| dc.description.abstract | The loggerhead (Caretta caretta) and hawksbill (Eretmochelys imbricata) sea turtles are species that are distributed in tropical waters and maintain ecosystem balance in coral reefs, seagrasses, soft bottoms, among others. These species are in population decline due to anthropic and environmental pressures, which is why they are categorized as Vulnerable and Critically Endangered respectively (IUCN). Mitochondrial DNA (mtDNA) has been studied in threatened species to elucidate population identities, genetic structures, migratory behaviors, demographic events and phylogenetic patterns. This molecule has specific characteristics such as maternal inheritance, low or no recombination, high mutation rate, polyplasmy and heteroplasmy. The heteroplasmic mutations are related to pathologies of variable symptomatology and their study is relevant to determine part of the population status in priority species and thus provide useful information to develop management and conservation guidelines. It seems that oxidative stress, nutritional status and environmental pollution play an important role in the development of heteroplasmic mutations. In humans, 329 mitochondrial diseases related to the rRNA and tRNA genes have been described, and 336 to genes encoding proteins and the control region. For the conservation of C. caretta and E. imbricata species it is important to update and advance the knowledge of mitochondrial genetics by identifying their degree of heteroplasmy. This will allow us to understand the possible consequences of this phenomenon in the health and survival of these populations.
In this study heteroplasmy was identified and evaluated in turtle E. imbricata and C. caretta mitogenomas by RNAseq. The heteroplasmic mutations observed were related to the mutations present in humans.
The assembly of the mitogenomas Ei1, Cc1, Cc2 and Cc3 revealed sizes of 16498, 16633, 16461 and 16446 bp for each individual respectively. The variation between the lengths of the mtDNA's is mainly due to the extension of the hypervariable region. Regarding the percentage of heteroplasmy, Ei1 presented 1.7 % (286 of 16469 sites), Cc1 1.8 % (299 of 16573 sites), Cc2 7.1 % (1173 of 16461 sites) and Cc3 0.37 % (61 of 16446 sites). Although the mechanisms that fix heteroplasmic mutations in populations are not known, it is deduced that genetic drift influences the fate of this phenomenon. Additionally, individuals Ei1, Cc1 and Cc3 related four, six and two mutations respectively with human pathological mutations but none exceeded the phenotypic threshold. However, the individual Cc2 presented 41 heteroplasmic sites that were related to human pathologies of which only one (C3769A) exceeded the threshold with 66 %. We conclude that the presence of heteroplasmy in the mtDNA regions is independent of the length and location of these regions and that not all heteroplasmic mutations generate pathologies due to the fact that the phenotypic threshold must be overcome. | |
