Carotenoid deprivation and beta-carotene's effects on male and female turtle color.

Carotenoid-colored integuments commonly function as sexually selected honest signals because carotenoid pigments can be costly to obtain, ingest, absorb, metabolize or transport before being deposited into the integument. As such, carotenoid pigmentation is often sexually dichromatic, with males being more colorful than females. Sexual dichromatism may also occur in ultraviolet (UV) wavelengths, which is visible to organisms who possess UV-sensitive photoreceptors. The stripes and spots of painted turtles (Chrysemys picta) are carotenoid-based and reflect UV wavelengths. This research describes UV sexual dichromatism in painted turtles and shows how carotenoid deprivation changes spot and stripe color in male and female painted turtles. Adult turtles were fed a diet that was supplemented with carotenoids (i.e., C diet) or deprived of carotenoids (C-). Stripe and spot color were measured with UV-vis spectrometry, and blood was drawn from all turtles before and after the dietary treatment. HPLC analysis revealed five carotenoids (4 xanthophylls and beta-carotene) circulating in turtle blood. C-diet reduced yellow chroma and increased brightness of yellow and red stripes or spots, relative to the C diet, but there was no sexually dimorphic effect of carotenoid deprivation on color, nor did carotenoid deprivation affect UV reflectance. Carotenoid deprivation reduced all circulating carotenoids, but beta-carotene was the only pigment with a significant effect on post-experimental carotenoids, implying that changes in color were due in part to reduction in circulating levels of beta-carotene. Color generation appears to be complex in turtles and have dietary as well as non-dietary components.

The effect of dietary carotenoid increase on painted turtle spot and stripe color.

Determination of how carotenoid-based color patches change with pigmentary access is important to understanding color patch function in animals. We performed a carotenoid addition experiment on male painted turtles (Chrysemys picta) to determine if an increase in dietary carotenoids led to location-specific changes in painted turtle spot and stripe color. Turtles fed large quantities of carotenoids had increased yellow chroma in chin stripes and increased red chroma in the neck and carapace stripes, as well as reduced ultraviolet (UV) chroma in the neck (orange to the human eye) and fore -limb (red to the human eye) stripes. Turtles fed large quantities of carotenoid had reduced brightness (B1) in the hind-limb stripes (red to the human eye) as well as reduced red and UV chroma in the post orbital spot of turtles (yellow to the human eye) compared to turtles fed moderate amounts of carotenoid. These results imply that integumentary spot and stripe colors are dependent upon carotenoid access, and increased lutein access leads to increased yellow and red chroma, as well as reduced ultra-violet chroma and brightness in male painted turtles. These results are discussed with respect to dietary access to carotenoids and color in other model systems, and the possibility that spot and stripe color functions as a visual signal.

Host stress response is important for the pathogenesis of the deadly amphibian disease, Chytridiomycosis, in Litoria caerulea.

Chytridiomycosis, a disease caused by Batrachochytrium dendrobatidis, has contributed to worldwide amphibian population declines; however, the pathogenesis of this disease is still somewhat unclear. Previous studies suggest that infection disrupts cutaneous sodium transport, which leads to hyponatremia and cardiac failure. However, infection is also correlated with unexplained effects on appetite, skin shedding, and white blood cell profiles. Glucocorticoid hormones may be the biochemical connection between these disparate effects, because they regulate ion homeostasis and can also influence appetite, skin shedding, and white blood cells. During a laboratory outbreak of B. dendrobatidis in Australian Green Tree Frogs, Litoria caerulea, we compared frogs showing clinical signs of chytridiomycosis to infected frogs showing no signs of disease and determined that diseased frogs had elevated baseline corticosterone, decreased plasma sodium and potassium, and altered WBC profiles. Diseased frogs also showed evidence of poorer body condition and elevated metabolic rates compared with frogs showing no signs of disease. Prior to displaying signs of disease, we also observed changes in appetite, body mass, and the presence of shed skin associated with infected but not yet diseased frogs. Collectively, these results suggest that elevated baseline corticosterone is associated with chytridiomycosis and correlates with some of the deleterious effects observed during disease development.

Perch-height specific predation on tropical lizard clay models: implications for habitat selection in mainland neotropical lizards.

Predation has been hypothesized to be a strong selective force structuring communities of tropical lizards. Comparisons of perch height and size-based predation frequencies can provide a unique window into understanding how predation might shape habitat selection and morphological patterns in lizards, especially anoles. Here I use plasticine clay models, placed on the trunks of trees and suspended in the canopy to show that predation frequency on clay models differs primarily according to habitat (canopy vs. trunk-ground), but not according to size. These data are discussed in light of observed lizard abundances in the lowland forests of Costa Rica, and are presented as partial explanation for why fewer lizards are found in tree canopies, and more lizards are found on ground-trunk habitats.

