Along-shelf connectivity and circumpolar gene flow in Antarctic silverfish (Pleuragramma antarctica)

The Antarctic silverfish (Pleuragramma antarctica) is a critically
important forage species with a circumpolar distribution and is unique
among other notothenioid species for its wholly pelagic life cycle.
Previous studies have provided mixed evidence of population structure over
regional and circumpolar scales. The aim of the present study was to test
the recent population hypothesis for Antarctic silverfish, which
emphasizes the interplay between life history and hydrography in shaping
connectivity. A total of 1067 individuals were collected over 25 years
from different locations on a circumpolar scale. Samples were genotyped at
fifteen microsatellites to assess population differentiation and genetic
structuring using clustering methods, F-statistics, and hierarchical
analysis of variance. A lack of differentiation was found between
locations connected by the Antarctic Slope Front Current (ASF), indicative
of high levels of gene flow. However, gene flow was significantly reduced
at the South Orkney Islands and the western Antarctic Peninsula where the
ASF is absent. This pattern of gene flow emphasized the relevance of
large-scale circulation as a mechanism for circumpolar connectivity.
Chaotic genetic patchiness characterized population structure over time,
with varying patterns of differentiation observed between years,
accompanied by heterogeneous standard length distributions. The present
study supports a more nuanced version of the genetic panmixia hypothesis
that reflects physical-biological interactions over the life history.