Signaling for Love

After searching for months, she was chest-deep in an Ecuadorean rainforest stream, finally recording the sound of a male frog’s mating call. Then she spotted the frog repeatedly raise its legs. She balanced on a slippery rock with only one foot to capture the frog’s signaling behavior on video.

The researcher climbing by the side of the waterfall to record video of the glass frog’s visual signaling (Rebecca Brunner from gizmodo.com/drowned-out-by-noise-these-horny-frogs-wave-their-arms-1846068443).

Welcome back (to you and me). You of course know it’s almost Valentine’s Day. Beginning with this blog’s first Valentine’s Day, I’ve often offered a special post to revere the occasion. 

Those posts have featured such topics as musical flowers (Happy Valentine’s Day!), the effects of intimate (aka, French) kissing on oral microbiota (Valentine Kisses), Hershey Kisses (Kisses Addendum) and even túngara frogs (All for Love).

Remembering the Túngara Frog
If you missed or don’t recall that last post, I strongly recommend catching up. The túngara frog is as romantically inspiring as a frog might be and a prelude to today’s equally romantic if not particularly inspiring frog.

The túngara frog take away was that the male’s mating call, in addition to attracting females, alerts his rivals. Worse, though he can silence his calls, predatory bats use the ripples in the water generated by his calls to echolocate the frog. Couldn’t the frog find a safer environment? Unfortunately, he’s driven by love not security.

But it’s time we move on to today’s frog valentine.

The Ecuadorian Glass Frog
Most male frogs rely on mating calls to attract females, an invitation mode with obvious shortcomings in noisy environments. To better advertise and overcome background noise, a few frog species around the world supplement their mating calls with visual signaling.

A doctoral candidate at the University of California, Berkeley, working with a professor affiliated with Ecaudor’s Universidad San Francisco de Quito, has added a species of glass frog, Sachatamia orejuela, to that list.

Glass frogs are small (1 to 3 in; 3 to 7.5 cm) tree frogs found in tropical Central and South America. Taxonomically, they are in the Centrolenidae family. Most are green in color, and many have transparent or translucent underbelly skin, providing a window to inner organs.

The Sachatamia orejuela glass frogs are native to rainforests of Ecuador and Colombia. They are found almost exclusively on rocks and boulders within the spray of waterfalls. The rushing water and slippery surfaces offer protection from predators, and their color or lack thereof affords excellent camouflage. Relatively little is known about the species' mating and breeding behavior.

(A) The Ecuadorian glass frog, Sachatamia orejuela; (B) This species is found in the spray zones of waterfalls (Rebecca Brunner from brill.com/view/journals/beh/157/14-15/article-p1257_9.xml).

Field Data Collection
The U.C. Berkeley researcher was recording the sound of a male frog’s mating call, when she first observed his signaling behavior--cyclical foot-flagging, head-bobbing and hand-waving--all well after sundown.

Visual signaling sequence of Sachatamia orejuela. (A) not calling or displaying, (B) vocal sacs inflated while calling, (C) arm-waving, (D) double foot-flagging (Rebecca Brunner, illustrations by Robert Tyler, from brill.com/view/journals/beh/157/14-15/article-p1257_9.xml).

Although she had spent months searching for a calling male, of which there was no official record, she realized that documenting the frog’s visual signaling was even more significant. Enhancing her discovery, she observed another male glass frog a few meters away performing the same actions.

Wrap Up
The researcher documented the frog’s mating call, which was at a frequency higher than other glassfrog species, perhaps to be discerned against the rumbling of the waterfall. She also documented the visual signaling behavior observed at night.

She points out that the frog species known to signal visually are in different taxonomic families on different continents. The signaling behaviors likely evolved independently, but in response to similar environments, a concept called convergent evolution.

Happy Valentine's Day! And thanks for stopping by.

P.S.
Glass frogs background:
en.wikipedia.org/wiki/Glass_frog
www.pnas.org/content/117/23/12885
allthatsinteresting.com/glass-frog
Study of Sachatamia orejuela in Behaviour journal: brill.com/view/journals/beh/157/14-15/article-p1257_9.xml
Articles on study on EurekAlert! and Gizmodo websites:
www.eurekalert.org/pub_releases/2021-01/uoc--gfl011521.php
gizmodo.com/drowned-out-by-noise-these-horny-frogs-wave-their-arms-1846068443