Is she really into me? Sexual conflict and deception in green poison frogs

That men can be easily distracted by any hint at sex, especially when communicated by attractive women, is no surprise to us humans. More surprising is that this male preoccupation with sex might be used by female frogs as well to mislead male frogs and enhance their own fitness (the number of surviving offspring). This seems to be the case with females of the green poison frog (Dendrobates auratus). Because whenever a male frog with whom she recently mated, tries to indulge himself into the habit of promiscuous mating, the female will try keep him from it. She does so by leading him to believe she too wants to mate with him, seducing him and then after courting him for some time, blowing him off.

First a quick detour to human sexual behaviour:  a 2006 study carried out at the Belgian university of Leuven gave credit to the claim of man’s undivided attention to sex. In this study men from the age of 18-28 were split up into different groups and played a financial game within these groups. The men of one of these groups were asked, while playing the game, to rate images of attractive women, while the men in another group rated pictures of landscapes. The results showed a significant effect. The members of the first group performed worse at their task of playing the financial game, were less able to focus and behaved more impulsively in the game than men of the second group. Thus supporting the popular claim of women that men can only think about one thing and one thing only.

Why do I mention this study? Because humans and frogs are not that different. It seems far-fetched to draw a parallel between the sexual behaviour of a frog and that of humans, however let’s bear in mind that one vital force is driving this behaviour in them and us and that is maximization of the individual’s fitness. And this doesn’t differ between me and the frog oit there in the cold that is now here in Holland looking for a place to spend his winter in hibernation. I do not want to start a discussion about how much of our behaviour is involuntary and biologically determined, but let me give another example of congruent behaviour. To give another example: In frogs generally speaking, females are the picky sex (i.e. mate choice) and only when impressed will they mate with a male, while male frogs will mate with any female that is willing to mate with them. In humans this basically works in the same way (this is why a sexual conflict might arise, something I will come back to later).

Back to the frogs. Like I said before, females of the green poison frog have probably learned to use deception as a tool to ensure their fitness is maximized. This is discussed in a review article by Summers (in press) that focuses on sexual conflict and deception in this particular frog species. First we need to know how deception is defined  here: “deception occurs when a signal that normally precedes a specific action or occurrence is given by an individual but this individual then does not perform the behaviour that normally follows.” While we might think that deception is restricted to animals with cognitive abilities like ours, it is a widespread behaviour in the animal kingdom. It does not require any theory of mind, i.e. I understand what you are thinking and feeling and therefore I can anticipate to your thoughts. Especially within the context of sexual selection, in which some individuals are reproducing more than others (due to mate choice mostly by females) deception occurs regularly.

Some male bluegill fish for example mimic females of their species, deceiving the dominant territorial males in their surroundings. Instead of having to fight for a territory and subsequent access to females, they use this strategy to stay under the radar of the other males. In this way they can mate with females without having to invest in fighting and guarding their females. Another wonderful and more sophisticated example of deception is shown by the male mourning cuttlefish, a species that has the ability to voluntarily change pigmentation of its body. When he is caught in the middle between on one side a male and on the other side a female with which he would like to mate, he can show on one side of his body coloration that gives him a feminine appearance and on the opposite side of the body show coloration to the female to impress her and solicit mating. So at the same time he is flirting with the female and deceiving the male. As for deception by females, female sparrows use copulation solicitation behaviour, i.e. proposing sex to the male, to distract the male sparrow from other females in the vicinity he might want to mate with. This behaviour is primarily caused by a sexual conflict: while the male sparrow will raise its fitness by mating with multiple females, the females has the most to gain by bonding with only one male that will take good care of her offspring leading to an increase in her fitness.

 

This sexual conflict is also seen in green poison frogs. Although tropical poison dart frogs are very small creatures and their behaviour is not widely studied, they do exhibit a large repertoire of complex behaviours. Between the more than 175 species of poison dart frogs many different forms of parental care and social behaviours exist. Males are generally territorial and use a range of behaviours to defend the boundaries of their territory. Characteristically for frogs, males will use calls, vocal communication, from their special chosen perch in their territory, but also postural changes, chases and sometimes even physical contact.

But in courtship and parental behaviour they even more resemble us, more than we have probably imagined. Courtship can be an elaborate event, lasting up to more than six hours. The female initiates the courtship, approaching the calling male. The male will move away from her and remain calling at her, she will come closer to him again, he will move away from her and call to her again, ultimately  leading her to the site where she can lay her eggs. During this dance of getting closer to each other and moving away, the frogs will be near enough sometimes to touch each other and even stroke and nudge to each other, as if in a sign of affection. Then after mating the male frog will take care of the eggs, by keeping them moist enough and removing any fungi or other possible lethal threats.

After hatching, as in many other poison frog species, the male takes care of the tadpoles by getting them on his back and delivering them each separately to a pool of water (mostly in a tree hole) in which they can develop into froglets. Because ideally each tadpole gets its own pool of water and not all pools of water in the vicinity are suitable the male can spend considerable time on locating these pools, so this is quite an undertaking for such a small animal. The male can take care of several clutches of eggs at the same time and will, if given the chance, mate with any available female. Raising several clutches of eggs at the same time comes with a cost: to keep all the eggs moist and in good condition takes a lot of effort and suitable pools for the developing tadpoles are not easy to find. So some tadpoles might end up in unsuitable pools of water and perish, but the biggest cost is incurred when tadpoles  end up in a pool where already a (larger) tadpole has taken up its residency and tadpoles of this  species are voraciously cannibalistic. Even with these costs, raising several clutches would still be favourable for the male, who would raise more of his offspring, but the fitness of each female would be negatively influenced, because of tadpoles and eggs that would be lost. That’s why a sexual conflict exists .

 

 

 

 

 

To prevent a male from mating with another female, a female, of whose recently laid eggs he is the father, might therefore deceive him into thinking that she is ready to mate with him again. She will commence the courtship, like normally, with approaching the calling male. He will move away from here, calling to her and she will come closer to him again, maybe stroking him and nudging at him. In this way she is dancing the courtship dance they would normally do.  He is moving away from her and directing her to the site in his territory where she could lay a new clutch of eggs. She follows him for 10, 20 maybe 30 minutes and she might be showing him these apparent signs of affection, belonging to the courtship ritual. But then her interest seems to fade away and she leaves in the middle of the courtship dance, before the actual mating could have taken place. The male is left behind and his precious time, that he could have devoted to fathering the offspring of another female, is wasted. For the female it probably has been a success, because this might mean he will mate with less females in the coming time, raise fewer eggs  and therefore have more time to spend on the eggs he did manage to fertilize. If this leads to a higher percentage of the eggs hatching and developing into froglets, the female will have raised her fitness. And the male, he has had to succumb to her powers of deception.