Species distribution, hybridization and connectivity in the genus Chionodraco: unveiling unknown icefish diversity in Antarctica

Aim The species of the genus Chionodraco (Notothenioidei) are the most
abundant icefish on the continental shelf of the Weddell Sea. While
previous studies indicated that only Chionodraco hamatus and Chionodraco
myersi inhabit the Weddell Sea, the third Chionodraco species, Chionodraco
rastrospinosus, was recently sampled in the area. Since C. rastrospinosus
is supposed to be found only at the Antarctic Peninsula and Scotia Arc,
this study aimed at confirming the species classification of C.
rastrospinosus by molecular methods and identifying its putative source
population. Given the documented evidence of introgression among the three
species, we tested whether the newly found C. rastrospinosus shared any
genetic variability with the other Chionodraco species. To explain the
pattern of distribution of the Chionodraco species, we aimed at estimating
the hydrodynamic connectivity between the Antarctic Peninsula and the
Weddell Sea. Location Antarctic Peninsula, southern Scotia Arc and the
south-eastern Weddell Sea Methods We genotyped 19 microsatellites and
sequenced the mitochondrial D-loop for 560 Chionodraco individuals. We
simulated the dispersal of more than 3 million drifters (Lagrangian
model). Results The molecular analyses support the presence of C.
rastrospinosus in the Weddell Sea and its homogeneity with C.
rastrospinosus from the Antarctic Peninsula. Bayesian clustering
identifies three putative hybrids among C. rastrospinosus and the other
congenerics. Lagrangian simulations do not support connectivity driven by
the oceanographic features of the Antarctic Peninsula and Weddell Sea via
passive larval dispersal only. Main conclusions This study documents, for
the first time, the presence of C. rastrospinosus in the Weddell Sea
unveiling more biodiversity than previously known in this region. The
sympatry of the three Chionodraco species explains the occurrence of
occasional, ongoing events of hybridization in the genus. Alternative
possible hypotheses need to be tested in future studies about the
mechanisms maintaining the interspecific connectivity in Chionodraco spp.