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     

Genetic structure of camouflage grouper,<Emphasis Type="Italic"> Epinephelus polyphekadion</Emphasis> (Pisces: Serranidae), in the western central Pacific

The objective of the present study was to investigate the population genetic structure of the commercially important camouflage grouper, Epinephelus polyphekadion (Bleeker, 1849), in the western and central Pacific Ocean to improve existing management. Camouflage grouper are widely distributed in the Indo-Pacific and form brief, seasonal, spawning aggregations that are often heavily fished. The present study examined populations sampled in 1997-1998 at five sites in the western central Pacific spanning a geographic distance of ~5,000 km: New Caledonia, Great Barrier Reef, Palau, Marshall Islands, and Pohnpei (Micronesia). Primer pairs were developed to examine genetic variation at three polymorphic microsatellite loci. Cluster analysis, using genetic distance, revealed three regional groupings: (1) Palau, (2) Pohnpei and the Marshall Islands, and (3) the Great Barrier Reef and New Caledonia. Highly significant allele frequency differences were observed among sites. At Pohnpei, significant allele frequency differences in successive years were also apparent, possibly related to genetic variation among cohorts or between local spawning groups. The inter-annual differences at Pohnpei suggest that there may be further genetic structuring over relatively modest distances, a finding relative to determining management units for this commercially valuable species and suggests that future studies need to incorporate possible small-scale temporal or spatial components into study design.     

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     

In situ swimming and settlement behaviour of larvae of an Indo-Pacific coral-reef fish, the coral trout Plectropomus leopardus (Pisces: Serranidae)

Late larvae of the serranid coral trout Plectropomus leopardus (Lacepède), captured in light traps, were released during the day both in open water and adjacent to two reefs, and their behaviour was observed by divers at Lizard Island, northern Great Barrier Reef. Coral trout larvae (n = 110) were present in light-trap catches from 18 November to 3 December 1997, including new moon (30 November). The swimming speed of larvae in open water or when swimming away from reefs was significantly greater (mean 17.9 cm s⁻¹) than the speed of larvae swimming towards or over reefs (mean 7.2 cm s⁻¹). Near reefs, larvae swam at average depths of 2.7 to 4.2 m, avoiding 0 to 2 m. In open water, swimming depth varied with location: larvae >1 km east of Lizard Island swam steeply downward to >20 m in 2 to 4 min; larvae >1 km west oscillated between 2.6 and 13 m; larvae 100 to 200 m east of Lizard Island oscillated between 0.8 and 15 m. Nearly all larvae swam directionally in open water and near reefs. In open water, the average swimming direction of all larvae was towards the island, and 80% (4 of 5) swam directionally (p < 0.05, Rayleigh's test). Larvae swam directionally over the reef while looking for settlement sites. The frequency of behaviours by larvae differed between two reefs of different exposure and morphology. Depending on site, 26 to 32% of larvae released adjacent to reefs swam to open water: of these, some initially swam towards or over the reef before swimming offshore. In some cases, offshore-swimming seemed to be due to the presence of predators, but usually no obvious cause was observed. Depending on the reef, 49 to 64% of the larvae settled. Non-predatory reef residents aggressively approached 19% of settlers. Between 5 and 17% of the larvae were eaten while approaching the reef or attempting to settle, primarily by lizardfishes but also by wrasses, groupers and snappers. A higher percentage of larvae settled in the second week of our study than in the first. Average time to settlement was short (138 s ± 33 SE), but some larvae took up to 15 min to settle. Average settlement depth was 7.5 to 9.9 m, and differed between locations. No settlement took place on reef flats or at depths <4.2 m. Larvae did not appear to be selective about settlement substrate, but settled most frequently on live and dead hard coral. Late-stage larvae of coral trout are capable swimmers with considerable control over speed, depth and direction. Habitat selection, avoidance of predators and settlement seem to rely on vision. Received: 7 July 1998 / Accepted: 26 January 1999     

Phylogenetic relationship among several genera of Dictyotaceae (Dictyotales, Phaeophyceae) based on 18S rRNA and partial rbcL gene sequences

