Kingsolver Joel G
Department of Zoology, NJ-15, University of Washington, Seattle, Washington, 98195.
Evolution. 1995 Oct;49(5):932-941. doi: 10.1111/j.1558-5646.1995.tb02328.x.
Wing melanin pattern varies seasonally among generations in many populations of the butterfly Pontia occidentalis, leading to distinctly different wing phenotypes during spring and summer generations. Estimates of directional selection on wing pattern can therefore quantify the imperfection of this phenotypically plastic (polyphenic) response in generating "optimal" phenotypes for each seasonal generation. Mark-release-recapture (MRR) studies were used to estimate directional selection on six wing traits in a natural population of P. occidentalis during both spring and summer weather conditions. Estimated survival and recapture probabilities varied substantially among the four MRR studies. When differences between males and females were detected, the survival and recapture probabilities were higher for males than for females. Estimated selection coefficients suggested that the direction of selection on one wing trait important for thermoregulation, melanin on the base of the dorsal hindwings (trait hb), fluctuated seasonally; there was evidence of directional selection for increased hb in the spring studies and for decreased hb in the summer studies. Such fluctuating seasonal selection on hb implies that the seasonal polyphenic response may not be sufficient to eliminate selection on this trait; the slope of the reaction-norm mapping hb onto seasonal environmental cues is too shallow, resulting in further selection on the reaction norm. Adaptive evolution of the reaction norm may be constrained by phenotypic and genetic correlations with other wing traits that experience different patterns of selection and by variable weather conditions within seasons and among years.
在西方粉蝶（Pontia occidentalis）的许多种群中，翅黑色素模式在不同世代间会随季节变化，导致春夏季世代的翅表型明显不同。因此，对翅模式的定向选择估计可以量化这种表型可塑性（多型现象）反应在为每个季节世代产生“最优”表型方面的不完善程度。标记重捕（MRR）研究被用于估计在春季和夏季天气条件下西方粉蝶自然种群中六个翅性状的定向选择。在四项标记重捕研究中，估计的存活率和重捕概率差异很大。当检测到雄性和雌性之间的差异时，雄性的存活率和重捕概率高于雌性。估计的选择系数表明，对体温调节很重要的一个翅性状——后翅背基部的黑色素（性状hb）的选择方向随季节波动；在春季研究中有增加hb的定向选择证据，而在夏季研究中有降低hb的证据。对hb的这种波动季节性选择意味着季节性多型反应可能不足以消除对该性状的选择；将hb映射到季节性环境线索上的反应规范斜率太浅，导致对反应规范的进一步选择。反应规范的适应性进化可能受到与经历不同选择模式的其他翅性状的表型和遗传相关性以及季节内和年份间多变天气条件的限制。
