Mertens water monitor
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Mertens water monitor ( Varanus mertensi ) |
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| Glauert , 1951 |
The Mertens water monitor ( Varanus mertensi ) or Australian water monitor is a species of monitor lizard ( Varanus ) native to Australia . It is probably the monitor lizard that is most strongly tied to water.
features
The Mertens water monitor reaches a total length of up to 1.3 m with a head-trunk length of 48 cm. Overall lengths of just over 1 m are typical of fully grown specimens. The nostrils are strongly shifted dorsally (= above), which means that the Mertens water monitor can breathe in the water while only having to lift small parts of its snout out of the water. The tail is about 1.5 times as long as the head and torso, has a clearly pronounced keel on the top and is strongly compressed at the sides as a rudder tail. The scales of the Mertens water monitor are very smooth and make wet specimens in particular appear very slippery.
The upper side of the body is black to brown or gray and drawn with scattered small yellowish dots. The underside is yellow to cream in color, and the neck and chest are lightly flecked with gray.
distribution and habitat
The species inhabits northern Australia from the Kimberley in the east to the west of the Cape York Peninsula . Their occurrences are tied to permanent bodies of water, such as rivers, lakes and permanent billabongs .
Way of life
General
Like all monitor lizards, the Mertens water monitor is also diurnal. The animals spend the night in burrows, which are straight corridors 0.3–3.2 m long with an enlarged chamber at the end of the embankment, and whose entrances are often only slightly above the water surface. The burrows are left at around 8 a.m., used as a refuge in the event of disturbances and at around 4 p.m. the monitor lizards return to the burrow at night. Occasionally the monitor lizards also sleep in the water, in hollow tree trunks or on branches that hang over the water. In the event of disturbances, the monitor lizards submerge. In contrast to many other Australian monitor lizards, Mertens water monitor usually does not keep a seasonal rest period and remains active all year round; this is related to the year-round availability of food in permanent waters. Only in rare cases do the Mertens water monitors bury themselves during a rest period in the dry season from May to October. The Mertens water monitor is a little prudent thermoregulator, but usually keeps its body temperature around 34 ° C.
nutrition
The Mertens water monitor flickers and searches for prey both on land and in the water. In shallow water it can use its tail to carry fish towards its mouth, and in deep water it runs to the bottom. The food spectrum includes aquatic prey animals and those living on the bank such as crustaceans, beetles, fish, spiders, various insects, aphipods, frogs, reptile eggs, birds and small mammals. They are known for digging up buried turtle eggs.
Reproduction
The male Mertens water monitor are spermatogenic in the dry season from July to September and store their sperm until December to March. During this period of the rainy season, the females' vitellogenesis , and thus also the mating season, occurs. Due to the premature production of the sperm, the Mertens water monitor is always ready to mate at the earliest possible point in time. In the Mertens water monitor, too, typical comment fights take place between the males who fight for females. The clutches are laid in the early dry season and contain 3–14 eggs. The young then hatch during the height of the next rainy season when the maximum amount of food is available.
Systematics
It was first described in 1951 by the herpetologist Ludwig Glauert . Type locality is Moola Bulla , Western Australia (18 ° 12'S, 127 ° 30'E). The specific epithet honors the German herpetologist Robert Mertens (1894–1975), who in 1942 wrote an important monograph on monitor lizards. Within the genus Varanus , Varanus mertensi is assigned to the subgenus Varanus based on its hemipenis structure . DNA analyzes indicate a particularly close relationship with Varanus giganteus and Varanus spenceri , and confirm the classification based on the hemipenis morphology.
Danger
Like other Australian monitor lizards, the Mertens water monitor is endangered by the ( neozoic ) aga toad ( Bufo marinus ) introduced into Australia . They die when they ingest the toxins from the skin by trying to eat the toad. In the case of a population on the Daly River ( Northern Territory ), the population decline one year after the arrival of the cane toads was estimated to be up to 92% compared to the population before the arrival of the cane toads.
swell
- K. Christian (2004): Varanus mertensi . In: ER Pianka & DR King (Eds.): Varanoid Lizards of the World . Indiana University Press, Bloomington & Indianapolis. ISBN 0-253-34366-6
Individual evidence
- ^ PJ Mayes (2007): The Use of Burrows and Burrow Characteristics of the Semi-Aquatic Varanus mertensi (Reptilia: Varanidae) . Mertensiella 16 ( Advances in Monitor Research III ): 312-321
- ^ PJ Mayes, GG Thompson & PC Whiters (2005): Diet and foraging behavior of Varanus mertensi (Reptilia: Varanidae) . Wildlife Research 32: 67-74
- ↑ a b c P. J. Mayes, SD Bradshaw & FJ Bradshaw (2007): Reproductive Seasonality in the Semi-Aquatic Monitor, Varanus mertensi (Reptilia: Varanidae) . Mertensiella 16 ( Advances in Monitor Research III ): 322-335
- ↑ AJ Fitch, AE Goodman & SC Donnellan (2006): A molecular phylogeny of the Australian monitor lizards (Squamata: Varanidae) inferred from mitochondrial DNA sequences . Australian Journal of Zoology 54: 253-269
- ↑ JS Doody, B. Green, R. Sims & D. Rhind (2007): A Preliminary Assessment of the Impacts of Invasive Cane Toads (Bufo marinus) on Three Species of Varanid Lizards in Australia . Mertensiella 16 ( Advances in Monitor Research III ): 218-227
Web links
- Varanus mertensi in The Reptile Database
- PJ Mayes (2006): The ecology and behavior of Varanus mertensi (Reptilia: Varanidae) . Theses: Doctorates and Masters. Paper 42. Edith Cowan University.
- S. Ward, J. Woinarski, T. Griffiths & L. McKay (2006): Mertens Water Monitor, Varanus mertensi (PDF; 525 kB) . Northern Territory Government, Threatened Species of the Northern Territory.