It's no secret that some of the most vulnerable species from around the world are struggling in the face of climate change. Endangered species and highly specialized ones are losing their habitats and resources to rising seas, melting permafrost, changing flora, and drying lands. However, new research has revealed that some of the world's most adaptable animals are also suffering, with the hearty and common mosquitofish serving as a prime example.

Frank Seebacher, a researcher from the University of Sydney, recently investigated how species that are used to colder climes are finding themselves living in uncomfortable environments, and many simply can't acclimate fast enough.

"We now have evidence that even mosquitofish, which are really good at acclimating, none the less pay a price if they move from cold to warm environments," Seebacher recently told ABC News. "They do worse. So if the climate becomes more variable, they won't do as well as a population."

That actually came as a huge surprise for Seebacher and his colleagues, who recently published their findings in the journal Royal Society Open Science.

That's because the mosquitofish is a pretty impressive warrior of ecosystems, proving both highly specialized, and yet successful at invading and adapting to new habitats.

With two widespread subspecies found along the east and west coasts of the United States and Mexico, this fish can live in both cold and warm climes. It's also specialized to feed on the larvae of mosquitoes and the eggs of other insects, which made it hugely popular in early efforts to fight mosquito populations across the globe.

Unfortunately, they also proved to be aggressive and voracious eaters with a taste for other foods when put in unfamiliar territory. In Australia, they have become a bit of a nuisance, breeding well beyond control and stealing resources, even as they eat the eggs and fry of local fish. And all this trouble comes from a fish that is barely larger than your thumb.

You'd think that nothing could stop this scrappy invader, but Seebacher says that rapid climate change has proven itself a threat. (Scroll to read on...)

To demonstrate this, the research team collected an assortment of mosquitofish from Sydney's Manly Dam. They then acclimated these fish to temperatures that their cousins in the Northeast frequent - down to about 20 degrees Celsius (68 degrees Fahrenheit).

After leaving the fish in this cold habitat for three weeks, they were then exposed to warmer waters, and assessed for swimming performance. They were found to tire much faster in warming waters, compared to fish that had been left in 28 degree water from the start of the trial.

"While they are good at remodeling their biochemical processes depending on what temperatures they experience, there is still this trade off and they pay a price," Seebacher explained. "So, if they are really good at compensating for a cold environment, like in winter, they do worse when it gets warm again. It's called a generalist-specialist tradeoff."

So what does this mean? The researchers argue that it serves as a simple example of how even ecosystems riding on hearty animals like the mosquitofish are in for some trouble as the world continues to warm, and the hardships should be accounted for along with everything else.

And that warming is not due to let up. This past year was recently confirmed by three separate international climate authorities as the hottest year ever recorded - a milestone in a continuing a trend of near-constant net warming across the globe since the 1890s.

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