Diversity and Sexual Dichromatism in Treefrog Throat Coloration: Potential Signal Function?

Abstract

Sexual dichromatism, where males and females of the same species differ in coloration, is best studied in diurnal animals. Nocturnal animals such as frogs do not seem good candidates for widespread sexual dichromatism, or for the use of visual signals in social communication in general. Yet, up to 25% of treefrog species (Anura: Hylidae) show some degree of sexual difference in their dorsal coloration. The ventral side of frogs is hidden during rest, but the throat region becomes visible in active individuals, especially in calling males. We compiled a database of 249 treefrog species that include members of all seven subfamilies of the Family Hylidae. We document that the throat region of male frogs is frequently colorful and of a different color than the abdomen (ventral dichromatism), that there is interspecific variation in throat coloration, and that males and females differ in throat coloration (sexual dichromatism). We also examined intraspecific variation in throat coloration, using Eastern Gray Treefrogs, Dryophytes versicolor (Hyla versicolor) as the focal species. Here, we document throat color is sexually dimorphic, that it varies among males, is associated with better body condition, and on average is darker in mated compared to unmated males. Our study finds that throat color dichromatism is the most prevalent type of sexual dichromatism in treefrogs, and that throat coloration may have sexual signal function.