Tympanoctomys

from Wikipedia, the free encyclopedia
Tympanoctomys
Red viscacha rat (Tympanoctomys barrerae)

Red viscacha rat ( Tympanoctomys barrerae )

Systematics
Order : Rodents (Rodentia)
Subordination : Porcupine relatives (Hystricomorpha)
Partial order : Hystricognathi
without rank: Guinea Pig Relatives (Caviomorpha)
Family : Trug rats (Octodontidae)
Genre : Tympanoctomys
Scientific name
Tympanoctomys
Yepes , 1942

Tympanoctomys is a genus from the South American rodent family of the turtle rats (Octodontidae). Two species living today are placed in the genus, the better known is the red viscacha rat ( Tympanoctomys barrerae ), another, the Kirchner viscacha rat ( Tympanoctomys kirchnerorum ), was only described in 2014. Both species inhabit extremely dry areas in the west of Argentina , which means that their range is highly fragmented. They live underground in complex burrows and are pure herbivores, with salt plants predominating. Overall, however, little is known about the way of life. Tympanoctomys is the first genus of mammals to beassumed to havea tetraploid set of chromosomes . The population of both species is considered threatened. The genus was introduced in 1942. In addition to the more recent species, Tympanoctomys cordubensis is known to be extinct, which has been passed down from the Pleistocene deposits of central and eastern Argentina.

features

Habitus

Tympanoctomys species are small representatives of the tug rats and are mouse-like in shape with a total length of 25 to 30 cm, the tail is about the length of the rest of the body. The weight varies between 50 and 100 g. The fur on the back is mostly reddish or yellowish-brown in color, on the belly it appears whitish. The tail is densely hairy and two-tone with a darker tint on the top and a cream-colored underside. At the end of the tail there is a long, brush-shaped tuft of hair that is more pronounced in the red viscacha than in the Kirchner viscacha. The head is large, the ears are small and have a tuft of hair at the base. Stiff, bundle-like hairs that grow on the palate behind the upper incisors are unique . The front and rear feet each have four toes, the back sides have thick hair. The hind foot is relatively short, the four claws are well developed.

Skull and dentition features

The skull is short and wide, when viewed from above it has a pear-shaped shape, so that it is wider in the area of ​​the skull than on the zygomatic arches . The length of the skull is 27 to 39 mm, the width on the short and deep zygomatic arches 17 to 19 mm, on the brain skull up to 21 mm. The greater width of the posterior skull is mainly due to the extreme inflation of the tympanic membranes . These are also very extensive in their length and take up almost half the length of the skull, so within the tympanum Tympanoctomys has the largest tympanic bubbles. The rostrum, on the other hand, is narrow and the nasal bone short and flat. The frontal bone typically widens backwards.

The lower jaw is short and wide with lengths between 17 and 22 mm. The bit is significantly reduced and only consists in each case a cutting tooth, a bicuspid and three molar per arch, the dental formula is accordingly: . This means that a total of 20 teeth are formed. The incisors are vertical or point backwards ( orthodontic or opisthodontic ). They are wide and have orange enamel . Between them and the posterior teeth there is a diastema , that of the lower jaw is moderately deepened. The back teeth are all extremely high crowned ( euhypsodont ). The shape of the molars resembles a figure 8 when viewed from above, but the two flap-like extensions created by the central constriction are clearly compressed at the front and back. The largest tooth is the last premolar, in which another tongue-side constriction occurs on the chewing surface. The rearmost molar is greatly reduced in size and also 8 or comma shaped. The length of the upper and lower row of teeth is 5 to 6 mm each.

genetics

What is noteworthy about Tympanoctomys is that the animals may have one tetraploid chromosome set, that is, they have four chromosome sets instead of the usual two, with the red viscacha rat being the first mammal to be suspected of this. The core DNA has a weight of 16.8 pg (picograms), which is twice as much as in the closely related but diploid tassel rats, such as the visca rat ( Octomys ) or the brushtail rat ( Octodontomys ). The karyotype comprises 50 pairs of chromosomes , 36 pairs of which represent metacentric to submetracentric chromosomes and 14 pairs represent subtelocentric autosomes (2N = 102). However, the diploid number is lower than would be expected from a simple doubling of the karyotype. As is typical of polyploid organisms, the sperm are on average larger than in diploid organisms .

Some scientists, on the other hand, attribute the high weight of nuclear DNA not to a tetraploid set of chromosomes, but to an increased concentration of heterochromatin in the cell nuclei.

distribution

The representatives of the genus Tympanoctomys are common in southern South America. The red viscacha rat occurs in central-western Argentina , but is only occupied by around a dozen sites, which are spotty in the provinces of Mendoza , La Pampa and Neuquén over an area of ​​around 490 km in north-south and 280 km in east -West direction are distributed. The second species, the Kirchner Viscacha rat, lives in a small area around 550 km further south in the province of Chubut . It is only known from a single population ; some subfossil finds dating back to around 5400 years have been documented along the Río Chubut . The genus is endemic to particularly arid landscapes, the habitats include salt pans , sand dunes, and scrubland. The height distribution ranges from 300 to 1400 m.

