Cytogenetic analysis of Oedalechilus labeo (Pisces: Mugilidae), with a report of NOR variability

 A cytogenetic analysis by several staining techniques was carried out on Oedalechilus labeo specimens from the west coast of Italy, in order to extend the karyological knowledge on Mediterranean mullets. The karyotype of the species is composed of 46 acrocentric and 2 subtelocentric chromosomes. Constitutive heterochromatin was found to be restricted to the centromeres. Fluorochrome staining revealed a uniform base composition along the chromosome arms. Nucleolus organizer regions (NORs) are located on the short arms of chromosome pair 9 and can be either homomorphic or quite heteromorphic in size. In some specimens chromomycin A₃-staining and fluorescence in situ hybridization with 18S rDNA revealed a third additional and inactive NOR on the short arms of a medium-sized chromosome. This is the first report of NOR variability in Mugilidae, a family generally characterized by a quite conservative karyotype. Heterochromatin composition and NOR location differentiate O. labeo from a cytotaxonomical point of view from the Liza species studied, Liza being considered the genus from which the genus Oedalechilus derived. Received: 10 April 1999 / Accepted: 21 October 1999     

Fecundity and reproductive effort in Ophryotrocha labronica (Polychaeta: Dorvilleidae)

Reproductive effort in terms of fecundity and energy allocation was studied in Ophryotrocha labronica La Greca and Bacci, 1962 a small, semicontinuous iteroparous species. In O. labronica fecundity is more or less constant throughout life, and the total fecundity of the 64 couples examined in this experiment only declined by 12% from the first to the last spawning. No linear relationship was found between fecundity and body size.␣The energy content of germinal and somatic tissues was determined by differential scanning calorimeter. The␣reproductive effort and a reproductive index based on the fifth spawning were evaluated to compare the␣patterns of energy allocation of a semicontinuous iteroparous species with semelparous and annual iteroparous species. The reproductive index ranged from 0.20 to 0.77, with an average of 0.480. The average reproductive effort was 0.840, ranging from 0.60 to 0.96. These figures highlight the enormous amount of energy that O. labronica allocates to reproductive tissues. Received: 23 July 1997 / Accepted: 20 October 1998     

Replication,C and Ag-NOR chromosome-banding in two anguilliform fish species

The chromosomes of the Conger conger and Echelus myrus (Anguilliformes: Teleostei), were analysed by conventional (C and Ag-NOR) and by replication-banding techniques. Both species had a diploid number of 38 and one chromosome pair with C-positive nucleolar organizer regions (NOR). These cytogenetic traits are mainly consistent with those recorded for anguilliform species in general. The replication-banding pattern allowed us to identify individual chromosome pairs, to detect different classes of chromatin, and to suggest chromosome evolutive mechanisms in these two species. The results confirm the superiority of replication patterns in resolving longitudinal differentiation of fish chromosomes, that is not generally possible from structural bands.     

Evolution and systematics in Haliotidae (Mollusca: Gastropoda): inferences from DNA sequences of sperm lysin

Abalone taxonomy and systematics have remained unresolved: neither stable species-level nomenclature nor a cladistic hypothesis of relationships among species have been established. To infer the phylogeny of the genus Haliotis and to identify species using molecular data, we compared complementary DNA (cDNA) sequences of sperm lysin from 27 species-group taxa from California, Japan, Australia, New Zealand, Taiwan, Borneo, Madagascar, South Africa, Greece, France, Italy and the Azores. The lysin cDNA sequences reveal that 22 of the 27 taxa are clearly distinguishable by >20 nucleotide differences. Of the remaining 5, H. coccinea from the Azores may be a subspecies of H. tuberculata, if not a sibling species (10 nucleotide differences). The other four taxa are most probably the same species as one of the 22 taxa: the lysin sequences are almost identical between H. madaka and H. discus hannai, H. conicopora and H. rubra, H. diversicolor supertexta and H. diversicolor aquatilis, and H. tuberculata lamellosa and H. tuberculata tuberculata. The phylogeny of lysin cDNA suggests that there are three groups among the 27 species-group taxa: (1) all California species and 3 Japanese species (H. gigantea, H. discus hannai, and H. madaka): (2) 1 New Zealand species (H. iris); (3) 1 Japanese species (H. diversicolor aquatilis), Indo-West Pacific species and European species. These groups can be assigned to three previously recognized subgenera (Nordotis, Paua and Padollus) in the genus Haliotis. Two historical hypotheses are proposed to explain the biogeography and evolution within these abalone: (1) Tethyan distribution of the ancestral abalone, during the Cretaceous, followed by extinction in most of the habitat, but radiation in California and Southeast Asia which later spread to the other areas; (2) North Pacific rim distribution of the ancestral abalone, followed by dispersal to the other areas during the Paleogene.     

