An Irish researcher has built the most accurate family tree yet for the 1,100 species of bat, writes Dick Ahlstrom.
Bats get a very bad press, according to the lead author of a research paper on the small mammals. They are often inappropriately linked to Dracula, but they can make pleasant pets and will "purr" in the hands of their owners.
"Bats are wonderful, lovely creatures, they are actually very friendly," says Emma Teeling, a lecturer in evolution at the zoology department in University College Dublin.
Injured bats that are hand-reared become very tame and can recognise their owners, she says. They are also unique among mammals for a variety of reasons, not just because they are the only ones which fly, she adds.
Their 1,100 distinct species make up about 20 per cent of all mammals and their lineage dates back nearly to the demise of the dinosaurs 65 million years ago. Despite this, about 60 per cent of the bat fossil record remains missing, says Teeling.
Bats also buck the received wisdom that creatures with high metabolic rates die young. Despite having one of the highest rates of all mammals, they can live for a startling 33 years, the current known record. It has also been suggested that they may have some natural immunity to RNA viruses.
Teeling is lead author on a paper published last week in the journal Science in which she and colleagues put together a comprehensive family tree for bat species based on an analysis of their DNA. It provides an unparalleled look at the true relatedness of the various species, helps to provide dates for divergences as the species evolved and also pinpoints when the earliest "protobat" first took to the air and employed echo location to seek out an insect meal while on the wing.
"It is the first time that every bat family was included in the family tree," she explains. The molecular analysis was done while she was working in the US at the National Cancer Institute in Frederick, Maryland. "I am very enthusiastic about bats. I believe their genes hold very interesting details."
This type of genetic analysis allows researchers to spot and date mutations in an animal's genome, critical points in the evolutionary pathway where divergences occur.
It reveals the level of relatedness between distinct species and combined with the fossil record helps trace the family tree backwards in time to the origin of a species.
"I am trying to reconstruct the evolutionary history of bats by looking at their genes," she explains.
The previous best family tree for bats was published in 1997. Relatedness between species in the tree was based on morphological studies, measurement of bones, teeth, skull and limb shape and other physical features.
Until genetic technologies allowed the cataloguing of genomes and genes this was the best available approach, but it can lead to errors, says Teeling. For example the common wisdom held that bats evolved from primates, with the flying lemur a key link in this presumed tree, given physical similarities.
It was also assumed that of the two main families of bats - the non-echo locating, fruit-eating megabats and the smaller, omnivore, echolocating microbats - the megabats must have evolved first. Researchers believed that megabats would not have discarded this valuable mutation and that echolocation must have been a later evolutionary development.
Teeling and her colleagues' analysis changed all of this, however. The study revealed inconsistencies very early on, showing up problems in the morphologically based tree.
"The molecular data came along and totally rearranged the tree," she says. It clearly showed that the microbats predated the megabats.
The study also helps to establish a more accurate history for the bat species when linked to the existing fossil record, despite this being an exceptionally patchy record. "There is about 30 million years of missing fossil history," Teeling says.
The study shows the family dates back to between 71 and 58 million years.
"By 55 million years ago these creatures were flying and echolocating," she believes. The molecular study was aided greatly by the morphological family tree, she adds. "These molecular trees are useless without the morphology."