Sepiola COI and Vibrio gapA gene sequences

Symbiotic marine bacteria that are transmitted through the environment are
susceptible to possible abiotic factors (salinity, temperature, physical
barriers) that separate them from their hosts. Given that many symbioses
are driven by host specificity, environmentally transmitted symbionts can
alter symbiont preference depending on conditions over space and time. In
order to determine whether the population structure of environmentally
transmitted beneficial associations reflects host specificity or
biogeography, we analyzed the genetic structure of Sepiola atlantica
(Cephalopoda: Sepiolidae) and their Vibrio symbionts (V. fischeri and V.
logei) in four Galician Rías (Spain). This geographical location is
characterized by a jagged coastline with a deep-sea entrance into the
land, ideal for testing whether such population barriers exist due to
genetic isolation. We used haplotype estimates combined with nested clade
analysis to determine the genetic relatedness for both S. atlantica and
Vibrio bacteria. Analyses of molecular variance (AMOVA) were used to
estimate variation within and between populations for both host and
symbiont genetic data. Our analyses reveal a low percentage of variation
among and between host populations, suggesting that these populations are
panmictic. In contrast, Vibrio symbiont populations show a certain degree
of genetic structure, demonstrating that the hydrology of the rias is
driving bacterial distribution (and not host specificity). Thus, for
environmentally transmitted symbioses such as the sepiolid squid-Vibrio
association, abiotic factors can be a major selective force for
determining the population structure of one of the partners.