Where once there were two

Monday, July 16, 2012
Rafe Brown


Funny, just after I waxed cathartic about figuring out that one species was actually two, today I experienced a kind of reversal.  Shrub frogs of the genus Philautus in the Philippines are, in my opinion, nearly impossible to tell apart.  In my experience, unless you hear their mating calls, you don't stand much of a chance of being able to identify them‚ because they are so similar in physical appearance.  Then, to make matters worse, all their calls sound like "rattles‚" or "crunches."  Sometimes one species will go "Crunch!" and another will sound like "Cruuuunch," but they are  all variations on just a few themes.  It's all very confusing.

For the last several days it has been misty and wet, without steady rain.  We have encountered two apparent species of Philautus, one large and another small, with a pointy snout. I was pretty sure: the big "species," consistently has had a greenish color scheme and the little one yellow or brown. 

Anyway, today it rained.  Hard.  Everyone retreated to their tents and hunkered down for the afternoon, it poured and poured, the camp frothed up in chocolate brown mud and, as it got dark, I finally heard a new frog call nearby -- could it be one of the Philautus species?  I turned on my headlamp and crawled through the bushes behind my tent and was confronted with a pair of frogs in amplexus (the male grasping the female during mating) on the leaf of a shrub. In just a glance I realized my mistake the big frog‚ was the female and the small frog was the male and the two were actually the same species.

Sexual size dimorphism, or the discrepancy in body size between males and females, is near universal in frogs around the world.  In almost all anurans (frogs and toads), females are larger than males, sometimes strikingly so.  In a few very special groups, the males are larger than the females.  Sometimes the appearance between the sexes is so marked that even the experts get confused and name the male of a species one scientific name and the female another.  These shrub frogs fooled me for a week, but at least it finally rained and I didn't make that mistake.