Karyotype differentiation between two species of carangid fishes,genusTrachurus (Perciformes: Carangidae)

A karyological study ofTrachurus trachurus andT. mediterraneus (Perciformes: Carangidae) was conducted by standard, fluorochrome staining (CMA₃, mithramycin, quinacrine mustard, DAPI), C-, Ag-NOR, and Alu-I banding methods. The karyotypes of both species consisted of 2n = 48 chromosomes, but of different FN:T. trachurus possessed a chromosome complement of 2 metacentric and 46 acrocentric elements, fundamental number (FN) = 50 andT. mediterraneus, a chromosome complement of 4 metacentric, 4 submetacentric, 14 subtelocentric and 26 acrocentric chromosomes, FN = 70. In neither of the two taxa investigated were heteromorphic sex chromosomes observed. The nucleolar organizer region was interstitially located on the long arm of the Ist pair of chromosomes in both species, intermediate inT. mediterraneus and subterminal inT. trachurus. Constitutive heterochromatin was found in nearly all centromeric and telomeric regions inT. trachurus; inT. mediterraneus it formed less intense telomeric and centromeric bands and thin interstitial bands on eight chromosome pairs. In addition, the C-positive material reacted differently to the digestion with endonuclease Alu-l in the two species. The results are discussed and compared with karyological data known for other species of Carangidae.     

Karyotype, nucleolus organiser regions and constitutive heterochromatin in Ostrea angasi (Molluscae: Bivalvia): evidence of taxonomic relationships within the Ostreidae

Chromosome preparations from gill tissue of the Australian flat oyster Ostrea angasi Sowerby were studied with conventional Giemsa staining, C-banding and silver staining techniques. A diploid complement of 2n = 20 was observed, consisting of five metacentric, three submetacentric and two subtelocentric pairs. Constitutive heterochromatin was distributed as large centromeric blocks in Chromosome Pairs 3, 6, 8, 9 and 10. The nucleolus organizer regions (NORs) were located terminally on long arms of Chromosome Pairs 9 and 10. This allowed the identification of homologous chromosomes in submetacentric and subtelocentric pairs. Intraspecific variability in NOR pattern as revealed by differences in the number of silver-stained NORs (Ag-NORs) per cell was found to be very common. Comparison of the patterns of karyotype, C-band and Ag-NORs between species of the larviparous oysters for which data have been published demonstrate that the chromosomal structure of the endemic Australian and New Zealand species O. angasi shows little similarity to the Southern Hemisphere oysters O. (Eostrea)puelchana Orbigny and Tiostrea chilensis (Philippi) and the Indo-West Pacific oyster O. denselamellosa, but very high resemblance to the European species O. edulis. Received: 12 August 1996 / Accepted: 16 September 1996     

Jugendstadien von Desmoscolex-Arten (Nematoda,Desmoscolecidae) und deren Bedeutung für die Taxonomie

A moulting specimen of Desmoscolex balticus sp.n. indicates that all species of the genera Eudesmoscolex, Eutricoma, and Prodesmoscolex are, in reality, juvenile stages of species of the genus Desmoscolex.     

Molecular phylogeny and evolution of the pelagic copepod genus Neocalanus (Crustacea: Copepoda)

Portions of the mitochondrial genome (ca. 4 kb), encoding three protein-coding (COI, ND4L, ND6) and two ribosomal RNA (srRNA, lrRNA) genes, were sequenced for all six currently recognized species, plus one form, of the pelagic calanoid copepod genus Neocalanus. In Neocalanus gracilis, the ND6 gene was not found in the sequenced portion of the mitochondrial genome. Unambiguously aligned sequences were subjected to Bayesian, maximum-likelihood, maximum-parsimony, and neighbor-joining analyses using Eucalanus bungii as an outgroup. The resultant tree topologies from these four methods were congruent, robust, and all nodes were supported by high bootstrap values and posterior probabilities of 92–100%. Two tropical and subtropical species (N. gracilis and N. robustior) occupied the most basal position, and a subantarctic (N. tonsus) and three subarctic Pacific species (N. cristatus, N. plumchrus, and N. flemingeri) diverged subsequently. Transequatorial dispersal of the ancestral population during glaciations is suggested for this pattern of speciation, in which sister clades exhibited antitropical distributions. Although the area of ocean is much broader in the subantarctic than the subarctic Pacific, a higher number of species occur in the subarctic Pacific (three) than the subantarctic (one). The possibility that marginal seas, such as Japan Sea and Okhotsk Sea, function as natal areas for the divergence of species is discussed.     

