Karyotype morphology in Hyperiella dilatata Stebbing 1888 (Amphipoda: Hyperiidae) from the Ross Sea (Antarctica)

Summary The chromosome complement and some karyological features were investigated in the pelagic amphipod Hyperiella dilatata Stebbing 1888 from the Ross Sea (Antarctica). The diploid karyotype consists of 48 metacentric and 10 submetacentric elements (2n = 58). The presence of secondary constrictions and supernumerary chromosomes is described. Available chromosome numbers of Hyperiidea exhibit a wide range of distribution, among which Hyperiella dilatata is the closest to the modal number of other amphipods.     

Cytogenetics of the bathydraconid fish Gymnodraco acuticeps (Perciformes, Notothenioidei) from Terra Nova Bay, Ross Sea

In the framework of the I.C.E.FISH (International Collaborative Effort on Antarctic Fish Adaptive Evolution) project, during the 1998-1999 season at the Italian shore-based Terra Nova Bay Station, the broad fields of adaptation and evolution of the fish suborder Notothenioidei were tackled through the integration of many disciplines. As a representative contribution of I.C.E.FISH, a cytogenetic study of the bathydraconid fish Gymnodraco acuticeps is reported. The Bathydraconidae is a heterogeneous notothenioid taxon whose intra-family relationships are very uncertain. The conventional karyotype and the location of nuclear ribosomal genes, by means of fluorescence in situ hybridisation, contributed to species-specific characterisation and provided the basis for comparative analyses. The karyotype of G. acuticeps consists of 48 chromosomes (2 metacentric, 2 submetacentric and 44 acrocentric); major ribosomal cistrons correspond to a large region in a single chromosome pair. Mapping of the available karyotypic data on a molecular phylogenetic tree provided information on chromosomal diversification during the cladogenesis of the bathydraconids.     

The chromosomal complement of the artedidraconid fish Histiodraco velifer (Perciformes: Notothenioidei) from Terra Nova Bay, Ross Sea

The karyotype of Histiodraco velifer from the Antartic Ocean was analyzed using various banding methods and in situ hybridization with a telomeric probe. A male and a female had a diploid set of 46 chromosomes (6 submetacentric + 40 acrocentric, FN = 52); the nucleolar organizer was CMA3-positive and was located on the short arm of a medium-sized submetacentric pair. All chromosomes stained uniformly with DAPI, whereas C-banding revealed heterochromatic blocks that were mostly located centromerically and telomerically and were resistant to ALUI digestion. The substantial identity of the karyotype of H. velifer with that of the other artedidraconids investigated so far suggests that chromosome changes must have played a less than significant role in the speciation among the lineages of this fish family endemic to Antarctica.     

Mental barbel and meristic variation in the Antarctic notothenioid fish Dolloidraco longedorsalis (Perciformes: Artedidraconidae) from the Ross Sea

A collection of 58 specimens of Dolloidraco longedorsalis from the southwestern Ross Sea was studied for intraspecific variation in the number of second dorsal and anal rays, number of vertebrae, and length and shape of the mental barbel - a key diagnostic and taxonomic character in this family. Ranges for meristics are compact and extend documented values to 13 for anal rays and 37 for vertebrae. There is a nearly twofold difference in the relative length of the mental barbel. There are no significant differences between the sexes in any meristic or morphometric feature. The terminal expansion of the barbel exhibits four types, documented with illustrations and histology: typical expanded form (43%), not expanded or tapered (33%), slightly expanded (22%), and large expansion (2%). There is no relationship between absolute and relative barbel length and sex or barbel type and sex. There is no relationship between barbel type and size of the specimen. Twenty-five percent of specimens have the epidermis of the terminal expansion arranged as broad ridges or mounds. The mental barbel of D. longedorsalis is therefore individually variable with no evidence of sexual dimorphism, and the type of barbel does not vary ontogenetically. Histological analysis of the barbel reveals that the terminal expansion consists of a thick epidermis and that dermal papillae are responsible for the pattern of surface projections sometimes present. The epidermis near the tip of the barbel is twofold thicker in specimens with a terminal expansion. The distal morphology of the barbel, whether straight or expanded, probably has little functional significance. The barbel is richly supplied with nerves and blood vessels and the core consists of pseudocartilage. The barbel is probably a somatosensory organ.     

Underwater video observation of the Antarctic toothfish Dissostichus mawsoni (Perciformes: Nototheniidae) in the Ross Sea, Antarctica

A towed benthic camera system captured images of a ca. 66-cm-long Antarctic toothfish partially under a boulder at 76°30'S, 174°59'E (depth 454 m) in the southern Ross Sea. This is noteworthy because, excluding McMurdo Sound, there are only two published records for this species in the Ross Sea and none in an offshore locality. Adult Dissostichus mawsoni are neutrally buoyant and live and feed in the lower reaches of the water column. Benthic perching is unexpected, suggesting that this subadult is not neutrally buoyant.     

