<div data-thumb = "https://3c1703fe8d.site.internapcdn.net/newman/csz/news/tmb/2019/giantantarct.jpg" data-src = "https://3c1703fe8d.site.internapcdn.net/ newman / gfx / news / 2019 / giantantarct.jpg "data-sub-html =" Giant sea spider, Colossendeis robusta, used in the thermal tolerance correction tests carried out by Shishido and his colleagues at the McMurdo Station in Antarctica. Credit: Photo by Tim Dwyer, ARCUS. ">
Scientists have wondered for decades why marine animals that live in the polar oceans and in the deep sea can reach giant sizes there, but nowhere else. University of Hawaii & # 39; i at Manoa zoology Ph.D. Student Caitlin Shishido, along with researcher Amy Moran of UH and her colleagues at the University of Montana, went to Antarctica to test the prevailing theory, the "oxygen temperature hypothesis," according to which animals living in Extreme cold can grow to giant sizes due to its metabolism. slow. The animals they studied were marine spiders, marine relatives of terrestrial spiders that breathe through their legs.
The study, published in the April 10 edition of Proceedings of the Royal Society B, was carried out in the McMurdo station, in the Antarctic, and in the UH. "The idea is, it's a lot of work for the animals to capture oxygen and carry it to their cells," Shishido said. "It's a much bigger job for big animals than for small ones, and if the cold temperatures make you need less oxygen, you can grow to a bigger size."
To test whether giant spiders were more affected by warming than small spiders, the researchers exercised the spiders to exhaustion by flipping them over and counting the number of times they could straighten out to a range of temperatures, from their normal level of -1.8 ° C all the way to 9 ° C. Against the predictions, the giant animals kept the smallest at any temperature.
"We were surprised that not only giant animals could survive at much higher temperatures than they usually see, but they also grappled with warm temperatures like the smaller ones," Shishido said. "That is not supposed to happen, the larger animals must exhaust their oxygen supply and run out of gas long before the small ones." This should be especially true for sea spiders, which are "skin respirators": they do not have gills or lungs to help get oxygen, but they have to rely on diffusion across the surface of the legs.
How do gigantic marine spiders look like circumventing the laws of physics? This was a mystery, until Shishido and Aaron Toh, a UH undergraduate student, used microscopes to look closely at their legs. The legs of the sea spiders are covered with pores, and the researchers discovered that as marine spiders grow, their exoskeletons become increasingly porous. "The exoskeletons of the really big ones look almost like Swiss cheese," Shishido said.
The researchers cautioned that these were short-term experiments and that the long-term effects of warming on giant animals are not yet understood. However, it seems that, thanks to their holey cuticles, these giant polar animals may not be as vulnerable to warming oceans as previously thought.
Size matters for creatures with cold polar waters.
Caitlin M. Shishido et al, Polar giantness and the hypothesis of oxygen and temperature: a test of thermal limits superior to body size in Antarctic pycnogonids, Proceedings of the Royal Society B: Biological Sciences (2019). DOI: 10.1098 / rspb.2019.0124
The giant Antarctic sea spiders get warmed by getting holey (2019, April 10)
recovered on April 11, 2019
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