Picky squirrel

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Picky squirrel
Pointed Squirrel (Tupaia spec.)

Pointed Squirrel ( Tupaia spec. )

Systematics
without rank: Synapsids (Synapsida)
Class : Mammals (mammalia)
Subclass : Higher mammals (Eutheria)
Superordinate : Euarchontoglires
without rank: Euarchonta
Order : Picky squirrel
Scientific name
Scandentia
Wagner , 1855
Familys

The shrews (Scandentia) are an order of mammals (Mammalia) from the forest areas of Southeast Asia with over 20 known species. They resemble squirrels , have historically been considered close relatives of the shrews , but are actually close to primates . Their alternative name Tupaias comes from the Malay word "tupai", which is used regionally for both croissants and shrews.

Pointed squirrels are primarily ground dwellers and, with the exception of one species, climb occasionally. They are omnivores and have exceptionally low brood care for higher mammals .

Occurrence

The distribution area of ​​the pointed squirrel extends across Southeast Asia to the Wallace Line . This includes the islands of Borneo , Java , Sumatra and the island of Palawan, which belongs to the Philippines . On the mainland, the area extends over Indochina including the Malay Peninsula to northeast India and parts of southern China .

No species of pointed squirrel occurs in the entire range of the order. The northern tip squirrel ( Tupaia belangeri ), which extends over most of the mainland range, and the common tip squirrel ( Tupaia glis ) with populations on the Malay Peninsula and also the largest insular distribution reach the greatest extent. Borneo has a particularly high diversity of the pointed squirrel: ten species have been detected there so far. The reasons for this could be size and habitat diversity, or that the shrews have their phylogenetic origin on Borneo and spread from there. They live in forest areas and occasionally as crop followers on plantations.

morphology

features

Pointed squirrels have a slender body and long tail. This is mostly hairy, with the exception of the feather-tailed pointed squirrel ( Ptilocercus lowii ). A long muzzle is characteristic. Pointed squirrels reach 10 to 23 centimeters head-trunk length and 9 to 24 centimeters tail length, depending on the species. The weight ranges from 45 to 350 grams.

The coat color varies from olive gray to rust brown and is lighter on the belly. The fur is dense and soft. The outer hairs are long and straight, the woolly hair short and soft. With the exception of the genus Dendrogale and the feather tail, pointed squirrels have a light shoulder stripe. Few species have additional markings on the face or a dark stripe on the back.

The ears are small and have a primate-like cartilaginous auricle with a membranous earlobe. They are slightly hairy, only with the feather-tailed shrewfish are they bare and relatively large.

Skeleton, skull and teeth

The spine of the pointed horns consists of seven cervical vertebrae , twelve to 13 rib-bearing thoracic vertebrae , six to seven lumbar vertebrae , three cross vertebrae and 24 caudal vertebrae . The collarbone is well developed. The bones of the forearm are not fused together, nor are those of the lower leg . Moonbone and scaphoid bone , two carpal bones , are completely fused together in the Tupaia and Anathana genera , while these two bones are less fused in Ptilocercus and Dendrogale . The thumb can be spread apart, but it cannot be opposed (i.e. opposite the other fingers), which means that shrews do not have a real clasp hand; instead, they use their crescent-shaped claws to climb .

The long snout region that is characteristic of shrews is formed by the nasal bone . The temporal bones are very small and are increasingly displaced by the parietal bone in the course of the individual development of the skull . The posterior arch ( postorbital arch ) is formed by the frontal bone and the cheekbone . There are over-eye windows ( foramen supraorbitale ) and under-eye windows ( foramen infraorbitale ).

2 · 1 · 3 · 3  =  38
3 · 1 · 3 · 3
Schematic representation of the tooth formula

The tooth formula of the pointed squirrel is I 2/3, C 1/1, P 3/3, M 3/3. The incisors of the upper jaw are similar to canines and are also used in a canine-like manner: the upper incisors are used for holding and grasping rather than biting off. There is often a large diastema between the incisors due to the long muzzle region . The lower incisors with their elongated crowns form a tooth comb , which is also present in giant gliders and wet-nosed monkeys. The function of these tooth combs is not known; they may play a role in feeding or grooming their fur. In contrast to lemurs, the canines of shrews are not involved in the formation of the tooth comb. The upper canines are similar to the premolars. In the structure of the premolars, the feather-tailed pointed squirrel and the mountain tupajas differ from the other pointed squirrels: Their canines are particularly small and have two roots. The lower canines are generally larger than the upper ones. A premolar, the P 4 , has a cusp called a protocon with its own root. The upper molars have three roots and are characterized by further cusps (mesostyle) placed between the different tooth tips. The lower molars are typical of mammals and hardly deviate from the usual pattern.

