Insect eater
| Insect eater | ||||||||||||
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European mole ( Talpa europaea ) |
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| Eulipotyphla | ||||||||||||
| Waddell , Okada & Hasegawa , 1999 | ||||||||||||
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The insectivores (Eulipotyphla, formerly Lipotyphla or Insectivora) are an order of mammals . It is a species-rich group of relatively small animals whose teeth are adapted to a predatory way of life. Systematically they are among the most controversial groups of mammals and have an eventful history of classification behind them. In the system used here, five families, the hedgehogs (Erinaceidae), the shrews (Soricidae), the moles (Talpidae), the slit weevils (Solenodontidae) and the extinct Caribbean shrews (Nesophontidae) are added, whereby the hedgehogs belong to this group is controversial. Other families such as the tenreks and the golden mulle , which have great similarities in body structure and were previously also considered part of this group, are no longer included due to molecular genetic studies.
features
In contrast to many other groups of mammals, there are no clear key diagnostic features that distinguish insectivores from other mammals.
Physique and limbs
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The head body length of the insectivore varies between 3 and 45 centimeters, the weight between 2 grams and 2 kilograms. The shrews in particular are small, the Etruscan shrew is one of the smallest mammals at all. The largest representatives are the great rat hedgehog and the slit weevil .
The fur is short and mostly soft, only the hedgehogs have spines on their upper side as an effective weapon of defense. The color of the fur is usually kept in inconspicuous gray or brown tones. These animals often have skin glands on various parts of the body, anal glands are probably present in all species.
The limbs of the insectivores are short and, apart from the digging tools of the moles, relatively unspecialized. The front and rear legs are approximately the same length, the feet each end in five toes, the thumb and big toe cannot be compared to the other toes . Most insectivores are sole eaters .
Head and teeth
The skull is elongated and flat, especially the facial skull protruding forward. The muzzle is long and flexible, the eyes are usually small and the auricles are also often reduced.
| Tooth formula | I. | C. | P | M. | |
|---|---|---|---|---|---|
| 26-44 | = | 1-3 | 1 | 2-4 | 3 |
| 1-3 | 0-1 | 2-4 | 3 | ||
The teeth of the insectivores are provided with pointed cusps and sharp melting strips and are well adapted to their carnal diet . Most species have a comparatively large number of teeth and in some moles and hedgehogs the original number of teeth 44 of the higher mammals has been preserved. Each half of the jaw has one to three incisors , one in the upper jaw and one or no canine teeth in the lower jaw , two to four front molars and three rear molars . In total, they have 26 to 44 teeth and the tooth formula shown here. The arrangement and construction of the teeth vary. The cusps of the posterior molars are mostly w-shaped (dilambdodont) and only in the slit weevils are v-shaped (zalambdodont). In general, there is a tendency to reduce the number of milk teeth , in many species the newborns are born with the permanent set of teeth or it breaks through shortly afterwards.
Insectivores are the only poisonous higher mammals . The sand weevil and some species of shrew produce a neurotoxin in the salivary gland that helps them overwhelm larger prey.
Sensory perception
The most important role in foraging for food is played by the sense of smell , which is excellently developed in most insectivores. Also the hearing is good, many shrews and possibly the Schlitzrüssler are for echolocation capable. They send out rows of high-pitched squeaking sounds that they can use to explore their habitat. It is unclear whether echolocation is also used to track down the prey. Long whisker hairs on the face serve as the sense of touch , while moles have additional whisker hairs on their tails. The snout region is rich in tactile cells , the bucket's organ on the mole's snout is particularly sensitive . With this organ they can perceive not only tactile stimuli, but also electrical stimuli. This means that they can use it to feel the weak electrical fields that arise when the prey animals' muscles move. This organ is most pronounced in the finger-shaped skin appendages of the star mole rat . The sense of sight, on the other hand, plays only a subordinate role in all insectivores.
