Karyotypes of Manatees: New Insights into Hybrid Formation (Trichechus inunguis × Trichechus m. manatus) in the Amazon Estuary

Abstract

Great efforts have been made to preserve manatees. Recently, a hybrid zone was described between Trichechus inunguis (TIN) and the Trichechus manatus manatus (TMM) in the Amazon estuary. Cytogenetic data on these sirenians are limited, despite being fundamental to understanding the hybridization/introgression dynamics and genomic organization in Trichechus. We analyzed the karyotype of TMM, TIN, and two hybrid specimens (“Poque” and “Vitor”) by classical and molecular cytogenetics. G-band analysis revealed that TMM (2n = 48) and TIN (2n = 56) diverge by at least six Robertsonian translocations and a pericentric inversion. Hybrids had 2n = 50, however, with Autosomal Fundamental Number (FNA) = 88 in “Poque” and FNA = 74 in “Vitor”, and chromosomal distinct pairs in heterozygous; additionally, “Vitor” exhibited heteromorphisms and chromosomes whose pairs could not be determined. The U2 snDNA and Histone H3 multi genes are distributed in small clusters along TIN and TMM chromosomes and have transposable Keno and Helitron elements (TEs) in their sequences. The different karyotypes observed among manatee hybrids may indicate that they represent different generations formed by crossing between fertile hybrids and TIN. On the other hand, it is also possible that all hybrids recorded represent F1 and the observed karyotype differences must result from mechanisms of elimination.

Ancestral chromosomal signatures of Paenungulata (Afroteria) reveal the karyotype of Amazonian manatee (Trichechus inunguis, Sirenia: Trichechidae) as the oldest among American manatees

“…Comparative analyzes from the APK indicate that L. africana (2n = 56) underwent 5 fusions, 4 fissions, and 1 inversion/centromere repositioning on chromosome 3 (LAF 3) to constitute the current karyotype; P. capensis (2n = 54) underwent 4 fusions and 2 fissions; T. m. latirostris underwent 5 fusions and 2 inversion/centromere repositioning (TML 5 and 7) [ 2 ]. From the same perspective of analysis by Pardini et al [ 2 ], the analysis from this present study showed that T. inunguis showed a karyotype modification of 1 fusion (in TIN 9), 1 pericentric inversion (TIN 1) (by Noronha et al [ 22 ]) and 2 inversion/centromere repositioning (TIN 2 and 4), indicating a more conserved karyotype with APK than other paenungulates (Table 3 ).…”

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Fig. 1 G-banded karyotype of Trichechus inunguis (2n = 56, FN = 92) [ 22 ], with chromosomal mapping plotted from hybridizations with whole chromosome probes from Trichechus manatus latirostris (2n = 48, FN = 92)

Fig. 2 FISH with probes from Trichechus manatus latirostris (TML) in Trichechus inunguis (TIN).

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“… G-banded karyotype of Trichechus inunguis (2n = 56, FN = 92) [ 22 ], with chromosomal mapping plotted from hybridizations with whole chromosome probes from Trichechus manatus latirostris (2n = 48, FN = 92) …”

“…Additionally, when comparing by G band and chromosome painting the TML, TIN, Loxodonta africana (LAF) and Procavia capensis (PCA) species, we observed that TIN 1 underwent a pericentric inversion when compared to TML 1; and, TIN 2 (TML 5) and TIN 4 (TML 7) underwent centromere inversion/repositioning when compared to LAF (LAF 5 and LAF 17; LAF 4) and PCA (PCA 4; PCA 3), respectively [ 2 , 22 ].…”

“…This variation in karyotypes is remarkable, with a difference of four Robertsonian rearrangements [ 19 ] between T. manatus and T. inunguis , considering the short divergence time (1.34 myr) between these species. More recent data from Noronha et al [ 22 ] and De Oliveira et al [ 20 ], based on karyotypic analysis, demonstrated chromosomes rearrangements and the natural occurrence of hybrids from reproduction between T. inunguis and T. manatus or different generations (F1, F2). Cytogenetic data for T. senegalensis have not yet been described.…”