Population genomics of an Octopus species identify oceanographic barriers and inbreeding patterns: Demultiplexed reads of 71 Octopus insularis individuals

Coastal marine ecosystems are highly productive and important for global
fisheries. To mitigate over-exploitation and to establish efficient
conservation management plans for species of economic interest, it is
necessary to identify the oceanographic barriers that condition divergence
and gene flow between populations with those species, and that determine
their relative amounts of genetic variability. Here, we present the first
population genomic study of an Octopus species, Octopus insularis, which
was described in 2008 and is distributed in coastal and oceanic island
habitats in the tropical Atlantic Ocean, Gulf of Mexico and the Caribbean
Sea. Using genomic data, we identify the South Equatorial current as the
main barrier to gene flow between southern and northern parts of the
range, followed by discontinuities in the habitat associated with depth.
We find that genetic diversity of insular populations significantly
decreases after colonization from the continental shelf, also reflecting
low habitat availability. Using demographic modelling, we find signatures
of a stronger population expansion for coastal relative to insular
populations, consistent with estimated increases in habitat availability
since the Last Glacial Maximum. The direction of gene flow is coincident
with unidirectional currents and bidirectional eddies between otherwise
isolated populations. Together, our results show that oceanic currents and
habitat breaks are determinant in the diversification of coastal marine
species where adults have a sedentary behavior but paralarvae are
dispersed passively, shaping standing genetic variability within
populations. Lower genetic diversity within insular populations implies
that these are particularly vulnerable to current human exploitation and
selective pressures, calling for the revision of their protection status.