Sunday, June 17, 2007

Blind as a bat? Don't think so....

ScienceDaily brings the news that researchers have found out that fruit bats (aka flying foxes) are not blind during daylight.

The retinas of most mammals contain two types of photoreceptor cells, the cones for daylight vision and colour vision, and the more sensitive rods for night vision. Nocturnal bats were traditionally believed to possess only rods.

Now scientists at the Max Planck Institute for Brain Research in Frankfurt and at The Field Museum for Natural History in Chicago have discovered that nocturnal fruit bats (flying foxes) possess cones in addition to rods. Hence, fruit bats are also equipped for daylight vision. The researchers conclude that cone photoreceptors might be useful for spotting predators and for social interactions at periods of roosting during the day. Flying foxes often use exposed treetops as daytime roosts, where they assemble in large colonies (Brain, Behavior and Evolution, online May 2007).

The original article is unfortunately hidden behind a pay-wall (but for those with access, it can be found here), so I haven't read it. However, even the ScienceDaily article taught me a few things.

I wasn't really aware of how night/day vision worked, but the fact that there are two different mechanics for seeing duing night and day explains why some people with pretty good eyesight are more or less blind when it's dark.

The second fact I wasn't aware of, was that fruit bats (Chiroptera) sub-order doesn't echolocate. It's only the microbats (Microchiroptera) sub-order that does. I honestly thought that all bats did so, but then, I'm not sure that I actually knew that fruit bats and flying foxes are the same.

One interesting fact that the study picked up, is that some of the fruit bat species are colourblind.

The studied flying fox species (genus Pteropus) were shown to have two spectral cone types, the so-called blue cones that detect short-wave light, and the so-called green cones that detect middle-to-long-wave light. With these two cone types, flying foxes have the prerequisite for dichromatic colour vision, the common mammalian condition.

Curiously, the retinas of the three other studied genera Rousettus (rousette fruit bat), Eidolon (straw coloured fruit bat), and Epomophorus (epauleted fruit bat) completely lack blue cones, they possess only green cones. "With just one cone type, spectral discriminations are not possible, so these species must be colour blind", says Leo Peichl. "A loss of blue cones is a rare event in evolution, it has been found in only a few mammals." The scientists conclude that for the three affected fruit bat genera colour vision is less crucial than for the flying foxes.

Rather interesting.

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