Wente Wendy H, Phillips John B
Department of Biology, Indiana University, Bloomington, Indiana 47405, USA.
Am Nat. 2003 Oct;162(4):461-73. doi: 10.1086/378253. Epub 2003 Oct 16.
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.
太平洋树蛙（Hyla regilla）背部的颜色通常要么是绿色，要么是棕色。已知绿色和棕色个体的出现频率会随季节波动。先前的研究人员普遍认为，绿色和棕色体色代表一种“固定”的多态性，且两种体色比例的季节性变化是两种颜色形态差异存活的结果。在此我们报告，除了太平洋树蛙“固定”（即不变色）的绿色和棕色形态外，还有一些个体能够在绿色和棕色之间变换色调。我们研究群体中颜色变换能力的分布是双峰的，这表明“变色者”是一种独特的形态，而非颜色变换能力连续分布的一个极端情况。我们的研究结果表明，背景亮度而非色调触发了新发现形态的颜色变化，且这种变化需要数天到数周时间才能发生。如此缓慢的颜色变化不太适合青蛙在不同颜色的底物之间移动时进行短期颜色变化。相反，栖息地特征和/或微生境利用的季节性变化可能维持了颜色变换能力。颜色多态性和颜色变换能力似乎代表了在异质、季节性变化的环境中对不同选择压力下拟态的两种不同反应。
