Cytogenetic diversity of notothenioid fish from the Ross sea: historical overview and updates

Abstract

Cytogenetics provides a unique platform to study in situ structural, functional, and evolutionary aspects of the genome. As such it holds powerful promise in decoding mechanisms and processes of genome architectural changes and their role in organism’s diversification and evolution. Since the early 80s, such an approach has been applied to the study of the Antarctic notothenioid fishes. In almost three decades, the cytogenetic information has expanded to cover half of the known species inhabiting the high Antarctic waters. Although started 10 years later, cytogenetic studies of species from the Ross sea region have provided valuable contributions to this bulk of knowledge. Here, we synthesize the currently available cytogenetic information on Antarctic notothenioid fishes from the Ross Sea Region, inclusive of both conventional karyotyping and gene mapping. In addition, new karyotypic data on four species (Lepidonotothen squamifrons, Trematomus scotti, T. loennbergii, and T. lepidorhinus) are provided. In discussing these data, specific focus is made on the patterns and subtleties of cytogenetic diversity at inter- and intra-specific levels aiming at contributing to the refinement of the knowledge of fish diversity in a region, the Ross Sea area, whose primary ecological value is widely recognized

Multiple independent chromosomal fusions accompanied the radiation of the Antarctic teleost genus Trematomus (Notothenioidei:Nototheniidae)

“…Within the suborder Notothenioidei, the family Nototheniidae is both the most speciose [6,7,19,28] and the most prone to chromosomal rearrangements [24,57,61]. The specific hybridization of 22 of 40 randomly selected BACs from N. coriiceps to 18 representatives within the Nototheniidae suggests, as anticipated, strong sequence conservation within the family.…”

“…Their diversification involved several rounds of species radiation events [6,[14][15][16][17][18], which led to ecological, speciesspecific, and genetic differentiation [16,[19][20][21]. In some clades, chromosomal changes accompanied lineage diversification [22][23][24][25]. Because fixation of chromosomal change can lead to reproductive isolation [26,27], characterization of these chromosomal repatterning events is an important step toward reconstruction of the evolutionary history of the Antarctic teleosts [13,20,28].…”

“…The "proto-karyotype" of n = 24 acrocentrics has been hypothesized to be the plesiomorphic state for the notothenioid sub-order [50,51], because n = 24 is found in the families Bovichtidae [50,52], Pseudaphritidae, and Eleginopsidae [52,53], the latter being the closest taxon to the Nototheniidae. Many sub-families of the mostly Antarctic endemic family Nototheniidae have quite conserved karyotypes (Channichthyinae: n = 24 [22,54], Artedidraconinae: n = 23 [24,55,56]), whereas other sub-families display high variability in chromosome numbers. The most striking chromosomal diversity has been found within the genus Trematomus of the subfamily Trematominae [23,24,57], in which haploid chromosome numbers range from 29 to 12 [51,57].…”

“…Many sub-families of the mostly Antarctic endemic family Nototheniidae have quite conserved karyotypes (Channichthyinae: n = 24 [22,54], Artedidraconinae: n = 23 [24,55,56]), whereas other sub-families display high variability in chromosome numbers. The most striking chromosomal diversity has been found within the genus Trematomus of the subfamily Trematominae [23,24,57], in which haploid chromosome numbers range from 29 to 12 [51,57]. Besides, species in the genus Notothenia of the Nototheniinae, have also experienced massive chromosomal reductions in karyotypes (n = 11, 12 and 13) [22,24,25].…”

“…The most striking chromosomal diversity has been found within the genus Trematomus of the subfamily Trematominae [23,24,57], in which haploid chromosome numbers range from 29 to 12 [51,57]. Besides, species in the genus Notothenia of the Nototheniinae, have also experienced massive chromosomal reductions in karyotypes (n = 11, 12 and 13) [22,24,25].…”