Biology subjects

Babarovic, F.

Publications and source records attributed to Babarovic, F..

3 recordsLinked to original sources

bioRxiv2023

Historical contingency influences the diversity of feather nanostructures in cuckoos

Structural coloration is widespread in animals, yet we know relatively little about its evolution and development. While previous studies have explored adaptive functions of structural color, a key gap is our lack of understanding of how historical contingency (path-dependency of biological processes) influences the loss and gain of this complex trait. We shed light on this question by describing feather nanostructures responsible for plumage colors in the cuckoos (family Cuculidae), a group with widespread occurrence of shiny, metallic plumage (metallic luster). The melanosomes found in feathers with metallic luster have specialized shapes: hollow rods, thin solid rods, hollow platelets, or solid platelets. In contrast, it is generally assumed that drably colored feathers possess thick, rod-shaped melanosomes. However, we uncover that this assumption is unfounded in cuckoos. We describe metallic luster in the plumages of 126 cuckoo species and map its phylogenetic distribution. This reveals that metallic luster is widespread in cuckoos but has likely been lost several times. We then use transmission electron microscopy to describe the feather nanostructures of 21 cuckoo species. Surprisingly, the drab feathers of many cuckoo species contain melanosomes with specialized shapes. We propose that historical contingency greatly influences nanostructure diversity in cuckoos. Specialized melanosome shapes can be retained in the plumages of drab species, potentially making it easier for metallic luster to evolve again in the future. This discovery supports the idea that historical contingency plays a key role in shaping the evolution of plumage color diversity.

evolutionary biology↗

bioRxiv2023

The mechanistic basis of evolutionary transitions between grey, slate, and blue colour in Tanagers (Thraupidae)

Both pigmentary and structural colours share many common elements of their feather anatomy, i.e. keratin, air and melanin packed in the melanosomes, despite utilizing different mechanisms of the colour production. This means that evolutionary transitions between pigmentary and structural colours can be achieved through a simple adjustment of these elements. Recently, an evolutionary hypothesis for the transition between pigmentary grey, through slate and finally to structural blue colour has been proposed and confirmed in the clade Tanagers on a macroevolutionary level. Here, we investigate mechanistic basis of this evolutionary pathway. By using SAXS (small-angle X-ray scattering) we have quantified important elements of spongy layer in medullary cells that is crucial for colour production by coherent scattering of light wavelengths. We have quantified five elements of the spongy layer: nanostructure complexity, average hard block thickness, average soft block thickness, filling fraction and Io value. We report that across different categories of feather colour, i.e. blue, slate and grey, nanostructure complexity, filling fraction and Io value explained variation in the chromatic component of the colour (between the three colour categories). Chromatic variation within the colour category was explained by filling fraction in the case of slate colour and by nanostructure complexity and average hard block thickness in the case of blue colour. We propose that variation in different elements or combination of elements of the spongy nanostructure has been utilised in feather colour evolution, both within and between colour categories, to overcome developmental constraints imposed by self-assembly processes.

evolutionary biology↗

bioRxiv2023

Evolutionary dynamics of pigmentary grey and non- iridescent structural blue colouration in Tanagers (family: Thraupidae)

3.1Birds are one of the most colourful animal groups in the world and there are multiple ways by which they achieve this feature. Mechanisms of colour production range from pigmentary (pigment deposition) to structural (nanostructural arrangements), or the combination of both. Despite the huge breadth of colour gamut, the basic components of feathers are shared across all of them (keratin, air and presence of pigments in accordance with the colour produced). It has been shown that in some instances, colour evolution between pigmentary and structural colours can proceed by rearrangement of the nano-structural elements of feathers. Here, we investigated evolutionary transitions between pigmentary grey and non-iridescent structural blue. We focus on the Thraupidae (tanagers and allies) that display a variety of blues and greys including a potential transition state that we refer to as slate. We used digitally calibrated images of birds to quantify colour and determine the distinctiveness of slate colour in colourspace. Following, we identify the most likely pathway for the evolution of the colour blue: from grey via slate colour. Our research reveals a new pathway in the evolution of blue colour.

evolutionary biology↗