The smallest animal with a backbone known to science, a fish from the carp family, has been discovered in the peat swamps of Indonesia.
Mature females of the fish species Paedocypris progenetica reach just 7.9mm (3/10 in) in length, making them the smallest vertebrates yet identified by a tenth of a millimetre.
The previous size record for a vertebrate was held by the Indo-Pacific goby, another fish, at 8mm. Britain's smallest fish, and vertebrate, is the marine Guillet's goby, Lebetus guilleti, which measures 24mm.
The species was discovered in the highly acidic peat swamps of the Indonesian island of Sumatra by a team led by Ralf Britz, a zoologist at the Natural History Museum in London.
"This is one of the strangest fish that I've seen in my whole career," Dr Britz said.
"It's tiny, it lives in acid and it has these bizarre grasping fins. I hope that we'll have time to find out more about them before their habitat disappears completely."
The species is transparent and lives in dark tea-coloured swamp waters, which at pH3 are 100 times more acidic than rainwater. Although these swamps were once thought to harbour very few animals, recent research has shown that they are home to a highly diverse range of species that occur nowhere else.
The peat swamps were damaged by forest fires in 1997, and are also threatened by logging, urbanisation and agriculture. The scientists behind the discovery said that several populations of P. progenetica had already been lost.
"Many of the peat swamps we surveyed throughout South-East Asia no longer exist and their fauna is eradicated," Dr Britz said. "Populations of all the highly endemic miniature fishes of peat swamps have decreased or collapsed."
Details of the discovery are published today in the journal Proceedings of the Royal Society of London, Series B. The male fish grow to 8.6mm, and boast enlarged pelvic fins with exceptionally large muscles relative to the size of the rest of their bodies. The researchers believe that these may be used for grasping females during sex. The females are smaller still, reaching 7.9mm.
The smallest known mammal is Kitti's hog-nosed bat, Craseonycteris thonglongyai, from western Thailand, which measures between 2.9cm and 3.3cm long.
2008年2月13日星期三
2008年2月7日星期四
Teacher Ants Show Students the Way to Food
Ants have a myriad of complex social behaviors despite possessing only teeny brains. Now new research suggests that teaching should be added to the list of ant accomplishments.
Nigel Franks and Tom Richardson of the University of Bristol in England studied so-called tandem running in Temnothorax albipennis ants, during which two ants run a course between nest and food with various stops and starts en route. The researchers found that the lead ant who knows the way to the food slows down as the follower familiarizes itself with the route and will not proceed until the follower taps it on the back. The two also maintain a variable but matching speed and distance over time.
"This behavior is beautifully simple," Richardson says. "If one experimentally removes the follower and taps the leader with a hair at a rate of two times per second or more, the leader will continue."
Biologists have a definition of a teacher in the world of animals: any individual who sacrifices some potential gain in order to educate a naïve counterpart. In a report published today in Nature Franks and Richardson argue that true teaching also requires feedback between the teacher and the student. The ant duos qualify on both counts. "The teacher provides information or guidance to the pupil at a rate suited to the pupil's abilities and the pupil signals to the teacher when parts of the 'lesson' have been assimilated and that the lesson may continue," Franks notes. "True teaching always involves feedback in both directions."
In the case of the ants, the teachers sacrificed their own speed, as evidenced by the observation that they reached the food source four times more quickly on their own than when they had a student in tow. But the students found food more than a minute faster with the help of teaching and then often themselves became teachers for other ants. Sometimes, however, knowledge of a food source needs to be communicated faster than one-on-one training can accomplish. In those situations, large ant groups often broadcast such information through pheromone trails or other means. But tandem running proves that teaching may develop even in organisms that lack large brains, providing help for pupils with the tiniest of intellects. --David Biello
Nigel Franks and Tom Richardson of the University of Bristol in England studied so-called tandem running in Temnothorax albipennis ants, during which two ants run a course between nest and food with various stops and starts en route. The researchers found that the lead ant who knows the way to the food slows down as the follower familiarizes itself with the route and will not proceed until the follower taps it on the back. The two also maintain a variable but matching speed and distance over time.
"This behavior is beautifully simple," Richardson says. "If one experimentally removes the follower and taps the leader with a hair at a rate of two times per second or more, the leader will continue."
Biologists have a definition of a teacher in the world of animals: any individual who sacrifices some potential gain in order to educate a naïve counterpart. In a report published today in Nature Franks and Richardson argue that true teaching also requires feedback between the teacher and the student. The ant duos qualify on both counts. "The teacher provides information or guidance to the pupil at a rate suited to the pupil's abilities and the pupil signals to the teacher when parts of the 'lesson' have been assimilated and that the lesson may continue," Franks notes. "True teaching always involves feedback in both directions."
In the case of the ants, the teachers sacrificed their own speed, as evidenced by the observation that they reached the food source four times more quickly on their own than when they had a student in tow. But the students found food more than a minute faster with the help of teaching and then often themselves became teachers for other ants. Sometimes, however, knowledge of a food source needs to be communicated faster than one-on-one training can accomplish. In those situations, large ant groups often broadcast such information through pheromone trails or other means. But tandem running proves that teaching may develop even in organisms that lack large brains, providing help for pupils with the tiniest of intellects. --David Biello
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