On the horizon
New archerfish facts found
Archerfish are famous for knocking prey off low-hanging branches at the water's edge with a thin stream of water. Once in the water, the prey – from flies to small lizards – are easy pickings. Researchers once held that archerfish blasted all prey with equal force. But a team of German zoologists has discovered that the fish hunt with far more finesse.
The fish tailor their shots to the prey they are trying to hit. The bigger the target, the more force. Indeed, the team discovered that the fish deliver some 10 times the amount of force needed to overcome the target's ability to adhere to a surface – regardless of target.
The fish also pull off this feat in the most energy-efficient way. Rather than increase the pressure of their jet of water, they simply increase the amount of water in the jet. Why? Because it would take the fish twice as much energy to double the pressure as it would to double the amount fired, the team calculates.
The researchers also found that this "tailoring" ability is innate; fish kept for two years in a setting that required relatively little energy to knock prey off its perch adopted the more sophisticated approach when returned to the wild. The results appear in the current issue of the journal Current Biology.
The hunt for hydrocarbon oceans on Saturn's moon, Titan, has frustrated astronomers. The Cassini mission to Saturn has found evidence of what may be seasonal lakes of methane or a methane/ethane mix in Titan's version of the Arctic. But oceans? Astronomers have come up dry.
Now, University of Arizona planetary scientist Donald Hunten offers an explanation. Instead of oceans, Titan hosts broad areas covered with a layer of dust more than a mile thick. The dust, he argues, consists of smog particles around which ethane molecules have condensed – a concoction he dubs "smust." This, he says, would explain the broad dark patches and arrays of dunes Cassini images have revealed on the moon's surface. He sets out his argument in Thursday's issue of the journal Nature.
Ever since dinosaurs died out some 60 million years ago, mammals have ruled the land, generating new species relatively frequently. Mammal species last an average of 2.5 million years. But the factors driving this turnover rate remain a puzzle. Now, a team of European paleontologists says the trigger could be the coming and going of Earth's ice ages, which are tied to changes in Earth's orbit as well as its tilt and "wobble" as it spins on its axis.
Arguments for this "astronomical forcing" of the rise and fall of mammal species have been contentious. Evidence for a climate correlation has been suggestive, at best, researchers say. For this study, the team looked at the fossil record for rodents in central Spain. The record it examined spans from 24.5 million to 2.5 million years ago.
At least for rodents, the team found a strong correlation between astronomically induced climate change and species "turnover." They tied the turnover to the expansion and contraction of ice sheets and changes in rainfall and snowfall patterns, among other changes. The group suggests that the pattern "probably holds for other groups" of mammals as well. The results appear in Thursday's issue of the journal Nature.
