Abstract
Sea turtles migrate across ocean basins to reach foraging and breeding grounds, but still exhibit significant population structure on their nesting beaches due to natal homing behavior. Although five species of sea turtles nest in West Africa, the genetic structure of many species in this region has not been adequately explored. We investigated the diversity of mitochondrial (control region) and nuclear (microsatellites) DNA for Olive Ridley (Lepidochelys olivacea) samples collected from two coastal communities in Ghana during four nesting seasons: 2006, 2014, 2015 and 2016. The control region of mtDNA was successfully sequenced for tissue samples from 45 individual sea turtles (17 from Ada Foah and 28 from Mankoadze). Analysis revealed six variable positions defining five haplotypes, of which one was previously undescribed (Lo91). Haplotype analysis indicated one substitution between ocean basins: a shared haplotype with the Western Atlantic population, but no shared haplotypes with Australia. This is indicative of population expansion from a small ancestral population and supports the scenario of colonization of the Atlantic Ocean via founder effect. Eleven microsatellite loci were used to analyze two years of samples (2015 and 2016) from Mankoadze. This comparison revealed the subsequent nesting cohorts were not genetically distinct and can therefore be considered a single population for management and conservation (FIS=0.085, P=0.703; FST=0.025, P=0.286). This population was compared to six females from Ada Foah across seven loci. The two locations are less related than expected under a model of random chance, show signs of outbreeding, and reflect moderate variation between two potential subpopulations (FIS=-0.160, P=1.00; FST=0.104, P=0.002). Pending further investigation, management entities should implement conservation strategies which consider nesting cohorts between years as single populations and nesting sites as separate populations. This study addresses a lack of basic information in this region regarding genetic variability of Olive Ridley sea turtles and is the first of its kind to address this knowledge gap by providing a refined understanding of population structure of this species in Ghana. A full understanding of the population structure at varying spatial and temporal scales is vital for long-term viability and appropriate management across jurisdictional boundaries. Further research is required to fully understand connections to potential migratory routes and foraging areas