Way of life

Tympanoctomys is nocturnal and solitary. The animals live underground in complex burrows that are dug in sand hills. The burrows have several entrances, food chambers, continuous and blind tunnels and can be laid out on up to three different levels. It is noteworthy that the entrances are positioned on flat slopes in such a way that they let sunlight directly into the tunnel system in winter when the sun is on average lower, but not in summer when the sun is higher. The animals are pure herbivores that feed mainly on the leaves of halophytes such as Atriplex , Allenrolfea , Heterostachys and Suaeda . When eating, they hold the leaves with their front paws and rub the leaf surface with their lower incisors. As a result, they free the leaf epidermis of excess salts and thus reduce the excessive absorption of electrolytes . As a special feature, two bundles of bristles have formed on the sides of the palate opposite the lower jaw incisors, which help with rubbing through vibrations. They act as a second pair of front teeth when cleaning. This enables Tympanoctomys to remove salt from food faster than other rodents in arid regions can. As a special adaptation to the extremely dry climatic conditions, the kidneys are designed to enrich urine to a high degree, which reduces water loss. Reproduction has been little studied. All known young animals have so far been born in February. Young weigh 4 g and have closed eyes. After four days the body weight has about doubled, on the sixth day they open their eyes. The youngsters eat their first solid food when they are ten days old, also rubbing the leaves.

Systematics

Internal systematics of the Trug rats according to Gallardo et al. 2013
 Octodontidae  



 Aconaemys


   

 Spalacopus



   

 Octodon


   

 Octodontomys




   

 Octomys


   

 Pipanacoctomys


   

 Tympanoctomys





Template: Klade / Maintenance / Style

Tympanoctomys is a genus from the family of Trug rats (Octodontidae), which in turn belong to the guinea pig relatives (Caviomorpha). The Trug Rats comprise just over half a dozen species, all of which are native to South America and inhabit diverse biotopes , from more humid bush and forest landscapes to rocky regions to desert-like areas. The closest relatives of Tympanoctomys include the golden viscacha rat ( Pipanacoctomys aureus ) and the viscacha rat ( Octomys mimax ). In some newer nomenclatures the golden vizcacha rat and in addition, which is Chalchaleros-viscacha rat ( Salinoctomys loschalchalerosorum ) within the genus Tympanoctomys performed. According to molecular genetic studies, the turtle rats emerged in the Upper Miocene around 7.8 million years ago. Their emergence goes hand in hand with changes in the landscape and habitat fragmentation in connection with the folding of the Andes . Tympanoctomys then formed in the transition from the Pliocene to the Pleistocene around 2.5 million years ago. A split into the two species that exist today probably took place around a million years later, which correlates with the end of a major ice age phase in Patagonia. The current, fragmented distribution of the genus is possibly a relic, it was probably much more extensive during the cold phases of the Pleistocene.

Tympanoctomys in the narrower sense comprises two species that are alive today and one that is extinct:

The extinct form Tympanoctomys cordubensis occurred in the late Lower Pleistocene 900,000 to 780,000 years ago in the central area of ​​what is now Argentina, to the east outside of today's distribution area. But only two sites are known, one near Córdoba and one on the Atlantic coast near Mar del Plata . The previous finds include two lower jaws. The form was set up more than 50 years before the introduction of the red viscacha rat as a living representative, but was originally called Pithanotomys cordubensis . It was not until 2002 that he was assigned to Tympanoctomys .

The genus Tympanoctomys was scientifically named by José Yepes in 1942 . Thus Yepes had the Red viscacha rat, the 1941 Octomys barrerae their first description to received, a new position, he had the name but when nudum nouns used in 1940. The generic name Tympanoctomys is made up of the Greek word τύμπανο ( tympano "timpani", "drum") and the scientific name of the viscacha rat. The first part of the word relates to the inflated tympanic bladder , the second to the 8-shaped rear molars.

Threat and protection

Both species are endangered in their existence. They represent habitat specialists that only occur in limited, extremely dry areas. The distribution area of ​​the red viscacha rat is therefore strongly fragmented, the Kirchner-Viscacha rat has so far only been detected at one locality.

literature

  • M. Monica Díaz, Rubén M. Barquez and Diego H. Verzi: Genus Tympanoctomys Yepes, 1942. In: James L. Patton , Ulyses FJ Pardiñas and Guillermo D'Elía (eds.): Mammals of South America, Volume 2: Rodents . University of Chicago Press, 2015, pp. 1043-1048