Internal anatomy
The brain of many insectivores is simple and small in comparison to body mass, but the olfactory bulb is well developed. The small brain used to be a sign of their originality, but is now associated with their way of life. In other mammalian groups, too, species that live mainly on the ground and orient themselves mainly through their sense of smell have a comparatively small brain. In the case of insectivore species that live underground or in the aquatic environment, the brain is correspondingly larger and more differentiated.
The digestive tract is very simply built. The appendix is always missing, this feature was previously used for systematic classification ( see history of systematics ). The intestine is a simple tube and very short compared to the length of the body.
In the males, the testicles are always outside the abdominal cavity in scrotum- like skin folds, the cremaster folds. A penis bone is only present in some moles. The females have a two-horned uterus .
Distribution and habitats
The range of the insectivores includes Eurasia , Africa as well as North and Central America . In South America they are absent with the exception of the small ear shrews , which inhabit the northwestern part of the continent, as well as in the Australian - oceanic area. The shrews are common in the entire area mentioned above, the hedgehogs are only found in the Old World (Eurasia and Africa), the moles in Eurasia and North America. The sand weevil and the extinct Caribbean shrews are restricted to the Caribbean islands .
Insectivores inhabit a wide variety of habitats and are found in forests and grasslands as well as in arid habitats. However, they usually avoid areas that are too cool.
Way of life
habitat
Most insectivores are terrestrial (ground dwellers). Some species can climb well, but there are no pronounced tree dwellers among them. Several representatives such as water shrews and desmans are adapted to an aquatic way of life. They can swim well and show adaptations to this life form with webbed feet, flattened tails and water-repellent fur. Many species of moles, but also some shrews, lead an underground burrowing way of life.
Social behavior and activity times
The social behavior of most species is poor, most of the insectivores live solitary outside of the mating season. Often they are territorial and they react very aggressively to other conspecifics; fights can also occur during encounters.
Some species are both diurnal and nocturnal, while others mainly search for food during the night. As resting places, they dig their own burrows or take over those of other animals or use other protected places such as crevices, holes in the ground or the like. Often they make a nest of dried leaves and grass in it. Some culture-following species are also found in human habitations. Brief periods of mild rigidity ( torpor ) occur in some species, such as some shrews. The hedgehogs in temperate areas hibernate for longer .
nutrition
Insectivores feed mainly on insects and their larvae, other arthropods and various worms . Sometimes they also ingest small vertebrates ( snakes , lizards , frogs , fish and others) and carrion. To a lesser extent, they also consume plant material such as fruits, seeds and nuts.
Reproduction
The reproduction of the insectivores is variable. In general, however, the newborns are nestled, they are born naked and blind, but grow quickly. The gestation period is between 20 and 50 days. The litter size does not only depend on the species, but can also vary within a species depending on the season (with several litters per year) and on the distribution area. Slotted weevils usually only give birth to one or two young animals, with some hedgehog and shrew species it can be up to ten, in exceptional cases even more.
After one to three weeks the young animals open their eyes, after three to eight weeks they are weaned. Sexual maturity can already occur in shrews after two to three months, with the other representatives usually in the second half of their life.
Insectivores and humans
Insectivores were and are not used in particular by humans, nor are they regarded as pests or threats, so that they were rarely hunted. With the exception of the white-bellied dwarf hedgehog , they also play no role in pet keeping . Today's threats to these animals come primarily from the destruction of their habitat and the introduction of neozoa into their home regions. As with other groups of mammals, species endemic to small islands are particularly at risk.
Among the species that have become extinct in the last millennia, including the Caribbean shrews , two Schlitzrüsslerarten and representatives of the Shrew genus asoriculus that were native to some Mediterranean islands. The IUCN lists 17 species as “ critically endangered” and another 86 as endangered or vulnerable . For many species, however, precise data are missing.
Systematics
For a long time, the insectivores served as a "taxonomic wastepaper basket" in which all groups were classified whose affiliation was not clear. External characteristics of these groups were, among other things, a sharp "insectivore bite". Overall, the insectivores have long been regarded as the basal group of placenta animals. According to this point of view, they were regarded as the “primitive” remnants of the Mesozoic mammals from which most of the other taxa of today would have evolved. Although they have preserved some primitive mammal characteristics and are an ancient group in terms of their tribal history, they are well adapted to their habitat and way of life and are by no means a "primitive" group. More precise morphological diagnoses and molecular genetic investigations have helped to illuminate the external and internal systematics, even if there is not yet unanimity on all points.
