Blue Eye Colour Research Articles

Cohort effects in a genetically determined trait: eye colour among US whites

Background : While the inheritance of eye colour is likely polygenic, blue eye colour is thought to follow an inheritance pattern similar to that of a recessive trait. Consequently, age-related differences in the prevalence of blue eye colour would be unanticipated. Aim : This study explores the finding and explanation for birth cohort differences in the prevalence of blue eye colour in the US white population. Subjects and methods : Data from the first (1971-1975) and third (1988-1994) US National Health and Nutrition Examination Surveys (NHANES-I and NHANES-III), nationally representative surveys of the US population, were analysed. Trends in eye colour prevalence by birth cohort were analysed together with mortality rates according to eye colour. US census data (1980) were examined to explore cohort differences in ancestry and assortative mating by ancestry. Results : The prevalence of blue eye colour among non-Hispanic whites in NHANES-III was 57.4% (95% CI: 50.1-64.7) for individuals born between 1899 and 1905 compared to 33.8% (95% CI: 31.3-36.5) for those born between 1936 and 1951. No association was found between survival and eye colour, nor was a cohort effect evident for primary ancestry. However, proportions reporting only one ancestry in census data declined with successive birth cohorts. Conclusions : A cohort effect in blue eye colour prevalence was found for the US white population. A secular trend of decreasing assortative mating by ancestry is the likely explanation.

Interdependence of eye and hair colour, skin type and skin pigmentation in a Caucasian population.

Eye colour, hair colour and skin colour are important risk factors for malignant melanoma and non-melanoma skin cancers. There are few studies in which the distribution of these pigmentary factors in risk populations has been assessed. The purpose of this study was to investigate the prevalence of the major eye and hair colours and the distribution of skin types and skin pigmentation in a Caucasian population. In 892 Danish Caucasians, eye colour, hair colour and skin type were assessed and facultative and constitutive skin pigmentation were measured objectively using skin reflectance spectroscopy. Blue eye colour and blond hair colour and skin type II were the most frequent (60%, 67% and 33% of subjects, respectively). All four major eye colours and four major hair colours (with the exception of red hair colour) were found within skin types I-IV and we could not predict the skin type or the constitutive skin pigmentation. Skin type could not be taken to classify individuals reliably according to their facultative or constitutive skin pigmentation.

Male Mating Preference in Sticklebacks: Effects of Repeated Testing and Own Attractiveness

In sticklebacks, Gasterosteus aculeatus, males have conspicuous nuptial coloration, whereas females are cryptically coloured. Usually females are the choosy sex in mate choice, but under certain conditions males may be choosy too. Females signal their spawning readiness, among others, by displaying a head-up courtship posture while pointing at the preferred male. We tested the male's preference for this posture by offering males a simultaneous choice of two stylized dummies of ripe females, one in head-up posture and one horizontal. The males directed relatively more courtship to the head-up dummy, and tended to do the more so the more intense the blue iris of their own eyes (corrected for differences in male length). Because the blue eye colour is a criterion of female choice in this population, attractive males tended to be choosier. Upon repeated presentation of the dummies to the same males on subsequent days, the malcs' preference for the head-up dummy disappeared, but there was no change in total courtship activity. When confronted with a different, more realistic pair of dummies, the same males showed again a preference for the head-up posture suggesting that male preference can be influenced by experience.

Mutation Causing Blue Eyes and Transparent Pupal Cuticle in Colias eurytheme (Lepidoptera: Pieridae)

A blue-eyed phenotype of Colias eurytheme Boisduval appeared within a normally green-eyed laboratory population. A transparent pupal cuticle was invariably associated with the blue-eyed phenotype rather than the typical yellowish brown of the wild phenotype. Genetic analyses of pedigree data showed that blue eye color is probably inherited as a single recessive autosomal allele. It seems likely that the blue allele prevents production of a yellow pigment that normally colors the pupal cuticle and generates green eye color when in combination with underlying blue. Mating success and female fecundity did not seem to be pleiotropically affected by eye color under laboratory conditions. However, indirect evidence suggests that the fitness of homozygous blue larvae may be lower than that of heterozygotes.

Experimental investigations of the evolutionary significance of sexually dimorphic nuptial colouration in Gasterosteus aculeatus (L.): the relationship between male colour and male behaviour

The intensities of red body and blue eye colour in dull (and possibly bright) males reliably signals their behavioural vigour. Males with medium intensity colouration signal that they are more vigorous than their dull conspecifics; however, there is no association between colour and behavioural intensity within this group. A truth in advertising mechanism is thus potentially very powerful at either end of the colour intensity spectrum but is less effective for fish whose colouration is in the central section of the spectrum. Males with medium intensity colouration may be more strongly influenced by stochastic factors such as previous experiences or colour relative to neighbours. The increased importance of personal history introduces a source of disorganization into the mating system that may oppose the directional force of truth in advertising and thereby increase the ambiguity of the male colour signal.

Experimental investigations of the evolutionary significance of sexually dimorphic nuptial colouration in Gasterosteus aculeatus (L.): temporal changes in the structure of the male mosaic signal

Although classically described as "red," the three-spined stickleback male's nuptial signal is a complex mosaic of at least three colours: blue eyes, black dorsal–lateral body, and red ventral–lateral body. Seven variables (intensity, hue, and distribution of red body colour; intensity and hue of blue eye colour; intensity and distribution of black body colour) were scored for 19 males across an entire breeding cycle. These variables interacted to produce four distinct male colour mosaic signals corresponding with the stage a male had reached in the breeding cycle. No single variable was sufficient for the delineation of all breeding stages: however, the distribution of red body colour reliably distinguished the courting male from nesting and parental males. Variability in signal intensity between courting males was greatest for the red component of the nuptial signal and both intra- and inter-male variability in the overall intensity of red was greatest during courtship. Based upon these results, future investigations of the role of intersexual selection in shaping the male nuptial signal in this species should offer females a choice between males differing in the intensity of red rather than the traditional "red" versus "nonred" dichotomy.