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二氧化碳浓度上升令帝王蝶不适

This is Scientific American - 60-Second Science. I'm Marissa Shieh. One of the delights of summer is to see monarch butterflies dancing through the air.

But it's becoming harder to see them in certain locales- in some places the population has dropped by as much as 90 percent.

And climate change may make life even more challenging for these charismatic insects. That's because higher carbon dioxide levels can lower the amount of toxins in milkweed-

the monarch caterpillar's food. The caterpillars use those toxins to protect themselves from a deadly parasite that produces spores.

When the caterpillars are really small. . . those spores get into the monarch's gut and they break apart and they start drilling holes in the gut lining and reproducing

and just doing nasty parasite things that are bad for the monarchs. Leslie Decker, an ecologist at Stanford University.

Decker and her colleagues raised hundreds of monarchs. They fed half of the caterpillars milkweed grown at current CO2 levels.

The other half got milkweed grown at nearly double those CO2 levels. What we found is that elevated CO2 changes the medicinal quality of the milkweed in a way that makes monarchs sicker.

They're less able to tolerate their pathogen, so the parasite becomes more hurtful. . . to them. And it also reduces their overall lifespan when they're infected in comparison to uninfected monarchs.

The caterpillars that ate milkweed grown with more carbon dioxide grew into butterflies that died as much as a week earlier than the normal life span.

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