Demographic history shapes genetic variability in cryptic fish species
of high ecologic and economic relevance
Abstract
Human overexploitation of natural resources has placed conservation and
management as one of the most pressing challenges in modern societies,
particularly regarding highly vulnerable marine ecosystems. Although a
large effort has been made to design Marine Protected Areas (MPAs)
worldwide, it is still unclear how many species actually exist in these
MPAs, what is the genetic connectivity between areas with different
protective regimes, and what is their relative genetic diversity. We
answer these questions using morphologically cryptic species of the
genus Mugil that are sympatric in the largest MPA in the Tropical
Southwestern marine province. Population structure analyses show the
existence of five highly divergent species (FST > 0.855)
and no genetic divergence between two estuaries with different
protection status (FST = 0.005). Sympatric individuals are assigned to
single clusters and show strong concordance among hundreds of
independent gene trees, consistent with full reproductive isolation and
no ancestral nor ongoing hybridization. Differences of genetic diversity
within species suggest that effective population sizes differ up to
two-fold, probably reflecting differences in the magnitude of population
expansions during the evolutionary history of these species, rather than
recent impact of fisheries. Together, our results suggest that designing
MPAs with areas of integral protection in between areas where fisheries
are permitted could be an effective way to manage cryptic species that
cannot have species-specific quotas. More generally, this work shows a
cost-efficient approach that is transferable to other marine or
terrestrial organisms of special concern, helping to implement
science-based regulations for management and conservation.