Tag Archives: plumage

A warbler’s flashy yellow throat? There are genes for that

warbler2.JPG

(University of British Columbia. 8 Oct 2017; Photo Alan Brelsford)

Birds get their bright red, orange and yellow plumage from carotenoid pigments—responsible for many of the same bright colours in plants. But how songbirds turn carotenoids into the spectacular variety of feathered patches found in nature has remained a mystery.

Now University of British Columbia (UBC) research might have pinpointed some of the genetic machinery responsible for the plumage colouration in Audubon’s and myrtle warblers, related but distinctly feathered North American songbirds.

“Audubon’s and myrtle warblers interbreed in a narrow band across British Columbia and Alberta,” says David Toews, co-author of a new Proceedings of the Royal Society paper exploring the birds’ colouration.

“Those hybrid warblers, while considered oddities to some birders, were key for this study because their plumage traits and genes are all jumbled and mixed, allowing us to link their differing colours to genetic markers and hopefully the genes responsible.”

Both types of warblers use colourful carotenoid pigments to make several yellow feather patches, including their yellow-rumps—the birds are colloquially referred to as ‘butter butts’.

But only Audubon’s also used carotenoids in their telltale yellow throats. Myrtles have white throats and the hybrids have a mix of white and yellow.

The study identified several genomic region s— one including a member of the scavenger receptor gene family that affects carotenoids in other animals—that might be involved in this selective distribution of yellow carotenoid colours.

“We found strong associations with several genomic regions across a handful of distinct plumage traits” explains co-author Alan Brelsford. “Now we can now dig even deeper into these regions to understand the mechanisms that make warblers so colourful and diverse.”

“This study is unusual in that it focused on variation in multiple colour patterning traits,” says co-author Darren Irwin, a professor of zoology at UBC. “Two of the plumage differences between the species, eye spot and eye line colouration, appear to be encoded by a single region in the genome.”

Advertisements

How do birds get their colors?

(Physiological and Biochemical Zoology, Physorg 5 August 2017)

A new article in Physiological and Biochemical Zoology explores the role of melanins in creating complex plumage patterns in 9,000 species.

Birds’ feathers, or plumage, are some of the most strikingly variable animal characteristics that can be observed by the naked eye. The patterns that we see in birds’ feathers are made up of intricate combinations of mottles, scales, bars, and spots. But, how are these colors and patterns made?

We already know why birds have colored feathers. For many birds, plumage coloration may make them less visible to predators by helping them to blend in to their surroundings, or more appealing to potential mates by helping them to stand out from their peers. These aspects are well known. A greater mystery has been how the patterns are created on a cellular level.

Dr. Ismael Galván and his team of expert researchers studied plumage coloration to see what types of pigments were present in birds’ complex feather patterns. Plumage coloration mainly happens courtesy of two types of pigments: melanins, which produce a range of black, grey, brown, and orange colors, and carotenoids, which are used by specialized feather structures to generate brighter color hues.

Birds cannot produce carotenoids on their own. For feathers with bright colors, birds must consume food items that contain these pigments, and the carotenoids circulate through the bloodstream and to the feather follicles. Birds’ bodies do not have direct cellular control of synthesizing and depositing carotenoids; nor do they have control of the specialized feather structures, which react to the consumed carotenoids with a mechanism that is not regulated by specialized cells.

Melanins, on the other hand (or should that be “on the other wing”), are synthesized by in the birds’ bodies in special cells called “melanocytes,” which work together with feather follicles to achieve a fine control of pigmentation. Although studies frequently focus on carotenoids in bird coloration, Dr. Galván and group are the first to test whether melanins are indeed the only pigmentary element that birds’ bodies directly control on a cellular level.

Galván says, “Knowing beforehand that different pigments and structures produce different types of colors in feathers, we examined the appearance of the plumage of all species of extant birds and determined if the color patches that they contain are produced by melanins or by other pigmentary elements. We also identified those plumage patterns that can be considered complex, defining them as those formed by combinations of two or more discernible colors that occur more than two times uninterruptedly through the plumage.” This study was very large in scope, examining about 9,000 bird species, with the goal of supporting a general conclusion for all birds, to finally answer the question of how birds develop colorful and detailed patterns.

The team found that about 32% of the species studied have complex plumage patterns, with the vast majority of these complex patterns produced by melanins rather than carotenoids. Metaphorically, if the birds were artists, they would use carotenoids as a broad brush to produce color patches, with melanins as a detail paint brush to produce more intricate designs.

A few birds are exceptions to this rule: Three bird families do have complex plumage patterns without melanins. Fruit doves, cotingas and one type of stork have unusual colors that appear to be produced by their bodies making metabolic modifications to the carotenoid pigments that they consume.