Neat.
I was excited to see this noted: "Just because parts of us can fluoresce doesn’t mean they’re doing so for any particular purpose. The same is true for many other fluorescing elements in the natural world, from glowing fur to feathers, says visual ecologist Michael Bok at Lund University in Sweden, who was not involved in the study. “There’s a lot of meaningless fluorescence in the world,” he says."
But then the article spends much time speculating on possible adaptive benefit. "And it takes place in a way that matches frogs’ activity and ecology, and the physiology of their eyes. Researchers can’t hop to any definitive conclusions, but this suggests that fluorescence may allow frogs to communicate with each other, says Whitcher. While frogs are very vocal communicators, this may serve as a secondary means of being in touch, she adds."
And: "So it stands to reason that, if many of these frogs can see green glows that other creatures can’t, then maybe
they’re making green glows as a way to signal one another, or at least declare their presence to each other." (emphasis added, to point out blatant adaptationism, which I'll discuss below)
And: "“It’s quite likely that those species are using their vision to perform complex tasks like signaling. They didn’t find this kind of fluorescence in aquatic species, which have much smaller eyes and live in murky waters, so it does seem that
this is something that evolved by a sensory drive to serve a very specific purpose.”" (As it turns out, fluorescence is present in aquatic caudate amphibians. This is an important point.
Source.)
And: "This fluorescence, they propose, could be for a different target audience, such as predators. "
But the following claim suggests another alternative that wasn't mentioned: "Every single species they studied showed some level of fluorescence." The alternative is that fluorescence in these taxa is a conserved trait that isn't associated with any particular adaptive benefit. This alternative hypothesis is supported by the fact that fluorescence is widespread in amphibians, and so is very unlikely to have "evolved [...] to serve a very specific purpose". This last quote illustrates 'adaptationism', the idea that if a species has a trait then that trait confers adaptive benefit to that species. Adaptationist assumptions are pretty widespread (particularly among herp keepers in an informal way), and pretty misleading.
If an ancestral taxon evolved fluorescence as a response to adaptive pressure, descendant taxa could have that gene (it is likely a pretty small sequence) simply because it wasn't selected against, or is linked to some other ubiquitous sequence that has adaptive value, or at most is exapted (an already existing trait newly exploited for some novel purpose, rather than evolved for a specific purpose as is claimed a couple times in the piece).