Three party symbiosis: acoelomorph worms,corals and unicellular algal symbionts in Eilat (Red Sea)

Epizoic worms were found to occur on certain coral colonies from reefs off the coast of Eilat (Red Sea). We identified 14 coral species infested by acoelomorph worms at a depth range of 2–50 m. The host corals were all zooxanthellate and included both massive and branching stony corals and a soft coral. Worms from all hosts were identified as belonging to the genus Waminoa and contained two distinct algal symbionts differing in size. The smaller one was identified as Symbiodinium sp. and the larger one is presumed to belong to the genus Amphidinium. Worm-infested colonies of the soft coral, Stereonephthya cundabiluensis, lacked a mucus layer and exhibited distinct cell microvilli, a phenotype not present in colonies lacking Waminoa sp. In most cases, both cnidarian and Acoelomorph hosts displayed high specificity for genetically distinctive Symbiodinium spp. These observations show that the epizoic worms do not acquire their symbionts from the “host” coral.     

Reproduction and larval development in three scalpellid barnacles, Scalpellum scalpellum (Linnaeus 1767), Ornatoscalpellum stroemii (M. Sars 1859) and Arcoscalpellum michelottianum (Seguenza 1876), Crustacea: Cirripedia: Thoracica): implications for reproduction and dispersal in the deep sea

We studied reproduction and larval development in three species of pedunculated barnacles with different depth distribution, that is, Scalpellum scalpellum (30–200 m), Ornatoscalpellum stroemii (100–1,600 m) and Arcoscalpellum michelottianum (64–5,190 m). Morphology, position and number of males in the female/hermaphrodite, type of larval development and the number and size of eggs were recorded. All three species have a pair of pocket-like receptacles, each of which can host only a single male in O. stroemii, up to five males in S. scalpellum and up to 12 males in A. michelottianum. Eggs and larvae were smallest in S. scalpellum, intermediately sized in O. stroemii and largest in A. michelottianum. Brood size was comparable for S. scalpellum and O. stroemii, but five times higher in A. michelottianum. The ratio for body/egg size is almost similar in S. scalpellum and A. michelottianum, but much smaller in O. stroemii. Both S. scalpellum and A. michelottianum have nauplii that spend upwards of 10 days in the plankton while the larvae of O. stroemii hatch as cyprids that settle soon after release. All these reproductive data indicate that O. stroemii invests considerably more in each propagule than the other two species. We hypothesize that the observed differences in reproductive system and mode of development in the three species represent adaptations to their different habitats. S. scalpellum are mainly transported by currents in the coastal sublittoral zone. O. stroemii is presumably spread by intermediate deep currents along the shelf and shelf-slope, while A. michelottianum occurs on seamounts and is probably transported by demersal currents over wide areas of inhospitable soft-bottoms. Our observations are in accordance with the general pattern that, egg-size and propagule-size are positively correlated to bathymetric and geographic distribution, and that the continental slope environment represents a high disturbance environment, where a short larval stage is an advantage.     

Karyotype analysis of the sea urchinParacentrotus lividus (Echinodermata): evidence for a heteromorphic chromosome sex mechanism

A consistent diploid number of 2n = 36 was determined for the sea urchinParacentrotus lividus from the Gulf of Palermo by analysis of mitotic chromosomes of both early developing embryos and male gonads. The haploid numbern = 18 was determined by counts of spermatocyte bivalents at diakinesis. A heteromorphic chromosome sex mechanism of the XY type is likely present in this species. This is indicated by the occurrence of a chromosomal pair, pair No. 2, which is heteromorphic in both morphology and size in about 50% of the mitotic figures (metaphases and anaphases) of einbryos. In addition, heteromorphism of the same pair of chromosomes occurred during spermatogonial metaphases in the five male specimens investigated here. The detection of a low chromosome number (2n = 36) compared to other echinoids (2n = 42 to 44), a heteromorphic chromosome sex system and the involvement of three chromosome pairs in nucleolar organization (NORs) provide evidence of the specialization of theP. lividus karyotype.     

