How Seahorses Use Their Heads

Dwarf seahorses swim slowly. That doesn't seem to hurt their ability to catch prey， however. What they lack in speed they make up for in stealth. Their jaws approach their prey， undetected， until they're closer than the thickness of a penny. Then the fish strike before their snack can escape. Scientists recently reported they've found the secret to this seahorse's sneak attack： the unusual shape of its head.

Seahorses often eat copepods， tiny shrimplike crustaceans that share the same watery neighbor-hoods as the fish. But copepods will swim away quickly when they sense a predator nearby. They need only two or three milliseconds of warning， says a marine biologist at the University of Texas at Austin. That amount of time is about as long as it takes a fly to flap its wings.

A dwarf seahorse can strike in less than half that time. But to succeed， the fish has to practically swim right up to the copepod without scaring it away. That's where the head trick comes in， the marine biologists found that as a seahorse swims， a small zone of water in front of its head barely moves. And that calm water is key， they reported.

Copepods use antenna hairs to sense danger， like the whoosh of water that precedes an attacking predator. But because of the shape of its head， a dwarf seahorse won't stir up the water. So the copepods never know whats coming.

Dwarf seahorses are some of the slowest-swimming fish in the sea. And because their snouts are shorter than that of other seahorses， they must strike from a closer distance. But thanks to their head shape， they can still catch "one of the most capable escape artists on the planet".

Dwarf seahorses and some copepods inhabit underwater meadows of sea grass in the Gulf of Mexico and other parts of the Caribbean. The meadow's slow water flow makes nearby movements， like a watery whoosh， easier for copepods to detect. But dwarf seahorses use their heads to sneak around.

This could be a running contest between prey and attacker. The copepods evolve， or develop over a long period of time， better escapes. Then seahorses evolve better stealth， explains a biologist at Ghent University， he did not work on the new study.

To investigate the seahorses secret， Gemmell and his coworkers shined lasers through water in a tank containing dwarf seahorses and copepods. Particles suspended in the water bumped the laser light and caused tiny changes in its direction. By studying these changes， the scientists could tell how the fluid moved. When they studied the lasers path around the head of attacking seahorses， the scientists observed a little spot near the top of the snout where the water stayed calm.

1. Dwarf seahorses swim slowly but they can still catch prey by using the strategy of ____.

A. sneak attack B. sudden attack

C. frontal attack D. fierce attack

2. The dwarf seahorse can successfully approach its prey without being detected is because ____.

A. it is very short

B. it has a special jaw

C. it has an unusual head shape

D. it has a strange snout

3. How does a copepod find a predator is approaching？ ____.

A. By using its smell

B. By using its sight

C. By using its antenna hairs

D. By using laser light

Investments will Pay Longevity Dividend

In recent years， researchers studying the biological underpinnings of the aging process have made impressive （A） p in understanding the genetics， （B） b ， and physiology of aging. With adequate research support， we could be in reach of a breakthrough similar to those in public （C） h in the 19th century and medicine in the 20th.

Recently there are several articles on aging appearing in a renowned geroscience （老年學(xué)）（1） j that discuss the contemporary pursuit of scientific means to extend the period of healthy life by slowing aging in people. The pioneering work of high-profile researchers who add visibility to the value of geroscience in the eyes of both the scientific community and the general （D） p .

We all know that many childhood diseases were brought under control by antibiotics and vaccines once scientists understood they essentially had a single cause： microbes. If the diseases of late life also have a single （2） c （aging itself）， then researchers should be able to develop classes of therapeutics by targeting aging mechanisms in a way similar to targeting microbial （E） i . However， scientists may face difficulty in convincing skeptics - among the biomedical community， public and private funders of （F） r ， and the general public - that （3） a aging is a viable and more efficient approach to reducing the risk of all fatal and disabling diseases and improving well-being across the life cycle.

It should be emphasized that the research scien-tists are doing is not focused on delaying aging at the （4） e of an extended period of infirmity at the end of life. Although people who benefit from advances in aging science will probably live longer， the extension of healthy life is the primary goal. In addition， reductions in the infirmities of old age and increased economic value to individuals and societies would come from the extension of healthy life.

（A， B， C， D， E， F FOR CROSS， 1， 2， 3， 4 FOR DOWN. The first letters of the absents were given）

Let's go for a hike

A hiker walked for two days. On the second day the hiker walked 2 hours longer and at an average speed 1 mph faster than he walked on the first day. If during the two days he walked a total of 64 miles and spent a total of 18 hours walking， what was his average speed on the first day？