Perch-height specific predation on tropical lizard clay models: implications for habitat selection in mainland neotropical lizards

Predation has been hypothesized to be a strong selective force structuring communities of tropical lizards. Comparisons of perch height and size-based predation frequencies can provide a unique window into understanding how predation might shape habitat selection and morphological patterns in lizards, especially anoles. Here i use plasticine clay models, placed on the trunks of trees and suspended in the canopy to show that predation frequency on clay models differs primarily according to habitat (canopy vs. trunk-ground), but not according to size. These data are discussed in light of observed lizard abundances in the lowland forests of Costa Rica, and are presented as partial explanation for why fewer lizards are found in tree canopies, and more lizards are found on ground-trunk habitats. Rev. Biol. Trop. 57 (3): 859-864. Epub 2009 September 30.

Existe la hipótesis de que la depredación es una fuerte fuerza selectiva que estructura las comunidades de lagartijas tropicales. Las comparaciones de las frecuencias de altura de la percha y de depredación con base en el tamaño pueden proveer una ventana única en el entendimiento de cómo la depredación podría moldear la selección del hábitat y los patrones morfológicos en las lagartijas, especialmente anoles. En este estudio uso modelos de plasticina, ubicados en troncos de árboles y suspendidos en el dosel para mostrar que la frecuencia de depredación en los modelos de plasticina difiere primariamente según el hábitat (dosel vs. tronco-suelo) pero no según el tamaño. Estos datos se discuten a la luz de las abundancias de lagartijas observadas en los bosques de bajura de Costa Rica, y se presentan como una explicación parcial a porqué menos lagartijas se encuentran en los doseles, y más lagartijas se encuentran en los hábitats suelo-tronco.

How dewlap color reflects its carotenoid and pterin content in male and female brown anoles (Norops sagrei).

Sexually selected colors in animals can be created by multiple pigments (e.g., carotenoids, melanins, pterins), but how these pigment classes interact to generate intraspecific color variation has rarely been tested, especially in reptiles. We examined full-spectrum color variation as well as pterin (i.e., drosopterin) and carotenoid (i.e., xanthophyll) pigment concentrations in the yellow and red sexually dichromatic dewlaps of male and female Brown Anoles (Norops sagrei) to understand their color-generating mechanisms and information content. Reflectance curves showed significant sexual differences in dewlap color that could only partially be explained by pigment composition. For example, drosopterin concentration correlated significantly with red chroma in the male's dewlap center. In females, drosopterin concentration correlated significantly with yellow and red chroma along the dewlap edge. In addition, xanthophyll concentration showed a significant inverse correlation with hue in the center of female dewlaps only. There were several other correlations between pigment concentrations and spectral variables, which hinted at ways that pigments produce color in male and female dewlaps, but these were non-significant after statistically correcting for multiple comparisons. These results demonstrate that sexes differ in how pigment classes influence dewlap spectral variation, but also that there may be other aspects of the integument not measured here that also influence dewlap color.

A field test of female mate preference for male plumage coloration in eastern bluebirds.

A growing body of evidence shows that female birds use male plumage coloration as an important criterion in mate choice. In the field, however, males with brighter coloration may both compete better for high quality territories and be the object of female choice. Positive associations between territory quality, male-male competitive ability, and female preferences can make it difficult to determine whether females actively choose the most ornamented males. Male eastern bluebirds (Sialia sialis) display brilliant ultraviolet (UV)-blue plumage coloration on their heads, backs, wings, and tails, and chestnut coloration on their breasts which is positively correlated with condition, reproductive effort, and reproductive success. We tested the hypothesis that female bluebirds prefer males that display brighter and more chromatic coloration by widowing males in the field and allowing replacement females to choose partners. We controlled for the influence of territory quality on female choice by widowing dyads of males with adjacent territories. We found no evidence that UV-blue or chestnut plumage coloration, body size, or body condition predicted the male with which females would pair. We found no support for the hypothesis that the coloration of male eastern bluebirds functions as a criterion in female mate choice.

Contributions of pterin and carotenoid pigments to dewlap coloration in two anole species.

Animals can acquire bright coloration using a variety of pigmentary and microstructural mechanisms. Reptiles and amphibians are known to use two types of pigments - pterins and carotenoids - to generate their spectrum of colorful red, orange, and yellow hues. Because both pigment classes can confer all of these hues, the relative importance of pterins versus carotenoids in creating these different colors is not always apparent. We studied the carotenoid and pterin content of red and yellow dewlap regions in two neotropical anole species - the brown anole (Norops sagrei) and the ground anole (N. humilis). Pterins (likely drosopterins) and carotenoids (likely xanthophylls) were present in all tissues from all individuals. Pterins were more enriched in the lateral (red) region, and carotenoids more enriched in the midline (yellow) region in N. humilis, but pterins and carotenoids were found in similar concentrations among lateral and midline regions in N. sagrei. These patterns indicate that both carotenoid and pterin pigments are responsible for producing color in the dichromatic dewlaps of these two species, and that in these two species the two pigments interact differently to produce the observed colors.