Alternative male phenotypes exist in many species and impact mating system dynamics, population genetics, and mechanisms of natural and sexual selection that operate within a population. We report on the discovery of a cryptic male phenotype in the mangrove rivulus fish (Kryptolebias marmoratus), one of only two self-fertilizing hermaphroditic vertebrates. In this androdiecious species, males are infrequent, often making up less than 5% of a population; and they have historically been described as having an orange color and lacking or having a very faded outline of the well-defined caudal eyespot (ocellus) that is obvious in hermaphrodites. The cryptic male we describe varies subtly from the hermaphrodite phenotype, without visible orange pigmentation on the body and retention or only minor fading of the ocellus. This male morph was identified by a loss of a defined melanistic “fingerprinting” on the caudal fin seen in hermaphrodites, not previously used as diagnostic for hermaphrodites, and replaced by a diffuse deposition of pigment across the fin. Individuals were identified as male with 85.7% accuracy when using these criteria. We report that in nine populations, spanning three geographically distinct regions in Florida, across two and a half years, 0.3% of the 6057 mangrove rivulus collected exhibited this cryptic male phenotype and were confirmed to have testes via dissection. Overall, 2.3% of the animals were male (normal and cryptic phenotypes), and cryptic males represented 12.9% of all males collected. Even a minor increase in individuals identified as male in a species where males make up such a small portion of the population can have important implications for population genetics. Opportunities for outbreeding are likely enhanced, which has significant evolutionary ramifications.

中文翻译：

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红树林 Rivulus 鱼的隐秘雄性表型，Kryptolebias marmoratus

替代雄性表型存在于许多物种中，并影响交配系统动态、种群遗传学以及在种群内运作的自然和性选择机制。我们报告在红树林河鱼 (Kryptolebias marmoratus) 中发现了一种神秘的雄性表型，这是仅有的两种自体受精雌雄同体脊椎动物之一。在这个雄性的物种中，雄性很少见，通常占种群的不到 5%；历史上，它们被描述为具有橙色，并且在雌雄同体动物中明显的尾眼点（ocellus）没有或非常褪色的轮廓。我们描述的神秘雄性与雌雄同体的表型略有不同，身体上没有可见的橙色色素沉着，也没有保留或只有轻微的眼部褪色。这种雄性变种的特征是在雌雄同体的尾鳍上丢失了一个确定的黑色“指纹”，以前没有用作雌雄同体的诊断，取而代之的是遍布鳍的色素的扩散沉积。使用这些标准时，个体被识别为男性，准确率为 85.7%。我们报告说，在跨越佛罗里达州三个地理不同区域的九个种群中，在两年半的时间里，收集的 6057 条红树林河中的 0.3% 表现出这种神秘的雄性表型，并通过解剖证实具有睾丸。总体而言，2.3% 的动物是雄性（正常和隐性表型），隐性雄性占收集到的所有雄性的 12.9%。在雄性只占种群这么少的物种中，即使被确定为雄性的个体略有增加，也会对种群遗传学产生重要影响。远交的机会可能会增加，这会产生重大的进化后果。