Individual evidence

  1. ^ A b c d e M. Monica Díaz, Rubén M. Barquez and Diego H. Verzi: Genus Tympanoctomys Yepes, 1942. In: James L. Patton, Ulyses FJ Pardiñas and Guillermo D'Elía (eds.): Mammals of South America, Volume 2: Rodents. University of Chicago Press, 2015, pp. 1043-1048
  2. ↑ a b c d e f g h Pablo Teta, Ulyses FJ Pardiñas, Daniel E. Udrizar Sauthier and Milton H. Gallardo: A new species of the tetraploid vizcacha rat Tympanoctomys (Caviomorpha, Octodontidae) from central Patagonia, Argentina. Journal of Mammalogy 95 (1), 2014, pp. 60-71
  3. ↑ a b c d e f g h Gabriela B. Diaz, Ricardo A. Ojeda, Milton H. Gallardo and Stella M. Giannoni: Tympanoctomys barrerae. Mammalian Species 646, 2000, pp. 1-4
  4. ↑ Diego H. Verzi, M. Monica Díaz and Rubén M. Barquez: Familiy Octodontidae Waterhouse, 1839. In: James L. Patton, Ulyses FJ Pardiñas and Guillermo D'Elía (eds.): Mammals of South America, Volume 2: Rodents. University of Chicago Press, 2015, pp. 1023-1024
  5. ↑ Milton H. Gallardo, JW Bickham, RL Honeycutt, RA Ojeda and N. Koehler: Discovery of tetraploidy in a mammal - The red viscacha rat is unaffected by having double the usual number of chromosomes. Nature 401, 1999, p. 341
  6. ^ MH Gallardo, CA González and I. Cebrián: Molecular cytogenetics and allotetraploidy in the red vizcacha rat, Tympanoctomys barrerae (Rodentia, Octodontidae). Genomics 88, 2006, pp. 214-221
  7. ↑ Marta Svartman, Gary Stone and Roscoe Stanyon: Molecular cytogenetics discards polyploidy in mammals. Genomics 85, 2005, pp. 425-430
  8. ↑ Alexander S. Graphodatsky, Vladimir A. Trifonov and Roscoe Stanyon: The genome diversity and karyotype evolution of mammals. Molecular Cytogenetics 4, 2011, p. 22 ( [1] )
  9. ↑ Adela M. Bernardis, Anahí E. Formoso and Ulyses FJ Pardiñas: Range extension of Tympanoctomys barrerae (Lawrence, 1941) (Rodentia: Octodontidae) in Patagonia and southernmost record. Check List 9 (6), 2013, pp. 1571–1572
  10. ↑ Agustina A. Ojeda, Milton H. Gallardo, Fredy Mondaca and Ricardo A. Ojeda: Nuevos registros de Tympanoctomys barrerae (Rodentia, Octodontidae). Mastozoología Neotropical 14 (2), 2007, pp. 267-270
  11. ↑ Milton H. Gallardo, Daniel E. Udrizar Sauthier, Agustina A. Ojeda and Ulyses FJ Pardiñas: Discovery of desert-adapted Tympanoctomys barrerae in Central Patagonia, Argentina. Mammalia 73, 2009, pp. 158-161
  12. ↑ Daniel E. Udrizar Sauthier, Ulyses FJ Pardiñas and Eduardo P. Tonni: Tympanoctomys (Mammalia: Rodentia) en el Holoceno de Patagonia, Argentina. Ameghiniana 46, 2009, pp. 203-207
  13. ^ M. Rocío Torres, Carlos E. Borghi, Stella M. Giannoni and Andrea Pattini: Portal orientation and architecture of burrows in Tympanoctomys barrerae (Rodentia, Octodontidae). Journal of Mammalogy 84 (2), 2010, pp. 541-546
  14. ^ Stella M. Giannoni, Carlos E. Borghi, and Ricardo A. Ojeda: Feeding behavior of Tympanoctomys barrerae, a rodent specialized in consuming Atriplex leaves. Journal of Arid Environments 46, 2000, pp. 117-121
  15. ↑ Susan L. Berman: A Desert Octodontid Rodent, Tympanoctomys barrerae, Uses Modified Hairs for Stripping Epidermal Tissue From Leaves of Halophytic Plants. Journal of Morphology 257, 2003, pp. 53-61
  16. ^ Gabriela B. Diaz and Ricardo A. Ojeda: Kidney structure and allometry of Argentine desert rodents. Journal of Arid Environments 41, 1999, pp. 453-461
  17. ↑ a b Milton H. Gallardo, Elkin Y. Suárez-Villota, José J. Nuñez, Rodrgo A. Vargas, Ronie Haro and Nélida Köhler: Phylogenetic analysis and phylogeography of the tetraploid rodent Tympanoctomys barrerae (Octodontidae): insights on its origin and the impact of Quaternary climate changes on population dynamics. Biological Journal of the Linnean Society 108, 2013, pp. 453-469
  18. ↑ Augustina A. Ojeda: Phylogeography and genetic variation in the South American rodent Tympanoctomys barrerae (Rodentia: Octodontidae). Journal of Mammalogy 91 (2), 2010, pp. 302-313
  19. ^ Diego H. Verzi, Eduardo P. Tonni, Orlando A. Scaglia and Jorge O. San Cristóbal: The fossil record of the desert-adapted South American rodent Tympanoctomys (Rodentia, Octodontidae). Paleoenvironmental and biogeographic significance. Palaeogeography, Palaeoclimatology, Palaeoecology 179, 2002, pp. 149-158
  20. ^ R. Ojeda and C. Bidau: Tympanoctomys barrerae. The IUCN Red List of Threatened Species. Version 2015.2. ( [2] ); last accessed on July 2, 2015

Web links

Commons : Tympanoctomys  - collection of images, videos and audio files