In Texas field crickets (Gryllus texensis), males come in two types: a flying long-winged form, and a non-flying short-winged form. These crickets’ forms are correlated with their interests in reproduction: short-wingers court females much more than fliers do. In this new paper, Guerra and Pollack predict the different interest of males in reproduction would be reflected in their willingness, and ability, to fight with other males.
Doesn’t that sound like a simple thing to test? You might think all you gotta get some crickets, put them together, watch them fight, and you’re ready to write up the paper! Not so fast, speedy. Watch the factors pile up, and you’ll get a sense of how performing a behavioural test of even a simple hypothesis can be trickier than you think.
Unfortunately, what appears to be a simple test is complicated by the flying males losing their ability to fly. So instead of a simple face-off between the mobile “colonists” and the flightless “desperados,” you have a more complex set of nine match-ups: each morph against the other two, and a control set of fights against the same morph.
There’s also the chance that the act of flight itself would affect the males’ aggression, because that had been shown to influence courtship.
To make things even more complicated, tn most studies of animal aggression, the number one factor in determining who wins and loses is not morph, but size. So the authors also have to track body size and account for it.
Ooooh, and hormones affect aggression, so testes size better be a variable to consider, too.
The results are tricky to summarize, since not only are there a lot of different match-ups, but fights are measured in different ways: Who starts the fight? Who wins the fight? How intense was the fight?
The trends, however, were that the short-winged males tended to be the most aggressive ones in terms of the initiation of aggression and the level of aggression, as predicted.
As to the question they might ask in the movies, “Are you going to bet on the man with the big muscles or the man with the big cajones?” I’m not sure about men, but in crickets, it was the case that both mattered. Indeed, those factors mattered more than the type of wings and flight capability the animals had.
Flying changed aggression levels of the long-winged males, but, surprisingly, not the probability of winning. This paper suggests that fighting can affect mating success, although there are no direct tests in this paper. There’s still a lot to work out in this system, not least of which is how all these variations are going to result in greater or lesser reproductive success. Is this a stable system? Or ar their conditions under which the colonists might out compete the desperadoes, and vice versa?
Guerra, P., & Pollack, G. (2010). Colonists and desperadoes: different fighting strategies in wing-dimorphic male Texas field crickets Animal Behaviour DOI: 10.1016/j.anbehav.2010.02.002