Macroevolutionary bursts and constraints generate a rainbow in a clade of tropical birds

Abstract

Media Submission 25How do elaborately coloured animals evolve? In this study we investigated the brush-tongued parrots, the lories and lorikeets, to identify the evolutionary patterns that gave rise to spectacular ornamentation in nature. We found that these parrots are as colourful as all other birds combined, and that multiple evolutionary trends combine to generate their remarkable colour palette. Feather regions that would make birds more visible to predators had constrained evolution, 30 whereas those likely used for courtship signaling radiated recently to disparate parts of their overall colour palette. We found a mosaic of evolutionary patterns, which indicates that independent selective pressures and stochasticity were responsible for producing these beautifully coloured birds. 35 Abstract 40Bird plumage exhibits a diversity of colours that serve functional roles ranging from signaling to camouflage and thermoregulation. Macroevolutionary research on the evolution of plumage colour has focused on the impact of natural selection, but drift and sexual selection likely play important roles in originating brilliant colours and patterns. One kaleidoscopic group is the lorikeets, or brush-tongued parrots, which have radiated across Australasia. To quantify and 45 characterize plumage colour, we imaged taxa using visible-light and UV-light photography of museum specimens. We measured colour from 35 plumage patches on each specimen and modeled colour across lorikeets' evolutionary history. Lorikeets occupy a third of the avian visual colour space, which is qualitatively similar to the colour space occupied by all birds. We found that the wing and back were less variable than the breast and face. Crown and forehead 50 colour was best explained simply by phylogeny. At a macroevolutionary scale, the evolution of elaborate colours in lorikeets involved an interplay wherein regions likely under natural selection were constrained during the radiation while regions known to be involved in signaling underwent late-burst evolution. Overall, patch-specific modeling showed that plumage diversity in the lorikeets was likely generated by a mosaic of evolutionary processes. 55 60 65 70 75

Body size and climate as predictors of plumage colouration and sexual dichromatism in parrots

“…Darker parrots are more frequent in wetter environments, as predicted by Gloger's rule (Rensch, 1936). Support for Gloger's rule has already been found at the intraspecific level in parrots (in the crimson rosella Platycercus elegans ; Ribot et al., 2019) and also at the interspecific level among lorikeets (Merwin et al., 2020). We now show that it is a general pattern that applies at the interspecific level based on all 398 extant parrot species.…”

“…Different studies have evaluated how abiotic factors affect bird plumage colour evolution and a variety of hypotheses have been proposed to explain colour variation both within and across avian taxa (Dale et al., 2015; Merwin, Seeholzer, & Smith, 2020; Miller et al., 2019; Ribot, Berg, Schubert, Endler, & Bennett, 2019). Previous studies showed that achromatic (light‐to‐dark) variation in birds is related to climate variables such as temperature and precipitation (Delhey, 2017, 2018, 2019; Heidrich et al., 2018; Merwin et al, 2020; Miller et al., 2019; Pinkert, Brandl, & Zeuss, 2017; Ribot et al., 2019). Specifically, a negative relationship between melanin pigmentation and temperature has been reported in several taxa (Delhey, 2018; Heidrich et al., 2018; Pinkert et al., 2017), in support of the thermal melanism hypothesis (Clusella Trullas, van Wyk, & Spotila, 2007).…”

Body size and sexual selection shaped the evolution of parrot calls

“…Sexual dichromatism has the advantage of being easier and more objective to compute compared to cross‐species scores of colour elaboration, because conspecific males and females usually differ only in the degree to which they express an identical pattern of ornamentation, and different species often differ on multiple aspects of ornamentation that are difficult to integrate and compare in a biologically‐relevant manner. This is an important advantage because, for example, plumage coloration in different body parts of parrots may have different functions and patterns of evolution (Merwin et al, 2020). Moreover, different colours or body parts may also differ in the degrees to which they evolve sexual dichromatism (Taysom et al, 2011), all of which complicate the comparison of ornamentation, especially between species differing strongly in their pattern of plumage colour ornamentation.…”

Woodpecker drum evolution: An analysis of covariation in elements of a multicomponent acoustic display among and within species

“…2018, 2020; Merwin et al. 2020; Wylde and Bonduriansky 2020; Avendaño and Cadena 2021). Additionally, there is an equally robust body of literature characterizing phenotypic variation to understand how selection shapes individual diversity within a given species (Westcott 1992; Loyau et al.…”

“…2014; Merwin et al. 2020). However, addressing this objective can be incredibly challenging, especially when display behavior is highly complex (Melo and Marroig 2015; Wilkins et al.…”