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Female Butterflies Reverse Sex Roles When Colder

January 7, 2011

A new study published Thursday in the journal Science has found that female butterflies that grow up in colder temperatures become more aggressive as adults, actively chasing males for sex and food.

“Behavior in these butterflies is changed by the temperatures experienced during development,” said study co-author Kathleen Prudic of Yale University, who studied female Squinting Bush Brown Butterflies (Bicyclus anynana).

Researchers were curious as to why some females had ornate wing markings that resembled eyes, like the attractive wings found in males who usually have to compete for the females’ attention.

During the study, researchers looked closer at the upbringings of the flashy females. They found that their early days were marred by chillier climates than the females that let the males do the chasing.

Comparing the behavior of butterflies that grew up as caterpillars in cozy warm conditions of 80 degrees Fahrenheit compared to 62 degrees Fahrenheit, the team found that the females that grew in the warmer conditions mated with males with flashy wings. “However, the roles were reversed in cooler drier climates. Females played the role of suitors and flashed their eye spots to choosy males,” the study said.

While not visible to the human eye, pattern reflections make the ones doing the courting appear brighter in the eyes of those being courted, Prudic explained in a telephone interview with The Associated Press.

“It makes them more noticeable “¦ kind of like a nice car,” she said.

When the butterflies mate, males deliver necessary nutrients to the females in addition to sperm. Since cooler, drier weather provides fewer resources for butterflies, these extra nutrients can be important to the females, who display to as many males as possible to obtain extra resources.

Females with the brightest spots tend to have the most success.

“Males, on the other hand, become very careful about choosing who they give these resources to because once they do, they live shorter lives,” said Prudic.

Image Caption: When temperatures are cooler, female Bicyclus anynana actively court males, which take on the same role when temperatures are warmer. Credit: William H. Piel and Antonia Monteiro/Courtesy of Yale University

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