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Impairment of mixed melanin-based pigmentation in parrots

Parrots and allies (Order Psittaciformes) have evolved an exclusive capacity to synthesize polyene pigments called psittacofulvins at feather follicles, which allows them to produce a striking diversity of pigmentation phenotypes. Melanins are polymers constituting the most abundant pigments in animals, and the sulphurated form (pheomelanin) produces colors that are similar to those produced by psittacofulvins. However, the differential contribution of these pigments to psittaciform phenotypic diversity has not been investigated. Given the color redundancy, and physiological limitations associated to pheomelanin synthesis, this study assumed that the latter would be avoided by psittaciform birds. This hypothesis was tested by using Raman spectroscopy to identify pigments in feathers exhibiting colors suspicious of being produced by pheomelanin (i.e., dull red, yellow and grey- and green-brownish) in 26 species from the three main lineages of Psittaciformes. The non-sulphurated melanin form (eumelanin) were detected in black, grey and brown plumage patches, and psittacofulvins in red, yellow and green patches, but no evidence of pheomelanin was found. As natural melanins are assumed to be composed of eumelanin and pheomelanin in varying ratios, these results represent the first report of impairment of mixed melanin-based pigmentation in animals. Given that psittaciforms also avoid the uptake of circulating carotenoid pigments, these birds seem to have evolved a capacity to avoid functional redundancy between pigments, likely by regulating follicular gene expression. The study provides the first vibrational characterization of different psittacofulvin-based colors and thus helps to determine the relative polyene chain length in these pigments, which is related to their antireductant protection activity. informacion[at]ebd.csic.es: Neves et al (2020) Impairment of mixed melanin-based pigmentation in parrots. J Experim Biol. DOI 10.1242/jeb.225912


https://jeb.biologists.org/content/early/2020/05/08/jeb.225912
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Invasive rats on a coral atoll

Invasive rats on a coral atoll

Invasive rats are found on most island groups of the world, and usually more than one species has invaded. On tropical islands populations of different invasive rat species can co-exist on very small islands, but the population dynamics of such co-existing rat species, their impact on each other, and the mechanisms of coexistence are not well known. This lack of knowledge is a barrier to improving the success rate of tropical island rat eradications. Through an exhaustive trapping eradication campaign, the population structure of historically established Rattus exulans has been studied on a small tropical island, where R. rattus have colonised within the last fifty years and over-invaded. This R. exulans population has been contrasted with a nearby island population where R. exulans exist alone. Recently invaded R. rattus numerically and morphologically dominate R. exulans; however stable isotope analyses show that the trophic position of R. exulans remains consistent regardless of the presence of R. rattus, once differences in trophic foundations of islands are accounted for. Although the trophic position of both rat species is indistinguishable, R. rattus is able to dominate R. exulans through interference competition. This eradication attempt was interrupted by a tropical cyclone and ultimately unsuccessful, but there is some evidence that R. rattus reduced control device availability to R. exulans, which has important implications for multi-species control operations. informacion[at]ebd.csic.es Russell et al (2015) Invasive rat interactions and over-invasion on a coral atoll Biol Cons (185) 59–65 doi:10.1016/j.biocon.2014.10.001