By Henry Fountain
Published: January 10, 2006
The Light of Love
In the animal world, there are many kinds of signals that pass between the sexes when it comes to choosing a mate, like the colors of plumage in birds. Naturally, humans have tended to concentrate on what they can see. In recent years, however, scientists have been studying the ultraviolet spectrum.
In some bird species, females assess potential mates by gauging the reflection of ultraviolet light off the males' plumage.
If UV signals work in seduction, might they also work in battle? A study by Jessica Stapley and Martin J. Whiting at the University of Witwatersrand in South Africa shows that they do.
The researchers studied Platysaurus broadleyi, an African flat lizard. In males of this species, the throat is highly reflective in the ultraviolet range, which is invisible to humans. When a male encounters another male, it makes a display by expanding its throat. The other male may challenge it and make a display of its own, in which case a fight can ensue, or it may back off.
The researchers tested this signaling mechanism by applying UV-absorbing sunscreen to the throats of some males. (As a control, other lizards had plain moisturizing lotion applied.) The researchers found that when males had their UV reflectance reduced, they were more likely to be challenged by other males and the encounter was more likely to escalate into a fight.
The study, published in the journal Biology Letters, shows that males use UV reflectance, and not other factors like body size, as an initial gauge of aggressiveness and fighting ability. Reducing UV reflectance had no effect on fighting ability, however, so some of the lizards got more than they bargained for when they picked a fight with a low-UV opponent.
Hot Water Shrimp
Hydrothermal vents in the deep ocean are very odd places, with extremely hot water under high pressure spewing out of cracks in the seafloor. The environment is rich in hydrogen sulfide, metals and minerals.
Many organisms live around hydrothermal vents, including shrimp of the family Bresiliidae. As befitting their odd environment, these shrimp are rather strange -- for one thing, they're blind.
They are thought to have diverged from other shrimp relatively recently (perhaps 20 million years ago). But little is known about how and when some of these crustaceans made it to the deep ocean vents.
A genetic analysis by Gaku Tokuda and colleagues at the University of the Ryukyus in Okinawa, Japan, has provided some answers.
The study, which was published in Biology Letters, showed that shrimp found at a hydrothermal vent site 5,000 feet down in the Okinawa Trench were only distantly related to the main lineage of decapod crustaceans (shrimp, lobsters and crabs).
They were more closely related to another family of shrimp that live in completely different conditions -- shallow seas or fresh water. So the researchers suggest that it is likely the deep-sea shrimp evolved from those that lived in shallows.
The researchers also compared the Okinawa Trench shrimp with some of the same genus from another deep-sea site (though without vents) at Sagami Bay, 1,200 miles to the northeast. The two had much in common genetically, and by studying the differences the researchers were able to determine that the two probably became separated less than 100,000 years ago.
They also have an idea how it happened: the Okinawa shrimp could have hitched a ride on the Kuroshio current, which flows from the East China Sea to the North Pacific. Other deep-sea creatures may have been dispersed by similar currents, they say.
Excavate Luxor, Remotely
If you've wondered what an archaeological dig in an exotic locale is like, Betsy Bryan, a Johns Hopkins archaeologist, is offering a glimpse on the Web. Her latest dig in the Mut Temple precinct at Luxor, Egypt, is being chronicled this month at www.jhu.edu/neareast/egypttoday.html, with photographs by Jay VanRensselaer and commentary by Dr. Bryan.
Saving the Fish to Save the Reefs
These are not good times for coral reefs. Ravaged by warming oceans, pollution and disease, they need all the help they can get.
Marine reserves, protected areas where fishing is banned, might be useful in helping reefs thrive. ''People have used marine reserves to manage reef fish for many years,'' said Peter J. Mumby, a biologist at the University of Exeter in Britain. ''They are a potential tool to manage reefs, as well.''
But is what's good for the fish good for the coral? In the Caribbean, scientists haven't been sure. Reserves that allow predatory fish like grouper to flourish, the thinking goes, may be inadvertently harming the reefs by reducing the grouper's prey, parrotfish that help the coral to grow.
So Dr. Mumby and colleagues set out to see whether this was so, studying fish populations at a reserve in the Bahamas. Their finding, published in the journal Science, is that parrotfish, far from being wiped out, are prospering. ''This reserve that allowed predators to come back also allowed parrotfish to come back,'' Dr. Mumby said.
Parrotfish graze on reefs, eating seaweed that can crowd out the coral, outcompeting it for nutrients and space. Until about 20 years ago, long-spine sea urchins also ate the seaweed. But disease eliminated most of the urchins, leaving the parrotfish as the only grazer.
The researchers found that, at the Bahamian reserve, grouper thrived. And these predators did sharply reduce the population of smaller parrotfish species. But Dr. Mumby and his colleagues found that parrotfish longer than about six inches were too big for the grouper to eat. So larger species actually showed population gains.
The larger parrotfish were also prodigious grazers. So while the loss of smaller parrotfish caused a slight reduction in grazing, the larger fish more than made up for it. In all, there was a net doubling of grazing, leading to a fourfold reduction in the amount of seaweed on the reef.
''This is the first time that anyone has shown that setting up a marine park could have a beneficial effect on reducing the seaweed,'' Dr. Mumby said. But more than that, he added, it is another indication of the complex interconnections in any ecosystem. ''It's never that simple,'' he said. ''Ecosystems are always full of surprises.''
Drawing (Drawing by Chris Gash)