Matthew Toomey - College of Engineering & Natural Sciences

Matthew Toomey

Biological research: Defending against neurotrauma and the science of animal coloration

Two faculty members in The University of Tulsa’s Department of Biological Science recently published research findings in the prestigious journal Current Biology. Assistant Professor Alexandra Kingston was the lead author on a paper examining the protection snapping shrimp are afforded by a helmet-like extension of their exoskeleton. For his part, Assistant Professor Matthew Toomey was the lead author on a study that revealed a hitherto unknown mechanism that produces the color red in birds and fish.

Shockwaves and biological armor

woman with long dark hair smiling with a closed mouth
Alexandra Kingston

Snapping shrimp produce shock waves by rapidly closing their claws. These highly territorial creatures snap their claws when they are warding off rivals and when they seek to stun or kill other crustaceans and fish.

For Alexandra Kingston and fellow researchers at the University of South Carolina, the question they sought to answer was how snapping shrimp survive frequent, close-range encounters with shock waves? Do they have any physical mechanisms to protect themselves against neurotrauma brought about by their own actions and those of other shrimp? Their investigation pivoted on these creatures’ orbital hoods — helmet-like extensions of the exoskeleton that cover the eyes and brains of many species of snapping shrimp but are absent in other crustaceans.

As reported in Current Biology, the team began with behavioral trials that showed shock wave exposure slowed shelter-seeking and caused a loss of motor control in shrimps from which removed orbital hoods had been removed. The behavior of shrimp whose orbital hoods had not been altered, however, was not significantly affected.

close-up images of a shrimp, shrimp's claw and head of a shrimp
Snapping shrimp (A) produce shock waves with their snapping claws (B) but are protected from these shock waves by a helmet-like armor (C) that covers their head and eyes.

Pressure recordings led Kingston and her colleagues to discover that orbital hoods of Alpheus heterochaelis dampen shock waves. “This protection,” she noted, “most likely comes about when orbital hoods trap and expel water so that kinetic energy is redirected and released away from shrimps’ heads.”

While the discovery about how shrimp protect themselves against brain injuries is fascinating in itself, Kingston points out that these findings have a potential application for humans, such as soldiers, who are at risk of blast-induced neurotrauma. “There is not yet a helmet for humans that effectively prevents the transfer of energy from shock waves to neural tissues,” Kingston remarked. “But our research strongly suggests potential applicability to future efforts at designing armor systems that protect humans from shock waves.”

Red in feather and scale

man with short hair and glasses and trim beard smiling with a closed mouth
Matthew Toomey

It is an unusual Tulsa garden that is not graced for much of the year by the vivid red of male cardinals. Yet, precisely how and why cardinals produce these beautiful hues has not been well understood.

The red plumage of the cardinal and many of the reds, oranges and yellows that adorn birds and fish are produced through the accumulation and modification of carotenoid pigments from the foods they eat. Animals consume yellow carotenoids (e.g., lutein and zeaxanthin) and somehow turn them into red ketocarotenoids. “Although biologists have long known that carotenoid coloration plays a key role in social interactions, including mate choice, the mechanism animals use to convert yellow carotenoids to red were largely unknown,” Matthew Toomey remarked.

two small mostly green birds perched on a horizontal stick
Red-throated parrot finches — one of the species Toomey et al. studied (image by Pedro Miguel Araújo)

Along with colleagues in Portugal, France and the United States, Toomey spent the past decade identifying the enzymes that catalyze the chemical conversion of yellow into red coloration that are critical for coloration and vision: “In our Current Biology paper, we describe for the first time a two-step enzymatic mechanism that mediates the production of ketocarotenoids in birds and fish.”

Toomey and his co-researchers note that discovery of this enzymatic pathway for ketocarotenoid biosysnthesis has major implications for understanding the evolution of color diversity in vertebrates – specifically, the potential connections between coloration and basic metabolic pathways. “We anticipate that our work will provide a basis for interpreting the results of genetic mapping studies aimed at identifying loci that regulate color patterning,” Toomey commented. “More generally, our findings open new avenues for understanding the mechanisms underlying the evolution of visual ornaments, color vision and animal diversity.”

The natural world is endlessly fascinating and its mysteries are far from solved. Why not embark on a lifetime of discovery with TU’s Department of Biological Science?


Genome research published in Science explains color differences in birds

A University of Tulsa researcher has helped discover the gene responsible for creating sexual dimorphism in birds. Assistant Professor of Biological Sciences Matthew Toomey and an international team of biologists published the article “A genetic mechanism for sexual dichromatism in birds” this week in the prestigious research journal Science. 

Sexual dichromatism is a term describing the phenomenon observed in many bird species, in which males and females exhibit striking differences in coloration. Typically, male birds display flashy, colorful feathers, while females tend to be drab. Scientists have proposed that the explanation for this difference is that male birds are competing among other males for the attention of females. Although outwardly males and females can display very different color patterns, their genomes are nearly identical. How then do these color differences between the sexes arise? Toomey’s research collaboration explains for the first time how changes in the expression of a single gene can generate dramatic coloration differences between male and female birds. 

genome research
Photo courtesy of Geoff Hill.

To investigate the mechanisms of sexual dichromatism, Toomey and his colleagues studied the mosaic canary (pictured). This breed of canary was created by bird fanciers decades ago by breeding the yellow canary species, where males and females are the same color (monochromatic), with a sexually dichromatic species, the red siskin. The initial goal of the bird fanciers was to produce a red canary. In 2016, Toomey and the team found that these red canaries carry red siskin genes for an enzyme that converts yellow pigments to red. Along with monochromatic red canaries, bird breeders also produced mosaic canaries that carry the red siskin genes for both redness and sexual dichromatism. To identify the gene for dichromatism, Toomey and the group sequenced the genomes of the dichromatic mosaic canaries, compared them to the typical monochromatic canary and identified differences associated with the gene for enzyme β-carotene oxygenase 2 (BCO2). 

Toomey and his colleagues recently discovered that BCO2 plays a key role in breaking down pigments controlling the coloration of the beaks and legs of birds by studying another oddly colorful canary, the urucum breed. “We compared the urucum canary breed, which has uniquely colorful beaks and legs, to typical canaries, with drab beaks and legs,” he explained. “We found that the urucum birds have a mutation in BCO2 that renders it non-functional. The urucum birds become colorful in the beak and legs because they are not able to break down pigments the way a typical canary does. This result suggests that bright beak and leg coloration might be easily switched on and off through the course of evolution with simple changes in the expression of BCO2.” 

In the dichromatic mosaic canaries, the research team showed that the expression of BCO2 differs between sexes. Female mosaic canaries express higher levels of the enzyme than males, which destroys colorful pigments in developing feathers and leads to the relatively drab appearance of females. The research team also observed female-biased expression of BCO2 in other dichromatic bird species suggesting that may be a common mechanism of dichromatism amongst birds. 

This result paves the way for deeper investigations into how other factors such as mating systems, nesting behaviors, predation pressures and light environments affect bird coloration. Toomey explains, “We now have an unprecedented opportunity to trace how coloration has evolved in response to these evolutionary pressures, through specific genetic regulatory changes.”    

See the published research in Science.