To date, only one mitogenome from an Antarctic amphipod has been published. Here, novel complete mitochondrial genomes (mitogenomes) of two morphospecies are assembled, namely, Charcotia amundseni and Eusirus giganteus. For the latter species, we have assembled two mitogenomes from different genetic clades of this species. The lengths of Eusirus and Charcotia mitogenomes range from 15,534 to 15,619 base pairs and their mitogenomes are composed of 13 protein coding genes, 22 transfer RNAs, 2 ribosomal RNAs, and 1 putative control region CR. Some tRNAs display aberrant structures suggesting that minimalization is also ongoing in amphipod mitogenomes. The novel mitogenomes of the two Antarctic species have features distinguishing them from other amphipod mitogenomes such as a lower AT-richness in the whole mitogenomes and a negative GC- skew in both strands of protein coding genes. The genetically most variable mitochondrial regions of amphipods are nad6 and atp8, while cox1 shows low nucleotide diversity among closely and more distantly related species. In comparison to the pancrustacean mitochondrial ground pattern, E. giganteus shows a translocation of the nad1 gene, while cytb and nad6 genes are translocated in C. amundseni. Phylogenetic analysis based on mitogenomes illustrates that Eusirus and Charcotia cluster together with other species belonging to the same amphipod superfamilies. In the absence of reference nuclear genomes, mitogenomes can be useful to develop markers for studying population genetics or evolutionary relationships at higher taxonomic levels.
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We describe Malawidopsis gen. nov., a new genus of Cypridopsinae Kaufmann, 1900 from the African ancient Lake Malawi. The genus comprises at least 17 new species, which makes it a significant ostracod radiation in this lake, parallel to a similar (but independent) cypridopsine radiation in Lake Tanganyika. Three of these new species are here described: Malawidopsis stellae gen. et. sp. nov., the type species of the new genus; M. ruwaydae gen. et. sp. nov. and M. antoniae gen. et. sp. nov.. The other new species are briefly illustrated and described, but are left in open nomenclature (sp. A, B, C, etc.). Cypridopsis cunningtoni Sars, 1910 and Potamocypris fuelleborni Daday, 1910 are transferred to Malawidopsis gen. nov. and are identical to Malawidopsis spec. F and Malawidopsis spec. N, respectively. The new tribe Plesiocyprisopsini trib. nov. is erected, and comprises the cypridopsine genera previously in the Cypridopsini s.l. with the right valve overlapping the left valve, at least anteriorly. Potential drivers of speciation within this endemic clade in Lake Malawi are briefly discussed. Bathymetry might have been important, with most species being restricted to shallower depths and only four species also occurring at depths of 75 m or more, but very few specimens were retrieved from greater depths. Most species occurred on coarse sand, but this sediment category coincides with shallower stations. Overall, most species appear to have a wide geographical distribution in the lake, so no geographical parapatric speciation is apparent. The occurrence of all species in sexual populations and the significant differences in the male sexual organs and the valves suggest that sexual selection might have been the most important driver in the speciation process of this species flock, but this should be further explored. Following deep coring results in Lake Malawi, the present clade could be (at least) c one million years old.
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