26/11 – SEMINÁRIO DE DADOS (Mestrado) – GEOVANA JENIFFER ORTELÃ GONÇALVES

SEMINÁRIO DE DADOS (Mestrado)

GEOVANA JENIFFER ORTELÃ GONÇALVES

Global Phylogeography of the Olive Ridley Turtle (Lepidochelys olivacea): Implications for Conservation

Orientador: Dr. Nelson J. Rosa Fagundes

Coorientador: Dr. Sandro Luis Bonatto

Avaliador: Dr. Thales Renato O. de Freitas

Data: 26 de novembro de 2025 (quarta-feira)

Horário de início: 12h

Presencial: Anfiteatro do Departamento de Genética da UFRGS (Campus do Vale, prédio 43312)

Abstract:

The olive ridley turtle (Lepidochelys olivacea) is distributed circumglobally, occurring in tropical and subtropical ocean regions, except for the North Atlantic. The species is classified as Vulnerable both on the IUCN Red List and on Brazil’s National List of Threatened Species. Despite its wide geographic range, L. olivacea populations face multiple global threats, including egg and meat harvesting and trade, coastal development and habitat degradation, marine pollution, climate change, and bycatch in fisheries. Considering the current biodiversity crisis and climate change, as well as the lack of comprehensive population genomic studies for sea turtles, this study aimed to investigate the demographic history, global genetic structure, and conservation risk factors of L. olivacea, to support more effective management strategies. To achieve this, we sequenced whole genomes from 49 individuals distributed across the major ocean basins: the Atlantic (n = 27; Brazil = 23, French Guiana = 4), the Pacific (n = 11; United States = 1, Costa Rica = 6, Mexico = 4), and the Indian Ocean (n = 11; Sri Lanka = 2, Malaysia = 2, Australia = 7). Sequencing reads were aligned to the species’ reference genome, and the resulting variant set (VCF) underwent filtering steps. The analyses revealed three genetically well-differentiated populations corresponding to the Atlantic, Pacific, and Indian oceans. The Atlantic population exhibited a marked demographic decline approximately 2,000 years ago, followed by recovery — a pattern not observed in the other populations. This demographic event had been previously suggested by other studies and is possibly related to intensive hunting by human populations. This historical dynamic is consistent with the high proportion of runs of homozygosity (ROH) detected in the Atlantic population (approximately 17% of the genome), as well as its lower heterozygosity (0.037%). These values contrast with those observed in the Pacific and Indian populations, which showed ROH proportions between 2.8% and 3.3% and heterozygosity values of 0.044% and 0.047%, respectively. Contemporary estimates of effective population size also differed among ocean basins: 3,134.6 individuals (95% CI = 2526.7–4127.3) for the Indian Ocean and 1,126.4 individuals (95% CI = 1089.7–1165.6) for the Atlantic. For the Pacific, the linkage disequilibrium method was unable to estimate the contemporary effective population size. Taken together, these findings indicate that Atlantic populations of L. olivacea require priority in conservation actions due to their lower genetic diversity and greater homozygosity. Future analysis will compare the degree of non-synonymous and synonymous variants across populations to check the possibility of a higher genetic load in the Atlantic population. Additionally, the historical patterns of relationships among populations will be investigated in order to test the hypothesis of recurrent ocean colonizations by the species over time.