Diversity of feeding strategies in loggerhead sea turtles from the Cape Verde archipelago

Abstract

As biodiversity worldwide is decreasing, to preserve adaptive potential, the importance of maintaining species’ genetic and trait diversities is increasing. An efficient foraging strategy is a critical trait for an organism’s fitness, as it affects its physiology and reproduction. Understanding such strategies is especially relevant for species with long feeding migrations such as sea turtles. Using carbon and nitrogen stable isotopes combined with mitochondrial sequencing, we explored the diversity of feeding strategies in genetically differentiated nesting groups of loggerhead sea turtles (Caretta caretta) within the Cape Verde Archipelago. Here, we reveal a pattern where turtles from most islands use two distinct oceanic feeding strategies, including one putatively linked to a 15N-enriched zone of the West African upwelling area. On the Eastern island of Boavista, an additional third strategy exists used by turtles feeding mostly neritically. Contrary to previous paradoxical assumptions, oceanic turtles, that represent the vast majority of the population, are not smaller than neritic turtles and therefore do not seem to feed in a suboptimal environment. Our results also suggest that the number of feeding strategies may correlate with demography, whereby a greater feeding strategy diversity matches demographic signs of recent expansion after a population bottleneck for turtles nesting on the island of Boavista. Overall, the feeding ecology of Cape Verde loggerhead turtles is complex and likely shaped by an interaction between environmental and population parameters. Our results stress the importance of conservation efforts to prevent loss of critical diversity in endangered species.