The systematic position of some boring sponges (Demospongiae,Hadromerida) studied by molecular analysis

A phylogenetic analysis of some bioeroding sponges of the family Clionaidae (Order Hadromerida) was performed to resolve some taxonomic problems both at the specific and the supraspecific level using the D2 and D3 regions of 28S rDNA. Species belonging to the genera Cliona, Cliothosa, Spheciospongia (fam. Clionaidae) and Diplastrella (fam. Spirastrellidae) from the Mediterranean Sea and Celebes Sea (Indonesia) were analysed. In the phylogenetic tree, the species clustered on two main branches, one comprising Cliona celata, C. rhodensis, C. utricularis, and Cliothosa hancocki, and the other made up of C. viridis, C. nigricans, C. schmidti, C. jullieni, Spheciospongia solida and S. vagabunda. Above the species level, data do not support the separation of the genus Cliothosa from Cliona, while they do support the inclusion of some massive boring species, previously assigned to the genus Spirastrella, in the family Clionaidae. At the species level, data demonstrated the genetic identity of taxa C. viridis and C. nigricans, in spite of their considerable morphological differences. In contrast, the yellow species commonly attributed to C. celata are probably to be considered as a complex of sibling species with a number of distinct taxa present in the Mediterranean. Data also showed the identity of the Mediterranean and Pacific populations of C. schmidti, suggesting the status of a Tethyan relict for this species.     

Mitochondrial and nuclear rRNA based copepod phylogeny with emphasis on the Euchaetidae (Calanoida)

Phylogenetic relationships within the copepod family Euchaetidae and between representatives of three copepod orders (Calanoida, Harpacticoida, and Poecilostomatoida) were investigated using partial nucleotide sequences of the mitochondrial 16S rRNA and the nuclear 28S rRNA genes. DNA isolation, polymerase chain reaction, cloning, and DNA sequencing techniques were customized for these crustaceans. Our results support the monophyly of each copepod order, but in contrast to traditional morphology-based phylogenies of copepod orders, the Poecilostomatoida are basal to the Calanoida and Harpacticoida on our DNA-based phylogenetic tree. Phylogenetic trees generated by maximum parsimony, neighbor-joining, and maximum-likelihood analyses support the classification of the genera Euchaeta and Paraeuchaeta in the family Euchaetidae; results, however, suggest that Euchaetaacuta Giesbrecht is more closely related to species of the genus Paraeuchaeta than to those of Euchaeta, although limited taxon sampling may be partially responsible for this result. Phylogenetic mapping using the most parsimonious 16S tree suggests that the morphological synapomorphies distinguishing the genus Euchaeta evolved independently twice during the history of the Euchaetidae. Further, phylogenetic mapping suggests that the most recent common ancestor of the Euchaetidae and the Aetideidae was a deep-living, vertically migrating copepod, and that a bathypelagic, vertically migrating lifestyle characteristic of Paraeuchaeta is an ancestral trait of the family Euchaetidae which was lost apomorphically by Euchaeta. The application of a molecular clock suggests that the sibling species Euchaeta rimana Bradford and Euchaeta marina (Prestandrea) diverged due to the emergence of the Panamanian land bridge. Received: 9 October 1997 / Accepted: 5 August 1998     

Phylogeny of Opsanus spp. (Batrachoididae) inferred from multiple mitochondrial-DNA sequences

 Species of the toadfish genus Opsanus are increasingly used as experimental organisms in biomedicine and evolutionary/ecological physiology. Despite their importance, little is known of the phylogenetic relationships among Opsanus species. DNA sequence data for portions of the mitochondrial 12S rRNA, cytochrome oxidase I and cytochrome b genes were generated and analyzed from the four recognized Opsanus species and three outgroup taxa. Results of these analyses indicate an evolutionarily rapid divergence of three lineages within the genus. O. beta and O. pardus were resolved within the same lineage, and could not be distinguished with these mitochondrial sequence data. These data and paleoclimatic theory support a hypothesis of speciation based on the formation of allopatric populations during periods of elevated water temperature in the northern Caribbean. Received: 6 July 1999 / Accepted: 15 March 2000     

Cytogenetic characterization of the greater amberjack, Seriola dumerili (Pisces: Carangidae), by different staining techniques and fluorescence in situ hybridization

