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First published online April 17, 2009
Journal of Experimental Biology 212, ii (2009)
Copyright © 2009 The Company of Biologists Limited
doi: 10.1242/jeb.032045
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Inside JEB |
HEART RATE INDICATES LARVAL THERMAL TOLERANCE
kathryn{at}biologists.com
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While global warming is becoming an uncomfortable reality for many terrestrial species, it also poses a significant threat to marine creatures. Daniela Storch from the Alfred Wegener Institute in Germany explains that many studies have aimed at understanding how aquatic adults cope in hot water, but very little is known about the ways that their larvae deal with temperature fluctuations. Knowing that surviving the larval stage is critical for any population, Storch and her colleagues Hans-Otto Pörtner and Miriam Fernández decided to find out how kelp crab first stage larvae manage as waters cool and warm (p. 1371).
Travelling to Fernandez's lab at the Pontificia Universidad Católica de Chile, Storch collected female crabs with eggs from a warm northern site on the central Chilean coast and a cooler site at Melinka in the south of the country. Back in the lab, Storch waited for each female's eggs to hatch before tethering individual microscopic larvae to glass rods in small chambers midway through their first larval stage and recording their behaviour.
Storch first cooled the larvae's water from 11°C to 7°C and then further down to 3°C. Allowing the larvae to adjust at each temperature for an hour, she filmed them through a microscope and also measured their oxygen consumption to see how their activity and metabolism changed with the cold. Having cooled the larvae, Storch tethered others and repeated the process while she slowly warmed their water from 11°C to 27°C in 4°C steps.
After completing the experiments, Storch, Jessica Barria and Pedro Santelices were able to correlate the larvae's oxygen consumption with their temperature and activity, to find out how the temperature changes affected the larvae. They found that as they cooled the northern and southern larvae, both populations began swimming enthusiastically until it became too cold, when they became inactive. Storch admits that this was a surprise, as cooling the larvae should have slowed them down, but suspects that the animals were trying to swim away from the uncomfortable water and find more pleasant conditions. However, when she warmed the two populations, the southern population began struggling and were unable to swim at higher temperatures where the northern population were quite content. The warm adapted northern larvae coped better with the warm water than the cold adapted southern population.
The temperature changes also affected the larvae's metabolism, with their oxygen consumption rising, although the cold adapted southern population's metabolic rate was higher than that of the warmer northern population, reflecting their adaptation to the cold climate. And when Storch monitored the larvae's cardiac activity, she saw that the crustaceans' heart rates increased as the temperature rose, but levelled off at the highest and lowest temperatures.
Summarising the larvae's reactions to the changing water temperatures, Storch says that the larvae's activity decreases first as the temperature changes, then their oxygen consumption levels off before finally the heart fails. `Swimming activity is a good indicator of thermal tolerance,' says Storch. She concludes that both populations seem well adapted to their own locations' thermal windows, but they could be forced to find new locations if temperatures continue to rise.
References
Storch, D., Santelices, P., Barria, J., Cabeza, K.,
Pörtner, H.-O. and Fernández, M. (2009). Thermal
tolerance of crustacean larvae (zoea I) in two different populations of the
kelp crab Taliepus dentatus (Milne-Edwards). J. Exp.
Biol. 212,1371
-1376.
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