A field cricket (Gryllus campestris) in the wild. Researchers have observed male crickets risking their own lives to defend female mates from predation - an act of chivalry that earns them more sex, but also greatly increases their risk of being killed.
Credit: Robert Zanon/Wikimedia Commons
LONDON: Displaying an act of chivalry thought to occur mainly in smarter animals who learn the behaviour, male crickets have been observed putting their lives on the line to protect their female partners from predation.
Male insects often stay close to their female partners after mating - a form of 'standing guard' previously thought of as an attempt to prevent them mating with rival males, ensuring the birth of their offspring.
But research published last week in the journal Current Biology shows this behaviour is more likely a form of chivalry, designed to protect females from predators rather than a means to keep other males at bay. It also dramatically increases the male's likelihood of being killed.
"We aimed to study how sexual selection works in a wild insect population and how behaviour influences the number of offspring each individual leaves," explained biologist and lead author Rolando Rodríguez-Muñoz from the University of Exeter in England.
"We expected males to escape from predators as soon as the predators approached the burrow but we saw that for males it seems to be more important to guard the females than escape predation, which is quite surprising," he said.
Male crickets 'man up' under attack
Rodríguez-Muñoz and his team used a network of infrared cameras to monitor individual field crickets (Gryllus campestris) in the wild. This was the first time the behaviour of crickets has been monitored in their natural environment, with previous studies having been conducted in the lab.
The team found lone male and female crickets to have similar rates of predation, but when paired up, the males had a significantly higher risk of attack from predators.
Field crickets live in burrows, inside of which the females lay their eggs. When mating pairs came under attack, male crickets were seen to let females enter the burrow first, with males entering only when the females were securely inside, often with fatal consequences.
Cooperation between the sexes
The behaviour isn't entirely chivalrous in the classical sense, however, as there are some sexual payoffs for the males. Researchers observed that the more time a male spent with a female to protect her, the more sexual intercourse he got in return.
"If they don't get matings they usually leave the burrow within an hour, if they get a mating they stay for at least a day and get several more matings," explained Rodríguez-Muñoz.
"In that time, males are always out of the burrow when the female is and if the female is inside, the male is close to the entrance to protect the female from predation"
This 'guarding' behaviour was previously thought to cause conflict between the sexes with males wanting to ensure the birth of their offspring and females wanting to find the strongest, most genetically apt males in order to produce the healthiest offspring.
But the new findings indicate a cooperation between the sexes, with male crickets ensuring their genes are passed on to the next generation and females increasing their chance of survival.
Males act in own interest
"Of course the males are not really being 'chivalrous', they are acting in their own interests! The male crickets in this system gain more offspring by staying with females" commented Roger Butlin, an evolutionary biologist at the University of Sheffield in England.
"The alternative of trying to mate with many females might reduce predation risk but it would also mean that the males might lose the chance of fathering the next generation of crickets, either because their recent mates are themselves eaten or because they go on to mate with other males. Females give up the chance to mate with other males but gain protection".
The males are trading in a longer life for one with more reproductive success, ensuring the survival the passing of their genes on to the next generation. The team now hope to study whether this behaviour continues over the next few generations and also to discover the genetic basis of this behaviour.
"In the future, if we have populations with a lower male density or lower predation rate in the wild we could find that males stop being so chivalrous and are more selfish," said Rodríguez-Muñoz.
"It will be very interesting to see what the genetic component of this behaviour is as we know it's not something they learn in this sort of species".