The partial sequences of the 18S rRNA gene and the rbcL gene, RuBisCo spacer region of representatives of the Dictyotaceae were determined and compared to resolve their phylogenetic relationships. A total of 1,861 base pairs of 18S rDNA sequences were aligned and examined. There was a high similarity of nucleotide sequences within the tribe Dictyoteae (99.4-99.6%) and the tribe Zonarieae (92.8-99.8%). The largest intergeneric divergence within the Dictyotaceae was 7.31%, between Dilophus and Zonaria. The aligned 422 bases of partial rbcL gene sequences gave a similar phylogenetic relationship among taxa to those of the 18S rDNA sequences, although our alignment covered less than 30% of the whole gene. All genera of Dictyotales consisted of several clades forming a polychotomy in MP trees based on partial rbcL gene sequences and on 18S rDNA sequences. The genera within the tribe Dictyoteae formed a clade, a Dictyota-Phacydictyon-Dilophus clade, while genera of the tribe Zonarieae formed four clades: Padina; Distromium-Lobophora-Zonaria; Spatoglossum-Lobospira; and Dictyopteris-Spatoglossum. All genera of the Dictyotaceae included in these sequence analyses are classified into five groups, which have little phylogenetic resolution among them. The genera classified in the tribe Zonarieae according to Womersley's criteria do not appear to be monophyletic, based on our analyses. Although not all genera of Dictyotaceae were analysed, our data suggest that the status of the meristem cells should not be a criterion for separating tribes within the family Dictyotaceae and that other hierarchical systems should be adopted to properly reflect phylogenetic relationships.     

狼蛛优势种群的12S rRNA对长期农药胁迫的分子响应

应用12SrRNA基因序列分析探讨了狼蛛优势种群对长期农药胁迫的分子响应机制.研究显示:(1)拟水狼蛛Piratasubpiraticus和拟环纹豹蛛Pardosapseudoannulata在长期农药胁迫下的12SrRNA基因第三结构域序列均发生了明显改变,即碱基组成由315bp和300bp分别减少为301bp和299bp,转换/颠换为17/5和11/10,核苷酸变异百分数达到0.095和0.083,同源性仅分别为85.8%和91.7%;(2)分子水平上表明拟水狼蛛较拟环纹豹蛛对农药的胁迫更为敏感;(3)供试两种狼蛛标本的基因组DNA的4个碱基对中以A和T的变异频率最高,属农药敏感型碱基对;(4)长期农药胁迫下供试两种狼蛛标本的12SrRNA基因片段的共同突变位点规律显示:192～228片段是其农药胁迫的敏感区.图2表3参9     

Molecular data from the 16S rRNA gene for the phylogeny of Veneridae (Mollusca: Bivalvia)

Veneridae, a cosmopolitan and ubiquitous family in world-wide littoral environments, lists more than 500 species, many of which are often subject to intensive commercial exploitation due to their numerical dominance in benthic communities. Historically, the family has been divided into 12 subfamilies by M. Keen and, even though this taxonomical arrangement was adopted for convenience and does not necessarily reflect genetic relationships, as suggested by Keen herself, this classification is still accepted. To contribute to clarify the systematics and phylogeny of Veneridae, the portion of the nucleotide sequence corresponding to domains IV and V of the gene encoding the large subunit of mitochondrial ribosomal RNA was analysed in 14 species representative of 10 genera belonging to 6 different subfamilies. The results obtained using the maximum-parsimony and neighbour-joining methods indicate that the current placement of the genera into subfamilies does not always reflect a natural subdivision. In addition, the six species of Tapetinae studied, though confirmed to be a monophyletic clade, do not exhibit a correct attribution at the genus level.     

Age and growth of Electrona antarctica (Pisces: Myctophidae), the dominant mesopelagic fish of the Southern Ocean

Numerically and in biomass, the lanternfish Electrona antarctica is the dominant fish in the vast pelagic region of the Southern Ocean bounded on the north by the Antarctic Convergence and in the south by the Antarctic continental shelf. It is an important krill predator, and in turn is important in the diets of flighted and swimming seabirds. Further, it is the southernmost and coldest-dwelling representative of the globally distributed fish family Myctophidae. The present study was undertaken to estimate the species' growth rate and average life span, to incorporate the information in a basic energy budget, and to compare the growth of E. antarctica with more northerly confamilials. Fishes were aged using primary growth increments that were resolved on sagittal otoliths using three sequential techniques: thin-section grinding and polishing, etching, and scanning electron microscopy (SEM). Based on increment width (0.8 to 1.2 μm), continuity, and previous studies on confamilials, the microincrements were assumed to be deposited on a daily basis. Montages of SEM photomicrographs were constructed for each sagitta to allow the daily rings to be counted over the entire life span of 31 individuals representing the entire size range of the species. Results suggest a larval stage of 30 to 47 d and a maximum life span of 3.5 yr, with females growing faster than males in the last 1.5 yr of life and reaching a larger maximum size. Construction of a simple energy budget using the best information available suggests that a surplus of energy is available to support the observed growth rates (0.05 to 0.07 mm d⁻¹). The results of the present study contrast markedly with previous estimates of an 8 to 11 yr maximum age for E. antarctica. These results provide important data addressing the ecology and population dynamics of the pelagic Antarctic ecosystem. E. antarctica is the end-member species in the continuum of vertically migrating myctophids that extend from the equator to the polar circle. Its growth rate is consonant with that of all other myctophid species examined using primary growth increments to determine age. The present study, in conjunction with earlier studies, suggests that growth rates of mesopelagic species are far higher than previously thought. Received: 12 September 1997 / Accepted: 25 July 1998     

