Genetic Connectivity of the West Indian Manatee in the Southern Range and Limited Evidence of Hybridization With Amazonian Manatees

Abstract

The Antillean subspecies of the West Indian manatee is classified as endangered by the International Union for the Conservation of Nature (IUCN) Red List. In Brazil, the manatee population is listed as endangered with an estimated population size of 500–1,000. Historic hunting, recent habitat degradation, and fisheries bycatch have decreased the population size. The Amazonian manatee is listed as vulnerable by the IUCN with unknown population sizes within Brazil. The Antillean manatee occurs in sympatry with the Amazonian manatee in Brazil and hybridization has been previously indicated. To provide information on the genetic structure, diversity, and degree of hybridization in the sympatric zone near the Amazon River mouth, the mitochondrial DNA control region and 13 nuclear microsatellite markers were assessed on the two species. Samples were analyzed from the Antillean subspecies across its distribution in Brazil (n = 78) and from the Amazonian species (n = 17) at the Amazon River mouth and inland mainstem river. To assess the previously defined evolutionary significant units of Antillean manatees in the area, an additional 11 samples from Venezuela and Guyana were included. The Antillean manatee was found to be a single population in Brazil and had lower than average number of alleles (3.00), expected heterozygosity (0.34), and haplotype diversity (0.15) when compared to many other manatee populations. The low values may be influenced by the small population size and extended pressures from anthropogenic threats. Gene flow was identified with Venezuela/Guyana in admixed Antillean Brazil samples, although the two populations were found to be moderately divergent. The nuclear loci in Venezuela/Guyana Antillean manatee samples indicated high differentiation from the samples collected in the Amazon River (FST = 0.35 and RST = 0.18, p = 0.0001). No indication of nuclear hybridization was found except for a single sample, “Poque” that had been identified previously. The distribution of Antillean manatees in Brazil is extensive and the areas with unique habitat and threats would benefit from independent management and conservation actions. Gene flow, resulting in genetic diversity and long-term population stability, could be improved in the southern range through habitat restoration, and the establishments of travel corridors and protected areas, which are particularly important for successful parturition and neonatal calf survival.

Karyotypical Confirmation of Natural Hybridization between Two Manatee Species, Trichechus manatus and Trichechus inunguis

“…However, despite this, these two species are found in sympatry in the estuarine region of the Marajó Archipelago, a complex area near the Amazon delta, with rivers, lakes and where fresh and saltwater mix in distinctive patterns according to the rainfall regime [ 3 , 4 , 5 , 6 ]. Because of this, the possible occurrence of hybridization between T. manatus and T. inunguis has been analyzed by means of molecular studies, based on both mitochondrial and molecular DNA markers [ 1 , 7 , 8 ]. Unfortunately, the results of these studies are currently inconclusive [ 9 ].…”

“…Unfortunately, the results of these studies are currently inconclusive [ 9 ]. Therefore, while mitochondrial DNA (mtDNA) analyses have indicated the occurrence of interspecific hybrids in the estuarine sympatric region [ 1 , 7 ], the sequencing of nuclear (nuDNA) markers did not find evidence of hybridization in individuals sampled in the area, including individuals from the Guianas, proposed as part of the hybrid zone [ 8 ].…”

“…Unfortunately, up to now, ZOO-FISH is restricted to T. manatus [ 17 , 18 ], and the results strongly supported the close relationship between sirenians and elephants (Tethytheria) supporting the clade Paenungulata, which includes Sirenia, Proboscidea, and Hyracoidea [ 18 ]. Interestingly, although these two species show clear chromosomal differences [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ], there are no karyological studies in individuals from the sympatric area, except for one male found in illegal captivity, which was confirmed as being a hybrid between T. manatus and T. inunguis by mitochondrial and nuclear DNA data, as well as cytogenetic analysis [ 1 , 8 ].…”

First Description of a Satellite DNA in Manatees’ Centromeric Regions

“…These studies showed that the T. m. manatus populations from the Caribbean and up to the Amazon River mouth are phylogenetically closer to the populations of T. m. latirostris from the United States than to the Brazilian T. m. manatus populations south of the Amazon River mouth ( Vianna et al, 2006 ; Barros et al, 2017 ; Lima et al, 2019 , 2021 ). Hybrids between T. manatus and T. inunguis have also been reported on the sympatric area at the Amazon River mouth ( Vianna et al, 2006 ; Lima et al, 2019 ; Luna et al, 2021 ).…”

Mitochondrial Genetic Diversity, Population Structure and Detection of Antillean and Amazonian Manatees in Colombia: New Areas and New Techniques

“…Sequences were manually edited and aligned using Geneious Prime (www.geneious.com). In order to detect potential new haplotypes among the new samples included in this study, comparisons with haplotypes defined by García-Rodríguez et al (1998), Cantanhede et al (2005), Vianna et al (2006), Satizábal et al (2012), Lima et al (2019), Vilaça et al (2019), andLuna et al (2021). For T. manatus, these included sequences obtained from Florida, Cuba, Dominican Republic, Puerto Rico, Mexico, Belize, Panama, Colombia, Venezuela, French Guiana, and Brazil.…”