Microhabitat selection by the Pacific treefrog, Hyla regilla

Substrate colour choice can provide a means of predator avoidance through crypsis. We investigated background colour choice in the Pacific treefrog, Hyla regilla, a species that shows a complex colour polymorphism. Individuals from a single population can be fixed in body colour (the nonchanging green or brown individuals) or they can show an ability to change colour between green and brown (colourchanger morph). In the laboratory, we tested background choice behaviour of the nonchanging green and nonchanging brown frogs to determine whether these frogs have a preference for the matching background substrate. Nonchanging green frogs preferentially selected a matching background colour. Such a preference, however, was not observed in nonchanging brown frogs. When tested in the presence of a predator cue, small samples of both nonchanging green and nonchanging brown frogs showed a preference for the matching substrate. We also investigated whether colour-changers have a preference for a background that matches their own body coloration (phenotype matching) at the time of testing. Colour-changers did not select matching substrates. An alternative to phenotype matching is that substrate colour preference (i.e. that shown by nonchanging green frogs) could result from a sensory bias that is genetically linked to body colour. One possible cause of differences in spectral sensitivity and/or hue discrimination is a photopigment polymorphism in the retina. We used electroretinogram techniques to characterize the spectral sensitivity of the retina but found no evidence for differences in spectral sensitivity curves among the three morphs that would suggest a visual pigment polymorphism.