Monday, November 29, 2010

bats


Giant Golden-crowned Flying-fox, Acerodon jubatus.
Bats are mammals. Sometimes they are mistakenly called "flying rodents" or "flying rats", and they can also be mistaken for insects and birds. There are two traditionally recognized suborders of bats:
Not all megabats are larger than microbats. The major distinctions between the two suborders are:
  • Microbats use echolocation: megabats do not with the exception of Rousettus and relatives.
  • Microbats lack the claw at the second toe of the forelimb.
  • The ears of microbats do not close to form a ring: the edges are separated from each other at the base of the ear.
  • Microbats lack underfur: they are either naked or have guard hairs.
Megabats eat fruit, nectar or pollen while most microbats eat insects; others may feed on the blood of animals, small mammals, fish, frogs, fruit, pollen or nectar. Megabats have a well-developed visual cortex and show good visual acuity, while microbats rely on echolocation for navigation and finding prey.
The phylogenetic relationships of the different groups of bats have been the subject of much debate. The traditional subdivision between Megachiroptera and Microchiroptera reflects the view that these groups of bats have evolved independently of each other for a long time, from a common ancestor that was already capable of flight. This hypothesis recognized differences between microbats and megabats and acknowledged that flight has only evolved once in mammals. Most molecular biological evidence supports the view that bats form a single or monophyletic group.[5]
Researchers have proposed alternate views of chiropteran phylogeny and classification, but more research is needed.
Genetic evidence indicates that megabats originated during the early Eocene and should be placed within the four major lines of microbats.
Consequently, two new suborders based on molecular data have been proposed. The new suborder Yinpterochiroptera includes the Pteropodidae or megabat family as well as the Rhinolophidae, Hipposideridae, Craseonycteridae, Megadermatidae, and Rhinopomatidae families. The new suborder Yangochiroptera includes all the remaining families of bats (all of which use laryngeal echolocation). These two new suborders are strongly supported by statistical tests. Teeling (2005) found 100% bootstrap support in all maximum likelihood analyses for the division of Chiroptera into these two modified suborders. This conclusion is further supported by a fifteen-base pair deletion in BRCA1 and a seven-base pair deletion in PLCB4 present in all Yangochiroptera and absent in all Yinpterochiroptera.[6] The Chiropteran phylogeny based on molecular evidence is controversial because microbat paraphyly implies that one of two seemingly unlikely hypotheses occurred. The first suggests that laryngeal echolocation evolved twice in Chiroptera, once in Yangochiroptera and once in the rhinolophoids.[7][8] The second proposes that laryngeal echolocation had a single origin in Chiroptera, was subsequently lost in the family Pteropodidae (all megabats), and later evolved as a system of tongue-clicking in the genus Rousettus.[9]
Common Pipistrelle, Pipistrellus pipistrellus.
Analyses of the sequence of the "vocalization" gene, FoxP2 was inconclusive of whether laryngeal echolocation was secondarily lost in the pteropodids or independently gained in the echolocating lineages[10]. However, analyses of the "hearing" gene, Prestin seemed to favor the independent gain in echolocating species rather than a secondary loss in the pteropodids.[11]
In addition to Yinpterochiroptera and Yangochiroptera, the names Pteropodiformes and Vespertilioniformes have also been proposed for these suborders.[12][13] Under this new proposed nomenclature, the suborder Pteropodiformes includes all extant bat families more closely related to the genus Pteropus than the genus Vespertilio, while the suborder Vespertilioniformes includes all extant bat families more closely related to the genus Vespertilio than to the genus Pteropus.
In the 1980s, a hypothesis based on morphological evidence was offered that stated that the Megachiroptera evolved flight separately from the Microchiroptera. The so-called flying primates theory proposed that when adaptations to flight are removed, the Megachiroptera are allied to primates by anatomical features that are not shared with Microchiroptera. One example is that the brains of megabats show a number of advanced characteristics that link them to primates. Although recent genetic studies support the monophyly of bats,[14] debate continues as to the meaning of available genetic and morphological evidence.[15]
Little fossil evidence is available to help map the evolution of bats, since their small, delicate skeletons do not fossilize very well. However a Late Cretaceous tooth from South America resembles that of an early Microchiropteran bat. The oldest known definitely identified bat fossils, such as Icaronycteris, Archaeonycteris, Palaeochiropteryx and Hassianycteris, are from the early Eocene period, 52.5 million years ago[5]. These fossil bats were already very similar to modern microbats. Archaeopteropus, formerly classified as the earliest known megachiropteran, is now classified as a microchiropteran.
Bats were formerly grouped in the superorder Archonta along with the treeshrews (Scandentia), colugos (Dermoptera), and the primates, because of the apparent similarities between Megachiroptera and such mammals. Genetic studies have now placed bats in the superorder Laurasiatheria along with carnivorans, pangolins, odd-toed ungulates, even-toed ungulates, and cetaceans.[1]
"Chiroptera" from Ernst Haeckel's Kunstformen der Natur, 1904
Giant Golden-crowned Flying-fox, Acerodon jubatus.
