Cyclic Changes in the Chemical Defense of the Eastern North American Population of the Monarch Butterfly

帝王蝶毒性的季节性急剧增加 蝴蝶似乎对它们的春天和夏天至关重要 北美洲的殖民化。 帝王蝶幼虫以乳草为食 植物和螯合有毒的强心内酯。 这些 化学物质保护蝴蝶免受捕食， 苦，使鸟类呕吐。 帝王蝶每次迁徙 落入墨西哥，然后重新入侵北美东部， 春天 由于Cardenolides在每年的迁移中发生变化， 在一个循环中，以不同乳草物种为食的帝王蝶失去了它们的 不同程度的威慑力。 秋季迁徙者以 弱催吐乳草;随后的Cardenastine损失导致 他们在墨西哥的化学防御部分崩溃， 每年冬天，黄鹂和蜡嘴鸟都会吃掉数百万只蝴蝶。 然而，幸存下来并迁移回美国的帝王蝶 它们的卵产在剧毒的南方乳草上， 新一代明显有毒的蝴蝶， 春季向北迁移到加拿大。 使用鸟类和 Cardenolides的化学分析将记录假设的 春季世代的毒性增加。 结果应 提供了明确的证据证明以马利筋为基础的化学物质 君主的防御是一个可以预见的动态现象 与每年的迁徙周期密不可分。 %%% 对墨西哥中部冷杉林的砍伐正在破坏 帝王蝶的越冬栖息地。 正因为如此， 帝王蝶在北美东部的迁徙 被指定为一种濒危生物现象，一种新的 生物多样性保护。 该研究计划将记录 生物学的春天再迁移之前，预测崩溃的 在未来10到15年内帝王蝶的数量 也是 与保护东北部乳草生境有关 在美国，春夏季节帝王蝶数量的维持。

A dramatic seasonal increase in toxicity of monarch butterflies appears crucial to their spring and summer recolonization of North America. Monarchs larvae feed on milkweed plants and sequester poisonous cardenolides from them. These chemicals protect the butterflies from predation because they are bitter and cause birds to vomit. Monarch butterflies migrate each fall to Mexico, then reinvade eastern North America the following spring. Since cardenolides change during the annual migration cycle, monarchs feeding on different milkweed species lose their deterrent qualities at different rates. Fall migrants feed on a weakly emetic milkweed; subsequent cardenolide loss leads to a partial breakdown of their chemical defense in Mexico, where orioles and grosbeaks eat millions of butterflies each winter. However, monarchs that survive and migrate back to the USA lay their eggs on extremely poisonous southern milkweeds, producing a new generation of apparently toxic butterflies that complete the spring migration northward to Canada. Bioassays using birds and chemical assays of the cardenolides will document the postulated increase in toxicity of the spring generation. The results should provide definitive evidence that the milkweed-based chemical defense of the monarch is a predictably dynamic phenomenon inextricably entwined with its annual migration cycle. %%% Logging of the fir forests in central Mexico is destroying the overwintering habitat of the monarch butterfly. Because of this, the monarch's migration in Eastern North America has been designated an endangered biological phenomenon, a new category of biodiversity conservation. This research program will document the biology of the spring remigration before the predicted collapse of the monarch population over the next 10-15 years. It is also relevant to conservation of milkweed habitat in eastern North America for the maintence of monarch population in spring & summer.