Platyrrhine (New World) monkeys possess highly polymorphic color vision owing to allelic variation of the single-locus L/M opsin gene on the X chromosome. Most species consist of female trichromats and female and male dichromats. Howlers (genus Alouatta) are an exception; they are considered to be routinely trichromatic with L and M opsin genes juxtaposed on the X chromosome, as seen in catarrhine primates (Old World monkeys, apes, and humans). Yet it is not known whether trichromacy is invariable in howlers. We examined L/M opsin variation in wild howler populations in Costa Rica and Nicaragua (Alouatta palliata) and Belize (A. pigra), using fecal DNA. We surveyed exon 5 sequences (containing the diagnostic 277th and 285th residues for λmax) for 8 and 18 X chromosomes from Alouatta palliata and A. pigra, respectively. The wavelengths of maximal absorption (λmax) of the reconstituted L and M opsin photopigments were 564 nm and 532 nm, respectively, in both species. We found one M–L hybrid sequence with a recombinant 277/285 haplotype in Alouatta palliata and two L–M hybrid sequences in A. pigra. The λmax values of the reconstituted hybrid photopigments were in the range of 546~554 nm, which should result in trichromat phenotypes comparable to those found in other New World monkey species. Our finding of color vision variation due to high frequencies of L/M hybrid opsin genes in howlers challenges the current view that howlers are routine and uniform trichromats. These results deepen our understanding of the evolutionary significance of color vision polymorphisms and routine trichromacy and emphasize the need for further assessment of opsin gene variation as well as behavioral differences among subtypes of trichromacy.

中文翻译：

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三色 Alouatta 新世界猴野生种群中混合 L/M 视蛋白基因所证明的色觉变化

由于 X 染色体上单位点 L/M 视蛋白基因的等位基因变异，桔梗（新世界）猴具有高度多态性的色觉。大多数物种由雌性三色视者和雌性和雄性双色者组成。吼叫（Alouatta 属）是个例外；它们被认为通常是三色的，L 和 M 视蛋白基因并列在 X 染色体上，如卡他林灵长类动物（旧世界猴、猿和人类）。然而，不知道三色性是否在咆哮者中是不变的。我们使用粪便 DNA 检测了哥斯达黎加和尼加拉瓜 (Alouatta palliata) 以及伯利兹 (A.pigra) 的野生咆哮种群的 L/M 视蛋白变异。我们分别调查了来自 Alouatta palliata 和 A.pigra 的 8 条和 18 条 X 染色体的外显子 5 序列（包含 λmax 的诊断性第 277 和 285 残基）。在两种物种中，重组的 L 和 M 视蛋白光色素的最大吸收波长 (λmax) 分别为 564 nm 和 532 nm。我们在 Alouatta palliata 中发现了一个具有重组 277/285 单倍型的 M-L 杂交序列，在 A.pigra 中发现了两个 L-M 杂交序列。重组混合光色素的 λmax 值在 546~554 nm 的范围内，这应该导致与其他新世界猴种中发现的三色体表型相当。我们发现由于嚎叫者中 L/M 混合视蛋白基因的高频率而导致的色觉变化挑战了目前认为嚎叫者是常规和统一的三色视者的观点。