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. 2022 Apr 20;12(5):616.
doi: 10.3390/life12050616.

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

Edivaldo H C de Oliveira  1   2 , Anderson J B Gomes  3 , Alexandra F Costa  4   5 , Renata Emin-Lima  4   5 , Cibele R Bonvicino  6 , Maria C Viana  6   7 , Laura M A Reis  8 , Marcelo D Vidal  9 , Mirella V G Cavalcanti  10 , Fernanda L N Attademo  11 , Fábia O Luna  11 , Salvatore Siciliano  12
Affiliations

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

Edivaldo H C de Oliveira et al. Life (Basel). .

Abstract

Two species of manatees are found in Northern Brazil-the Antillean manatee (Trichechus manatus), which is found along the coast from Florida to Northeastern Brazil, and the Amazonian manatee (Trichechus inunguis), endemic to the Amazon drainage basin. These species show a sympatric distribution in the region of the Marajó Archipelago, an estuarine area surrounding the Amazon River mouth. There is evidence of the occurrence of interspecific hybrids in this area, based on mitochondrial DNA analyses, although the use of nuclear markers has not corroborated this proposal. Considering that these species show very distinct karyotypes, despite being closely related (2n = 48 in T. manatus and 2n = 56 in T. inunguis), hybrids would present distinct chromosome numbers. Based on this, we conducted cytogenetic analyses using classic and molecular techniques in three calves found stranded in the Marajó Island and Amapá coast. The results showed that one of them, morphologically classified as T. inunguis, presented the correspondent karyotype, with 2n = 56. However, the other two, which were phenotypically similar to T. manatus, showed 2n = 49. Despite the same diploid number, their G-banding patterns revealed some differences. The results of the distribution of some microsatellite sequences have also confirmed the heterozygosity of some chromosomal pairs in these two individuals. These results are the first indubitable confirmation of the occurrence of natural hybrids between T. manatus and T. inunguis, and also brings about some issues concerning the viability of hybrids, considering that these two individuals do not correspond to an F1 hybrid, but instead, both presented a possible F2 karyotype.

Keywords: fertility; heterozygosity; hybridization; introgression; karyotypes; sympatry.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Geographical location of the sites in Brazil where individuals analyzed in this study were either rescued, rehabilitated or both. Based on morphological features, individuals 1 and 3 were phenotypically classified as Trichechus manatus, and individual 2 as Trichechus inunguis.
Figure 2
Figure 2
Morphological features of Trichechus specimens examined in this study: (A) Individual from locality 1, a typical T. manatus in general appearance, with greyish color and presence of nails; (B) individual from locality 2, a typical T. inunguis in general appearance, with blackish coloration and absence of nails; and (C,D) individual from locality 3, coloration that resembles an Amazonian manatee (T. inunguis), but has nails as an Antillean manatee (T. manatus). In addition, its body size also follows the general description of T. inunguis. Photos by: (A) Fernanda Attademo, (B–D) Instituto Bicho D’água files.
Figure 3
Figure 3
(A) G-banded karyotype of Trichechus inunguis (individual 2) with typical 2n = 56 chromosomes; (B) C-banded metaphase show a low amount of heterochromatin, restricted to the centromeric regions of the chromosomes.
Figure 4
Figure 4
(A) G-banded karyotype of individual 1 with 2n = 49. Dash indicates chromosome 6, homologous to two unpaired acrocentric chromosomes; (B) C-banded metaphase showing the low amount of heterochromatin in the centromeric region of the chromosomes.
Figure 5
Figure 5
(A) G-banded karyotype of individual 3 with 2n = 49 chromosomes. Arrows show the difference in the centromeres position on chromosome 1; dash shows chromosome 8, homologous to two unpaired acrocentric chromosomes; (B) C-banded metaphase indicating the heterochromatin in the centromeric region of the chromosomes.
Figure 6
Figure 6
FISH experiment using 18/28S rDNA and telomeric sequence in metaphases of T. inunguis (A,B) and a hybrid individual (C,D), respectively. Red arrows show NOR site.
Figure 7
Figure 7
FISH experiment using microsatellite sequences (TA)15, (CGG)10, (GC)15, (GAG)10 and (CAG)10 in both hybrid specimens. Metaphases on the left correspond to individual 1, and on the right to individual 3. Arrows indicate the clusters of theses sequences in the chromosomes.
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