A frog in Swedish waters has a neat trick: It speeds up its growth rate when the weather is warmest during breeding season, in a country where "warm" doesn't last too long for that kind of thing.
The animal is the pool frog (Pelophylax lessonae), an amphibian that needs enough relative warmth to allow its tadpoles to develop as they should. And it's found a way to make hay - or growth, that is - while the Swedish sun is shining, according to a pair of scientists from Sweden's Uppsala University.
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In a study published in the journal Evolutionary Applications, the researchers describe the frog's ability to grow faster when the temperature rises.
The duo collected frog spawn, during their breeding seasons, from Baltic Sea regions in Poland, Latvia, and Sweden.
Using two rooms – one set to a low temperature for the species (19 degrees C.) and one to a higher temperature (26 degrees C.) – the scientists tested the growth rates of the spawn by breeding the tadpoles from the three countries.
The Uppsala scientists found that tadpoles from all three Swedish, Polish, and Latvian regions grew at the same rate under the lower temperature, but in the higher temperature the Swedish tadpoles grew faster than did the central European (Latvian and Polish) variety.
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In Sweden, the pool frog doesn't even think about breeding until the middle or latter part of May, when temperatures hit at least 16 degrees C., say the researchers.
"The period of time that these frog larvae have for development at northern latitudes is very limited," said study co-author Germán Orizaola in a statement.
"Since Sweden has briefer periods of high temperatures than Poland and Latvia do," he explained, "this increased growth capacity under warm conditions allows this frog to take full advantage of the short periods of high temperatures."
"As a result," Orizaola said, "it is able to complete its life cycle - which relies heavily on warm temperatures - at high latitudes such as in Scandinavia."
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The ability of a creature to use different strategies as their environments change is called plasticity, and the researchers say it's this that is key to the frog's survival.
"The fact that tadpoles bred in Sweden can maximize their growth during the brief periods of high temperatures that characterize these latitudes is indicative of the Swedish pool frog's increased plasticity," said Orizaola.
And that, the researchers say, it what allows the heat-dependent animals to maintain populations in such northerly latitudes.