Frogs in the pond in 2022

Dear Readers, this has to be my favourite New Scientist headline so far this year. See what you think:

Frogs have attempted sex with other species for millions of years.

Well, I don’t know about you but this seems like a pretty rubbish life strategy, though my observation of the frogs in my garden strongly suggests that this could be true. At the height of the breeding season, the frogs attempt to mate with other male frogs, they mob the females and if there were toads or goldfish in the pond I’m pretty sure that they’d try to mate with them as well. Frogs have been observed engaged in sexual congress with boots, turtles, dead frogs and frogs of a completely different species. 

One theory is that in situations of explosive breeding, where lots of males emerge from hibernation at once and there are relatively few females, grabbing whatever you can find and hanging on like billy-o would usually pay off. Frog mating involves amplexus, in which a male grabs a female and hangs on with a specially adapted ‘thumb’. He then waits until the female lays her eggs and fertilises them as they emerge, but a female might take hours, or even days, to be happy enough to lay, so he has to be capable of staying with her, and fending off other males, for that whole period. Possibly the occasional male grappling a stick or a goldfish is a small price to pay for the chance of successful reproduction.

What is interesting, though, is that even frogs that have different mating strategies from the ones in my pond also display what scientists call ‘misdirected amplexus’. Tree frogs, for example, sit around and call to attract a female, who comes to them, and who gives the male a little pat on the shoulder to indicate that she’s happy to mate, and yet even these species occasionally mate with the wrong species. What’s going on? Evolutionary biologists have studied the behaviour across 159 frog species, and have concluded that even the earliest frog species, dating back to some 220 million years ago, also made these kind of mistakes. It could even go back further, to the ancestors of frogs, salamanders and a type of amphibian called a caecilian.

Presumably if this behaviour was catastrophic, frogs wouldn’t have become the extremely successful and widespread species that they are today, but there is bad news. The incidence of frogs getting it wrong seems to be more widely reported in the 21st Century than previously, and scientists are concerned that habitat destruction, drought and noise might all be contributing to frogs not meeting enough females, and becoming more generally confused. Add this to the chytrid fungal disease which is causing the decline and even extinction of many frog species, and what can seem like a harmless quirk of behaviour could have serious implications for these fascinating animals.