Manatee genomics supports a special conservation area in the Guianas coastline under the influence of the Amazon River plume

Abstract

The West Indian manatee (Trichechus manatus) occurs along the Atlantic coastline and adjacent freshwater systems of South, Central and North America, from Alagoas (Brazil) to Florida (USA) and Greater Antilles. The Amazonian manatee (Trichechus inunguis) is the only Sirenian adapted exclusively to freshwater and endemic to the Amazon River basin. Previous studies have reported hybrids between T. inunguis and T. manatus close to the mouth of the Amazon River, composing a likely extensive hybrid zone along the Guianas coast of South America under the influence of the Amazon River plume. We have used ddRAD SNP data, and sequences of nuclear and mtDNA loci to characterize the genomic composition of manatees along the French Guiana coastline. We found this population to be formed by introgressed or later generation interspecific hybrids, and also describe the first T. inunguis found outside the Amazon River basin. Our results indicate that T. inunguis can survive in the Amazon River plume and have colonized independent water streams of the Guianas coastline where they likely hybridize with T. manatus. This hypothesis offers a plausible explanation for the known extension of the hybrid zone between the two species along the Guianas coastline. It also reinforces the importance of the Amazon plume, which flows westwards to the Guianas coastline and favors the dispersion of the freshwater species. This habitat functions as a large estuary-like system that provides an ecological continuum from Amazon River mouth to the disconnected waterflows of the Guianas, which deserves a status of special conservation area.