MISTIMED MIGRATION: Climate change may disrupt the temperature signals monarch butterflies rely on to time their annual migration.
Image: Flickr/wwarby
It's that time of year again when millions of migrants enter the southern United States from Mexico to a warm welcome. Monarch butterflies will soon start the second leg of their iconic migration having passed the winter in the Transvolcanic Mountains of Mexico.
But future generations of monarchs faced with changing climates may have a hard time finding their way home.
A monarch butterfly navigates using a sun compass in its mid-brain and circadian clocks in its antennae. But, until now, what makes a monarch reverse its direction has remained a mystery. New research shows that the chill at the start of spring triggers this switch.
Monarch butterflies, having flown south in the fall, reorient themselves and start flying north after they've been exposed to lower temperatures, according to the study published yesterday in Current Biology.
Steven Reppert and Patrick Guerra, neuroscientists at the University of Massachusetts, captured fall migrant monarchs and kept them under various light and temperature conditions.
After 24 days, they released the butterflies into a flight simulator. Monarchs maintained under fall temperature conditions continued due south. Monarchs that were subjected to temperatures similar to those in their overwintering grounds in Mexico of between 4 and 11 degrees Celsius reoriented themselves to fly north.
"How many days of the low temperature are needed or the actual temperatures themselves are just not known. All we know is that for 24 days, day and night, if we mimic temperatures in Mexico, on top of the mountains there, the butterflies then start traveling north," Reppert said.
A 'tremendous finding'
Orley Taylor, founder and director of the education outreach and research program at Monarch Watch, called that a "tremendous finding." A lot of species show reverse migration, but researchers don't know how they do that, said Taylor.
"In science, we have to go from signal to behavior. That's one of the beauties of this, that we have gone from signal to behavior," Taylor said.
The migration of the black-white-and-orange butterfly is unique in the lepidopteran world because its round trip is more like one undertaken by birds -- a journey in the fall from Canada and the northern United States to Southern California and Mexico. There, the monarchs spend the winter in "Goldilocks" microclimates -- low enough to keep their metabolic demands down but not so cold as to let them freeze.
In spring, they fly back into the southern United States, where they lay their eggs, which hatch into larvae that blossom into pupae. Later, a new generation of monarchs bursts forth and continues the journey north.
With temperature as the critical trigger for the monarch's northward journey, climate change could be a big spoilsport in its mass migration.
"What we've identified is a potential area of vulnerability. This area of temperature seems to be critical for their turnaround. If they don't have this cold-temperature environment, they seem to continue to go south," Reppert said.
Butterfly habitat at risk from logging
The authors point out that the monarchs fleeing the North American freeze end up in a delicately balanced Mexican microclimate where temperatures hover just above freezing.
Monarch butterfly watchers say that these microclimates are in jeopardy from logging and degradation in the Mexican forests.
"The butterflies, many of them, will seek out the darkest and coolest points of the forest, and that could allow them to reverse their compass and migrate north," said Taylor, who has watched the species' overwintering space shrink over the years from 7 hectares to less than 4 hectares.
The number of monarch butterflies has been falling in recent years for many reasons.
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5 Comments
Add Comment"How do Monarch's[sic] adapt when winter ends at different times each year?"
Reply | Report Abuse | Link to thisLike this:
"After 24 days, they released the butterflies into a flight simulator. Monarchs maintained under fall temperature conditions continued due south. Monarchs that were subjected to temperatures similar to those in their overwintering grounds in Mexico of between 4 and 11 degrees Celsius reoriented themselves to fly north."
You see, the climate is changing faster than animals can adapt. Usually, species would have many generations to adapt to natural variations in climate change. The unnatural variations we are causing with GHG emissions are WAY faster than what has happened in the recent geologic past.
BTW, the continued survival of monarch butterflies isn't "silly". Do you know how many other species along their migratory routes depend on them for pollination or food? What are the knock-on effects of a downward spiral in monarch numbers? Since you claim this is "silly", you should know these answers in order for you to make that assertion.
And the fact that we place no value on natural beauty is more a shortcoming of the current form of Capitalism we practice than anything you can help, so I won't hold it against you. What about natural "capital"? Shouldn't we account for that?
So, sault has a post in reply to Sisko. Where is Sisko?
Reply | Report Abuse | Link to thisTell me, is sault an endangered species that you have to protect?
Your article might have some merit, particularly in relation to habitat destruction. You are only talking about three hectares. Surely that can be reversed. Have any attempts been made to create artificial shade at near that site & to study the results?
I can not be bothered to comment further in light of you having deleted at least one post already. So, what is your policy in relation to deleting posts?
You invite people to comment. In my opinion, only obscene or highly abusive comments should be deleted. To delete comments otherwise is committing a fraud against those you have invited to participate.
If you feel so ill used, so mistreated, so harmed by the "fraud" you allege has been committed against you; feel free to leave.
Reply | Report Abuse | Link to thisYou comment on a site using a screen name to people you don't know beyond their screen name and whine that the creators of this site somehow owe you something.
I find it absolutely hilarious that you claim to have such a wonderful, perfect life; yet become furious that some comment you made was deleted?
Either get over it or leave. The creators of this site have the right to delete comments according to whatever standards they please.
I have no problem with them deleting comments as long as I know WHY they're deleting them. I have seen quite a few of my comments that I spent a lot of time researching and writing just get deleted while totally irrelevant / unscientific comments get to stay on the boards. I won't bother wasting my time making comments if I have no idea what sort of words will get them removed. SciAm has also started deleting ALL comments from some articles with no reason given either. If they're trying to foster better discussion, I can't think of many methods that could be worse.
Reply | Report Abuse | Link to thisIt seems to me that pretty much every site has guidelines so broad that they can pretty much delete whatever they feel like.
Reply | Report Abuse | Link to thisI honestly never put a huge effort into making comments anymore, partly because of that, and partly because (let's be honest) denialists never change their view regardless of the evidence.
As such, I think we all need to accept that if you don't like a sites decisions on this, then you should find another site.
Personally, when I bother to check comments, I enjoy seeing yours. But you need to do what you feel is best with your time.