Soft tissue anatomy

A lower tongue is characteristic of pointed squirrels . This is a leaf-like, muscle-free tissue on the underside of the moving part of the tongue, which has a fringed tip. It is used to clean the tooth comb. With the exception of a few representatives of the Tupaia genus , which were previously defined as Lyonogale, shrews have an appendix at the transition from the small intestine to the large intestine , which breaks down the vegetable cellulose and thus supports digestion.

Pointed squirrels have a well-developed, originally built Jacobson organ that lies in part of the nasal cavity and is openly connected to the rest of the nasal cavity and oral cavity via a special duct, the ductus incisivus . Hearing and sight are the primary senses of the shrews and dominate over the sense of smell. The retina consists mainly of cones ; With the exception of the nocturnal feather-tailed pointed squirrel, which this ability would not give any particular advantages, all pointed squirrels can distinguish colors well.

The testes are depending on the type permanently or during the reproductive period in the scrotum next to the penis . The glans is elongated and one penis bone is missing. The females uterus has two horns.

Way of life

Picky squirrel

activity

Unlike many other smaller mammals, pointed squirrels are diurnal. Feather-tailed shrews ( Ptilocerus lowii ) are nocturnal and are well adapted to this way of life with their large eyes, a reflective layer behind the retina , very large ears, long whiskers and a gray-black camouflage color. The mountain tupajas of the genus Dendrogale are presumably crepuscular, but not much is known about their way of life. For diurnal species, the activity peaks are in the early morning and late afternoon. Tree and earth caves are primarily used as sleeping places, but also crevices in the rock, hollow bamboo trunks and hollows under large roots and fallen trees. When they sleep, shrews lie curled up; when they take short breaks, they lie face down on branches. The high activity body temperature of 40 ° C is reduced to 36 ° C during nighttime sleep phases. In general, shrews are quite insensitive to temperature fluctuations and can tolerate temperatures between 5 and 40 ° C without any problems.

nutrition

The shrews feed on small arthropods , but also on other invertebrates and parts of plants, especially fruits and seeds, or scrape resins and sap from trees with their tooth comb. Very large pointed squirrels like the tana occasionally eat small vertebrates like lizards and small mammals and break open bird eggs. In captivity, large shrews were seen catching mice and young rats and killing them with a neck bite. Pointed squirrels almost always go for food on the ground and look for their food by digging through the leaf litter with their snouts and paws. The only exception to this are the tree-living pointed squirrels such as the feather tail. The prey is grabbed with the snout; only when the prey cannot be reached with the snout do shrews use their paws. Flying insects are caught with one or both paws in one quick movement. It is characteristic of shrews that all species hold the food with their front paws when eating.

Social behavior

Shrews usually live alone or in pairs, depending on the location 500 (plantation) to 10,000 square meters (natural forest) large districts that are fiercely defended against same-sex peers. The territories of the females overlap little or not at all; two to three female territories are covered by the territory of a male. Long-lasting, harmonious couple relationships are often formed, which can be recognized by the regular licking of greetings and mutual rest. Inharmonious pairs give birth to young animals, but eat them like normal prey.

Pointed squirrels react very aggressively to conspecifics that invade their territory: They fight violently, sometimes with bite wounds and scratches as a result. The intruder is usually driven away within seconds or minutes. In enclosures, the underdog cannot avoid the dominant shrewhorn, and despite good food intake, the weaker one loses a lot of weight, falls into a coma after a few days and finally dies.

