Character displacement, frequency-dependent selection, and divergence of shell colour in land snails Mandarina (Pulmonata)

Endemic land snails of the genus Mandarina of the oceanic Bonin Islands offer an exceptional example of habitat and character divergence among closely related species. In this study, microhabitat differences between sympatric ground-dwelling species were studied by distinguishing habitats on the basis of vegetation and types of litter. In all sites where two ground species coexisted, segregation occurred with each species showing preference for the microhabitat in which they were found. When they were in sympatry, one species was predominant in relatively wet and sheltered sites and the other in relatively dry and exposed sites. Although most species can live in both types of habitat, occupation by one species is inhibited by occupation by another. This suggests that competitive interaction between sympatric species caused segregation. Except for populations that have undergone interspecific hybridization, no examples were found of sympatric populations of two ground species sharing a similar shell colour. Species that were predominant in relatively wet and sheltered sites possessed shells with dark coloration and their colour patterns were mostly of one type. Species that were predominant in relatively dry and exposed sites possessed shells with bright coloration and their color patterns were polymorphic. Most populations from areas in which single species were distributed had shells with medium coloration. Microhabitat differentiation between sympatric species possibly caused diversification of shell colour, because bright shells are advantageous in sites where snails are largely exposed, and dark shells are advantageous in sites in where they are mostly sheltered from sunlight. In addition, frequency-dependent selection by predators hunting by sight may have operated to maintain colour polymorphism in the populations which are restricted to exposed habitats by competition with other sympatric species. This reveals the importance of interaction among closely related species as a cause of diversification in ecological and morphological traits.     

Expression levels of the tetratricopeptide repeat protein gene ttc39b covary with carotenoid-based skin colour in cichlid fish

Carotenoid pigments play a major role in animal body colouration, generating strong interest in the genes involved in the metabolic processes that lead from their dietary uptake to their storage in the integument. Here, we used RNA sequencing (RNA-Seq) to test for differentially expressed genes in a taxonomically replicated design using three pairs of related cichlid fish taxa from the genera Tropheus and Aulonocara. Within each pair, taxa differed in terms of red and yellow body colouration, and high‐performance liquid chromatography (HPLC) analyses of skin extracts revealed different carotenoid profiles and concentrations across the studied taxa. Five genes were differentially expressed in all three yellow–red skin contrasts (dhrsx, nlrc3, tcaf2, urah and ttc39b), but only the tetratricopeptide repeat protein-coding gene ttc39b, whose gene product is linked to mammalian lipid metabolism, was consistently expressed more highly in the red skin samples. The RNA-Seq results were confirmed by quantitative PCR. We propose ttc39b as a compelling candidate gene for variation in animal carotenoid colouration. Since differential expression of ttc39b was correlated with the presence/absence of yellow carotenoids in a previous study, we suggest that ttc39b is more likely associated with the concentration of total carotenoids than with the metabolic formation of red carotenoids.     

Beyond morphs: Inter-individual colour variation despite strong genetic determinism of colour morphs in a wild bird

Categorizing individuals into discrete forms in colour polymorphic species can overlook more subtle patterns in coloration that can be of functional significance. Thus, quantifying inter-individual variation in these species at both within- and between-morph levels is critical to understand the evolution of colour polymorphisms. Here we present analyses of inter-individual colour variation in the Reunion grey white-eye (Zosterops borbonicus), a colour polymorphic wild bird endemic to the island of Reunion in which all highland populations contain two sympatric colour morphs, with birds showing predominantly grey or brown plumage, respectively. We first quantified colour variation across multiple body areas by using a continuous plumage colour score to assess variation in brown-grey coloration as well as smaller scale variation in light patches. To examine the possible causes of among-individual variation, we tested if colour variation in plumage component elements could be explained by genotypes at two markers near a major-effect locus previously related to back coloration in this species, and by other factors such as age, sex and body condition. Overall, grey-brown coloration was largely determined by genetic factors and was best described by three distinct clusters that were associated to genotypic classes (homozygotes and heterozygote), with no effect of age or sex, whereas variation in smaller light patches was primarily related to age and sex. Our results highlight the importance of characterizing subtle plumage variation beyond morph categories that are readily observable since multiple patterns of colour variation may be driven by different mechanisms, have different functions and will likely respond in different ways to selection.     

Association between parasite load and orange,but not blue,male nuptial colouration in Etheostoma caeruleum

The hypothesis that males possessing more vivid nuptial colouration are of better quality with regard to individual measures of health such as parasite infection was investigated by taking spectral measurements of orange and blue bars in the nuptial males of a sexually dichromatic stream fish rainbow darter Etheostoma caeruleum to determine if male colouration in this species varied with parasite load in the form of black spot disease. The yellow chroma of orange bars, i.e. the relative contribution of wavelengths in the range of 550–625 nm to total brightness, was the only spectral measurement significantly associated with parasite counts. These results are discussed in the context of sexual selection and the potential of orange bars in E. caeruleum to serve as honest indicators of quality to potential mates.     

