When is Mate Choice Permanent in Tungara Frogs

A group out of the University of Texas, Austin, tested some variables that go into the female mate selection of Tungara frogs. Males of this species can often be heard using dynamic signaling to call females from quite a distance a way. The males have two somewhat distinct calls. The more preferable whine chuck sounds like a higher pitched whine followed by a sharp chuck or series of chucks and the less preferable monotonous whine. Previous research had been done on which method of calling was the most preferential so this group, continued on this path testing timing and volume of these signals.

The group wanted to test at which point a female mate choice was permanent. Using over 350 female frogs the researchers set up a stable testing environment. A football field like arena was set up approximately 2 meters in width and 3 meters in length. At either end of the arena there were target speakers that would play the whine or the whine chuck simultaneously. In the middle was a circular area called the release point where the females being tested were held under a small, perforated cone. “Switch boundaries” (equivalent to yard lines on a football field) were drawn at 60cm, 75cm, and 100 cm.

The experiments were run in a very controlled fashion to reduce errors in observations. In the control, the on speaker played the whine chuck while the other played the whine. The females were individually put in the center of the arena and held under the cone for 3 minutes while the male signaling was played. Once the 3 minutes were up the cone was release, the speakers continued to play and the female was drawn to one of the mate calling speakers. All 373 females were tested in the control and in all 373 control tests the female chose the whine-chuck speaker. This told the researchers that not only was the whine-chuck call the more preferable one, but that the females would actually travel to the speakers 100% of the time.

In the next 19 experimental procedures the Researchers manipulated the speakers volume, and switched the signaling calls once the females reached one of the switch boundaries. For example, in Experiment 1 once the female was released and reached the 75cm boundary of the whine-chuck speaker, the signals on the speakers were switched and the now distance whine-chuck speaker was amplified 2 decibels. This procedure was done for each of the 373 females. The next 18 experiments were all manipulations of experiment 1 that played with the volume and the distance of the females.

In almost all cases a percentage of females switched paths and went to the distant whine-chuck speaker. This showed the researchers that the female mate choice was not permanent at any of their boundary distances. Even though in some cases this percentage was small, a 100% permanent mate choice at a certain distance was never achieved.

Some Issues were noticed within the results and in the way the researchers quantified the data. The way the data was organized and quantified made it very ambiguous on which of the variables (distance or volume) was the prominent variable in choice reversal. A new experimental procedure testing one specific variable at a time should be done to determine which one is the more confounding variable.

Patrick Salome