Establishment genomics of the Indo-Pacific damselfish Neopomacentrus cyanomos, in the Greater Caribbean

The Regal Demoiselle, Neopomacentrus cyanomos is only the second Indo-Pacific reef fish (after the lionfish) to become well established in the Greater Caribbean (GC). It was first discovered, after it already was common, in the southwest Gulf of Mexico (SGM) in 2013. In 2019, an isolated second population was found at Trinidad, 3300 km away. The initial occurrence of this species only at two distant offshore oilfields supports the hypothesis that it was transported via an oil platform in water from its native range into the Atlantic. From there, populations spilled over to nearby reefs. In both its native range and the SGM, N. cyanomos lives in the relatively stable marine environment of coral reefs. In contrast, the Trinidad population lives on rocky reefs in a large, murky, brackish estuary with strong seasonal variation in salinity mostly due to inflow from the Orinoco River in Venezuela. Its capacity to successfully breed in that estuary indicates that N. cyanomos is a highly adaptable species. The existence of two distant, isolated populations of this non-native species in such very different environments presents a unique opportunity for the study of the biology of recently established non-native reef fishes. A previous study showed that both the SGM and Trinidad populations derive from the same two of four, largely allopatric, native-range mitochondrial DNA lineages. Here we analyzed native populations from the area of those two lineages in the Pacific and Indian oceans, and the two non-native populations in the GC using thousands of genomic markers (RAD sequences) to evaluate patterns of genetic differentiation, population structure and the potential role of natural selection to affect establishment success. Based on RAD sequences we show that native and non-native populations have very similar levels of genetic diversity (no evidence of bottleneck or founder effects). In addition, data showed that native Indian and Pacific Ocean individuals partition in separate genetic clusters and that non-native Atlantic individuals are prevalently of Pacific genetic origin (~ 95% of their genetic material belong to the Pacific Ocean cluster). Finally, we found that 32 loci were potentially under selection, and 12 of them corresponded to protein coding genes. Additional work will be necessary to determine the potential role of natural selection in the successful establishment of non-native species in the Caribbean.