The Closest Match: These Frogs Pick the Nearest Companion, Not the Best

When it comes to mating, this frog is hardly coy (Photo by Geoff Gallice / CC BY 2.0)

Amid stories of the US’s declining amphibian populations last week, the female strawberry poison frog has brought us some light relief. It appears that for her, rather comically, when it comes to choosing a mate there isn’t any complicated analysis going on. In fact, female strawberry poison frogs just tend to grab the nearest guy.

Researchers discovered this when they went frog tracking—literally—in the forests of Costa Rica. Previously, some scientists had entertained the idea that the female strawberry poison frog was drawn to the male she picked by his call. Male frogs engage in ‘lekking’, a practice that sees males gathering in a central place to compete for female attention. For strawberry poison male frogs, that means croaking amid a million other croakers, and trying to get heard. Researchers assumed that certain more distinctive baritones caught the female frog’s ear, signaling a strong and competitive male that would father healthy offspring. But after their unusual discovery, the researchers have started thinking differently.

By following 20 of the glistening, berry-like frogs, the avid trackers began to gather notes on the females’ mating habits, noting whether they went for the males with the largest territory, the most distinctive croaks, or the chunkiest physiques. What they surmised was that the females weren’t that concerned with any of these traits, and didn’t appear to visit males specifically to size them up. In fact, they seemed to just pick the first frog they hopped across.

The research team, led by Dr. Ivonne Meuche from the University of Veterinary Medicine in Hanover, Germany, also tested this finding by setting up speakers in the forest that played a variety of mating calls to any female that would listen. Of the 45 females that responded, none of them seemed to show any preference for the speaker according to the type of call: they just picked the nearest one.

As with most research, there are some limitations, and in this case it’s the fact that not all populations of strawberry poison frogs are necessarily dominated by females, as the one they studied was. This means that in other groups, there may be more scope for choosiness, since there will be less pressure to find a male fast, before another female beats you to it.

But the results of their analysis still seem to show that the practice of lekking in some populations did not necessarily evolve to fit the females’ preferences. The researchers do suggest that the females they studied in fact have very good evolutionary reasons for taking their seemingly lazier route.

It might not actually be beneficial to the frogs to be choosy about the males they find, they say, because if females outnumber males, they could risk losing out if they don’t act quickly enough. It also turns out that the intensely competitive scenario for the male strawberry poison frogs means that only the strong ones get to participate. As a result, most males tend to be a pretty good catch, the study shows. So by hedging their bets and grabbing the nearest guy, the female frogs have a better chance than not of finding a suitable mate.

So much for the male frog’s efforts to win the affections of his seemingly picky mate: he would do well to simply get closer. If only it were as simple for the rest of us.