On the Taxonomic Status of the Red Icefish Channichthys rugosus (Notothenioidei: Channichthyidae) from the Kerguelen Islands (South Ocean)

The presented work is the final part of the taxonomic revision of the Antarctic icefishes of the genus Channichthys Richardson, 1844 (Notothenioidei: Channichthyidae) from the Kerguelen Islands, the species composition of which was discussed until recently. Based on the morphological study of all available specimens from the ZIN and BMNH collections (including the holotype), a comprehensive redescription of the Red icefish Channichthys rugosus Regan, 1913 from the waters of the Kerguelen islands (South Ocean) was carried out, including external morphology, seismosensory system, gill apparatus, and axial skeleton. As a result, new diagnostic features of Red icefish were discovered and previously known ones were clarified, which made it possible to confirm the species validity. Comparison with other valid species icefishes was done. Channichthys rugosus differs from Ch. rhinoceratus Richardson, 1844 by a high anterior dorsal fin, the fin membrane of which reaches the apexes of its longest rays (does not reach in Ch. rhinoceratus), as well as a narrow and concave interorbital space (compared to the wider and flat one), by stronger granulation and a uniform reddish body color (dark spotted-marble in Ch. rhinoceratus). Channichthys rugosus differs from Ch. velifer Meissner, 1972 by the number of rays in the first dorsal fin (7–9 versus 9–12) and pectoral fin (18–20 versus 20–21), the presence of bone plaques in the proximal part of the medial lateral line (absent in Ch. velifer), and monochromatic reddish body coloration (spotted in Ch. velifer). Channichthys rugosus differs from Ch. panticapaei Shandikov, 1995 by the presence of only 1 row of gill rakers on the first gill arch (2 rows in Ch. panticapaei) and by light coloration (brownish-black in Ch. panticapaei).

From Settlers to Subspecies: Genetic Differentiation in Commerson’s Dolphins Between South America and the Kerguelen Islands

Commerson’s dolphins (Cephalorhynchus commersonii) are separated into the subspecies C. c. commersonii, found along southern South America (SA) and the Falkland Islands/Islas Malvinas (FI/IM), and C. c. kerguelenensis, restricted to the subantarctic Kerguelen Islands (KI). Following the dispersal model proposed for the genus, the latter is thought to have originated from SA after a long-distance dispersal event. To evaluate this biogeographic scenario, a distribution-wide, balanced sampling of mitochondrial DNA (mtDNA) control region sequences was designed. New tissue samples from southern Chile, Argentina, FI/IM, and KI were added to published sequences from SA and KI, for a total of 256 samples. Genetic diversity indices, genetic and phylogeographic structure, and migration rates were calculated. One haplotype was shared between subspecies, with which all haplotypes of C. c. kerguelenensis formed a distinct group in the haplotype network. A new haplotype for C. c. kerguelenensis is reported. Differentiation in haplotype frequencies was found among localities within the distribution of C. c. commersonii, yet the phylogeographic signal was only statistically significant between subspecies. Coalescent-based historical gene flow estimations indicated migration between the northern and southern portions of the species’ range in SA as well as between SA and the FI/IM, but not between these and the KI. The net nucleotide divergence between dolphins from SA and the FI/IM was lower than the recommended threshold value suggested for delimiting subspecies, unlike that found between C. c. commersonii and C. c. kerguelenensis. The results are consistent with the model of post-glacial colonization of KI by South American C. commersonii, followed by an ongoing divergence process and subspecies status. Thus, C. c. kerguelenensis may represent the most recent diversification step of Cephalorhynchus, where isolation from their source population is driving a process of incipient speciation.

Molecular Ecology and Systematics of Blue Mussels (Genus Mytilus) (Mytilidae; Bivalvia; Mollusca) in the Southern Hemisphere