The communication by means of sounds is rather weak in the pointed squirrels; Eight sounds are distinguished in the functional areas of contact, attention, alarm and aggression. The sounds are supported by the tail as an organ of expression; for example, he hits up and down when excited. When shrews in the nest are surprised or attacked by other shrews, they utter a growling, hissing hiss with their mouths wide open. This behavior also occurs in young animals that are disturbed in the nest. Pointed squirrels squeak and screech during fights. Excited representatives of the genus Tupaia chatter loudly, this is often interpreted as a collective call that is uttered when potential enemies have been sighted.

While the other communication patterns are only moderately pronounced, communication via smells is very pronounced. Pointed squirrels set extensive scent marks, which consist of the secretions of certain glands and, more rarely, of urine and feces . The scented secretions come from the glandular fields of the abdomen. They have an oily consistency and consist of more than 99% fat . This ensures a long shelf life of the fragrance under the climatic conditions there. Tupaia belangeri has glands on the chest and abdomen. The mammary glands are activated by the animal standing stiff-legged and rubbing the gland on the object to be marked. The abdominal gland is used when the pointed squirrel slips off a branch and presses the glands against that branch. The urine is deposited in droplets while walking. Tanas celebrate a kind of dance in which they moisten their paws with urine previously deposited on a smooth surface; this spreads the smell with every step. Captured shrews drop their feces in certain places in the cage; Like the other fragrances, the excrement probably serves mainly to mark the territory, but the information content probably goes beyond territory marking.

Reproduction and development

Pointed squirrels can reproduce all year round; depending on the species, however, there are particularly high-birth phases. The oestrus lasts eight to 39 days and is postpartum, which means in this case that copulation can take place immediately after birth, which then triggers ovulation . After mating is over, males show no further care for reproduction.

After a gestation period of 40 to 52 days, the young are born in a nest built by the mother animal, which is separated from the resting and sleeping places of the parent animals. The nest is padded with leaves and other plant material by the mother a few days to a few hours before birth. The litter size is one to three animals; The number of pairs of teats depends on the average litter size and is one to three depending on the species.

Cubs of the pointed squirrels are nesting , at birth they are hairless, and the auditory canals are closed, as are the eyelids. Common shrews have greatly reduced maternal care, which is expressed in the fact that the mother of a litter only nurses the young for five to ten minutes every two days and otherwise has no contact with the young. During the few minutes, neither the nest nor the young are cleaned. An attempt to explain this behavior interprets this behavior as protection against predators, since a suckling female is much more conspicuous than individual young animals. In order to compensate for the long suckling interval, the young animals consume a lot of milk (two to 15 grams, depending on the species); as a result, the young animals, which weigh only about ten grams, are literally bloated. In addition, with a fat content of 26% and a protein content of 10% , the milk is extremely nutritious. This milk enables them to maintain a body temperature of 37 ° C without the mother and grow up very quickly. During the suckling period, the mother recognizes her young by the smell that she transmits to them when suckling; When this smell was neutralized in experiments, the mother ate her own young.

Hearing is developed after ten days, the eyelids open after three weeks. They usually leave the nest after about a month; then they look like adults except for their height . Up to this point in time, the mother had only spent an hour and a half with the young. After leaving the nest, the young continue to grow rapidly and are fully grown and sexually mature by three to four months of age; then the mother drives the young out of its territory. Little is known about lifespan in the wild; in captivity it is usually nine to ten years.

Tribal history and systematics

Historical and current presentation

Giant gliders , together with primates, are the closest relatives of the shrews

The first depiction of a pointed squirrel was by William Ellis , who accompanied James Cook on his trip to the Malay archipelago around 1780. In his diary there was an entry that a strange animal had been shot near Saigon, referred to by Ellis as "squirrel" ( croissant ).

The first scientific description of the common shrew was made in 1820 by the French researchers Pierre-Médard Diard and Alfred Duvaucel , who, however, placed the animal as Sorex glis with the shrews . Accordingly, it was referred to in English as "tree shrew" (" tree shrew "). This laid the foundation for the long-established classification of shrews among insect eaters . In 1866 Ernst Haeckel placed the shrews together with the elephants in the taxon Menotyphla as a subgroup of insectivores with appendix and thus set them against the other insectivores without appendix in the taxon Lipotyphla .

