The team of biologists from Macquarie University in Sydney knew from previous research that warming ocean temperatures alter the way fish grow and develop. The researchers wanted to find out whether these changes would also affect fish behavior — specifically, whether sharks raised in a tank warmed to projected end-of-century temperatures would show a preference for swimming one direction or another when faced with a Y-shaped pathway. Basically, could global warming make sharks right- or left-handed?
Sharks, you may be tempted to point out, don't actually have hands (they have fins, which are genetically not so far off from human arms). So, when scientists talk about the right or left "handedness" of sharks and other marine creatures, they're talking about lateralization: the tendency for one half of an animal's brain to automatically control certain behaviors. With simple, automated behaviors (say, your preference for writing with your right or left hand), this theoretically frees up mental energy for an animal to perform more-complex cognitive functions. In fish, lateralization might mean a default preference for swimming a certain way, which can help those fish forage for food or form schools. [On The Brink: A Gallery of Wild Sharks]
"Since behavioral lateralization is an expression of brain function, it can be used as a barometer of normal brain development and function in some contexts," the researchers wrote in a study published this summer in the journal Symmetry. "Namely, exposure or development under climate change conditions."
Right shark or left shark?
To test whether warmer waters could force a shark to become lateralized, the researchers collected a clutch of Port Jackson shark eggs from the waters off of eastern Australia. The scientists incubated 12 eggs in a tank warmed to the current ambient temperature of the bay (about 70 degrees Fahrenheit, or 20.6 degrees Celsius) and 12 others in a tank that was gradually warmed to 74.5 degrees F (23.6 degrees C) to simulate those predicted end-of-century ocean temperatures.
Five sharks incubated in the elevated temperatures died within a month of hatching. To test whether the remaining sharks had developed lateralization, the team placed each of those animals in a long tank with a Y-shaped partition at one end. Behind the partition was a food reward; sharks just had to decide whether to swim to the right or left side of the Y to reach their snack.
The authors found that sharks incubated in the elevated temperatures showed a strong preference for turning right. The sharks in the control group showed no preference one way or the other.
To the researchers, this sudden-onset "right-handedness" is an indication that the sharks raised in the hotter tank may have developed lateralized brains as a mental shortcut. This would help them compensate for other developmental hurdles posed by their environment. [Images: Sharks and Whales from Above]
"Elevated temperature significantly increased developmental rates and metabolism, with associated costs in terms of energy allocation to growth and physiological processes," the researchers wrote. "Therefore, stronger lateralization may arise as an energy-saving mechanism."
Sharks born in hotter waters may be forced to develop more quickly and may be left with physically smaller brains than sharks who develop under today's conditions, the team wrote. With less mental energy to spare, sharks might have to automate certain behaviors — like always turning right when faced with an obstacle.
Understanding the precise consequences of warming oceans on shark behavior will require lots of further study, the researchers said. For its part, the Macquarie University team has donated the brains of the sharks in its study to be examined in further research. Soon, we may have a better idea of what makes a right-handed shark tick.
Left Shark could not be reached for comment.
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Originally published on Live Science.