The complete mitogenome of the snakehead Channa argus (Perciformes: Channoidei): genome characterization and phylogenetic implications

To better understand the phylogenetic status of the snakehead, Channa argus, we determined its complete mitogenome sequence using long-polymerase chain reaction and the direct sequencing method. The complete mitogenome sequence was 16,559?bp in length and contained 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and 1 control region (D-loop), the gene composition/order of which was identical to that observed in most other vertebrates. This was the first report of the mitogenome sequence in suborder Channoidei. Phylogenetic relationships of 14 perciform suborders based on mitogenome sequences were reconstructed using Bayesian inference and maximum likelihood methods. The results strongly supported the monophyly of Perciformes and the snakehead, as a representative species of suborder Channoidei, formed the most basal branch having sister relationship with the clade containing all other analyzed perciform fishes. The further phylogenetic analyses of six channid species, based on cytochrome b gene, suggested that two channid genera constituted reciprocally monophyletic clades. In addition, the relaxed molecular clock method was used to estimate divergence dates among major suborders of Perciformes and major species in Channoidei.     

Complete mitochondrial genome of Oxuderces dentatus (Perciformes, Gobioidei)

The complete mitochondrial genome (mitogenome) of Oxuderces dentatus was determined first. The genome was 17,116?bp in length and consisted of 13 protein-coding genes, 22 tRNA genes, 2 ribosomal RNA genes, and 2 main non-coding regions [the control region (CR) and the origin of the light strand replication], the gene composition and order of which was similar to most other vertebrates. The overall base composition of the heavy strand was T 27.9%, C 26.8%, A 30.2%, and G 15.1%, with a slight A+T bias of 58.1%. In addition to the discrete and conserved sequence blocks, unusual long tandem repeat unit (three 150-bp tandem repeat units and an incomplete copy of 146?bp) was also detected within CR. This mitogenome sequence data would play an important role in population genetics and phylogenetic analysis of the Gobioidei.     

Complete mitochondrial genome of Trypauchen vagina (Perciformes, Gobioidei)

The complete mitochondrial genome of Trypauchen vagina was determined first. The genome is 16,686 bp in length and consists of 13 protein-coding genes, 22 tRNA genes, 2 ribosomal RNA genes, and 2 main non-coding regions [the control region (CR) and the origin of the light strand replication], the gene composition and order of which was similar to most other vertebrates. The overall base composition of T. vagina is T 27.6%, C 27.6%, A 29.5%, and G 15.3%, with a slight A+T bias of 57.1%. In addition to the discrete and conserved sequence blocks, an incomplete tandem repeat unit is detected within the CR. This mitogenome sequence data would play an important role in population genetics and phylogenetic analysis of the Gobioidei.     

Karyotype and genome size variation in Ajuga L. (Ajugoideae–Lamiaceae)

Chromosome number changes and karyotype evolution play an important role in plant genome diversification and eventually in speciation. The genus Ajuga L. (Lamiaceae) has approximately 50 species distributed in temperate to subtropical regions. Four of these species are currently recognized in Korea (A. decumbens Thunb., A. multiflora Bunge, A. nipponensis Makino and A. spectabilis Nakai). Understanding the karyotype evolution in Ajuga has been hampered by the small size of their chromosomes and symmetrical karyotypes. Here we used classic Feulgen staining to establish chromosome numbers and construct karyotypes of the four species of Ajuga recognized in Korea and flow cytometry was used to study their variation in genome. The chromosome number of all investigated plants was 2n = 32. Still, the 2C DNA content ranged from 2.18 pg (A. decumbens) to 4.53 pg (A. multiflora). While the chromosome numbers were the same for all investigated species, the genome size variation could potentially be used as a taxonomic marker.     

Karyotype and genome size of Iberochondrostoma almacai (Teleostei, Cyprinidae) and comparison with the sister-species I.lusitanicum

This study aimed to define the karyotype of the recently described Iberian endemic Iberochondrostoma almacai, to revisit the previously documented chromosome polymorphisms of its sister species I.lusitanicum using C-, Ag-/CMA(3) and RE-banding, and to compare the two species genome sizes. A 2n = 50 karyotype (with the exception of a triploid I.lusitanicum specimen) and a corresponding haploid chromosome formula of 7M:15SM:3A (FN = 94) were found. Multiple NORs were observed in both species (in two submetacentric chromosome pairs, one of them clearly homologous) and a higher intra and interpopulational variability was evidenced in I.lusitanicum. Flow cytometry measurements of nuclear DNA content showed some significant differences in genome size both between and within species: the genome of I. almacai was smaller than that of I.lusitanicum (mean values 2.61 and 2.93 pg, respectively), which presented a clear interpopulational variability (mean values ranging from 2.72 to 3.00 pg). These data allowed the distinction of both taxa and confirmed the existence of two well differentiated groups within I. lusitanicum: one that includes the populations from the right bank of the Tejo and Samarra drainages, and another that reunites the southern populations. The peculiar differences between the two species, presently listed as "Critically Endangered", reinforced the importance of this study for future conservation plans.     