The insectivore thesis was rattled for the first time around 1910, when William K. Gregory gave indications that the shrews are closer to the primates . In 1920 the anatomist Wilfrid Le Gros Clark asserted that the shrews were the first sideline of primates and confirmed Gregory in this respect. He concluded this from structural comparisons of the skull, brain, muscles and reproductive organs. 1945 took over George Gaylord Simpson in his major work on the classification of mammals, Principles of Classification and a Classification of Mammals ( principles of classification and a classification of mammals ), this thesis, calling shrews as a primate from the group of lemurs. This was followed by a phase of intensive research in the hope that this would elucidate the evolution of primates, including humans. This led to the conclusion that the shrews are surviving images of our primate ancestors and can be described as semi-monkeys .

In 1969, Erich Thenius finally separated the shrews as a separate order Tupaioidea, but the name was corrected around 1972 by PM Butler, who pointed out that the name Scandentia, used as early as 1855 by Johannes Andreas Wagner, had higher priority.

Another difficulty in reconstructing the relationships was the rather poor fossil record. However, ten-million-year-old fossils of pointed squirrels have been found in the Indian Siwalik Mountains . The species was named Palaeotupaia sivalensis . This was probably, like most of today's shrews, an occasional climbing ground-dweller, which makes it unlikely that they descended from primates and the ground-dwelling insectivores. Even older fossils of Anagale gobiensis from the Oligocene have the same characteristics. This fossil species may have been an ancestor of the shrews; However, it is not included in this group due to features in the ear region.

In the second half of the 20th century, the primate thesis was also called into question with a number of objections. On the one hand, the primate-like features, i.e. shorter snouts, forward rotation of the eye socket and a better developed central nervous system , mainly apply to the few tree-dwelling shrews like the pygmy shrew ( Tupaia minor ). These similarities could also have arisen in the course of convergent evolution through parallel adaptation to life in the trees. On the other hand, there are sometimes enormous differences between the shrews and primates, especially when it comes to reproductive behavior: while shrews give birth to underdeveloped offspring and have little maternal care, primates give birth to well-developed offspring that they care for carefully. Therefore, the view prevailed that shrews are neither closely related to insectivores nor to primates and that they form a very distinct line of development of the placenta animals. This was still state of the art at the beginning of the 21st century.

Internal systematics of the Euarchontoglires according to Janečka et al. 2007
  Euarchontoglires  
  Glires  

 Rodentia (rodents)


   

 Lagomorpha (hare-like)



  Euarchonta  
  Primatomorpha  

 Dermoptera (giant glider)


   

 Primates (primates)



   

 Scandentia (Pointed Squirrel)




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The suspected closer relationship between the shrews and primates was initially confirmed in the transition from the 20th to the 21st century through molecular biological studies, such as the comparison of protein and DNA sequences, as well as immunobiological studies. The change resulted in the fact that the giant gliders , whose system itself has a very eventful history, are even closer to the primates and form with them the clade of the primatomorpha . Genetic studies from 2007 gave the following picture:

  • The group of Euarchonta , which includes shrews, giant gliders and primates , was formed around 87.9 million years ago .
  • The first order separated from the primatomorpha about 86.2 million years ago.
  • About 79.6 million years ago, the primatomorpha were separated into giant gliders and primates.

However, not all genetic investigations led to the same result, since in some later analyzes the shrews form the sister group of the Glires , which would make the common taxon with the giant gliders and the primates, the Euarchonta, paraphyletic .

Regardless of the close relationship of the shrews, the group split into the two current lines of the Tupaiidae and the Ptilocercidae in the further course of the tribal history according to previous molecular genetic investigations in the Paleocene around 60 million years ago. The further diversification of the Tupaiidae then began in the Eocene about 35 million years ago with the separation of the mountain Tupajas. The evolutionary center of the shrews can be assumed to be in Southeast Asia. In contrast, the occurrence of the Indian pointed squirrel is a relic of an originally much wider distribution, which is also supported by the early separation in the Lower Miocene almost 20 million years ago as well as individual fossil finds. The real pointed squirrels show the greatest diversity, the individual lines of which go back to the Upper Miocene.

