Figure 1. Members of Kim’s team collect samples in Massachusetts for their genetic research. Image courtesy of Anthony Baniaga.
In nature, the new kids on the block don’t tend to last very long. Non-native species, which move from their original ecosystem to a new one, often encounter unforeseen obstacles in their new environments. Sometimes, however, a species doesn’t just survive in a novel environment—it thrives. Such is the case of the Redbreast Sunfish (Lepomis auritus), a widely loved game fish whose native range spans the eastern states of North America.
The Redbreast Sunfish’s popularity among fishermen led to its introduction to bodies of water far beyond its native scope. Much to the short-term delight of fishermen, the sunfish quickly took to their new environments and established breeding populations. However, these new sunfish populations began to threaten local species. Some of these local species, like the Devils River Minnow and the Fountain Darter, are endangered and are thus in precarious situations. To make matters worse, Redbreast Sunfish introductions were spottily recorded. Without a detailed record, it is impossible to determine which populations belong to a native Redbreast Sunfish stock and which populations are composed of non-native, potentially invasive Redbreast Sunfish.
Armed with cutting-edge genetic technology, a wealth of fisheries knowledge, and a rather large net, Daemin Kim GSAS ’23 sought to solve this problem by drawing the line between native and non-native Redbreast Sunfish.
In collaboration with Yale professor Thomas Near and aquatic zoologist Jeffrey Simmons, Kim analyzed nearly two hundred Redbreast Sunfish DNA samples. These samples were sourced from every major watershed that the Redbreast Sunfish inhabits, including Texas and the Eastern United States. Kim analyzed specimens using double digest restriction-associated DNA (ddRAD) techniques, which target areas of common variation in the genome for sequencing rather than the entire genome. This procedure allows for rapid comparison of genetic profiles between and among Redbreast Sunfish samples. ddRAD is a recent addition to the fisheries scientist’s toolkit. When Kim was a master’s student, his research was limited to five individual genes. “Now, using ddRAD data, […] we get tens of thousands of loci,” Kim said.
Capitalizing on this advancement in genetic analysis, Kim identified several non-native Redbreast Sunfish populations. Some were found in the freshwaters of Texas, while others were found in the Tennessee River system and the Mobile River Basin. Kim also reconstructed the introductory pathways of the Redbreast Sunfish to each of its non-native locales. For example, he was able to determine that the surveyed non-native Redbreast Sunfish in Texas originate from a river in Florida.
Kim’s identification of non-native Redbreast Sunfish populations provides local fisheries and natural resources management organizations with vital ecological information. Targeted eradication of non-native Redbreast Sunfish could restore affected ecosystems, protecting threatened and endangered species by reestablishing an ecosystem’s original pecking order. Furthermore, Kim’s work has paved the way for similar studies designed to identify and combat non-native and invasive species around the planet.
A major struggle that Kim faced during his research is a common issue in scientific ventures: knowing when to stop. A species like the Redbreast Sunfish has an extensive population distribution. According to Kim, sampling every unique Redbreast Sunfish population in the US is practically impossible. Realizing this, Kim used his prior fisheries knowledge and field research to home in on the important players involved in ecosystem infiltration. The four examined Redbreast Sunfish populations in Texas, for example, had nearly identical genetic profiles. The distribution of these populations across the large state of Texas provided Kim with enough evidence to infer that all Texas Redbreast Sunfish populations likely share a common genetic predecessor from the Suwannee River in Florida. To maximize the efficiency of his research, Kim had to balance the resources available to him with the possible impact of his project.
While Kim acknowledges the doors opened by his sunfish research, he recognizes that the time he can spend studying the Redbreast Sunfish is limited. “I always have [a] hard time staying with the same taxonomy group,” Kim said. Currently, he is fascinated by darters, a diverse subfamily of freshwater fish with an enigmatic evolutionary history. Regardless of Kim’s future work, it is certain that this self-proclaimed “fish nerd” will continue to impact ichthyology for years to come.
[Citations]
Kim, D. (2024, March 29). Personal communication [Personal interview].
Kim, D., Simmons, J. W., & Near, T. J. (2024). Identification of non-native populations and reconstruction of invasion routes in the Redbreast Sunfish Lepomis auritus. Biol Invasions 26, 1241–1254. https://doi.org/10.1007/s10530-023-03241-x