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books. p. 112. ISBN 0730104680.
- ^ Mayes, P.J. (2005). "Diet and foraging behaviour of the semi-aquatic Varanus mertensi (Reptilia: Varanidae)" (PDF). Wildlife Research. 32: 67–74.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ "SSR164 - A preliminary risk assessment of cane toads in Kakadu National Park". Retrieved 2006-05-22.
- ^ Mitchell, D. (1995). "Predation on the Cane Toad (Bufo marinus) by the black kite (Milvus migrans)". Memoirs - Wueensland Museun. 38: 512–531.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ "NT frog 'eats' Cane Toad. 15/15/2004. ABC News Online". Retrieved 2006-05-09.
- ^ Phillips, Ben L. (2004). "Adapting to an invasive species: Toxic Cane Toads induce morphological change in Australian snakes". PNAS. 101(49): 17150–17155.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help); Unknown parameter|month=ignored (help) - ^ "Northern Australian Frog Database System". Retrieved 2006-05-20.
References
- Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books. ISBN 0730104680.
- Barker, J. (1995). A Field Guide to Australian Frogs. Surrey Beatty & Sons. ISBN 0949324612.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - "Cane Toad". Retrieved 2006-05-08.
- "Discover Life - Bufonidae: Bufo marinus (Linnaeus, 1758) - Cane toad, Giant toad, Marine toad, Sapo grande". Retrieved 2006-05-18.
- "ADW: Bufo marinus: Information". Retrieved 2006-05-23.
- Freeland, W.J. (1985). "The Need to Control Cane Toads". Search. 16(7-8): 211–215.