Carotenoids are important as pigments for bright coloration of animals, and as physiologically active compounds with a wide array of health‐related benefits. However, the causes of variation in carotenoid acquisition and physiology among species are poorly known. We measured the concentration of carotenoids in the blood of 80 wild bird species differing in diet, body size and the extent of carotenoid‐based traits. Preliminary analyses showed that diet significantly explains interspecific variability in plasma carotenoids. However, dietary influences were apparently overridden by phylogenetic relationships among species, which explained most (65%) of this variability. This phylogenetic effect could be due partly to its covariation with diet, but may also be caused by interspecific differences in carotenoid absorption from food to the blood stream, mediated, for example by endothelial carriers or gut parasites. Carotenoid concentrations also decreased with body size (which may be explained by the allometric relationship between ingestion rate and body mass), and correlated positively with the extent of carotenoid‐dependent coloration of plumage and bare parts. Therefore, the acquisition of carotenoids from the diet and their use for both health and display functions seem to be constrained by ecological and physiological aspects linked to the phylogeny and size of the species.

BackgroundHuman populations and breeds of domestic animals are composed of individuals with a multiplicity of eye (= iris) colorations. Some wild birds and mammals may have intraspecific eye color variability, but this variation seems to be due to the developmental stage of the individual, its breeding status, and/or sexual dimorphism. In other words, eye colour tends to be a species-specific trait in wild animals, and the exceptions are species in which individuals of the same age group or gender all develop the same eye colour. Domestic animals, by definition, include bird and mammal species artificially selected by humans in the last few thousand years. Humans themselves may have acquired a diverse palette of eye colors, likewise in recent evolutionary time, in the Mesolithic or in the Upper Paleolithic.Presentation of the hypothesisWe posit two previously unrecognized hypotheses regarding eye color variation: 1) eye coloration in wild animals of every species tends to be a fixed trait. 2) Humans and domestic animal populations, on the contrary, have eyes of multiple colors. Sexual selection has been invoked for eye color variation in humans, but this selection mode does not easily apply in domestic animals, where matings are controlled by the human breeder.Testing the hypothesisEye coloration is polygenic in humans. We wish to investigate the genetics of eye color in other animals, as well as the ecological correlates.Implications of the hypothesisInvestigating the origin and function of eye colors will shed light on the reason why some species may have either light-colored irises (e.g., white, yellow or light blue) or dark ones (dark red, brown or black). The causes behind the vast array of eye colors across taxa have never been thoroughly investigated, but it may well be that all Darwinian selection processes are at work: sexual selection in humans, artificial selection for domestic animals, and natural selection (mainly) for wild animals.Electronic supplementary materialThe online version of this article (10.1186/s12983-017-0243-8) contains supplementary material, which is available to authorized users.

The annual and seasonal diet of the bobcat (Lynx rufus) was determined from analysis of 188 feces in the Cape region of Baja California, Mexico, an arid zone with numerous subtropical elements in its flora and fauna. Bobcats fed mainly on lagomorphs, which reached 74% of occurrence, followed by rodents (40%), reptiles (15%), and birds (12%). No seasonal variations were observed. The results were consistent with those of studies elsewhere, indicating that bobcats still rely upon lagomorphs for much of their food in southern latitudes. This supports the hypothesis that lynx have evolved to prey on hares and rabbits. The prevalence of reptiles as prey of bobcats in our study area was the highest ever reported. They were reported as bobcat prey in only 1 of 20 studies from north of latitude 40°, but in 14 of the 18 studies carried out south of this latitude. With regard to feeding on reptiles, the habits of bobcats in Baja California Sur resemble those of other similar-sized felids in tropical areas, such as ocelots (Felis pardalis) and servals (Leptailurus serval).

The study of the role of carotenoids on the physiology and evolutionary ecology of birds demands methods for their quantification in the bloodstream. We compared color-chart scores of plasma hue with the actual concentration of plasma carotenoids obtained by spectrophotometry in 356 wild birds from 26 species. Repeatability of chart scores between three independent observers was high. However, color scores did not correlate with the spectrophotometric results in interspecific analyses. Within species (n = 3), one showed no relationship and two showed weak but significant positive correlations. Hemoglobin, and probably other substances, may mask the color of carotenoids, making the accurate use of color charts difficult. Spectrophotometry should be the method of choice as it permits precise quantifications of total plasma carotenoids and objective comparisons among studies.