History of the system
"Insectivora"
In 1758, Carl von Linné arranged the insectivores known to him ( European hedgehogs , European moles and some shrews ) in his work Systema naturae in the order of "Bestiae". This group was characterized by a long snout and included pigs and armadillos , among other things . Johann Karl Wilhelm Illiger summarized hedgehogs, shrews, moles with desmanes, tenreks and gold moles, for this order Thomas Edward Bowdich coined the scientific name Insectivora ("insect eater") in 1821 . In 1855, Johann Andreas Wagner also added the pointed squirrels , the elephants and the giant gliders to this order, whose range of shapes was thus considerably expanded.
"Lipotyphla" and "Menotyphla"
Ernst Haeckel announced in 1866 based on observations that some of these animals an appendectomy had and not others, the insectivores into two groups: the cecum loose Lipotyphla (hedgehogs, shrews, moles, Schlitzrüssler, tenrecs and golden moles) and provided with appendicitis Menotyphla (tree shrews, Elephant and giant glider). There have been repeated attempts to completely separate lipotyphla and menotyphla, so the former were sometimes regarded as relatives of predators and the latter as relatives of primates . Other scientists clung to the insectivore unit as a whole.
The end of the "Menotyphla"
Already at the end of the 19th century, the giant gliders were spun off from the Menotyphla as a separate order Dermoptera, so that only shrews and elephants were included. Although these two groups have some similarities in the structure of the skull, it was finally recognized that these animals differ significantly in their morphology from the Lipotyphla and are also not a natural group. Since the 1970s at the latest, the two groups have therefore been listed as separate orders: the shrews as Scandentia and the elephants as Macroscelidea. More recent molecular genetic studies support this separation: the elephants are now classified in the Afrotheria group and the giant gliders and shrews form the Euarchonta taxon with the primates , so they are not all closely related to the insectivores to form a common order with them .
The end of the "lipotyphla"
Even if there were no clear key diagnostic features, the lipotyphla were considered to be a natural group due to their large morphological similarities. As synapomorphies (common features derived) of this group were missing the cecum , the simple construction of the intestine , the reduction of the pubic symphysis and the expansion of the upper jaw bone ( maxilla ) in the orbit ( orbit ). Molecular genetic studies, however, contradict the morphological findings. Mark Springer et al. first put the gold mole outside of the insectivore in 1997 and classified it in the Afrotheria . In the following year Michael Stanhope et al. Recognized that the tenreks also belong to this group and form a common taxon ( tenrek-like ) with the gold mole , for which the name Afrosoricida (sometimes also Tenrecomorpha or Tenrecoidea) was coined. Numerous subsequent molecular studies have confirmed these results. Waddell, Okada & Hasegawa, introduced the name Eulipotyphla (“real” Lipotyphla) in 1999 for the remaining insectivores (hedgehogs, shrews, moles, slit weevers and Caribbean shrews) .
The end of the "Eulipotyphla"?
Analyzes of mitochondrial genes were carried out by Suzette Mouchaty et al. to the conclusion that the hedgehogs are not related to the other insectivores either. They saw in them the basal group of the higher mammals , which form the sister group of all other representatives of this taxon. Further investigations confirmed these results and led to the division of insectivores into Erinaceomorpha (hedgehogs) and Soricomorpha (shrews, moles, weevils and Caribbean shrews).
However, there is criticism of these studies. In particular, mitochondrial DNA sequences in these animals have undergone rapid evolution with a high mutation rate and therefore differ genetically more strongly from their closest relatives than they do from more distant species. Subsequent analyzes, including of cell nucleus genes and also of mitochondrial genes, confirmed the affiliation of the hedgehogs to the insectivores and the monophyly of the Eulipotyphla. While this view is controversial, it is gaining increasing evidence.
