Mosaic Evolution Generates Patches Of Vivid Colors In The Lories – Forbes


How to balance the evolutionary demands between being extremely colorful and attractive to potential mates whilst also being camouflaged from predators?
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The rainbow lorikeet (Trichoglossus moluccanus) is a nectar-feeding species of parrot found in … [+] Australia. It is common along the eastern seaboard, from northern Queensland to South Australia. Its habitat is rainforest, coastal bush and woodland areas. (CC0 / Public domain.)
Lories and lorikeets are a group of small- to medium-sized nectar-feeding parrots comprising more than 100 species. They are native to New Guinea, eastern Indonesia, Australia, and many of the archipelagos within Oceania. These parrots are cloaked in a truly dazzling array of colors: ranging from vibrant lime-green and lemon yellow to sunset orange and eye-watering scarlet to vibrant blue and iridescent black — and even including colors that humans cannot see. Which raises the question: how do these parrots manage to be so astoundingly colorful without becoming lunch for a hungry predator?
Previous research has shown that feather colors evolve to perform a wide variety of functions, including thermoregulation and climactic adaptation, but understanding that fine balance between sexual signalling and camouflage is what most interested a team of evolutionary biologists at the American Museum of Natural History. They studied museum specimens of lories and lorikeets (loriinae) because many of these species are experts at both staying hidden from hungry lizards and hawks whilst simultaneously being brilliantly colorful enough to attract mates.
Unlike many birds, where males are colorful and have gaudy feather ornaments whilst females are cryptic, lories are monomorphic: both males and females are brilliantly colorful and rarely can be distinguished visually by color patterns alone. But interestingly, many of these parrots’ color patterns follow the same basic scheme: colorful faces and heads, breasts and bellies with green backs and upper wing surfaces. Could these patches of plumage colors be the result of mosaic evolution?
The term, “mosaic evolution,” was originally coined following discoveries of fossilized body parts of Archaeopteryx, the iconic early bird, which fascinated researchers with its combination of ancestral ‘reptilian’ and derived avian features. Mosaic evolution has since become a central motif for understanding avian origins and diversification.
Basically, mosaic evolution describes the process where traits evolve either at different rates or in different ways. Traits that are strongly correlated with each other are expected to show a coordinated response to selection, whereas dissociated traits evolve independently and at different rates. Such relationships amongst characteristics are governed by genetic, developmental, and functional associations, and these can give rise to distinct groups of traits that evolve semi-independently.
Rainbow Lorikeet (Trichoglossus moluccanus) in Brisbane, Queensland. (Credit: Andrew Mercer / CC … [+] BY-SA 4.0)
Knowing the strong relationships between colors and mate selection in the lories, the researchers predicted that plumage color patches involved in sexual signalling would be less evolutionarily constrained than plumage color patches on the back and wings, because camouflage would be compromised if a new color suddenly popped up in those areas. Further, because environmental adaptation may drive evolution towards or away from particular color states, the scientists also proposed that the colors of specific plumage regions in the lories varied with climate.
The researchers tested these hypotheses by photographing 98 historic museum specimens of Australasian lories and lorikeets under visible light — and because lories can see colors in the UV range, they also photographed them under UV light.
“The range of colors exhibited by lorikeets adds up to a third of the colors birds can theoretically observe”, the study’s lead author, Jon Merwin, said in a statement. “We were able to capture variation in this study that isn’t even visible to the human eye.”
The researchers collected data from 35 plumage patches on the face, head, back, wings, breast, and lower abdomen from each specimen and fed them in to a special computer program that translates color data into ‘bird vision’. These color data were modelled onto the tree of life for the lories to test whether particular color patches on the birds are more likely to evolve under certain scenarios.
The study revealed that, as predicted, plumage colors do not evolve as a single trait in the lories: modelling the 35 plumage regions either independently, in functional groups, or all together showed that evolutionary changes proceeded more much rapidly for color patches clustered together into distinct regions on the head and belly than on the wings and back. The researchers also found that wing patches evolved more strongly in accordance with climate than did plumage regions used in signalling (e.g., head), which diversified in a rapid burst.
These findings support the hypothesis that the extraordinary color diversity in the lories was generated by a mosaic of evolutionary processes acting differently on distinct subsets of plumage regions. Mosaic evolution is a pattern whereby plumage regions in different parts of the body are partitioned, thereby providing an evolutionary mechanism to evolve bright colors for signalling whilst also preserving the ability to remain camouflage or to adapt to local climactic conditions.
Jon T. Merwin, Glenn F. Seeholzer & Brian Tilston Smith (2020). Macroevolutionary bursts and constraints generate a rainbow in a clade of tropical birds, BMC Evolutionary Biology 20:32 | doi:10.1186/s12862-020-1577-y
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