Subtaxa

Internal systematics of the shrews according to Roberts et al. 2011
 Scandentia  
  Ptilocercidae  

 Ptilocercus


  Tupaiidae  

 Dendrogals


   

 Anathana


   

 Tupaia





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The list presented here follows the Handbook of the Mammals of the World (2018).

Tana ( Tupaia tana ), representation by Joseph Smit (1836–1929)
  • Family Tupaiidae
  • Family Ptilocercidae
    • Genus Ptilocercus
      • The feather-tailed pointed squirrel ( Ptilocercus lowii ), the only representative of the genus and family, is native to the south of the Malay Peninsula, northwest Borneo, north Sumatra and the surrounding islands. It is small (50 grams in weight), active at night, can see binocularly and is mainly characterized by a tassel at the end of the otherwise hairless tail. The upper incisors are large and the earlobes are large, membranous, and movable. Females have two pairs of teats.

In the 20th century in particular, the Philippine pointed squirrel was part of the (largely) monotypical genus Urogale . According to various genetic studies at the beginning of the 21st century, the actual shrewfish do not form a closed group with regard to the Philippine shrewdrum. It was therefore proposed in 2011 to combine the genus Urogale with the genus Tupaia , which the Handbook of the Mammals of the World in 2018 also took into account. Compared to other Tupaia species, the very young splitting of the Calamian-Spitzhörnchen and Palawan-Spitzhörnchen in the transition from the Lower to the Middle Pleistocene casts doubt on the independent species status of the former.

Pointed squirrels and humans

There is little mutual influence between the shrews and humans, but some species have become rare due to habitat loss. Some populations are cultural followers, yet they play no special role either economically or in mythology. Orchards are sometimes damaged by the shrews.

literature

  • Louise H. Emmons: Tupai: A field study on bornean tree shrews . University of California Press, published 2000. ISBN 0-520-22291-1
  • Robert D. Martin: Spitzhörnchen . In: David MacDonald (ed.): The great encyclopedia of mammals . Könemann in Tandem Verlag GmbH, Königswinter 2004 (translation of the English original edition from 2001); Pp. 426-431. ISBN 3-8331-1006-6 .
  • Nadja Schilling: Scandentia (Tupaiiformes), pointed squirrels, Tupaias . In: W. Westheide and R. Rieger: Special Zoology. Part 2: vertebrates or skulls. Spektrum Akademischer Verlag, Munich 2004; Pp. 549-553. ISBN 3-8274-0900-4 .
  • Ronald M. Nowak: Walker's Mammals of the World . 6th edition. Johns Hopkins University Press, Baltimore 1999, ISBN 0-8018-5789-9 (English).
  • K. Kolar among others: shrews and monkeys . In: Bernhard Grzimek (Ed.): Grzimeks Tierleben Mammals 1 . Bechtermünz Verlag, Augsburg 2000 (reprint of the dtv edition from 1979/80); Pp. 243-296. ISBN 3-8289-1603-1 .
  • DE Wilson, DM Reeder (Ed.): Mammal Species of the World . Johns Hopkins University Press, Baltimore 2005. ISBN 0-8018-8221-4

