TLR4 and TLR8 variability in Amazonian and West Indian manatee species from Brazil.

Tatiana Maia De Oliveira,Jairo Moura Oliveira,Tibério Cesar Tortola Burlamaqui,André Luiz Alves De Sá,Alex Garcia Cavalleiro De Macedo Klautau,Maria Paula Cruz Schneider,Fernanda Löffler Niemeyer Attademo,Fábia De Oliveira Luna,Michael F Criscitiello,Breanna Breaux,Leonardo Sena

doi:10.1590/1678-4685-gmb-2019-0252

Abstract

Amazonian (Trichechus inunguis) and West Indian (Trichechus manatus) manatees are aquatic mammals vulnerable to extinction found in the Amazon basin and the coastal western Atlantic. Toll-like receptors (TLR) play a key role in recognizing pathogen-associated molecular patterns using leucine-rich repeats (LRRs). We described the diversity of TLR4 and TLR8 genes in these two species of manatee. Amazonian manatee showed seven SNPs in TLR4 and the eight in TLR8, while West Indian manatee shared four and six of those SNPs, respectively. In our analysis, TLR4 showed one non-conservative amino acid replacement substitution in LRR7 and LRR8, on the other hand, TLR8 was less variable and showed only conserved amino acid substitutions. Selection analysis showed that only one TLR4 site was subjected to positive selection and none in TLR8. TLR4 in manatees did not show any evidence of convergent evolution compared to species of the cetacean lineage. Differences in TLR4 and TLR8 polymorphism may be related to distinct selection by pathogens, population reduction of West Indian manatees, or an expected consequence of population expansion in Amazonian manatees. Future studies combining pathogen association and TLR polymorphism may clarify possible roles of these genes and be used for conservation purposes of manatee species.

Highlights

Sirenians are herbivorous aquatic mammals distributed in tropical and subtropical regions of the Americas, western coast of Africa, and Oceania (Husar, 1977; Domning, 1981; Bonde et al, 2012), evolutionarily related to elephants (Loxodonta africana and Elephas maximus) in the Superorder Afrotheria
The frequency of the TLR4 SNPs varied between both species of manatees, but the number of SNPs were higher in Amazonian manatee in comparison to West Indian manatee for both TLR4 and TLR8, with no exclusive SNP for the latter species (Figures 2 and 3)
Four out of seven SNPs found in the TLR4 and six out of eight SNPs found in TLR8 of the Amazonian manatees were found in the West Indian manatee samples studied here

Summary

Introduction

Sirenians are herbivorous aquatic mammals distributed in tropical and subtropical regions of the Americas, western coast of Africa, and Oceania (Husar, 1977; Domning, 1981; Bonde et al, 2012), evolutionarily related to elephants (Loxodonta africana and Elephas maximus) in the Superorder Afrotheria. All manatee species have a vulnerable conservation status according to IUCN (2019) Their decreasing numbers throughout their range is a result of past and present hunting for both meat and the leather trade (Domning, 1981), which might have affected genetic flow among populations, especially of West Indian manatees (Luna, 2013). Research on pathogens afflicting manatees has been conducted both in captivity and in natural environments in order to assess their health status (Bossart et al, 1998, 2002; Bando et al, 2014; Vélez et al, 2018), but only a few genetic studies have focused on genes related to the immune response (Breaux et al, 2017, 2018; Sá et al, 2019). Poorly studied innate immune genes may provide insights on the health status of manatees (Gelain and Bonsembiante, 2019), and on distinct selective pressures the manatee species may have undergone in distinct habitats

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