In new research, ornithologists from the Field Museum and elsewhere analyzed the whole genomes of 30 diverse kingfisher species to identify the genomic signatures associated with convergent feeding behaviors and the ability to dive without sustaining brain damage.
Understanding the genetic basis of convergence at broad phylogenetic scales remains a key challenge in biology. Kingfishers are a cosmopolitan bird radiation with diverse colors, diets, and feeding behaviors — including the archetypal plunge-dive into water. Given the sensory and locomotor challenges associated with air-water transitions, kingfishers offer a powerful opportunity to explore the effects of convergent behaviors on the evolution of genomes and phenotypes, as well as direct comparisons between continental and island lineages. Eliason et al. use whole-genome sequencing of 30 diverse kingfisher species to identify the genomic signatures associated with convergent feeding behaviors. Image credit: Robert Balog.
“The type of diving that kingfishers do — what we call ‘plunge-diving’ — is an aeronautic feat,” said Dr. Chad Eliason, a researcher at the Field Museum.
“It’s a high-speed dive from air to water, and it’s done by very few bird species. But it’s a behavior that’s potentially risky.”
“For kingfishers to dive headfirst the way they do, they must have evolved other traits to keep them from hurting their brains,” added Dr. Shannon Hackett, associate curator of birds at the Field Museum.
Not all kingfishers actually fish. Many species of these birds eat land-dwelling prey like insects, lizards, and even other kingfishers.
Previously, the authors found that the groups of kingfishers that eat fish aren’t each others’ closest relatives within the kingfisher family tree.
That means that kingfishers evolved their fishy diets — and the diving abilities to procure them — a number of separate times, rather than all evolving from one common fish-eating ancestor.
“The fact that there are so many transitions to diving is what makes this group both fascinating and powerful, from a scientific research perspective,” Dr. Hackett said.
“If a trait evolves a multitude of different times independently, that means you have power to find an overarching explanation for why that is.”
In the study, the researchers examined the DNA of 30 species of kingfishers, both fish-eating and not.
They found that the fish-eating birds had several modified genes associated with diet and brain structure.
For instance, they found mutations in the birds’ AGT gene, which has been associated with dietary flexibility in other species, and the MAPT gene, which codes for tau proteins that relate to feeding behavior.
Tau proteins help stabilize tiny structures inside the brain, but the accumulation of too many tau proteins can be a bad thing.
In humans, traumatic brain injuries and Alzheimer’s disease are associated with a buildup of tau.
“I learned a lot about tau protein when I was the concussion manager of my son’s hockey team,” Dr. Hackett said.
“I started to wonder, why don’t kingfishers die because their brains turn to mush? There’s gotta be something they’re doing that protects them from the negative influences of repeatedly landing on their heads on the water’s surface.”
The authors suspect that tau proteins may be something of a double-edged sword.
“The same genes that keep your neurons in your brain in all nice and ordered are the things that fail when you get repeated concussions if you’re a football player or if you get Alzheimer’s,” Dr. Hackett said.
“My guess is there’s some sort of strong selective pressure on those proteins to protect the birds’ brains in some way.”
“Now that these correlated genomic variations have been identified, the next question is, what do the mutations in these birds’ genes do to the proteins that are being produced? What shape changes are there? What is going on to compensate in a brain for the concussive forces?”
“Now, we know which of the underlying genes are shifting that help create the differences that we see across the kingfisher family,” Dr. Eliason said.
“But now that we know which genes to look at, it created more mysteries. That’s how science works.”
The paper was published in the journal Communications Biology.
C.M. Eliason et al. 2023. Genomic signatures of convergent shifts to plunge-diving behavior in birds. Commun Biol 6, 1011; doi: 10.1038/s42003-023-05359-z
Source : Breaking Science News