Tropical dry and wet season polyphenism in the butterfly Melanitis leda (Satyrinae): Phenotypic plasticity and climatic correlates

Changes in wing pattern, colour, shape and size associated with seasonal polyphenism in Melanitis leda were quantified using a series of 155 butterflies collected by N. Manders on Mauritius in 1905. Butterflies of the wetter period were predominantly of the wet season form with large, well differentiated eyespots, short tails, smaller wings and a characteristic background colour. The dry season form occurred only in the drier period and has much smaller eyespots, longer tails, larger wings and a variable background. Many intermediates occurred, mainly in the drier period. These are associated with an absence of extreme seasonal change in Mauritius. The first principal component (PCI) describing the morphometric and colour data is closely related to the wing form (r = 0.80). Regression analyses using temperature and rainfall data for the 8 weeks before each capture showed that about 40% of variation in PCI could be accounted for by temperature in weeks 2–3 before capture. Many of the characters measured are redundant; a subset of seven morphometric characters yields a closely similar PCI. Analysis of is subset in an additional sample of 70 M. leda from Kenya showed that the seasonal polyphenism overrides a small degree of sexual dimorphism. The results are discussed with regard to seasonal changes in adult activity, resting backgrounds and visual predation. Wing phenotype characters are part of an array of coordinated morphological and life history traits which include ovarian dormancy and fat body development in dry season adults. A partial independence occurs in the proximal control of these traits as indicated, for example, by the larger wing and tail size, and smaller eyespots of the small number of the wet season form captured in the drier period in comparison to those of the wetter months.     

Ideological Whitening: does skintone shape colour-blind ideology adherence for Latina/os?

Prominent theories of the US racial order contend that phenotypically light Latina/os will elevate to an honorary White category as a result of their socio-economic advantages over darker Latina/os. Accordingly, light Latina/os are presumed to adopt colour-blind racial ideology to cement their elevated racial status. This study is among the first to examine the relationship between skintone and Latina/os’ colour-blind ideology adherence with nationally representative data. I examine these relationships with data from the 2006 Portraits of American Life Study, and test the robustness of findings across two alternative national data sets: the 2014 General Social Survey, and the 2006 Latino National Survey. Across data sets, different measurement approaches, and time periods, this study finds no evidence that skintone shapes Latina/os’ levels of colour-blind ideology adherence. The study concludes by considering why the racial ideology of light Latina/os is non-concordant with their elevated socio-economic status in relation to darker Latina/os.     

Chameleons communicate with complex colour changes during contests: different body regions convey different information

Many animals display static coloration (e.g. of feathers or fur) that can serve as a reliable sexual or social signal, but the communication function of rapidly changing colours (as in chameleons and cephalopods) is poorly understood. We used recently developed photographic and mathematical modelling tools to examine how rapid colour changes of veiled chameleons Chamaeleo calyptratus predict aggressive behaviour during male–male competitions. Males that achieved brighter stripe coloration were more likely to approach their opponent, and those that attained brighter head coloration were more likely to win fights; speed of head colour change was also an important predictor of contest outcome. This correlative study represents the first quantification of rapid colour change using organism-specific visual models and provides evidence that the rate of colour change, in addition to maximum display coloration, can be an important component of communication. Interestingly, the body and head locations of the relevant colour signals map onto the behavioural displays given during specific contest stages, with lateral displays from a distance followed by directed, head-on approaches prior to combat, suggesting that different colour change signals may evolve to communicate different information (motivation and fighting ability, respectively).     

Avian colour vision and avian video playback experiments

Video playback potentially allows the presentation, manipulation, and replication of realistic moving visual stimuli, in a way that is impossible with real animals or static dummies, and difficult even with mechanical models. However, there are special problems attached to the use of this technology; this article concentrates on the problem of accurate colour rendition. Video and television simulate the colour of objects rather than reproduce the spectrum of light that they naturally emit, transmit, or reflect. This simulation is achieved by using relatively narrow waveband light to stimulate the cone cells in the retina in a similar pattern to that produced by the natural object. However, species differ in the spectral tuning of their photoreceptors, so a faithful colour rendition for a human is unlikely to be achieved for another species. This problem is discussed with special reference to birds, a taxon renown for its colourfulness and frequent use in behavioural experiments but which has a very different colour vision from that of humans. We stress that the major pitfalls that can arise when using video playback with avian subjects can also occur in ’normal’ behavioural experiments. However, the problems of faithful colour rendition are particularly severe with video, and the major benefits that the technology brings will only be realised under a limited range of circumstances, with careful validation experiments. Received: 24 January 2000 / Received in revised form: 28 March 2000 / Accepted: 1 April 2000