Not always best to be the brightest

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One of the greatest puzzles of evolutionary biology is the color variation of the strawberry poison-dart frog on the Bocas del Toro Archipelago. Generally a shiny reddish-orange throughout its mainland Central American territory, Dendrobates pumiliocomes in as many as 30 color combinations on the Panamanian Caribbean island chain. Rising seas separated the archipelago from the mainland less than 9,000 years ago – a blip in evolutionary terms. How did such an array arise so quickly?

Given that environmental conditions do not seem to vary greatly between population locations, natural selection might play second fiddle to sexual selection in the D. pumilio riddle. To test that theory, Ph.D. student and STRI fellow Laura Crothers is studying how the frogs – males and females – respond to brightness and color variation.

More fiercely territorial than their size would suggest, the diminutive males regularly pick fights. Yet instead of taking on dimmer competitors – which, in theory, should be easier targets – they appear to attack the more brightly colored ones.

Energy spent calling to or wrestling with other males is energy not spent reproducing. So if dimmer and different-colored males fought less once isolated from the mainland, this could help explain the early in the divergence of color in these populations. For example, if most of the frogs in a population are orange, other males could ignore an unusual blue individual. “That would allow those really rare blue ones to increase slowly in that population because they are not getting beat up all the time,” says Laura. “They can focus all of their time on courting females.

 

Source: Smithsonian Tropical Research Institute

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