# The genome of African manatee Trichechus senegalensis reveals secondary adaptation to the aquatic environment

## TL;DR

The African manatee's genome reveals genetic changes linked to aquatic life, including dense bones and cold sensitivity, and shows signs of a small population size.

## Contribution

A chromosome-level genome assembly of the African manatee, revealing genes related to aquatic adaptation and population decline.

## Key findings

- Genes like CSF1R and LRRK1 are linked to dense bone formation in manatees.
- Loss of KCNK18 may increase cold sensitivity in African manatees.
- 392 genes show convergent evolution among fully aquatic mammals, related to skin, bones, and circadian rhythms.

## Abstract

Sirenians exhibit unique aquatic adaptations, showcasing both convergent adaptive features shared with cetaceans and unique characteristics such as cold sensitivity and dense bones. Here, we report a chromosome-level genome of the African manatee (Trichechus senegalensis) with high continuity, completeness, and accuracy. We found that genes associated with osteopetrosis have undergone positive selection (CSF1R and LRRK1) or pseudogenized (FAM111A and IGSF23) in the African manatee, potentially contributing to the dense bone formation. The loss of KCNK18 may have increased their sensitivity to cold water temperatures. Moreover, we identified convergent evolutionary signatures in 392 genes among fully aquatic mammals, primarily enriched in skin or skeletal system development and circadian rhythm, which contributed to the transition from terrestrial to fully aquatic lifestyles. The African manatee currently possesses a small effective population size and low genome-wide heterozygosity. Overall, our study provides genetic resources for understanding the evolutionary characteristics and conservation efforts of this species.

•De novo chromosome-level assembly of the African manatee genome•Genetic basis for increased bone density and enhanced cold sensitivity•Convergent evolutionary signatures among fully aquatic mammals•Currently low genome-wide heterozygosity and a small effective population size

De novo chromosome-level assembly of the African manatee genome

Genetic basis for increased bone density and enhanced cold sensitivity

Convergent evolutionary signatures among fully aquatic mammals

Currently low genome-wide heterozygosity and a small effective population size

Zoology; Molecular biology; Evolutionary biology