External system
Based on molecular genetic studies, the insectivores are now classified in the Laurasiatheria group . These species-rich, diverse group is after its putative origin, the continent Laurasia named and includes, among other things, the bats , Perissodactyla , Artiodactyla , and whales ( Cetartiodactyla ) and predators . The position of the insectivores within the Laurasiatheria is controversial. Most often their position appears as the sister group of all other representatives of this group, which are then summarized as Scrotifera . According to some scientists, however, they could also form a taxon Insectiphillia with the bats .
Internal system
The insectivores comprise around 450 species and thus form the third largest order in terms of number of species after rodents and bats . According to the system used here, five families are counted among the insectivores: the hedgehogs (Erinaceidae), the moles (Talpidae), the shrews (Soricidae), the sand weevils (Solenodontidae) and the extinct Caribbean shrews (Nesophontidae).
Assumptions about the descent relationships within the insectivores were just as controversial and complex as the question of the composition of the group. Due to external characteristics, the families, including the taxa no longer counted as insectivores, were grouped together in various ways in superfamilies or subordinate groups. (For example, for a long time, a close relationship between tenreks and slit weevils was considered likely due to the similar structure of the molars, as was a sister group relationship between shrews and moles.)
For biogeographical reasons, too , a close relationship between the sand weevils and the little-known Caribbean shrews seems likely. The common taxon of both groups is likely to have split off from the other groups as early as the Cretaceous and form the sister taxon of the other insectivores. Within the remaining groups, molecular studies came to the somewhat surprising (and morphologically unsupported) result that hedgehogs and shrews are closely related and the moles are the sister group of the two. Due to the controversial position of the hedgehogs, however, there is still no agreement on this point of view.
The presumed ancestry relationships within the insectivore can thus be reproduced in the following cladogram:
| Eulipotyphla (insect eater) |
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Fossil and Tribal History
The lack of clear diagnostic features also creates a great deal of uncertainty about the fossil and tribal history of insectivores. Fossils that cannot be clearly identified as close relatives of the recent forms are therefore in most cases controversial.
Several groups that represent possible ancestors or relatives of the insectivores are known from the Cretaceous and the Paleocene , such as the Leptictida , the Palaeoryctidae and the Nyctitheriidae . Litolestes , a relative of the hedgehogs from the Upper Paleocene around 60 to 56 million years ago, is the oldest known, relatively safe representative of the insect eater. It lived in North America, as did the hedgehog- shaped Leipsanolestes from the Lower Eocene , which presumably also belonged to the ancestors or relatives of the insectivores. Shrews have been recorded since the middle and moles since the late Eocene. At the latest in the Oligocene and Miocene , forms of these three groups are known from all continents of their current area of distribution, only South America may not have reached the shrews until the Pliocene , when the land connection of the Isthmus of Panama was closed. There are no fossils of slit weevils and Caribbean shrews that are older than the Pleistocene .
literature
- Tom S. Kemp: The Origin and Evolution of Mammals. Reprinted edition. Oxford University Press, Oxford et al. 2005, ISBN 0-19-850761-5 .
- Ronald M. Nowak: Walker's Mammals of the World. 2 volumes. 6th edition. Johns Hopkins University Press, Baltimore MD et al. 1999, ISBN 0-8018-5789-9 .
- Gerhard Storch : Lipotyphla, insect eater. In: Wilfried Westheide , Reinhard Rieger (Ed.): Special Zoology. Volume 2: Vertebrates or Skull Animals. Spektrum Akademischer Verlag, Heidelberg et al. 2004, ISBN 3-8274-0307-3 , pp. 514-524.
- Matthew RE Symonds: Phylogeny and life histories of the 'Insectivora': controversies and consequences. In: Biological Reviews. Vol. 80, No. 1, 2005, 80, pp. 93-128, doi : 10.1017 / S1464793104006566 , online (PDF; 508 kB) .
