Ants is expected to occur faster than in nuclear DNA due

Ants is expected to occur faster than in nuclear DNA due to the smaller effective population size [66]. On the one hand, our results contrast with those found in some other marine benthic organisms, including pycnogonids [41], nudibranchs [23], Antarctic isopods [67] and amphipods [9] in which mitochondrial and nuclear data agree on the delimitation of unrecognized species. On the other hand, Hemery et al. [22] found results similar to ours in the Antarctic crinoid Promachocrinus kerguelensis, in which mitochondrial markers and ITS defined two major groups but further differentiation into seven mitochondrial clades was not supported by ITS data. However, in P. kerguelensis the COI divergence among clades was lower than in the C. megalonyx complex, and the lack of resolution with ITS may be due to a taxon-specific lower mutation rate in P. kerguelensis. Similar results also occur in species with significantly different life histories, such as the stonefly Dinocras cephalotes [68], in which two highly divergent COI lineages occur in sympatry but no differentiation was found with nuclear data. In many cases, coexistence of highly divergent mitochondrial lineages within a single species can be explained by introgressive hybridization with other species (e.g. [69]). However, in this study, all mitochondrial haplotypes found within the C. megalonyx complex clearly form a monophyletic group and no introgression from other colossendeid species was found.rsos.royalsocietypublishing.org R. Soc. open sci. 2:…………………………………………Environmental change may lead to the breakdown of ecological barriers between reproductively isolated groups and therefore to `speciation reversal’ [70]. Although this has been demonstrated mostly for anthropogenic change, glaciations may possibly have similar effects on Antarctic shelf fauna by restricting distributions of benthic organisms to small refugia. This would imply that previously isolated lineages collapsed into a Wuningmeisu C web hybrid swarm, which may have led to strong mitochondrial uclear discordance. The question arises why such a pattern is not present in other Antarctic species that have been investigated. Possibly, due to differences in environmental conditions between glacial refugia, selection would have led to different adaptations [23]. While in some cases these differences were sufficient for reproductive isolation, this was apparently not the case for the C. megalonyx radiation.rsos.royalsocietypublishing.org R. Soc. open sci. 2:…………………………………………4.4. Out of Antarctica hypothesisWe found that there is a monophyletic `Subantarctic’ grouping restricted to South America, nested within the Antarctic C. megalonyx complex. This pattern suggests that the Subantarctic was get PD168393 colonized from the Antarctic and not vice versa, as also found e.g. in cephalopods [71]. As the holotype of C. megalonyx is a specimen from the South American shelf [72], it can be expected to belong to the Subantarctic group, to which the species name should therefore be restricted. C. megalonyx would then lose its status as an Antarctic pycnogonid, as the species would be restricted to the Subantarctic and possibly to South America.4.5. Multiple in situ glacial refugiaIn addition to biogeographic and systematic questions, this study also provides important data to the debate on Antarctic glacial refugia [19], in particular on their putative localities. Our results provide no support for the hypot.Ants is expected to occur faster than in nuclear DNA due to the smaller effective population size [66]. On the one hand, our results contrast with those found in some other marine benthic organisms, including pycnogonids [41], nudibranchs [23], Antarctic isopods [67] and amphipods [9] in which mitochondrial and nuclear data agree on the delimitation of unrecognized species. On the other hand, Hemery et al. [22] found results similar to ours in the Antarctic crinoid Promachocrinus kerguelensis, in which mitochondrial markers and ITS defined two major groups but further differentiation into seven mitochondrial clades was not supported by ITS data. However, in P. kerguelensis the COI divergence among clades was lower than in the C. megalonyx complex, and the lack of resolution with ITS may be due to a taxon-specific lower mutation rate in P. kerguelensis. Similar results also occur in species with significantly different life histories, such as the stonefly Dinocras cephalotes [68], in which two highly divergent COI lineages occur in sympatry but no differentiation was found with nuclear data. In many cases, coexistence of highly divergent mitochondrial lineages within a single species can be explained by introgressive hybridization with other species (e.g. [69]). However, in this study, all mitochondrial haplotypes found within the C. megalonyx complex clearly form a monophyletic group and no introgression from other colossendeid species was found.rsos.royalsocietypublishing.org R. Soc. open sci. 2:…………………………………………Environmental change may lead to the breakdown of ecological barriers between reproductively isolated groups and therefore to `speciation reversal’ [70]. Although this has been demonstrated mostly for anthropogenic change, glaciations may possibly have similar effects on Antarctic shelf fauna by restricting distributions of benthic organisms to small refugia. This would imply that previously isolated lineages collapsed into a hybrid swarm, which may have led to strong mitochondrial uclear discordance. The question arises why such a pattern is not present in other Antarctic species that have been investigated. Possibly, due to differences in environmental conditions between glacial refugia, selection would have led to different adaptations [23]. While in some cases these differences were sufficient for reproductive isolation, this was apparently not the case for the C. megalonyx radiation.rsos.royalsocietypublishing.org R. Soc. open sci. 2:…………………………………………4.4. Out of Antarctica hypothesisWe found that there is a monophyletic `Subantarctic’ grouping restricted to South America, nested within the Antarctic C. megalonyx complex. This pattern suggests that the Subantarctic was colonized from the Antarctic and not vice versa, as also found e.g. in cephalopods [71]. As the holotype of C. megalonyx is a specimen from the South American shelf [72], it can be expected to belong to the Subantarctic group, to which the species name should therefore be restricted. C. megalonyx would then lose its status as an Antarctic pycnogonid, as the species would be restricted to the Subantarctic and possibly to South America.4.5. Multiple in situ glacial refugiaIn addition to biogeographic and systematic questions, this study also provides important data to the debate on Antarctic glacial refugia [19], in particular on their putative localities. Our results provide no support for the hypot.