<p>The Mytilus edulis species complex, comprised of M. edulis, M. galloprovincialis and M. trossulus, is antitropically distributed in temperate coastal regions of all oceans and main seas of the world. This genus has been heavily studied in the Northern hemisphere but Southern hemisphere populations have received much less attention. This thesis aims to place Southern hemisphere blue mussels into global evolutionary relationships among Mytilus species and investigate aspects of their molecular ecology, including, effects of non-native Northern hemisphere species introductions, biogeography across the Southern hemisphere, regional phylogeographic patterns and population genetics within New Zealand. Southern hemisphere blue mussel phylogenetic reconstruction resulted in the detection of a monophyletic M. galloprovincialis lineage. Two new molecular markers developed with specificity for this lineage and congruence among phylogenetic investigations indicates a panhemispheric distribution of this M. galloprovincialis lineage with implications for naming a new sibling species of the M. edulis complex. This proposed new species, M. meridianus, is distributed in South America, the Kerguelen Islands, New Zealand and Australia at latitudes between ~ 30°S and ~ 55°S. Non-native M. galloprovincialis introduced from the Northern hemisphere have been present in NZ, Australia and Chile for at least ten years and hybridise with native blue mussels. Introgression is observed in New Zealand and Australian but not Chilean hybrid regions. The limited number of introduced mussels in Australia induces hybrid swamping of non-native alleles but an interlineage gender bias towards non-native maternal parents may result in eventual loss of the unique genomic content of native blue mussels in NZ. Southern hemisphere blue mussels form a monophyletic sister clade to a haplogroup shared by Northern hemisphere M. edulis and M. galloprovincialis. Although single gene histories are not congruent with respect to evolutionary relationships within the Northern hemisphere due to introgressive hybridisation after speciation, it is clear that Southern hemisphere blue mussels arose from a species native to the northeast Atlantic Ocean after speciation of the three ‘M. edulis complex’ members. Within the Southern hemisphere monophyletic clade lies three reciprocally monophyletic clades restricted to the geographic regions South America/Kerguelen Islands, New Zealand and Australia. Phylogeographic analysis indicates past gene flow between South American/Kerguelen Islands and New Zealand populations that has ceased at present day and ongoing gene flow between South America and the Kerguelen Islands likely via the West Wind Drift. Within NZ, population subdivision inferred from mtDNA indicates genetic variation is distributed within an east-west phylogeographic split on the North Island. These populations experienced gene flow in the past that has ceased at present day. Microsatellite allele frequencies indicate a different population subdivision within the northwest North Island that has been narrowed down to a 15 km stretch of coastline in a sheltered bay. The abrupt discontinuity within a small geographic area does not conform to classic population subdivision in this broad-cast spawning species, therefore, further investigation into the genomic content of northwest North Island mussels with respect to introgressed non-native genes is warranted. Resolving complex phylogenetic patterns from interspecific introgression is key to understanding the evolutionary history of Southern hemisphere M. galloprovincialis. Further characterisation of hybrid introgression would increase accuracy of (1) inferences of processes contributing to hybridisation dynamics and (2) population subdivision in NZ. Probing the basis for variation of hybridisation dynamics would help to predict the outcomes of Northern hemisphere M. galloprovincialis introductions in other areas of the world.</p>

Molecular Ecology and Systematics of Blue Mussels (Genus Mytilus) (Mytilidae; Bivalvia; Mollusca) in the Southern Hemisphere

<p>The Mytilus edulis species complex, comprised of M. edulis, M. galloprovincialis and M. trossulus, is antitropically distributed in temperate coastal regions of all oceans and main seas of the world. This genus has been heavily studied in the Northern hemisphere but Southern hemisphere populations have received much less attention. This thesis aims to place Southern hemisphere blue mussels into global evolutionary relationships among Mytilus species and investigate aspects of their molecular ecology, including, effects of non-native Northern hemisphere species introductions, biogeography across the Southern hemisphere, regional phylogeographic patterns and population genetics within New Zealand. Southern hemisphere blue mussel phylogenetic reconstruction resulted in the detection of a monophyletic M. galloprovincialis lineage. Two new molecular markers developed with specificity for this lineage and congruence among phylogenetic investigations indicates a panhemispheric distribution of this M. galloprovincialis lineage with implications for naming a new sibling species of the M. edulis complex. This proposed new species, M. meridianus, is distributed in South America, the Kerguelen Islands, New Zealand and Australia at latitudes between ~ 30°S and ~ 55°S. Non-native M. galloprovincialis introduced from the Northern hemisphere have been present in NZ, Australia and Chile for at least ten years and hybridise with native blue mussels. Introgression is observed in New Zealand and Australian but not Chilean hybrid regions. The limited number of introduced mussels in Australia induces hybrid swamping of non-native alleles but an interlineage gender bias towards non-native maternal parents may result in eventual loss of the unique genomic content of native blue mussels in NZ. Southern hemisphere blue mussels form a monophyletic sister clade to a haplogroup shared by Northern hemisphere M. edulis and M. galloprovincialis. Although single gene histories are not congruent with respect to evolutionary relationships within the Northern hemisphere due to introgressive hybridisation after speciation, it is clear that Southern hemisphere blue mussels arose from a species native to the northeast Atlantic Ocean after speciation of the three ‘M. edulis complex’ members. Within the Southern hemisphere monophyletic clade lies three reciprocally monophyletic clades restricted to the geographic regions South America/Kerguelen Islands, New Zealand and Australia. Phylogeographic analysis indicates past gene flow between South American/Kerguelen Islands and New Zealand populations that has ceased at present day and ongoing gene flow between South America and the Kerguelen Islands likely via the West Wind Drift. Within NZ, population subdivision inferred from mtDNA indicates genetic variation is distributed within an east-west phylogeographic split on the North Island. These populations experienced gene flow in the past that has ceased at present day. Microsatellite allele frequencies indicate a different population subdivision within the northwest North Island that has been narrowed down to a 15 km stretch of coastline in a sheltered bay. The abrupt discontinuity within a small geographic area does not conform to classic population subdivision in this broad-cast spawning species, therefore, further investigation into the genomic content of northwest North Island mussels with respect to introgressed non-native genes is warranted. Resolving complex phylogenetic patterns from interspecific introgression is key to understanding the evolutionary history of Southern hemisphere M. galloprovincialis. Further characterisation of hybrid introgression would increase accuracy of (1) inferences of processes contributing to hybridisation dynamics and (2) population subdivision in NZ. Probing the basis for variation of hybridisation dynamics would help to predict the outcomes of Northern hemisphere M. galloprovincialis introductions in other areas of the world.</p>