Meet the Scientist Using Micro-CT Scans to Explore Big Questions About Evolution

Corinthia Black studies the anatomical features of fishes and spiders to understand how life on Earth takes shape

In 1859, Charles Darwin’s groundbreaking On the Origin of Species concluded with one of its most shocking ideas of all: that “from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” This raised the obvious question of how life diversified into so many different shapes and sizes.

Over 150 years later, evolutionary biologists like Corinthia Black are still exploring this question. “I really just want to know why and how groups of animals became so diverse,” said Black, a postdoctoral fellow at the National Museum of Natural History. “I just want to know what the heck happened.”

While these questions may be old, Black’s research approaches are anything but. Throughout her career, she has combined detailed micro-CT scanning technology and cutting-edge genetic analyses to understand how animals like flatfishes can come from the same ancestor and yet look so different. Currently, Black is using her microscopic approach to investigate the form and function of spider muscles.

In this installment of Meet a SI-entist, Smithsonian Voices spoke to Black about her own evolution as a scientist and how her innovative techniques are breaking new ground on some of evolutionary biology’s oldest questions.

What was your pathway to becoming an evolutionary biologist?

When I was ten or twelve, I was that nerdy kid who wanted to study sharks. I never really grew out of it. I got SCUBA certified when I was fifteen, and that’s when I started really looking into science and all that it entails. My parents never went to college, so I didn’t know much about that world. I didn’t even know what evolution was until college.

I thought it would be best to get a biology degree and figure it out from there, so I went to a community college and then transferred to a four-year institution. At the time, I was still primarily interested in sharks. But after I met an ichthyologist, I started looking into other fish.

I realized that even the rivers and stream systems in Iowa where I grew up were home to tons of non-game fishes that are beautiful, diverse, and incredibly important ecologically. That’s what initially got me into ichthyology, and then I learned more about evolution and became fascinated with learning about how all this diversity came to be.

What makes fish good subjects for studying the evolution of diversity?

Fishes are found worldwide. They occupy almost all aquatic habitats, whether it be marine or freshwater, and they come in all different shapes and sizes. I always joke that if you can dream up a fish, it probably already exists.

For example, take catfishes, which I worked on for my PhD. It’s one of the largest orders of fishes — there are almost 4,000 known species, with an estimated total of upwards of 6,000 species. They are found worldwide in all different types of aquatic environments. One thing that interests me is that some catfishes are venomous, but we still don’t know whether or not the presence of venom has influenced the morphology or function of their fin spines. There’s just so many fascinating questions you can ask about evolutionary processes across this group alone.

How has new technology like micro-CT scanning allowed you to study the diversity of shape and function?

When I started, a lot of people were using linear measurements and trying to compare one individual to another individual. As time went on, people started to utilize geometric and morphometric techniques that allow you to look more at the shape and how that changes between individuals. Soon, I started working with two-dimensional images of X-rays, taking a bunch of X-rays of flatfishes and comparing how patterns changed from one specimen to another to visualize the diversification of shape.

When I started my PhD, I learned how to take images from CT scans — which are basically thousands of picture slices of the object that you’re interested in — and reconstruct them into a three-dimensional model. This allows you to isolate parts of the object that you’re interested in.

That really helped advance my research. Now, instead of looking at these two-dimensional images of three-dimensional animals, I can actually look at how they’ve changed in three dimensions.

On top of that, you can look at the architecture of muscles and infer their different functions. You can examine how both shape and function diversified in these animals across time and connect it to the major events that occurred — like the formation of new habitats or a major extinction event that allowed them to diversify.

How do natural history collections contribute to your research?

Every project I’ve ever done uses specimens from museum collections. Whether it’s working with a collaborator who used DNA that was collected during field work or physically taking the specimen out of a jar myself to X-ray or CT scan it, I’m constantly using specimens that have been collected over the years. When I worked with flatfishes, the oldest specimen was from around 1898. I almost just threw it in there for the opportunity to look at something that old.

I think it would be very difficult for one person to go out and collect everything that they need. To build these collections, you have people from across the world collecting all these different specimens over years and years. As a result, you can just go to a place like the Smithsonian and pull out the specimen that you’re interested in and place it in the CT scanner to reveal its hidden anatomy.

This interview has been edited for length and clarity.  

Meet a SI-entist: The Smithsonian is so much more than its world-renowned exhibits and artifacts. It is a hub of scientific exploration for hundreds of researchers from around the world. Once a month, we’ll introduce you to a Smithsonian Institution scientist (or SI-entist) and the fascinating work they do behind the scenes at the National Museum of Natural History.

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Benjamin Hack | Read More

Benjamin Hack is Science Writing Intern at the Smithsonian National Museum of Natural History. He covers anything and everything related to the natural world for Smithsonian Voices, the museum’s blog. Ever fascinated by ecology, Ben studied and conducted research in biology as an undergraduate at Cornell before transitioning into science communication. His work, which has appeared in magazines such as Audubon and Living Bird, highlights both the joy of nature and the dire challenges facing the world’s biodiversity. In his spare time, Ben can often be found outside birdwatching.