Despite new and ongoing reduction efforts, climate models predict CO2 emissions will continue to rise throughout the rest of the century, eventually reaching levels that will have extensive effects on marine life.
For her research, Jodi placed squid in seawater with current-day levels of carbon dioxide as well as those forecast for the future.
“I kept the squid in the different CO2 levels for seven days and I monitored any behavioural changes that occurred at the higher CO2. Seven days is a relatively short period of time, but previous research has shown behavioural changes occur within at least five days following CO2 exposure,” she says.
“Also, the two-toned pygmy squid has a lifespan of about 90 days, so seven days is quite a large portion of their life.”
Jodi found that exposure to high carbon dioxide levels led to behavioural changes in the squid, namely they became increasingly active.
“I measured three types of activity: the amount of time the squid spent moving, the total distance they moved and the average speed at which they moved. All of these showed increases at higher levels of CO2,” she says.
Jodi also investigated if and how an increase in carbon dioxide would impact the way the squid interacted with one another.
“I placed the squid in a tank that has a mirror along the entire length of one wall so they’re looking at a mirror image of themselves. But they don’t really recognise themselves; they see the mirror image as though it’s another squid,” she says. “I analysed the interactions the squid had with the mirror and found that at higher levels of CO2 the squid were more interested in their mirror image.”
Once the squid had been exposed to the higher levels of carbon dioxide they behaved more aggressively toward their reflection, spending longer periods of time up close to and touching the mirror.
“After discovering the increased activity and aggression I hypothesised that a specific receptor in the nervous system was involved in creating these behavioural changes,” Jodi says.
To explain the receptors’ role in behavioural outcomes, Jodi uses an analogy that compares the nervous system to a highway.
“The nervous system is made up of brain cells called neurons, and electrical signals travel along those neurons. The connections between neurons are like intersections, and they have receptors. The receptors act like traffic lights at a busy intersection, except instead of controlling the movement of cars through the intersection, receptors control the movement of the electrical signals between the neurons — or brain cells,” Jodi says.
“The receptor I was focusing on is a type of inhibitory receptor, which is similar to a red light at an intersection. As you can imagine, having red lights at a busy intersection is very important to control traffic flow. So, those inhibitory receptors are really important for controlling the flow of electrical signals.”
To discover if the receptors were underlying the behavioural changes, Jodi took her research a step further and commenced a pharmacological study where she administered pharmacological agents that targeted those specific inhibitory receptors in the squid’s nervous system.
“I placed the squid in the same conditions —the current-day levels of CO2 and the predicted future levels — and I treated them with the drugs before measuring their behaviour once again,” she says.
“The drugs acted specifically on those ‘red light’ receptors and I was able to determine that these receptors were changing function when the squid were exposed to higher levels of CO2.”
Jodi describes how elevated levels of carbon dioxide had caused the squid’s ‘red light’ receptors to become dim, stop working completely or even switch function entirely.
“Some have gone from a red stop light to a green go light, changing from inhibitory to excitatory. As you can imagine, this would send cars at an intersection into chaos. And that’s what I’m hypothesising is happening with the squid: the changes in function of this receptor are leading to those behavioural changes at higher CO2 levels,” Jodi says.