Long-distance island hopping without dispersal stages: transportation across major zoogeographic barriers in a Southern Ocean isopod

Abstract

Species integrity is maintained only if recurrent allelic exchange between subpopulations occurs by means of migrating specimens. Predictions of this gene flow on the basis of observed or assumed mobility of marine species have proven to be error-prone. Using one mitochondrial gene and seven microsatellite markers, we studied the genetic structure and gene flow in Septemserolis septemcarinata, a strictly benthic species lacking pelagic larvae and the ability to swim. Suitable shallow-water habitats around three remote islands (South Georgia, Bouvet, and Marion Island) are geographically disjunct, isolated by more than 2,000 km of uninhabitable deep sea (east-west) and also separated by the Polar Front (north-south), which serves as a strong demarcation line in many marine taxa. Although we did find genetic differentiation among the three island populations, our results also revealed that a scenario with recent gene flow explains our data best. A model assuming no gene flow after initial colonization of the islands performs significantly worse. The tests also favor an asymmetric gene flow pattern (west to east ≫ east to west) thus mirroring the directionality of major oceanographic currents in the area. We conclude that rare longdistance dispersal rather than vicariance or human-mediated transport must be responsible for the observed patterns. As a mechanism, we propose passive rafting on floating substrata in the Antarctic Circumpolar Current. The results demonstrate that the effectiveness of a physical barrier is not solely a function of its physical parameters but strongly depends on how organisms interact with their environment.

Nuclear and Mitochondrial Gene Data Support Recent Radiation within the Sea Spider Species Complex Pallenopsis patagonica

“…Also, the radiation of the many Antarctic P. patagonica species very likely started in the late Pliocene and increased during the Pleistocene (last 2.5 myr). Such patterns have been reported before (e.g., Held, 2000;Page and Linse, 2002;Thornhill et al, 2008;Krabbe et al, 2010;Leese et al, 2010;Hemery et al, 2012;Dietz et al, 2015a,b) suggesting that over evolutionary time scales the Polar Front has not been an impermeable barrier to gene flow in general, though we did not observe across Drake Passage exchange in more recent clades of P. patagonica s.l. However, in view of the above-mentioned limitations of molecular clock calculations, we advise to use the divergence estimates made here with caution.…”

Phylogeny of the taxon Paralaophontodes Lang (Copepoda, Harpacticoida, Laophontodinae), including species descriptions, chorological remarks, and a key to species

“…This is demonstrated by a number of molecular studies that have simply confirmed morphological data (e.g. Westheide and Schmidt 2003, Leese et al 2010, Nikula et al 2010, Brix et al 2011, Gollner et al 2011, Kieneke et al 2012, Brix et al 2014, including species with wide geographic distributions. Jörger et al (2014) has in fact found that molecular approaches are not always able to address all uncertainties regarding species delineation.…”

Distributional Patterns of Polychaetes Across the West Antarctic Based on DNA Barcoding and Particle Tracking Analyses

“…A potential explanation for the maintenance of genetic connectivity in brooding species or those lacking pelagic larvae includes the passive rafting of larvae or adults on floating substrate or ocean debris (Waters, 2008). Leese et al (2010) suggested that this method maintained connected shallow water isolated populations of the isopod Septemserolis septemcarinata across the sub-Antarctic. Furthermore, direct evidence of rafting on kelp has been observed in the widespread sub-Antarctic brooding bivalve Gasimardia trapesina (Helmuth et al, 1994), the sea slug Onchidella marginata (Cumming et al, 2014) and two species of sub-Antarctic amphipods (Nikula et al, 2010).…”