- Don E. Wilson , DeeAnn M. Reeder (Eds.): Mammal Species of the World. A taxonomic and geographic Reference. 2 volumes. 3. Edition. Johns Hopkins University Press, Baltimore MD 2005, ISBN 0-8018-8221-4 .
Web links
Individual evidence
- ↑ Information according to the IUCN Red List , accessed on February 5, 2007.
- ^ For example, William K. Gregory: The orders of mammals (= Bulletin of the American Museum of Natural History. Vol. 27, ISSN 0003-0090 ). American Museum of Natural History, New York NY 1910.
- ↑ Mark S. Springer, Gregory C. Cleven, Ole Madsen, Wilfried W. de Jong, Victor G. Waddell, Heather M. Amrine1, Michael J. Stanhope: Endemic African mammals shake the phylogenetic tree. In: Nature . Vol. 388, 1997, pp. 61-64, online (PDF; 569 kB) .
- ↑ Michael J. Stanhope, Victor G. Waddell, Ole Madsen, Wilfried de Jong, S. Blair Hedges, regory C. Cleven, Diana Kao‖, Mark S. Springer: Molecular evidence for multiple origins of Insectivora and for a new order of endemic African insectivore mammals. In: Proceedings of the National Academy of Sciences . Vol. 95, No. 17, pp. 9967-9972, doi : 10.1073 / pnas.95.17.9967 .
- ↑ Suzette K. Mouchaty, Anette Gullberg, Axel Janke, Ulfur Arnason: The phylogenetic position of the Talpidae within Eutheria based on analysis of complete mitochondrial sequences. In: Molecular Biology and Evolution. Vol. 17, No. 1, 2000, ISSN 0737-4038 , pp. 60-67, online .
- ^ For example, in Don E. Wilson, DeeAnn M. Reeder (Ed.): Mammal Species of the World. A taxonomic and geographic Reference. 2 volumes. 3. Edition. Johns Hopkins University Press, Baltimore MD 2005, ISBN 0-8018-8221-4 .
- ↑ Christophe J. Douady, Pascale I. Chatelier, Ole Madsen, Wilfried W. de Jong, Francois Catzeflis, Mark S. Springer, Michael J. Stanhope: Molecular phylogenetic evidence confirming the Eulipotyphla concept and in support of hedgehogs as the sister group to shrews. In: Molecular Phylogenetics and Evolution. Vol. 25, No. 1, 2002, ISSN 1055-7903 , pp. 200-209, doi : 10.1016 / S1055-7903 (02) 00232-4 .
- ↑ Masato Nikaido, Ying Cao, Masashi Harada, Norihiro Okada, Masami Hasegawa: Mitochondrial phylogeny of hedgehogs and monophyly of Eulipotyphla. In: Molecular Phylogenetics and Evolution. Vol. 28, No. 2, 2003, pp. 276-284, doi : 10.1016 / S1055-7903 (03) 00120-9 .
- ^ Total number based on Don E. Wilson, DeeAnn M. Reeder (Ed.): Mammal Species of the World. A taxonomic and geographic Reference. 2 volumes. 3. Edition. Johns Hopkins University Press, Baltimore MD 2005, ISBN 0-8018-8221-4 , but they use a different system.
- ↑ Based on Robin MD Beck, Olaf RP Bininda-Emonds, Marcel Cardillo, Fu-Guo Robert Liu, Andy Purvis: A higher-level MRP supertree of placental mammals. In: BMC Evolutionary Biology. Vol. 6, 93, 2006, ISSN 1471-2148 , doi : 10.1186 / 1471-2148-6-93 .
- ↑ Michael J. Novacek, Thomas M. Bown, David Schankler: On the Classification of the Early Tertiary Erinaceomorpha (Insectivora, Mammalia). American Museum Novitates 2813, 1985, pp. 1-22
- ^ Gregg F. Gunnell, Thomas M. Bown, J. Howard Hutchison, Jonathan I. Bloch: Lipotyphla. In: CM Janis, Gregg F. Gunnell, MD Uhen (Eds.): Evolution of Tertiary Mammals of North America, Vol. 2. Cambridge University Press, 2008, pp. 89-125