A cytogenetic analysis by several staining techniques was carried out on specimens of Seriola dumerili from the Tyrrhenian coast of Sicily. The karyotype was found to be composed of 48 chromosomes in all the specimens examined. All chromosomes are subtelo- and acrocentrics, except for one pair of small-sized submetacentric chromosomes. After Ag-staining, nucleolus organizer regions (NORs) can be observed on the short arms of a medium-sized subtelocentric chromosome pair, and after chromomycin A₃-staining a bright fluorescent signal is evident at the same sites. The 18S rDNA mapping by fluorescence in situ hybridization confirms this unique NOR location. The constitutive heterochromatin is mainly restricted to centromeres and the fluorochrome-staining by chromomycin A₃ and 4′,6-diamidino-2-phenylindole revealed a uniform base composition along the chromosomal arms; therefore stock/population-specific marker chromosomes cannot be identified. Such cytogenetic features, however, rule out the presence of morphologically differentiated sex-chromosomes in the greater amberjack. Received: 16 January 1997 / Accepted: 31 January 1997     

A pycnogonid-ophiuroid association

Three species of the ophiuroid genus Ophiocoma (O. doederleini de Loriol, O. pica Müller and Troschel and O. erinaceus Müller and Troschel) are host to the pycnogonid Anoplodactylus ophiurophilus Stock n.sp. on Aldabra atoll, Seychelles Islands. Infestation levels of the host ophiuroids from 3 localities differed markedly according to species, and lay between 83.7 and 3.6%. Host-specificity is related to microhabitats and feeding activities of the hosts. The position of the pycnogonids on the host (near the mouth along the ambulacra) and their feeding is related to food stealing and ectoparasitism. This is the first report of a pycnogonid-ophiuroid association.     

Free-living marine nematodes from Biscayne Bay,Florida, II. Oncholaimidae: descriptions of five new species and one new genus (Meyersia)

A new genus, Meyersia, and five new species of the nematode family Oncholaimidae, are described from Biscayne Bay, Florida, and environs, viz., Metoncholaimus pelor n. sp., M. amplus n. sp., Meyersia major n. gen., n. sp., M. minor n. sp., and Filoncholaimus prolatus n. sp. Also included in the genus Meyersia are Adoncholaimus bandaenis Kreis, 1932 and A. meridionalis Kreis, 1932.     

Chromosome number in ten species of the genus Tisbe (Copepoda: Harpacticoida)

Of 10 species of the genus Tisbe, 9 were shown to possess the same haploid number of 12, whereas only 1 has a haploid number of 8. The hypothesis is advanced that n=12 is the primitive condition in the genus Tisbe and that T. biminiensis with n=8, is a recent form.     

Cryptic species and population structuring of the Atlantic and Pacific seabob shrimp species, Xiphopenaeus kroyeri and Xiphopenaeus riveti

Seabob shrimps of the genus Xiphopenaeus are important fishery resources along the Atlantic and Pacific coasts of Central and South America. The genus was considered to comprise two species: the Atlantic Xiphopenaeus kroyeri (Heller, Sitzungsber Math Naturwiss cl kaiserliche Akad Wiss Wien 45:389–426, 1862), and the Pacific Xiphopenaeus riveti (Bouvier, Bull Mus Hist Nat Paris 13:113–116, 1907). In a recent review, Xiphopenaeus was regarded as a monotypic genus, on the basis that no clear morphological differences could be found between Pacific and Atlantic specimens (Pérez Farfante and Kensley, Mem Mus Nat Hist Nat Paris 175:1–79, 1997). In the present work, nuclear (allozymes), and mitochondrial (Cytochrome Oxidase I) genes were used to demonstrate the validity of X. riveti and reveal the presence of two cryptic species of Xiphopenaeus within X. kroyeri in the Atlantic Ocean. The high levels of molecular divergence among these species contrast with their high morphological resemblance. Interspecific sequence divergences (Kimura 2-parameter distance) varied from 0.106 to 0.151, whereas intraspecific distances ranged from 0 to 0.008 in Xiphopenaeus sp. 1, from 0 to 0.003 in Xiphopenaeus sp. 2, and from 0.002 to 0.005 in X. riveti. In addition, five diagnostic allozyme loci were found between sympatric samples of Xiphopenaeus sp. 1 and 2 along the Brazilian coast. The results suggest that Xiphopenaeus sp. 2 from the Atlantic is more closely related to the Pacific X. riveti than to the Atlantic Xiphopenaeus sp. 1. Furthermore, a high level of genetic structuring (Xiphopenaeus sp. 1: F _ST =0.026; P<0.05; Xiphopenaeus sp. 2: F _ST =0.055; P<0.01) was found in the Brazilian Xiphopenaeus populations, indicating the presence of different genetic stocks in both Atlantic species. These findings have important commercial implications as they show that the fisheries of the two Atlantic species must be managed separately, and that each one is comprised of different populations.Communicated by O. Kinne, Oldendorf/Luhe