Many reef fish can see in the ultraviolet,
but
the predators seem to have lost this
ability - possibly because it is
important
for predators to see contrast.
Image:
iStockphoto
In a remarkable new finding, scientists have reported that certain coral reef
fish use ultraviolet (UV) vision to tell the difference between their own and
other similar species.
Indeed, the otherwise rather plain-looking Ambon damselfish may even be able
to recognise individuals by their faces, in much the same way as humans do, the
researchers say in a paper in the latest issue of the journal Current
Biology.
The UV vision may act as a secret channel of communication because it is
invisible to the fishes' predators, the researchers speculate.
“We observed that certain fish had very distinctive ultraviolet markings on
their faces – and we wondered what they were using them for,” says lead author,
Dr Ulrike Siebeck of The Vision Centre and The University of Queensland (UQ).
In a series of carefully controlled experiments, the team exposed male Ambon
damselfish to males of the same and a different species (with similar overall
body coloration but different UV facial patterns) in conditions in which the UV
markings could and could not be seen.
They observed that there was only a difference in territorial reaction when
the UV facial patterns could be seen, demonstrating that these patterns are
necessary for the fish to discriminate between their own and another species.
In further experiments, in which the fish were shown pictures of the
different facial markings, the team demonstrated that they were reacting to the
specific shape of the u/v patterns on the intruder's face, not simply to their
ultraviolet colour, she says.
“We came to the conclusion that the fish are using ultraviolet reflecting
facial patterns to discriminate between their own species and other,
similar-looking fish species. Also that they are reacting to the actual pattern,
not simply the u/v light they were seeing.”
“Differences between patterns on the faces of individuals suggest that Ambon
damselfish may also be able to use the patterns for the discrimination of
individuals, in a manner directly comparable to the face-based recognition of
individuals performed by humans,” the team says in the paper.
However major predatory reef fish like coral trout, wrasse and rock cod do
not seem to have the ability to see ultraviolet markings.
“This means the damselfish are effectively exploiting a secret channel of
communication among themselves and with other similar, but harmless species –
one which cannot be detected by the fish that prey on them.
“This ability to see in the ultraviolet seems to have been retained in some
coral reef fishes, whereas carnivorous fish and many higher animals – including
humans – seem to have lost it,” Ulrike says.
“It means damselfish can see a wider spectrum of colours than we can, which
is remarkable when you consider how colourful coral reefs are naturally. They
must find them even more colourful places than we do.”
The team considers that predators like coral trout may have lost the ability
to see in the ultraviolet in order to detect contrast more easily, an important
factor in detecting prey at greater distances. Also, they are generally
longer-lived and may need to avoid u/v damage to their eye cells more than do
the shorter-lived damselfish.
The paper “A species of reef fish that uses ultraviolet patterns for covert
face recognition” by Ulrike Siebeck, Amira N. Parker, Dennis Sprenger, Lydia
Mathger and Guy Wallis appears in the latest issue of Current Biology.
Editor's Note: Original news release can be found here. More
images are available here.
|
