Tuesday, April 1, 2008

Penyelidikan Serangga

Serangga Dalam Penyelidikan Biologi

Serangga adalah haiwan yang paling tinggi kemandirian dan paling pelbagai dalam keseluruhan alam haiwan. Jumlah spesies serangga di dunia yang telah dikenalpasti dianggarkan menghampiri 1 juta dan beberapa pihak percaya jumlah sebenar termasuk yang belum dikenalpasti boleh mencapai 30 juta. Setiap spesies adalah ahli bagi kumpulan yang lebih besar atau Aturan (Order), terdiri dari lain-lain serangga yang mempunyai ciri –ciri fizikal yang sama (Triplehorn & Johnson, 2005).

Walaupun banyak serangga dianggap sebagai perosak dan selalu menimbulkan masalah yang serius, sebenarnya majoriti serangga tidak tergolong sebagai perosak dan banyak memberikan faedah. Dilaporkan bahawa aktiviti pendebungaan oleh sejenis spesies kumbang Africa, Elaeidobius kamerunicus telah berjaya meningkatkan keluaran industri minyak sawit di Malaysia sehingga RM100 juta setahun (Romoser & Stoffolano, 1998).

Army Ant (Cont.)

ITHACA, N.Y. -- Army ants, nature's ultimate coalition task force, strike their prey en masse in a blind, voracious column and pay no attention to the conventional wisdom of evolutionary biologists.

The common scientific belief has been that army ants originated separately on several continents over millions of years. Now it is found there was one evolution. Using fossil data and the tools of a genetics detective, a Cornell University entomologist has discovered that these ants come from the same ancestor, because since the reign of the dinosaurs, about 100 million years ago, army ants in essence have not changed a bit.

"Biologists have wondered why army ants, whose queens can't fly or get caught up by the wind, are yet so similar around the world. Army ants have evolved only once and that was in the mid-Cretaceous period," says Sean Brady, a Cornell postdoctoral researcher in entomology, whose study was conducted while he was doctoral candidate at the University of California-Davis.

Brady's paper, "Evolution of army ant syndrome: the unique origin and long-term evolutionary stasis of a novel complex of behavioral and reproductive adaptation," will be published on the Web by the Proceedings of the National Academy of Science (PNAS) Online Early Edition between May 5 and May 9 before being printed in PNAS.
Army ants are quite unlike the ants commonly found at family picnics. They have what scientists call the "army ant syndrome," comprising three characteristics: the ants are nomadic, they forage for prey without advance scouting, and their wingless queens can produce up to 4 million eggs in a month. While this syndrome is found in every army ant species around the world, scientific papers have postulated that army ants evolved these characteristics multiple times after the breakup of the supercontinent Gondwana about 100 million years ago.

In total, Brady studied the DNA of 30 army ant species and 20 possible ancestors within the army ant community, divided between the New World species in Ecitoninae and the Old World groups Aenictinae and Dorylinae. He specifically sought information from four different genes to uncover clues to their relationships. "Essentially I built a genetic family tree. Then I took that family tree and looked at its genetic tree rings to postulate what happened in the past," he said.

Brady combined the genetic data with the army ant fossil information and the ants' morphological (form and structure) information to establish ages for the different ant species. Combining this data, Brady found that all the species share some of the same genetic mutations. "If they share those mutations, we can infer they evolved from the same source," Brady said.

Instead of proving the common assumption that the Old World and the New World army ants developed their lineage independently on separate continents, the entomologist showed the ants evolved only once -- on Gondwana.

Brady examined the army ants' behavior on his trips to the Amazon jungle, Brazil's savanna region and the country's coastal rain forest near São Paulo. Periodically millions of army ants would march together through his camp, he says, like a flowing river of red. While the ants move silently, their presence is announced. "The other insects are scared, and they make noises as they flee the invading army," Brady says. "Ant birds follow the ants from the sky and feast on the remnants left behind by the ants. You will hear the high-pitched chirping of the other insects, and you'll hear them and other small animals scurrying in fear. They know what is next."

Army Ant (Eciton)


Eciton army ants have a bi-phasic lifestyle where they alternate between a nomadic phase and a stationary stage. In the stationary or statary phase ('statary' is an old English word meaning "to stand in place"), which lasts about three weeks, the ants remain in the same location every night. They make a nest out of their own bodies, protecting the queen and her eggs in the middle. This temporary home is known as a bivouac. In the nomadic phase the ants move their entire colony to a new location nearly every night for two weeks.

When the ants first enter the statary phase, the queen's body swells massively and she lays as many as 250,000 eggs in less than a week. While the eggs mature, the ants swarm with less frequency and intensity. When the eggs hatch, the excitement caused by the increased activity of the larvae causes the colony to enter the nomadic phase. The colony swarms much more intensely and nearly every day, and the ants move to a new location every night. After two weeks, around the time when the larvae begin to pupate, the colony again enters the statary phase, and the cycle begins anew.

Because of the regularity and intensity of E. burchelli and E. hamatum swarms, many insect, bird and butterfly species have evolved complex relationships with these ants. There are butterflies that lay their eggs on insects disabled by the ants. There are ant-mimicking staphylinid beetles, shaped like the ants they follow, that run with the swarm preying on stragglers or other insects injured or flushed by army ant activity; and there are some insects that spend their entire lives hidden in Eciton colonies mimicking ant-larvae. There are also more than 10 species 'ant-birds' that rely on the ants partially or completely for their food. Some of these birds actively check army-ant bivouacs each morning, follow the foraging trail to the swarm front, and prey on insects fleeing the ants.