Arafura wart snake
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Arafura wart snake |
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| Acrochordus arafurae | ||||||||||||
| McDowell , 1979 |
The arafura wart snake ( Acrochordus arafurae ) is an aquatic snake belonging to the family of the warthog snake (Acrochordidae) that is common in tropical Australia . Characteristic for the species is a pronounced sexual dimorphism and a low metabolic rate . The species is distributed in eastern Indonesia , Papua New Guinea , as well as in northern Australia ( Queensland and Northern Territory ). According to the IUCN, it is not considered endangered ( least concern ).
features
They are large, heavily built snakes that can reach a total length of up to two meters. As is typical of wart snakes, the skin is wrinkled; the small, conical scales lead to a grainy surface of the skin. The pronounced sexual dimorphism is characteristic : adult females have an average head-trunk length (from the tip of the snout to the cloaca ) of 135 cm, while adult males only 105 cm. Furthermore, females have a significantly heavier build, shorter tails and larger heads than males.
nutrition
Like other wart snakes, the Arafura wart snake feeds exclusively on fish ( piscivor ). The food intake takes place mainly in the rainy season because of the increased food supply. Fish are overwhelmed by choking with the help of the wrinkled, grainy skin. There are clear differences between the sexes. Males are less selective feeders than females; so stomach samples typically show the remains of various smaller fish. Stomach samples from adult females, on the other hand, only show a single, but large, prey animal. Juvenile females show the males' more generalized diet.
Way of life
The snakes are exclusively aquatic and inhabit fresh water. During the dry season they stay in billabongs , during the rainy season they populate the now flooded grassland. They are mostly nocturnal. Differences between the sexes could be found in the preferred water depths during the rainy season; so females are mainly caught in water depths of over one meter, while males mainly inhabit shallow water below one meter.
The population density of these snakes within the billabongs varies greatly, but can reach 100 snakes per hectare with a high food supply. The snakes are viviparous; a litter consists of an average of 17 pups.
metabolism
Like other wart snakes, the Arafura wart snake is a low-energy specialist and, as such, exhibits a remarkably low metabolism. These snakes eat relatively seldom and show the lowest reproduction rate that could be demonstrated in snakes: In one study, only 7% of the adult females were reproductive.
Like other aquatic snakes, the arafura wart snake takes in oxygen through both its lungs and skin. The perspiration can thereby cover up to 30% of the oxygen demand. The maximum diving time is temperature-dependent, as increased temperatures lead to an increased metabolism and an associated higher oxygen demand. At 20 ° C the animals can stay under water for up to 77 minutes, but only 28 minutes at 32 ° C.
Reasons for Sex Dimorphism
As with most snakes, the size dimorphism can probably be explained by sexual selection : Larger females can produce more offspring, so a larger body size produces more offspring. The proportional differences probably have other causes. The longer tail in the male is explained by the need to accommodate the hemipenis . In contrast, the larger heads of the females can possibly be interpreted as adaptations to the larger prey fish: As with all snakes, prey animals are always devoured as a whole, so the size of the head limits the maximum size of the prey animals.
Individual evidence
- ↑ a b c d R. Shine: Sexual differences in morphology and niche utilization in an aquatic snake, Acrochordus arafurae . In: Oecologia . tape 69 , no. 2 , 1986, p. 260-267 ( springerlink.com [PDF]).
- ↑ Acrochordus arafurae in the IUCN Red List of Threatened Species . ( The IUCN Red List of Threatened Species. 2012.2), accessed December 28, 2012.
- ^ A b Darryl Houston, Richard Shine: Sexual Dimorphism and Niche Divergence: Feeding Habits of the Arafura Filesnake . In: The Journal of Animal Ecology . tape 62 , no. 4 , September 1993, pp. 737 , doi : 10.2307 / 5393 , JSTOR : 5393 .
- ^ A b c d Richard Shine, Ecology of a Low-Energy Specialist: Food Habits and Reproductive Biology of the Arafura Filesnake (Acrochordidae) . In: Copeia . tape 1986 , no. 2 , April 9, 1986, pp. 424 , doi : 10.2307 / 1445000 , JSTOR : 1445000 .
- ↑ Kirstin Pratt: Metabolic rate, respiratory partitioning and the implications for dive duration in the bimodally respiring Arafura filesnake, Acrochordus arafurae . June 1, 2009 ( espace.library.uq.edu.au ).