Filtering rates of the juvenile Atlantic menhaden Brevoortia tyrannus (Pisces: Clupeidae), with consideration of the effects of detritus and swimming speed

From July to September 1982 feeding experiments were conducted with 138-mm fork length Atlantic menhaden Brevoortia tyrannus (Latrobe) (Pisces: Clupeidae) to determine their particle size-specific feeding abilities. Monoculture clearing-rate experiments showed that the minimum size of particles filtered, the minimum size threshold, for 138-mm fish is 7 to 9 m. Filtration efficiency for three species of phytoplankton below the minimum size threshold. Pseudoisochrysis paradoxa, Monochrysis lutheri, and Isochrysis galbana, averaged 1.0% (n=14). Tetraselmis suecica, Prorocentrum minimum, and 2-celled Skeleionema costatum, phytoplankton which are larger than the minimum size threshold and smaller than the 20-m upper limit for nanoplankton, were filtered at efficiencies averaging 21% (n=24). S. costatum chains of 3 to 6 cells, prey particles exceeding the size limits of nanoplankton, were filtered at average efficiencies ranging from 22 to 84%. The mean filtration efficiency for Artemia sp. nauplii (San Francisco Bay Brand) of 36% (n=7) was lower than for smaller phytoplankton prey. The presence of detritus at concentrations usually encountered in nature enhanced filtering efficiency and lowered minimum size thresholds at which phytoplankton were retained. For small food particles, filtering efficiency decreased as swimming speed of the menhaden increased. As menhaden grow, their feeding tepertoire shifts to larger planktonic organisms.Contribution No. 1201 Virginia Institute of Marine Science     

Circadian rhythms in the respiration of eight species of cardinal fishes (Pisces: Apogonidae): comparative analysis and adaptive significance

A comparative study was made of the entrained (12:12 LD) and endogenous (DD) respiratory rhythms of 8 species of cardinal fishes. Volumetric respirometers, designed specifically for long-term measurements of oxygen uptake by small fishes under controlled conditions, were used during standard 5 day experiments. Despite some individual variation, certain species-specific and genus-specific patterns of respiration emerged. Each species showed a persistant (advancing) rhythm of oxygen consumption during 3 days of DD. Light appeared to be the Zeitgeber, with the light-dark transition phasing the nocturnal peaks and the dark-light transition possibly phasing the diurnal ones. Genus-specific and species-specific trends in field behavior, habitat selection, and distribution were studied. There were correlations between the field behavior and the entrained respiratory rhythms of these nocturnally active fishes. Entrained and endogenous rhythms of each species showed characteristic similarities and were interpreted as integral components of a level of organization evolved for nocturnal life in the shallow marine environment.     

Life history and fishery of Lepidopus caudatus (Pisces: Trichiuridae) in the Catalan Sea (Northwestern Mediterranean)

The frostfish Lepidopus caudatus (Euphrasen, 1788) is a mesopelagic species; it occurs along the shelf and slope down to 450 m in the Catalan Sea. Its' fishery, population structure, growth, diet and reproduction was studied on the basis of commercial statistics from 1984 to 1990 and on samplings made in 1988 and 1989. L. caudatus is fished by two types of commercial method, trawl and long-line; catches by the latter method display a marked seasonality. The minimum size of fish caught is 26 cm total length by trawling and 71 cm by long-line. Maximum sizes are similar for both gears: 196 and 188 cm, respectively. L. caudatus exhibits fast growth and attains an age of 8 yr. It feeds on small mesopelagic prey. It is a partial spawner reproductive activity occurring from April to November. Males attain sexual maturity at 97 cm and females at 111 cm total length.     

