Calanus InDel genotypes from: No evidence for hybridization between Calanus finmarchicus and C. glacialis in a subarctic area of sympatry

In the North Atlantic and the Arctic Ocean, four species of the copepod
genus Calanus dominate the zooplankton biomass. Because
of their morphological resemblance, knowledge of their respective
distribution range has long been biased by misidentification, until the
recent use of molecular tools uncovered numerous areas of sympatry. As
hybridization between Calanus
finmarchicus and C. glacialis has been claimed
in the East-Canadian Arctic based on microsatellites, we investigated
further the potential for interbreeding in newly uncovered areas of
sympatry. Calanusspecies and stage composition were analyzed
during winter in two Norwegian subarctic fjords, using molecular markers
developed specifically for species identification and hybrid detection
between C. finmarchicus and C. glacialis.
Overall, Calanus glacialis were the most abundant
throughout the winter, followed by C.
finmarchicus and C. hyperboreus with only a few
records of C. helgolandicus. The presence
of C. glacialis, C. hyperboreus and C.
finmarchicus’ nauplii was recorded, indicating that these species
reproduce locally. In January and February, the simultaneous occurrence of
males and females of both C.
finmarchicus and C. glacialis suggested a
potential for inter-species mating. However, genetic admixture tests
performed on all 1126 individuals revealed no signal of hybridization,
implying a strong reproductive isolation mechanism. We conclude that no
evidence supports a potential for hybridization between C.
finmarchicus and C. glacialis and suggest that
the initial claim of hybridization
between Calanus species may have resulted from the use
of non-appropriate molecular tools.