Animal mating strategies and breeding behaviors offer some of the strangest and most impressive feats of nature that can be seen. From singing songs to woo your future mate to helping your mate get undressed, the animal kingdom sets the stage for all kinds of breeding behavior. However, the female frogs of the world have had enough. New research sheds light on female mate avoidance in the European common frog (Rana temporaria) – and it turns out they have a few tricks up their sleeves to avoid getting down and dirty.
Mating can present many adverse outcomes to the individuals involved and can even in some cases lead to the death of the individual. Female European frogs have therefore been found to develop three avoidance behaviors to prevent or stop the unwanted advances of the male frogs. The researchers have named these; rotation, release calls, and tonic immobility – or feigning death.
For those not familiar with the world of frog mating, European common frogs are what are known as explosive breeders. This means large gatherings of males and females occur in the spring, where male frogs will typically climb onto the backs of female frogs in a position known as amplexus. The male frogs will attempt to mate with as many females as possible, which can lead to mating balls of several male frogs all piled on top of one female. This can result in the females drowning as the male frogs cling to the females in the water.
“It can look disgusting, I have to say,” Dr Carolin Dittrich, from the Natural History Museum of Berlin and lead author of the study, told the New York Times.
Previously, scientists have believed the female frogs to be largely passive to this process – however, the team found that the three avoidance behaviors were more common among the smaller female frogs and that these smaller females were more successful in escaping amplexus. This suggests that the female frogs are much less passive during the explosive breeding phase than previously thought.
Two differently sized females were placed in boxes with a male and observed for a period of one hour. Footage was also recorded of the interactions for the team to analyze. The researchers observed all three avoidance behaviors both singularly and in combination, and found that smaller females used all three tactics more than larger females and had more chance of escaping the male mating attempts. Of the female frogs, 83 percent used the rotation tactic to escape making it the most popular choice, while nearly half of the females (48 percent) used the release calls. These calls are the female frogs mimicking the sounds males make, fooling the males on top of them to release.
“Males typically use release calls to signal other males that they are a male, so to let them go,” Dittrich told New Scientist.
Playing dead, or tonic immobility, where the female frogs stiffened their arms and legs happened in 33 percent of the females that were in amplexus by a male, this behavior happened alongside the other tactics of rotation and calling.
The team suggests that these tactics could be to prove the strength and endurance of a male, leading to better, fitter males who are able to cling on during the rotations passing down their genes to the female's eggs. However, since the behaviors were more often seen in younger females than older, it could also suggest that these are stress responses to the mating behavior.
The researchers further suggest that studying the stress corticosterone levels in these frogs could shed light on these behaviors and acknowledge that observations that they saw in a box may differ from the proportion of these behaviors in the wild.
“I think even if we call this species a common frog and think we know it well, there are still aspects we don’t know and perhaps haven’t thought about, " Dittrich told the Guardian.
The paper is published in Royal Society Open Science.