CHICAGO, July 24 (Xinhua) -- There is an internal timer going off like an alarm clock to rouse monarch butterflies, telling them it's time to mate and begin spring's northward migration weeks before warming temperatures and longer days, a study showed.
Researchers in the United States captured female monarch butterflies at overwintering sites in central California in November 2015, after they entered diapause. The live insects were brought back to a Chicago lab.
In an environmental chamber there, the butterflies were exposed to temperatures and day lengths approximating November in central California: 10 hours of light at about 17 degrees Celsius, followed by 14 hours of darkness at about 10 degrees.
In December and again in January, the researchers returned to the same overwintering sites, live-captured additional female monarchs and shipped them to the lab.
They then compared the reproductive maturity of the different groups by counting the number of eggs in each female. An abundance of mature eggs is an indication that the female has terminated diapause, while a paucity of mature eggs indicates that she is still in diapause.
"The monarchs collected from the wild in December showed increased reproductive development compared to the monarchs that had been in the laboratory since November," said University of Michigan biologist D. Andre Green. "This indicated that an environmental condition in the wild -- cold temperature -- sped up the timer."
As part of the same study, the researchers also analyzed gene expression in the different groups of monarchs to understand how the internal timer works. Results suggest that transient markings on histones, proteins around which DNA winds and that control gene expression, may act as a timing mechanism.
The results also show that calcium signaling in the butterfly's head is key, potentially linking the accumulation of cryoprotectants during cold weather to the internal timer.
The findings have important implications for North America's monarchs, whose populations have declined steadily for decades at the overwintering sites, as the climate changes.
The study was published Wednesday in Molecular Ecology.
