Fixed Green and Brown Color Morphs and a Novel Color‐Changing Morph of the Pacific Tree Frog Hyla regilla

Abstract

Pacific tree frogs Hyla regilla are typically either green or brown in dorsal coloration. The frequency of green and brown individuals is known to fluctuate seasonally. Previous investigators have generally assumed that the green and brown body colors represent a "fixed" polymorphism and that seasonal changes in the proportion of the two body colors are a consequence of differential survival of the two color morphs. Here we report that, in addition to the "fixed" (i.e., non-color-changing) green and brown morphs of H. regilla, there are some individuals that can change hue between green and brown. The distribution of color-change ability in our study population is bimodal, suggesting that "color changers" are a distinct morph rather than one extreme of a continuous distribution of color-change ability. Our findings suggest that background brightness, not hue, triggers color change in the newly discovered morph and that this change requires days to weeks to occur. Such slow color change is not well suited for making short-term changes in color as a frog moves between differently colored substrates. Rather, seasonal changes in habitat characteristics and/or microhabitat use are likely to maintain color-change ability. Color polymorphism and color-change ability appear to represent alternative responses to divergent selection for crypsis in a heterogeneous, seasonally variable environment.

Adaptive shell color plasticity during the early ontogeny of an intertidal keystone snail

“…Although most studies on the relationship between plasticity and adaptation have ignored the consequences on fitness (4), environmentally determined body coloration and its consequences for predator avoidance is a good example for testing whether phenotypic plasticity is adaptive (5). Because the environment is often a mosaic of patches with contrasting distribution of color background patterns (6), phenotypic plasticity may represent a generalist strategy evolved by cryptic species to avoid visual predation. Consequently, in species with cryptic coloration, survivorship in the presence of visual predators should improve as they blend with the surrounding background (7-10).…”

The Evolution of Color Polymorphism: Crypticity, Searching Images, and Apostatic Selection

“…It has been studied extensively in pulmonate snails (Cain & Sheppard 1954, Clarke et al 1978, Cook 1998), but it is common among other mollusks as well (e.g., Atkinson & Warwick 1983, Whiteley et al 1997). There are cryptic polymorphic spiders (Bonte & Maelfait 2004, Oxford & Gillespie 1998, crustaceans (Devin et al 2004, Hargeby et al 2004, Merilaita et al 2001, and even vertebrates (Olendorf et al 2006, Wente & Phillips 2003. Examples occur throughout the Acridid and Tetrigid grasshoppers (Figure 2) (Dearn 1990, Nabours et al 1933, where many species are so variable that color is wholly inadequate as a basis for classification (Rowell 1971).…”

“…We refer to this category as specialist polymorphisms. Because diversity is limited by the number of substrate types, specialist polymorphisms generally involve fewer, more distinctive forms, often only green and brown (Dearn 1990, Edmunds 1976, Owen 1980, Poulton 1890, Wente & Phillips 2003 or dark and light (Kettlewell 1973). In many cases, the dimorphism is genetically determined; in others, it is a polyphenism, a developmental difference in color pattern cued by physical or chemical signals (Edmunds 1976, Greene 1996, Rowell 1971.…”

Communication in Noisy Environments Ii: Visual Signaling Behavior of Male Foot-flagging Frogs staurois Latopalmatus

“…In addition to fixed color patterns, some animals undergo color changes during their lifetime. Ontogenetic change of coloration is generally unidirectional and usually occurs at the onset of sexual maturation of an individual (Hoffman and Blouin 2000;Wente and Phillips 2003;Galan 2008). Hormonal changes are suggested to affect ontogenetic variations in coloration (Richards 1982;Hayes and Menendez 1999;Hoffman and Blouin 2000).…”