Bats are mammals. Sometimes they are mistakenly called "flying rodents" or "flying rats", and they can also be mistaken for insects and birds. There are two traditionally recognized suborders of bats:
Not all megabats are larger than microbats. The major distinctions between the two suborders are:
  • Microbats use echolocation: megabats do not with the exception of Rousettus and relatives.
  • Microbats lack the claw at the second toe of the forelimb.
  • The ears of microbats do not close to form a ring: the edges are separated from each other at the base of the ear.
  • Microbats lack underfur: they are either naked or have guard hairs.
Megabats eat fruit, nectar or pollen while most microbats eat insects; others may feed on the blood of animals, small mammals, fish, frogs, fruit, pollen or nectar. Megabats have a well-developed visual cortex and show good visual acuity, while microbats rely on echolocation for navigation and finding prey.
The phylogenetic relationships of the different groups of bats have been the subject of much debate. The traditional subdivision between Megachiroptera and Microchiroptera reflects the view that these groups of bats have evolved independently of each other for a long time, from a common ancestor that was already capable of flight. This hypothesis recognized differences between microbats and megabats and acknowledged that flight has only evolved once in mammals. Most molecular biological evidence supports the view that bats form a single or monophyletic group.[5]
Researchers have proposed alternate views of chiropteran phylogeny and classification, but more research is needed.
Genetic evidence indicates that megabats originated during the early Eocene and should be placed within the four major lines of microbats.
Consequently, two new suborders based on molecular data have been proposed. The new suborder Yinpterochiroptera includes the Pteropodidae or megabat family as well as the Rhinolophidae, Hipposideridae, Craseonycteridae, Megadermatidae, and Rhinopomatidae families. The new suborder Yangochiroptera includes all the remaining families of bats (all of which use laryngeal echolocation). These two new suborders are strongly supported by statistical tests. Teeling (2005) found 100% bootstrap support in all maximum likelihood analyses for the division of Chiroptera into these two modified suborders. This conclusion is further supported by a fifteen-base pair deletion in BRCA1 and a seven-base pair deletion in PLCB4 present in all Yangochiroptera and absent in all Yinpterochiroptera.[6] The Chiropteran phylogeny based on molecular evidence is controversial because microbat paraphyly implies that one of two seemingly unlikely hypotheses occurred. The first suggests that laryngeal echolocation evolved twice in Chiroptera, once in Yangochiroptera and once in the rhinolophoids.[7][8] The second proposes that laryngeal echolocation had a single origin in Chiroptera, was subsequently lost in the family Pteropodidae (all megabats), and later evolved as a system of tongue-clicking in the genus Rousettus.[9]
Common Pipistrelle, Pipistrellus pipistrellus.
Analyses of the sequence of the "vocalization" gene, FoxP2 was inconclusive of whether laryngeal echolocation was secondarily lost in the pteropodids or independently gained in the echolocating lineages[10]. However, analyses of the "hearing" gene, Prestin seemed to favor the independent gain in echolocating species rather than a secondary loss in the pteropodids.[11]
In addition to Yinpterochiroptera and Yangochiroptera, the names Pteropodiformes and Vespertilioniformes have also been proposed for these suborders.[12][13] Under this new proposed nomenclature, the suborder Pteropodiformes includes all extant bat families more closely related to the genus Pteropus than the genus Vespertilio, while the suborder Vespertilioniformes includes all extant bat families more closely related to the genus Vespertilio than to the genus Pteropus.
In the 1980s, a hypothesis based on morphological evidence was offered that stated that the Megachiroptera evolved flight separately from the Microchiroptera. The so-called flying primates theory proposed that when adaptations to flight are removed, the Megachiroptera are allied to primates by anatomical features that are not shared with Microchiroptera. One example is that the brains of megabats show a number of advanced characteristics that link them to primates. Although recent genetic studies support the monophyly of bats,[14] debate continues as to the meaning of available genetic and morphological evidence.[15]
Little fossil evidence is available to help map the evolution of bats, since their small, delicate skeletons do not fossilize very well. However a Late Cretaceous tooth from South America resembles that of an early Microchiropteran bat. The oldest known definitely identified bat fossils, such as Icaronycteris, Archaeonycteris, Palaeochiropteryx and Hassianycteris, are from the early Eocene period, 52.5 million years ago[5]. These fossil bats were already very similar to modern microbats. Archaeopteropus, formerly classified as the earliest known megachiropteran, is now classified as a microchiropteran.
Bats were formerly grouped in the superorder Archonta along with the treeshrews (Scandentia), colugos (Dermoptera), and the primates, because of the apparent similarities between Megachiroptera and such mammals. Genetic studies have now placed bats in the superorder Laurasiatheria along with carnivorans, pangolins, odd-toed ungulates, even-toed ungulates, and cetaceans.[1]
"Chiroptera" from Ernst Haeckel's Kunstformen der Natur, 1904
The traditional classification of bats is:
  • Order Chiroptera
The traditional classification of bats is:
  • Order Chiroptera
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