Further thoughts on comparative analyses of coloration

IF 1.9 3区 生物学 Q1 ZOOLOGY
Tim Caro, Natasha Howell
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Our independent measures were activity cycle, where we expected diurnal mammals to be more colourful; social group size, where we expected more social mammals to be more colourful; sexual dimorphism, with dimorphic species (showing evidence of sexual selection) expected to be more colourful; mating system, with polygynous species expected to be more colourful owing to the possible use of colour patches in male–male competition over mates; and congener overlap, where we expected species in danger of hybridization to be more colourful in order to signal species identity. Using these coarse measures, we found rather few significant associations, raising questions as to whether our independent measures were sufficiently sensitive to uncover signatures of social communication involving colour patterns. In part, our variables were dictated by the large breadth of species we examined. 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引用次数: 0

Abstract

Responding to our recent publication (Howell & Caro, 2024), Penteriani (2024) raises some important issues about independent measures used to tease out predictions about the social significance of coloration, the taxonomic level at which to conduct comparative analyses, and how to score colour patterns. For example, across terrestrial non-volant mammals, we found little evidence of social signalling involving coloration or colour patterns based on coarse social and ecological associations. Our independent measures were activity cycle, where we expected diurnal mammals to be more colourful; social group size, where we expected more social mammals to be more colourful; sexual dimorphism, with dimorphic species (showing evidence of sexual selection) expected to be more colourful; mating system, with polygynous species expected to be more colourful owing to the possible use of colour patches in male–male competition over mates; and congener overlap, where we expected species in danger of hybridization to be more colourful in order to signal species identity. Using these coarse measures, we found rather few significant associations, raising questions as to whether our independent measures were sufficiently sensitive to uncover signatures of social communication involving colour patterns. In part, our variables were dictated by the large breadth of species we examined. These were, in effect, ‘lowest common denominators’ that are documented for every species; they were not nuanced. Whether a solitary lifestyle means that individuals are less likely to signal socially is difficult to answer – we appreciate that these are not necessarily correlated.

The second issue is the taxonomic levels over which we analysed data. Findings at the Class level may not be reflected at the Order level; Order-level results may not be replicated at the Family level, and so on (Martins, 1996). Using comparative phylogenetic methods, many of our predictions did not hold up across the Class, or some Order levels for which we had sufficient data, even though we often based our hypotheses on associations already uncovered by others at Genus or Family levels. Thus for bears, conspicuous faces and chest bibs do seem to signal individual identity (Penteriani et al., 2020, 2023; although not tested phylogenetically owing to small sample size), but this association is washed out at the level of carnivores when other non-ursid species are included. What to do? Unfortunately, there is no clear solution. Higher taxonomic levels with greater numbers of species allow more statistical power and enable general conclusions to be formulated; lower taxonomic levels generate specific conclusions for certain groups, but species numbers can be so low for some groups that statistical tests are questionable. In our recent paper (Howell & Caro, 2024), we opted for the higher-level analyses; in others we have used Family-level analyses (Caro et al., 2014; Ortolani & Caro, 1996). Despite our higher-level attempt, we, like Penteriani (2024), value examining lower-level associations: mice are unlike bears, and duikers are unlike equids, both ecologically and morphologically.

A third point is that Howell and Caro's (2024) measures of pattern, which included adjacent blocks of colour, stripes and complex patterns, do not capture variations in shapes of colour patches in sun bears (Helarctos malayanus; Penteriani et al., 2020) and that may exist for giant panda (Ailuropoda melanoleuca) eye spots (unpublished data). Differences in these patterns may provide information on individual identity or age to conspecifics. Teasing out these proposals using phylogenetic analyses presents a challenge.

With some notable exceptions (e.g. West & Packer, 2002; Santana et al., 2012; Penteriani et al., 2020), most mammals do not rely on pelage coloration to communicate visually. One possible explanation is that many are solitary. If conspecifics are absent for much of an animal's life, it is reasonable to suggest that signalling might better involve odour, which lasts longer than a visual signal; the latter being a form of communication that is effective only when individuals can see each other. Nonetheless, there are other explanations for mammals being drab including the near ubiquity of dichromatic vision in mammals or intense predation pressure that many face.

