Data from: Sensory limitations and the maintenance of color polymorphisms: viewing the ‘alba’ female polymorphism through the visual system of male Colias butterflies

Although color polymorphisms are a widespread and conspicuous component of extant biodiversity, the selective pressures that act to maintain multiple morphs within populations remain poorly understood in most cases. In particular, the role that visual system limitations may play in maintaining multiple color morphs is not well explored. We used a female-limited color polymorphism common to the butterfly genus Colias, called the ‘alba’ polymorphism, to investigate the hypotheses that mate-searching males may struggle to discriminate pale ‘alba’ females from co-occurring heterospecific white butterflies and/or heterospecific ‘alba’ females, or that ‘alba’ females may be more difficult to detect than non-‘alba’ females in natural scenes. Such perceptual limitations may influence the relative mating rates of ‘alba’ versus non-‘alba’ females, contributing to the evolutionary persistence of both morphs. Based on receptor-noise-limited modeling of the male Colias visual system, we find that ‘alba’ females exhibit chromatic and luminance contrasts against background foliage that are most similar to the ‘alba’ females of other co-occurring Colias species and females of the co-occurring white butterfly Pieris rapae. When compared to other co-flying butterflies including non-‘alba’ females, ‘alba’ females are consistently lower in chromatic contrast against background, but higher in luminance contrast. When viewed side-by-side, we estimate that male Colias should be able to discriminate ‘alba’ females from other co-occurring heterospecific butterflies, including heterospecific ‘albas’. However, under field conditions that involve larger distances in space or time, males are likely to face challenges discriminating between conspecific ‘alba’ females and co-occurring heterospecific white butterflies, particularly heterospecific ‘alba’ females. Our results suggest that constraints arising from male visual function may be involved in the maintenance of this color polymorphism, particularly in populations that co-occur with other ‘alba’-polymorphic Colias species. We argue that such visual system constraints may play a larger role in the maintenance of color polymorphism than has been empirically appreciated to date.

尽管体色多态（color polymorphism）是现生生物多样性中普遍存在且极具辨识度的特征，但绝大多数情形下，维持种群内多种形态的选择压机制仍未得到充分解析。尤为关键的是，视觉系统局限性在体色多态形态维持中的作用，尚未得到充分探究。本研究以黄粉蝶属（Colias）昆虫普遍存在的雌性限制性体色多态——‘alba’型多态——为研究对象，检验两项假说：其一，觅偶雄蝶难以将浅色的‘alba’型雌性与同域分布的异种白色蝴蝶，以及异种的‘alba’型雌性区分开来；其二，在自然生境中，‘alba’型雌性相较于非‘alba’型雌性更难被雄性识别。这类感知局限性可能会影响‘alba’型与非‘alba’型雌性的相对交配成功率，进而推动两种形态在演化中得以存续。基于黄粉蝶属雄蝶视觉系统的受体噪声受限模型（receptor-noise-limited modeling）分析，本研究发现：‘alba’型雌性与背景植被间的色彩对比度与亮度对比度，与其他同域分布黄粉蝶属物种的‘alba’型雌性，以及同域分布的菜粉蝶（Pieris rapae）雌性最为接近。相较于其他共飞蝴蝶（包括非‘alba’型雌性），‘alba’型雌性与背景间的色彩对比度始终更低，但亮度对比度更高。当并排观测时，我们推测黄粉蝶属雄蝶能够将‘alba’型雌性与其他同域分布的异种蝴蝶（包括异种的‘alba’型个体）区分开来。但在空间尺度或观测时长更大的野外条件下，雄蝶可能难以区分同种的‘alba’型雌性与同域分布的异种白色蝴蝶，尤其是异种的‘alba’型雌性。本研究结果表明，雄蝶视觉功能带来的感知限制，可能参与维持该体色多态，尤其是在与其他具‘alba’型多态的黄粉蝶属物种同域分布的种群中。我们认为，相较于当前已有的实证认知，视觉系统局限性在体色多态的维持中可能发挥着更为重要的作用。