Two years ago, Juan Díaz Ricaurte was hiking in the mountains of Brazil when a male yellow cururu toad attached itself to his boot. Díaz Ricaurte carefully untied the frog and set it back on the ground a few meters away; undaunted, he jumped back and wrapped his arms around the shoe again. “It was super focused on grabbing Juan’s boot,” said Filipe Serrano, Díaz Ricaurte’s fellow biologist, who witnessed the meet-cute. The frog appeared to have mistaken Díaz Ricaurte’s footwear for “a potential mate” and kept returning to grab it again. Little Lothario, Serrano said, “wouldn’t let it go.”
In a sense neither, Serrano or Díaz Ricaurte. The rendezvous eventually ended, but in the months that followed, the two researchers from the University of São Paulo couldn’t get the incident out of their heads. It wasn’t exactly the toad, or the boot, or even the doomed union between the two – frog mating, known as aplexus, usually involves a male clinging to a female, and it’s not uncommon for overzealous suitors to start a faulty initiative . embrace. What stuck with the couple, they told me, was the possibility that these fateful events, which they had both heard about before, could increase in frequency as frogs attempt to navigate an increasingly fractured world. Scientists call this an evolutionary trap. “The environment is changing and they are making more mistakes,” said Ulrika Candolin, a biologist at the University of Helsinki. The temperatures are rising; fraying habitats; animals are forced to mix with new and unknown species. Sex seems to inevitably take a hit for some species.
Serrano and Díaz Ricaurte, along with their colleague Marcio Martins, began looking for past stories of frog hugs gone wrong — formally named misdirected ampoules† They found nearly 400, a whole group of frogs clinging to things they could almost certainly never fertilize: dead frogs, incompatible frog species, and frog embryos still in eggs; coconuts, mangoes and apples; geckos, turtles, fish and snails; balls, rulers and plastic cups; and even some cow and yak manure. The compendium makes it clear that horny frogs can sometimes be seriously cheated.
What is not clear, however, is why. Misdirected amexus is not always cause for concern. A bit of boldness can suit a bachelor frog, especially in species that mate only a few nights a year, or in populations where females are particularly scarce. “Men will just go for anything they can get their hands on,” said Liz Lopez, a California wildlife biologist who has studied misdirected AMEXUS. The super tight hugs are an ideal way to put males in the right place at the right time, when their partners drop their eggs; they can also fend off other suitors who try to invade. Serrano calls it a “grab first, ask questions later” strategy – it’s much better to get too grabsy and make a blunder than give in to embarrassment and go totally unsexed. There are even rare instances of sexual snafus that end up pretty well: necrophilia that actually led to the extrusion and fertilization of viable eggs; interspecies associations that, under certain circumstances, produce offspring more adapted than staying with their own species.
But too many mistakes, and frogs can quickly get into trouble. Every mistake marks a missed opportunity – time that could have been spent finding a more suitable partner, then getting in touch with her. Some males cling to a mate for weeks, even months, and refrain from meals all the time. “That’s very expensive,” and hardly worth it if there are no offspring, says Juan Carvajal Castro, a biologist at St. John’s University who has studied Alexus. (Men who accidentally grab other males will sometimes provoke a cry of protest prompting them to let go; however, dead frogs and apples cannot give such warning calls.) A prolonged clamp in the open can also make deceiving males more vulnerable for predators and diseases, Díaz Ricaurte told me.
So there is danger in going south too often. Which it could very easily in today’s fast-paced world. The precious real estate on which frogs live and mate is becoming scarcer; Carvajal Castro notes that some species living in drier habitats, for example, can only mate after periods of rain fill local ponds — events that are becoming more widespread as climate change accelerates. Frogs also have trouble hearing and responding to the croaks and cries of potential mates in the growing urban rumor. Starved of the right partners, frogs may look elsewhere. And as humans continue to invade the wilderness, frogs are undoubtedly coming into contact with new species, or even unknown objects, more often, which could distract them from better prospects. Candolin, of the University of Helsinki, has witnessed exactly that disaster with male European glowworms, sometimes lured away from glowing females by luminescent garden lamps. “They fly around the lights, instead of mating and breeding, and they die there,” she told me.
Now, if something similar happens to frogs, the database of confused Serrano and Díaz Ricaurte followers won’t be able to fully prove it. To really make a case for climate change or disruption of habitats that mess with alexus, researchers would need to slowly and systematically monitor frog mating over time while monitoring local environmental conditions; they should compare amphibian populations between locations and try to figure out which ones had the most sexual success. In contrast, most of the incidents in the database were accidentally recorded by a select group of people who blatantly encountered a frog. “There’s a lot of potential for bias because of that,” said Karin Pfennig, a frog biologist at the University of North Carolina at Chapel Hill.
Still, Serrano is intrigued by the amount of evidence the team saw during the search, where the researchers “tried to report as much as possible about each sighting — air temperature, precipitation, altitude,” he told me. There to have there have been many reports of misdirected amplexus in super degraded habitats, and many of them to have has taken place in recent years. A recent study even suggested that climate change could prompt certain European toads to live with the wrong species. And there’s something to be said for the presence of human paraphernalia speckled in the database, which frogs wouldn’t have much to do with otherwise. Just ask the American toad who was spotted with a tennis ball in a Virginia park in 2007.
A wave of misdirected amphexus is something many scientists could easily miss: The natural tendency, Lopez told me, is just to think oh that’s weird and move on. But it’s worth taking a closer look at the phenomenon, she said, especially considering “all the other stressors on amphibians right now,” including deadly fungal outbreaks and dried-up ponds. Failed sexual encounters are the last thing frogs should add to their list of woes.
Sex, and the act of bringing it about, is fundamental to the existence of any frog. “People often see these events as errors and are dismissed as insignificant,” Pfennig told me. “Nobody thinks about putting them in a broader context.” A database is a starting point: the core of something that could grow into something bigger and, perhaps more importantly, inspire bigger, bolder projects to get to the root of a problem and develop solutions. Misdirected amexus could become a kind of early clock, delineating populations at risk; it could alert researchers to species teetering on the brink.
If the misdirected aproposus among frogs really increases at the hands of humans, it won’t be the first time humans have toyed with the mating habits of other species. Birds confused by traffic noises have trouble hearing their friends’ songs. Fish confused by chemical pollutants, which can disrupt social cues, have chosen sub-optimal mates. Beetles, lured in by the brownish sheen of textured glass, have attempted to locate beer bottles in the Australian west. Peeking at these acts of misplaced affection may seem strange, even voyeuristic. But sex is serious business, and maybe people owe it to their neighbors to take a good, long look every now and then.