Individual evidence

  1. ^ R. David Stone: Eurasian Insectivores and Tree Shrews: Status Survey and Conservation Action Plan. IUCN, 1995, Chapter 3, The Scadentia of Asia , page 59 on Google Books
  2. ↑ Kyoko Kohara et al .: Treeshrews as New Animal Models for Viral Infections. Research and Bioresources Vol.12 No.3, 2016, accessed March 29, 2019 .
  3. ^ Robert C. Hubrecht, James Kirkwood (editor): The UFAW Handbook on the Care and Management of Laboratory and Other Research Animals, Chapter 20 Tree shrews , p. 262, page on Google Books
  4. ^ Diard, PM, Duvaucel, A. (1820). "Sur une nouvelle espèce de Sorex - Sorex Glis" . Asiatick researches, or, Transactions of the society instituted in Bengal, for inquiring into the history and antiquities, the arts, sciences, and literature of Asia , Issue 14: pp. 470–475.
  5. ^ William K. Gregory: The orders of mammals. Bulletin of the American Museum of Natural History, 27, 1910, pp. 1-524
  6. ^ George Gaylord Simpson: The Principles of Classification and a Classification of Mammals. Bulletin of the American Museum of Natural History 85, 1945, pp. 1–350 (pp. 61 and 182–189)
  7. ↑ a b Jan E. Janečka, Webb Miller, Thomas H. Pringle, Frank Wiens, Annette Zitzmann, Kristofer M. Helgen, Mark S. Springer, William J. Murphy: Molecular and Genomic Data Identify the Closest Living Relative of Primates. Science 318, 2007, pp. 792-794
  8. ↑ William J. Murphy, Eduardo Eizirik, Stephen J. O'Brien, Ole Madsen, Mark Scally, Christophe J. Douady, Emma Teeling, Oliver A. Ryder, Michael J. Stanhope, Wilfried W. de Jong, Mark S. Springer : Resolution of the Early Placental Mammal Radiation Using Bayesian Phylogenetics. Science 294, 2001, pp. 2348-2351
  9. ↑ Peter J. Waddell, Hirohisa Kishino, Rissa Ota: A Phylogenetic Foundation for Comparative Mammalian Genomics. Genome Informatics 12, 2001, pp. 141-154
  10. ^ Robert W. Meredith, Jan E. Janečka, John Gatesy, Oliver A. Ryder, Colleen A. Fisher, Emma C. Teeling, Alisha Goodbla, Eduardo Eizirik, Taiz LL Simão, Tanja Stadler, Daniel L. Rabosky, Rodney L. Honeycutt, John J. Flynn, Colleen M. Ingram, Cynthia Steiner, Tiffani L. Williams, Terence J. Robinson, Angela Burk-Herrick, Michael Westerman, Nadia A. Ayoub, Mark S. Springer, William J. Murphy: Impacts of the Cretaceous Terrestrial Revolution and KPg Extinction on Mammal Diversification. Science 334, 2011, pp. 521-524
  11. ↑ Xuming Zhou, Fengming Sun, Shixia Xu, Guang Yang, Ming Li: The position of tree shrews in the mammalian tree: Comparing multi ‐ gene analyzes with phylogenomic results leaves monophyly of Euarchonta doubtfu. Integrative Zoology 10 (2), 2015, pp. 186-198
  12. ^ A b c Trina E. Roberts, Hayley C. Lanier, Eric J. Sargis, Link E. Olson: Molecular phylogeny of treeshrews (Mammalia: Scandentia) and the timescale of diversification in Southeast Asia. Molecular Phylogenetics and Evolution 60, 2011, pp. 358-372
  13. ↑ Gwen Duytschaever, Mareike C. Janiak, Perry S. Ong, Konstans Wells, Nathaniel J. Dominy, Amanda D. Melin: Opsin genes of select treeshrews resolve ancestral character states within Scandentia. Royal Society Open Science 6, 2019, p. 182037, doi: 10.1098 / rsos.182037
  14. ↑ Melissa Hawkins: Family Tupaiidae (Treeshrews). In: Don E. Wilson and Russell A. Mittermeier (eds.): Handbook of the Mammals of the World. Volume 8: Insectivores, Sloths and Colugos. Lynx Edicions, Barcelona 2018, ISBN 978-84-16728-08-4 , pp. 242–269 (p. 264)
  15. ↑ a b c Eric J. Sargis, Neal Woodman, Aspen T. Reese, Link E. Olson: Using hand proportions to test taxonomic boundaries within the Tupaia glis species complex (Scandentia, Tupaiidae). Journal of Mammalogy 94 (1), 2013, pp. 183-201 DOI: 10.1644 / 11-MAMM-A-343.1
  16. ↑ Kwai-Hin Han, Frederick H. Sheldon: Interspecific relationships and biogeography of some Bornean tree shrews (Tupaiidae: Tupaia), based on DNA hybridization and morphometric comparisons. Biological Journal of the Linnean Society 70, 2000, pp. 1-14
  17. ^ Trina E. Roberts, Eric J. Sargis, Link E. Olson: Networks, Trees, and Treeshrews: Assessing Support and Identifying Conflict with Multiple Loci and a Problematic Root. Systematic Biology 58 (2), 2009, pp. 257-270

Web links

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