Feb. 23 (UPI) -- When cockroaches square off, more often than not, the roach with the bigger respiratory system emerges victorious.
Male cockroaches compete with one another for access to breeding females, but even the most aggressive cockroaches don't fight all comers.
Like other animals, roaches do their best to avoid unwinnable conflicts by sizing up the size and power of would-be opponents.
Sometimes, that's easier said than done.
According to a new study, published Tuesday in the journal Animal Behavior, mismatches between cockroach competitors aren't always obvious.
To better understand the sexual competition between male cockroaches, scientists paired Madagascan hissing cockroaches in a makeshift arena and watched how the tussles played out. Researchers did their best to pair similarly sized roaches.
The two species deployed by the researchers, wide-horned hissing cockroaches and flat-horned hissing cockroaches, both use their horns to spear and flip opponents onto the ground.
But not all the roaches charge and lock horns. During the fights, more submissive cockroaches demonstrated what scientists dubbed "low aggression," repeatedly approaching their opponent before backing away and adopting a crouched position to avoid getting flipped over.
Based on the dominant and submissive behaviors displayed in the arena, researchers scored the aggression of each cockroach. Afterwards, scientists used CT scans to gauge the physiological differences between competitors.
The data revealed a strong link between respiratory volume and combat tactics. When comparing cockroaches with similar physical dimensions, researchers found those with bigger respiratory systems were more likely act aggressively in the arena.
"When studying contest behavior, it is important to consider not just the physical weaponry used by species, or the combative behaviors they employ, but also the underlying physiology that allows this energetically costly behavior to take place," study author Sophie Mowles, senior lecturer in animal and environmental biology at Anglia Ruskin University in Britain, said in a news release.
"When visible differences are removed by size-matching opponents, fights between male cockroaches are likely to escalate into trials of strength, and our study found that some cockroaches have much larger respiratory capacities than others, allowing them to dominate these contests," Mowles said. "The increased ability to effectively deliver oxygen to their body tissue may enhance the fighting ability of these dominant males."
Animals avoid unwinnable contests because their resources are precious, but evolution and sexual competition calls for some level of experimentation and risk-taking.
For some, investing energy in a bigger respiratory system proves profitable.
"Adaptations for prolonging aerobic respiration in these cockroaches have probably evolved as a way of maximizing oxygen exchange when burrowing through leaf litter, and we have shown that these adaptations also play a crucial role in physical contests between males, and therefore sexual selection," Mowles said.