- UID
- 994998
- 在线时间
- 小时
- 注册时间
- 2014-4-1
- 最后登录
- 1970-1-1
- 主题
- 帖子
- 性别
- 保密
|
元叔 挖坟挖到了这个 是不是这个啊 好像！
Brower has perfected a technique for tracking monarchs throughout the rest of the year, based on the butterflies' special relationship with milkweed plants. Monarchs lay their eggs on milkweed and, as larvae, eat the plants not only for nutrition but also for the toxins in the sap, which is poisonous to birds that prey on butterflies. The toxic compounds, known as cardiac glycosides, accumulate in larval tissues and persist after the larvae metamorphose into butterflies, making monarchs unpalatable to birds. "I've tasted the sap of the sandhill milkweed," says Brower, "and it's incredibly nauseating." Brower realized in the mid-1970s that he could use these poisons to understand monarch migration. The specific glycosides present in different species of milkweed vary from place to place, so analysis of a plant's glycosides can be used to determine its site of origin. Likewise, the glycosides in adult butterflies are a fingerprint of the plants on which the insects fed as larvae. "The light bulb went on," says Brower. His idea: If monarchs reflect the different arrays of glycosides in milkweeds, then he should be able to analyze butterfly glycosides and correlate individual insects with particular species of milkweed and with certain regions where the milkweed grew.
Traveling around the country, Brower trapped monarchs everywhere from the Great Lakes to Mexico and studied their glycosides. "We collected monarchs in the fall migration and established that over 90 percent fed on the northern milkweed pattern," he says. "Then we sampled the butterflies in Mexico and the ones along the Gulf Coast at the end of March and early April and, lo and behold, all of them had the same pattern. The same butterflies were going to Mexico and coming back in the spring."
Brower's work on glycosides helped to reveal the entire pattern of monarch migration. The first generation of monarch butterflies to return from Mexico stops along the Gulf Coast from Texas to Florida, where the insects lay eggs and die. The eggs hatch, and the new monarchs (with their distinctive southern milkweed fingerprint) head for the Great Lakes region. Later, the new generation of monarchs born around the Great Lakes flies to the East Coast, where they breed and die. Their offspring, fed on eastern milkweeds, then head south toward the Gulf Coast and on to Mexico, traveling as far as 90 miles per day and completing the great circle of monarch migration. |
|
京公网安备11010202008513号 京ICP证101109号 京ICP备12012021号
发表于 2014-3-28 14:20:46
收藏
收藏
发表于 2014-3-28 14:37:43
