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Climate change may bring dramatic behavior shifts

Shifting temperatures and rainfall expected to alter animal lifestyles

LIFE CHANGES Pantless treefrogs, the first frog species found that can deposit eggs either in water or out of it, might be able to adjust reproductive strategies if climate change disrupts local rainfall.

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BOULDER, Colo. — Warming climate may dramatically change not just where animals live, but how. Solitary sweat bees in northern climes are projected to become builders of social colonies, researchers reported July 31 at the annual meeting of the Animal Behavior Society. Closer to the equator, fitful rainfall may drive tree frogs to exchange plants for ponds as their place to lay eggs.

Previously, researchers found that some animals confronted by changing climate are likely to alter their timing of migration or shift their ranges poleward or up a mountain slope. But a new generation of research is finding that more fundamental changes may occur in animal life history.

In Scotland and Northern Ireland, the sweat bee Halictus rubicundus could largely switch from its solitary life to forming small colonies by 2080, said Roger Schürch of the University of Sussex in England.

The bee, which is widespread across the Northern Hemisphere, adopts a distinctly more social lifestyle in the warmer reaches of its range, including the south of England and Ireland. Each queen emerging in spring lays a batch of largely female eggs, feeding and tending them until they mature into a small workforce, which in turn raises the final generation of the year. The warmth, Schürch said, allows bees to move around briskly and make more foraging runs, which in turn allows bees to raise more offspring.

If transplanted north, however, families of the social southerners turn solitary like their new neighbors. And solitary northerners moved south tend to go social.

Using a program that generates hypothetical future weather under various climate scenarios, Schürch found that with high greenhouse gas emissions Belfast, Northern Ireland, should be toasty enough by about 2050 for its now-solitary bees to raise as many workers as counterparts in southern England do today, he said. And a bit farther north, warming should cause bees in Peebles, Scotland, to go social with southern-sized colonies by 2080.

Meanwhile, changing rainfall could affect the lifestyle of a tropical frog, said Justin Touchon of the Smithsonian Tropical Research Institute in Panama. Pantless tree frogs (Dendropsophus ebraccatus) there lay eggs that develop either on land or in the water. The frogs were the first species found to produce dual-habitat clutches.

At shady ponds, the tree frogs often attach their eggs to plants overhanging the water. As long as rain moistens the eggs during their first day they can hatch there, safe from voracious predators in the water. If rain fails to sufficiently wet the eggs that first day, the clutch dies. So around ponds with more open sun beating down, pantless tree frogs often just lay their eggs in the water.

That tendency to take a chance on rainfall grows stronger among pantless tree frogs as precipitation increases southward from Mexico to Ecuador, Touchon reported.

Cloudbursts during the rainy season, when pantless tree frogs breed, may get iffier as the climate changes. Touchon’s earlier work suggests that during the past four decades, rainstorms have become more likely to be skimpier or skip days and leave tree frog eggs to dry out. In response, frog populations may become more likely to lay eggs in water.

These research topics are “very exciting and a new direction,” says behavioral ecologist Timothy C. Roth II of Franklin & Marshall College in Lancaster, Pa. Studying how climate change might affect behavior and mental capacities of organisms, he says, has been “very underrepresented.”

And yes, climate change could affect mental powers, he says. He’s worked with Vladimir Pravosudov of the University of Nevada, Reno on chickadees that appear to need better spatial memory to cope with the harsh northern ends of their ranges. Warming may relax the pressures for the birds to stay as sharp.

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