Environmental correlates of internal coloration in frogs vary throughout space and lineages

Abstract

SummaryInternal organs of ectotherms have melanin-containing cells. Several studies analyzed their developmental origin, role in immunity, and hormonal regulation. However, little is known about how environmental variables influence the distribution and quantity of organ coloration. Here, we addressed how environmental variables (temperature, UV, and photoperiod) influence the internal coloration of amphibians after controlling for spatial and phylogenetic autocorrelations. Coloration in all organs was correlated with phylogeny. However, the coloration of the heart, kidneys, and rectum of hylids, R. schneideri, some Leptodactylus, and Proceratophrys were influenced by temperature and photoperiod, whereas that of the testicle, lumbar parietal peritoneum, lungs, and mesenterium of Leiuperinae, Hylodidae, Adenomera, most Leptodactylus were influenced by UVB and temperature variation. Therefore, the amount of internal melanin seems to be a key trait influencing species distribution of frogs throughout space, since it can protect internal organs against the deleterious effect of high UV-B, temperature variation, and photoperiod.SignificanceThe functions of internal coloration in fishes and frogs are little known. Internal pigmentation is commonly altered in fish and the degree of response is correlated with body transparency levels, suggesting possible adaptive functions. Here, we assume that internal melanin has protective functions against UV-B, temperature variation, and photoperiod. Thus it could influence frogs species distribution throughout space. The melanin coloration of each organ was influenced by distinct environmental variables depending on the lineages of species. Our results could direct further studies about the functions of internal coloration.

Idiosyncratic liver alterations of five frog species to land use changes in the Brazilian Cerrado

“…Although our statistical model explained much variation in the three substances, other climatic factors that have been changing as a consequence of human activities, such as temperature and Ultra-violet radiation can also change the amount of melanin in internal tissues of frogs (Franco-Belussi et al 2017). Changes in these environmental variables may promote changes in hepatic metabolism, such as increasing glycogen and lipid levels (Mizell, 1965; Barni & Bernocchi, 1991; Fenoglio et al 1992, Barni et al 2002).…”

Environmental correlates of internal coloration in frogs vary throughout space and lineages

“…Those were the organs that had some degree of pigmentation and exhibited phylogenetic signal in a previous study (Provete et al., ). For each specimen, we recorded the intensity of coloration on these organs/structures (see full dataset in Franco‐Belussi, Provete, & Oliveira, ), following the protocol of Franco‐Belussi, Zieri, Santos, Moresco, and Oliveira (). Briefly, the intensity of organ coloration was divided into four categories, ranging from absence to entirely colored, as follows: Category (0) absence of pigment cells on the surface of organs, in which the usual color of the organ is evident; Category (1) a few scattered pigment cells, giving the organ a faint coloration; Category (2) a large amount of pigment cells; and Category (3) a massive amount of pigment cells, rendering an intense coloration to the structure, changing its usual color and superficial vascularization (Franco‐Belussi et al., ).…”

“…Posteriorly, we tested for multicollinearity (Zuur, Ieno, & Elphick, ) and removed environmental variables with variation inflation factor (VIF) higher than 10. The reduced variables were BIO2, BIO7, BIO10, UV‐B, and photoperiod (see Franco‐Belussi et al., ). We then tested for spatial autocorrelation (SAC) in the environmental variables (Legendre & Legendre, ).…”

“…All data and R code used to run the analyses are deposited in FigShare (Franco‐Belussi et al., ) at https://doi.org/10.6084/m9.figshare.4707187.v1.…”

Testicular melanization in anuran species: ontogeny and sexual maturity

“…Some studies have established a link between the amount and distribution of melanin pigmentation in the testis depending on temperature variation and ultraviolet B (UVB) radiation (Franco-Belussi, Nilsson Sköld and Oliveira, 2016;Franco-Belussi, Provete and Oliveira, 2017), bacterial infections (Franco-Belussi, Castrucci and Oliveira, 2013), and exposure to hydrocarbons (Oliveira et al, 2017). Collectively, these studies support a cytoprotective function of testicular pigmentation.…”