Despite these quibbles, we think that Penteriani's (2024) critique is well placed, and we are pleased that he has drawn attention to these issues that dog phylogenetic comparisons.

对色彩比较分析的进一步思考
针对我们最近的出版物(Howell & Caro, 2024年),Penteriani(2024年)提出了一些重要问题,包括用于预测色彩社会意义的独立措施、进行比较分析的分类水平以及如何对色彩模式进行评分。例如,在陆生非啮齿类哺乳动物中,我们几乎没有发现涉及色彩或基于粗略社会和生态关联的色彩模式的社会信号。我们的独立测量指标包括:活动周期,我们认为昼伏夜出的哺乳动物的色彩更丰富;社会群体规模,我们认为社会性更强的哺乳动物的色彩更丰富;性双态性,二态性物种(显示性选择的证据)的色彩更丰富;交配系统,由于在雄性与雄性的配偶竞争中可能会使用色斑,因此多雌性物种的色彩更丰富;同类重叠,我们认为面临杂交危险的物种的色彩更丰富,以便发出物种身份信号。使用这些粗略的测量方法,我们几乎没有发现显著的关联,这让人怀疑我们的独立测量方法是否足够灵敏,能够发现涉及颜色图案的社会交流特征。在某种程度上,我们的变量是由我们研究的大量物种决定的。实际上,这些都是每个物种都有记录的 "最低共同标准";它们并不细致。独居生活方式是否意味着个体较少发出社会性信号,这个问题很难回答--我们知道这两者之间并不一定存在关联。类级的研究结果可能无法反映到目级;目级的结果可能无法复制到科级,等等(Martins,1996)。使用比较系统发生学的方法,我们的许多预测在我们有足够数据的类或某些目层次上并不成立,尽管我们的假设往往是基于其他人在属或科层次上已经发现的关联。因此,对于熊来说,显眼的脸部和胸围似乎确实是个体身份的信号(Penteriani 等人,2020 年,2023 年;尽管由于样本量较小,没有进行系统发育测试),但是当包括其他非臀目物种时,这种关联在食肉动物的层面上就被冲淡了。怎么办?遗憾的是,没有明确的解决方案。分类级别越高,物种数量越多,统计能力就越强,也就越能得出一般性结论;分类级别越低,就越能得出某些类群的特定结论,但某些类群的物种数量可能太少,以至于统计检验存在问题。在我们最近的论文(Howell & Caro, 2024)中,我们选择了更高层次的分析;在其他论文中,我们使用了科级分析(Caro et al.)第三点是,豪威尔和卡罗(2024 年)对图案的测量包括相邻色块、条纹和复杂图案,并没有捕捉到太阳熊(Helarctos malayanus; Penteriani et al、2020)和大熊猫(Ailuropoda melanoleuca)眼斑(未发表数据)可能存在的差异。这些模式的差异可能会为同种动物提供有关个体身份或年龄的信息。除了一些明显的例外(例如 West & Packer, 2002; Santana 等人, 2012; Penteriani 等人, 2020),大多数哺乳动物并不依靠体表的颜色来进行视觉交流。一种可能的解释是,许多哺乳动物都是独居的。如果在动物的一生中大部分时间都没有同类,那么我们有理由认为气味可能是更好的信号传递方式,因为气味比视觉信号更持久;后者是一种只有在个体能看到对方时才有效的交流方式。尽管如此,我们认为彭特里亚尼(Penteriani,2024 年)的批评是有道理的,我们很高兴他能提请我们注意这些影响系统发育比较的问题。
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来源期刊
Journal of Zoology
Journal of Zoology 生物-动物学
CiteScore
3.80
自引率
0.00%
发文量
90
审稿时长
2.8 months
期刊介绍: The Journal of Zoology publishes high-quality research papers that are original and are of broad interest. The Editors seek studies that are hypothesis-driven and interdisciplinary in nature. Papers on animal behaviour, ecology, physiology, anatomy, developmental biology, evolution, systematics, genetics and genomics will be considered; research that explores the interface between these disciplines is strongly encouraged. Studies dealing with geographically and/or taxonomically restricted topics should test general hypotheses, describe novel findings or have broad implications. The Journal of Zoology aims to maintain an effective but fair peer-review process that recognises research quality as a combination of the relevance, approach and execution of a research study.
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