Loser behaviour and fighting ability unconnected
Breeding beetles to be more ready to fight after a defeat didn’t improve their ability to do so. Andrew Masterson reports.
Fight avoidance behaviour evolved separately to actual fighting ability, at least in beetles, a study has found.
When animals of the same species fight – over access to a mate, for instance – the one which loses will often refrain from picking another battle, and actively back away from challenges, for a certain period of time.
This, says David Hosken from the UK’s University of Exeter, is dubbed “the loser effect”.
To tease out the evolutionary basis of this behaviour, Hosken teamed up with researchers from Okayama University and Tokyo Metropolitan University, both in Japan, and focussed on a combative, and common, species of insect called the broad-horned flour beetle (Gnatocerus cornutus).
Males of the species regularly battle over mating privileges. In most cases, the researchers observed, defeated beetles would wait about four days before entering the fray again.
Hosken and colleagues then selected the beetles in their cohorts that demonstrated the shortest loser effect duration, and selectively bred them over several generations.
The result was defeated beetles which shied away from further conflict for only three days – and launched back into battle even though their fighting abilities had not improved at all. It was a bit like the insect equivalent of a down-card stumblebum boxer demanding another fight even though he just lost four in a row.
“By selecting males who experienced the loser effect for the shortest time, we were able to breed beetles willing to fight again sooner,” says Hosken.
“It is fascinating that these males were no better at fighting. In other words, there is a complete disconnect between actual fighting ability and the duration of the loser effect.”
The results, the researchers write in a paper in the journal Proceedings of the Royal Society B, indicate that the loser effect and actual fighting ability evolved independently.
“It makes sense for animals to use past experience to decide whether to engage in a behaviour," says co-author Kensuke Okada, of Okayama University.
“Losing a fight is a useful clue of the likely benefits of further fighting for a particular individual. Some species also show a 'winner effect' – being more willing to fight after a victory – but that is not the case among broad-horned flour beetles.”