M. D. Regan, R. S. Dhillon, D. P. L. Toews, B. Speers-Roesch, M. A. Sackville, S. Pinto, J. S. Bystriansky and G. R. Scott
Aggressive interactions between individuals of the same species can result in the evolution of exaggerated body traits that improve success in these interactions, and subsequently, access to resources such as food and mates. Although conspicuous morphological adaptations such as antlers are usually what come to mind, metabolic processes that occur hidden within cells are required to sustain aggressive behaviour, so their enhancement may also be important for a successful outcome.
With this in mind, we designed a study to examine the intersection of aggressive behaviour and metabolic biochemistry using the Siamese fighting fish, a staple of the world’s pet shops. Male Siamese fighting fish are notoriously aggressive towards one another, fighting over access to territory and females. Because such aggressive behaviour is energetically costly, we hypothesized that more aggressive fish, which win more fights, would have a greater ability to generate cellular energy in their muscles than less aggressive fish, which tend to lose.
The eight of us met in Hamilton, Ontario to run the behavioural experiments together in Dr. Graham Scott’s lab at McMaster University. These experiments involved pairing equally-sized male Siamese fighting fish in tanks and allowing them to “fight” one another from either side of a glass divider. The glass divider was necessary for the reason you probably guessed: these fish will do each other harm. Our goal with the experiments was to accurately quantify aggressive behaviour of the fish and then examine how the metabolic pathways supplying energy to the fish’s muscle cells varied with aggression, and ultimately, fighting success. We used behavioural assays to quantify aggression and estimate winners and losers, and biochemical assays to quantify reliance on, and capacity for, aerobic and anaerobic energy supply pathways.
Siamese fighting fish bouts aren’t on the level of, say, Ali vs. Frazier in ’75. But we’d be lying if we said excitement didn’t run high during each 20-minute encounter, with the fish striking at each other in fits and starts through the glass divider. At the end of each bout, muscle samples were taken from each fish on which we made our biochemical measurements of metabolic fuels, metabolic wastes, and enzyme activity rates.
Our results were very much in line with our predictions: winning fish were better able to supply energy to their muscles during fights than losing fish, and they were able to do this using two major strategies. First, the muscles of winning fish were better able to supply energy from aerobic pathways, which was matched with greater breathing frequency during fighting (Siamese fighting fish have the ability to breathe air). Second, the muscles of winners also made greater use of anaerobic energy supply pathways and accumulated more lactic acid as a result. Overall, fighting success appears to require muscles with a greater biochemical ability to supply energy, as well as an all-out exploitation of these metabolic pathways during fights.