Aplanochytrium stocchinoi: a new Labyrinthulomycota from the southern ocean (Ross Sea, Antarctica)

Aplanochytrium stocchinoi, a new species of Labyrinthulomycota, is described from samples collected in Antarctica. Ultrastructural, life cycle and molecular data characterizing the new taxon are provided and compared with the features of other species included in the genus Aplanochytrium. The phylogenetic position of A. stocchinoi is investigated using the 18S rDNA as molecular marker and applying maximum parsimony, minimum evolution and maximum likelihood methods.     

Complete mitochondrial genome of three Branchiostegus (Perciformes, Malacanthidae) species: genome description and phylogenetic considerations

We cloned and sequenced the complete mitochondrial DNA (mtDNA) of three tilefishes (Branchiostegus albus, Branchiostegus argentatus, and Branchiostegus japonicus) to characterize and compare their mitochondrial genomes (mitogenomes). The mitogenomes of B. albus, B. argentatus, and B. japonicus were 16,532, 16,550, and 16,541 bp long, respectively, and all consisted of 37 genes (13 protein-coding genes, 2 ribosomal RNA, and 22 transfer RNA (tRNAs)), which are typical for vertebrate mtDNA. As in other bony fishes, most genes were encoded on the H-strand, except for the nad6 and eight tRNA genes that were encoded on the L-strand. Among the 13 protein-coding genes of all three tilefishes, 2 reading-frame overlaps were found on the same strand: atp8 and atp6 overlapped by 10 nucleotides, and nad4L and nad4 overlapped by 7 nucleotides. The identity of the nad4 gene between B. albus and B. argentatus was the lowest at 87%. Conversely, the identity of the nad6 gene between B. albus and B. japonicus was the highest at 99%. Most tRNA genes were similar in length among the three species, while the tRNA-Ser((AGY)) of B. japonicus was 9 bp longer than those of B. albus and B. argentatus. The control region of the mitogenome spanned 853, 862, and 856 bp in B. albus, B. argentatus, and B. japonicus, respectively. A maximum likelihood tree constructed using 11,035 sites contained five independent groups with bootstrap values of 100% in support of their divergence. All three tilefishes examined were clustered with the Pomacanthidae species in Group II.     

Sea urchins, sea stars and brittle stars from Terra Nova Bay (Ross Sea, Antarctica)

Although echinoderms constitute some of the most conspicuous taxa of the Antarctic benthic communities, the echinoderm fauna of Terra Nova has not been described yet. The present study provides the first species list of echinoids, ophiuroids and asteroids from Terra Nova Bay (30–500 m depth) and describes the depth distribution of these species. Preliminary observations of the summer reproductive condition of some of the species are also included.     

Karyotype and morphology of larvae of Chironomus (Chironomidae, Diptera) from the Caspian Sea

Karyotype and morphology of Chironomus sp. larvae from the Caspian Sea have been described. 2n = 8. Chromosomal arm combination is AB, CD, EF, G (cytocomplex thummi). All chromosomes display conjugation of homologues. Centromere areas are of s-type. The nucleolar organizer and two Balbiani rings are disposed in arm C, and another Balbiani ring is in arm B. Half larvae have heterozygotic paracentric inversions in arm D. The larva belongs to salinarius form. One scleritis is colorless, an occipital scleritis is light and irregularly colored. Premandible has 4-5 cogs. Epipharingeal ridge has 18-23 dens. This new species is close to salinarius group, especially to Ch. albidus Konst., but differs from it at the larva stage in the structure of non-massive basal antenna segment, in the presence of large quantity of premandible denses, in light color of occipital scleritis, and in a series of morphometric rates. A similarity berween Ch. paraalbidus and Ch. albidus, on the one hand, and Boeotendipes, on the other one, has been found out.     

Karyotype constancy and genome size variation in BulgarianCrepis foetida s. l. (Asteraceae)

Ten populations ofCrepis foetida from Bulgaria belonging to the three subspeciesfoetida, rhoeadifolia, andcommutata were analyzed karyologically using haematoxylin staining, Giemsa C-banding, fluorochrome banding, Ag-NOR staining, Feulgen cytophotometry (scanning densitometry and video-based image analysis), and propidium iodide flow cytometry. The quantitatively-evaluated karyotype structure was similar among all populations, with minor variation in a few intercalary sites only and in the amount of NOR-associated heterochromatin (satellites). In contrast to the karyotypic constancy the genome size ofC. foetida subsp.commutata was about 10% lower than those of the other two subspecies, which had similar genome sizes. The genome size measurements using three different methods resulted in highly correlated data. The genome size difference adds some weight to previous taxonomic opinions treatingC. foetida subsp.commutata at species level, asC. commutata. Prof. Dr. Stefan Kozhuharov (4 January 1933–24 August 1997).