Investigating mechanisms behind variation in color of killifish

Growing up in South India, Ratna Karatgi found herself moving between cities as her dad relocated for work. Though living in the city meant she was not exposed much to wildlife early on, she quickly became interested in zoology after working as a volunteer at the Madras Crocodile Bank Trust, an educational outreach-focused reptile zoo. There, she says that presentations and experiments by visiting researchers lit the spark for her.

“I didn’t have a distinct goal in mind at the time,” Karatgi said. “I knew I really liked animals, but I wasn't thinking about being a veterinarian or anything. So, I thought I would work at this zoo and see what happens. But then researchers from everywhere would visit the zoo and talk about their work, and I thought it was fascinating that people could actually do research and study animal behavior for a living.”

Following this path, she obtained a bachelor’s degree in Zoology from Stella Maris College before attending Jawaharlal Nehru Centre for Advanced Scientific Research to complete her masters in evolutionary biology. Karatgi described the transition as a dramatic shift from classwork-heavy undergraduate school to her intense, research-focused master’s program. She completed multiple lab rotations to learn new skills before settling into her master’s research on circadian rhythms of fruit flies. By this point, she was hooked on research, but was unsure about the next step.

“I knew I was interested in studying larger scale patterns in bigger animals (than a fly), preferably out in the wild, and I wanted to explore options outside of India,” she said. “The States or Canada were the places I was considering for doing a PhD. So, I decided to work as a research assistant in a lab at the Indian Institute of Science in Bangalore to really see if a career in research on behavior and evolution in wild animals was a good fit before making the move.”

While working as a research assistant, Karatgi studied intrasexual competition in regards to the color displays of peninsular rock agamas lizards during the breeding season. Males have bright colors in the breeding season, and this dynamic color change is used in signals for both fighting and mating.

Karatgi says this got her thinking about how variation in color is developed and maintained in other animal populations. After cold-emailing faculty in the US about taking her on as a PhD student, she says Rebecca Fuller (GNDP), a professor of ecology, evolution, and behavior at the University of Illinois Urbana-Champaign, was eager to have her join the team.   

Currently, Karatgi is a 5th year PhD student in the program in ecology, evolution and conservation biology. For her doctoral work, she explores how variation in killifish coloration is maintained across populations. Killifish are small fish that can come in different patterns of red, yellow, and blue, and these colors are used for signaling aggression and attracting mates. While red and yellow coloration are genetically based, the presence of blue is related to the environment, namely the light levels and amount of tannin (brown organic substance) in the water, that these fish reside in. Blue males are more abundant in murky, tannin-stained swamps, compared to springs which are much clearer.

She wanted to test if blue males were more abundant in swampy water because they have a competitive advantage in this environment, since this could lead to better access to territories in swampy water. So, for one of her studies Karatgi placed a blue male with a non-blue male and a female, and then measured the male’s aggressive behaviors such as attacks and fin flaring. She found that blue males are more likely to win competitive interactions in murky swamp water than in clear spring water, replicating the findings of a previous study on bluefin killifish from a different set of populations.

Because tannins affect how deeply light can pierce the water, Karatgi is also interested in how the lighting of the environment that the fish develop in affects their plasticity to become blue.

“We see so much variation in the extent of blue plasticity in killifish, and I’m trying to figure out what is preventing everyone from being equally plastic,” Karatgi explained. “There may be a critical period during development where fish need a specific lighting cue to turn blue. I’m interested in figuring out the precise stage during development when this cue is used to trigger the plastic blue coloration. So now all my experiments involve breeding and raising the fish to try to figure this out.”

In addition to being a student, Karatgi also served as the Outreach Coordinator for the Graduates in Ecology and Evolutionary Biology organization for two years, where she helped organize outreach events and connected researchers with the community.

“I like engaging in outreach,” Karatgi said. “I was not aware of opportunities for outreach when I was in India. But here in a university town, as a researcher, you can go talk to the librarian and be like, ‘Hey, can we come put up a showing or do a demonstration here?’ and they're totally up for it. My favorite event is the farmer’s market ‘Science at the Market’ stall.”

When asked about hobbies, she jokingly responded that, with how busy she is, “Hanging out with people, cooking and eating…that's pretty much most of what I do now during graduate school.” She then continued “I do like to read historical fiction, and when I need to de-stress I like to do nail art. I sort of picked that up after coming to graduate school, I find it very meditative and a nice way to calm down.” Karatgi also enjoys traveling to see her boyfriend at UC Santa Barbara, and her family in India.

When graduate school becomes too stressful, Karatgi says she thinks of an Urdu/Hindi saying by Faiz Ahmed Faiz that helps keep her optimistic:

Dil na-umid to nahin, nakaam hee to hai,
Lambee hai gam ki shaam, magar shaam hee to hai

Which translates to:
The heart has not lost all hope, but just a fight that is all,
The dusk of sadness is long, but it is just a dusk after all