With the onset of the monsoon season in Southeast Asia, a peculiar phenomenon occurs in the puddles formed by the first rains. The males of the toad species Duttaphrynus melanostictus, in about 10 minutes, shed their brownish color and don a vivid yellow.
This radical change in appearance is caused by hormones and coincides with the reproductive frenzy of the species, whose mating takes place once a year during only two days. However, the function of this color change was not known. Until now.
In a study led by the Vienna Zoo, it was discovered that the bright yellow coloration serves to indicate to the males who the other males are, since the females retain the brown color. With such a short mating window, it is useful for the males to know where the females are so as not to waste time making advances toward rival males of the same sex.
The research team, which published the findings in the journal ‘Ichthyology & Herpetology, placed, in a puddle in a forest in the Indian state of Karnataka, during the peak of the reproductive frenzy, two model toads created by a 3D printer: one that imitates a female and another that imitates a bright yellow male.
Observing the animals’ behavior, it was noticed that the males grabbed the brown model (the female) much more often than the yellow model (the male). Moreover, they found that body size, weight, nor color had any influence on the ability of the males to secure a partner.
Therefore, the researchers concluded that the yellow color is a way for the males to clearly tell rivals “I am a male, move along.”
After the mating period ends, the males lose their exuberant color and revert to the brown coloration. However, it remains unknown which traits attract females, whether the bright yellow is particularly captivating, nor whether females themselves exert any influence on mate choice—especially in frenetic moments when several males try to latch onto the same female.
