Salamanders shrink as mountain home heats up

Northern gray-cheeked salamander Northern gray-cheeked salamanders are one of the species that has been shrinking

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Salamanders living in the eastern US have shrunk in size in response to climate change, say researchers.

Scientists have studied the amphibians living in the Appalachian Mountains since 1957.

Analysis of the animals revealed that those caught since the 1980s were on average 8% smaller than earlier specimens.

Biologists warn that a reduction in body size could have fatal consequences for the animals.

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The findings are published in the journal Global Change Biology.

Between 1957 and 2007, Prof Richard Highton from the University of Maryland, US, collected hundreds of thousands of salamanders for scientific study.

He is now retired but the preserved specimens remain at the Smithsonian Institution's Museum Service Center in Suitland, Maryland.

Prof Highton's data highlighted a worrying decline in salamander numbers in the area from the 1980s onwards.

Dr Karen Lips, associate professor of biology at the University of Maryland, continued the research, capturing salamanders in the same sites in the Appalachian Mountains to survey their size and health.

As an amphibian expert, Dr Lips followed the spread of the deadly Chytrid fungus that has decimated populations of the animals worldwide.

She was keen to find out if such a disease was responsible for the salamanders' declines but DNA tests of both the museum specimens and the recently collected animals showed no evidence.

"We know they're disappearing, we can't find nearly the numbers of salamanders that we used to so what could possibly cause that?" asked Dr Lips, explaining how the scientists were initially puzzled by their results.

"We're working in protected parks, national parks, national forests so it wasn't the usual obvious habitat loss."

Tray of salamander specimens Specimens collected from 1957 to 2007 were preserved in the Smithsonian Institution
Dr Lips and Ed Kabay measure wild salamanders Dr Lips returned to the field with research assistant Ed Kabay to survey wild salamanders
A red-backed salamander in a bag ready to be weighed Species including this red-backed salamander were bagged and weighed

By analysing the original data and their more recent findings, Dr Lips and her team discovered that more than half of the species surveyed were, on average, 8% smaller than specimens collected before the 1980s.

"Body size is a really, really important factor for most animals," said Dr Lips, explaining how this shrinking could be connected to declining numbers.

"Bigger animals in general tend to get more mates, they have more offspring, they tend to win in any sort of battles - whether it's courtship or territorial behaviours."

"When you shrink that affects what can eat you, what you can eat, how successful you're going to be at reproducing. Bigger is generally better."

The animals most affected were those in the southern area of the mountains and at lower elevations.

Start Quote

They have to have a moist skin because they get all their oxygen and do all their gas exchange across their skin”

End Quote Dr Karen Lips University of Maryland, US

To investigate this geographic divide, researchers reviewed detailed weather records which revealed that the affected amphibians' homes were getting hotter and drying out.

"When things get warmer body size often gets smaller in cold-blooded animals," said Dr Lips, citing research into aquatic species and fossil records.

"The group that we're working on - the Plethodons - is a whole family of salamanders and they're lungless," she said.

"In that sense they probably are more sensitive than other amphibians: They have to have a moist skin because they get all their oxygen and do all their gas exchange across their skin."

To understand how their shrinking size could be affecting the salamanders, Dr Michael Sears from Clemson University, South Carolina, created a simulation.

This artificial amphibian could be used to estimate how much energy the smaller salamanders used compared with their predecessors.

Because the animals' metabolisms speed up as temperatures rise, the modern salamanders were found to use 7 to 8% more energy to maintain their daily activity.

Dr Lips explained that this has knock-on effects for the amphibians, which might have to compensate by spending more time hunting for food than for mates.

According to the biologist, the future looks troubled for the species.

"In terms of climate change, the Appalachian mountains where we're working are predicted to be impacted pretty heavily and it's a global biodiversity hotspot for salamanders."

Alongside her team of students, Dr Lips intends to continue the research to find out whether the shrinking salamanders will be able to adapt to their changing environment.

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