Not all cockroaches are equal and some have larger respiratory systems, making them more likely to win physical mating battles, a new study has found.
Fights between similar-sized male cockroaches are likely to become trials of strength, researchers suggest.
They found some of the insects have much larger respiratory capacities than others, allowing them to dominate in the battles.
Dr Sophie Mowles, senior lecturer in animal and environmental biology at Anglia Ruskin University (ARU), said: “When studying contest behaviour it is important to consider not just the physical weaponry used by species, or the combative behaviours they employ, but also the underlying physiology that allows this energetically costly behaviour to take place.
“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.
“The increased ability to effectively deliver oxygen to their body tissue may enhance the fighting ability of these dominant males.
“Adaptations for prolonging aerobic respiration in these cockroaches have probably evolved as a way of maximising 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.”
During laboratory contests, researchers closely matched the cockroaches for size so there were no visible differences in their fighting capabilities.
Heavily weaponised male wide-horned hissing cockroaches use their horns as they compete for females through vigorous contests, often butting and flipping their male opponents onto their backs.
The encounters can also involve behaviour which includes repeated approaches towards the opponent, which may retreat or adopt a low posture to guard against being overturned.
During the contests, researchers scored actions reflecting these dominant and submissive behaviours in each cockroach.
A CT scan of each cockroach was then carried out allowing the researchers to study their whole body, including the size of their respiratory system.
The study, published in Animal Behaviour, found significant differences in the respiratory volumes of the cockroaches, and these were directly associated with their fighting prowess.
The dominant individuals were found to have larger respiratory volumes compared to their similarly-sized submissive opponents.