On the evolution of nest raiding and male defensive behaviour in sticklebacks (Pisces: Gasterosteidae)

Summary We develop a model to explain the evolution of nest raiding by female sticklebacks based on enhanced female reproductive success derived by creating mating opportunities with the male whose nest has been destroyed. Our model depends critically on the shape of the function relating percentage hatch success to the number of eggs in a male's nest, and the probability that the female will later mate with the male whose nest was raided. Raiding by females will be favoured when the number of eggs in the nest is high providing high egg numbers reduces the percentage hatch rate. High probabilities of mating with the male in question also favour raiding. A second model suggests that males cannot reduce the probability of being raided by limiting the number of eggs in the nest. Instead selection should favour their increasing the number of eggs in the nest. Tests of these models are suggested and their relation to other factors which may influence the evolution of cannibalism are discussed.     

Pleistocene diversification of the Pomacentrus coelestis species complex (Pisces: Pomacentridae): historical biogeography and species boundaries

Pleistocene eustatic changes in sea level are often invoked to explain genetic divergence among marine organisms. However, molecular phylogenies have revealed relatively few examples of speciation events dating to the Pleistocene. We present a species-level hypothesis of the timing of evolution for the Pomacentrus coelestis species complex (Pomacentridae), based on the nuclear S7 intron and the mitochondrial Cytb gene, and reconstruct ancestral range distributions across the timetree. Ancestral range reconstruction suggests the complex originated in the Coral Triangle and East Indian Ocean, with subsequent range expansion outward from this region. We suggest that land barriers to dispersal (e.g., Indo-Pacific barrier) may be responsible for the divergence between Indian (P. alleni, P. similis, P. caeruleopunctatus, and P. caeruleus) and Pacific (P. micronesicus, P. auriventris, and P. coelestis) species groups, and subsequent isolation by Pleistocene sea-level fluctuations in certain areas of the Coral Triangle (glacial refugia) may play an important role in the diversification of this species complex. Additionally, our analyses show cryptic lineages within P. micronesicus and highlight the need for comprehensive sampling within and among species to reveal recent speciation events.     

Comparisons of the feeding activity and diets of male and female cunners Tautogolabrus adspersus (Pisces: Labridae)

The diel distribution of feeding activity during the spawning season was compared for territorial male and female cunners Tautogolabrus adspersus in Conception Bay, Newfoundland, Canada between June and August, 1978. Territorial males feed significantly less often than females and concentrate their feeding activities in the morning, whereas females feed as frequently in the afternoon as in the morning. Based on the contents of alimentary tracts, territorial males, non-territorial males, and females have different diets. Since these three groups share the same habitat, the observed dietary differences probably reflect differences in their foraging behaviour. The relevance of these findings to the concept of time minimizer and energy maximizer is discussed.     

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.     

Morphological and functional development of larval and juvenile Limanda yokohamae (Pisces: Pleuronectidae) reared in the laboratory

Morphological and behavioural aspects in larval development need to be studied in detail to understand the early life history better, and to gain a comprehensive knowledge on early life stages for fish species important in aquaculture and fisheries. In the present study, larvae of Limanda yokohamae (Günther) were reared to observe their behavioural development, and to obtain specimens for studying the morphological features and the intestinal development at Ohno, Hiroshima, Japan, in 1987. Swimming activity was monitored at several larval stages, and swimming speed was recorded until settlement and after-feeding behaviour was initiated. A slight increment of swimming speed was observed with larval growth. Larvae changed their swimming behaviour from surface waters to the bottom of the rearing tank when their eyes began to move. Morphological development of pigmentation patterns, fin development, squamation and the development of the digestive tract were described and illustrated in detail to characterize development stages, especially those relating to metamorphosis. During metamorphosis, growth ceased and rapid changes in allometric growth were accompanied by differentiation of the digestive tract. After metamorphosis there was steady growth, allometric growth achieved a constant value, and both the scales and digestive organs were fully formed. Metamorphosis was therefore a crucial developmental milestone, including a critical phase during which survival potential was lowered.     

Local variation in mortality rates and life-expectancy estimates of the coral-reef fish Centropyge bicolor (Pisces: Pomacanthidae)

Mortality rates of the coral reef fish Centropyge bicolor were based on the disappearance of known individual fish. Data were collected over three years from 1978 at four sites around Lizard Island, Queensland, Australia. To measure disappearance, membership of 36 harems (comprising about 150 fish at any one time) was determined at bimonthly intervals. Mortality rates varied significantly among the four study areas. A tenfold difference in mean mortality occurred between two of the areas. The ranking of areas according to mortality rate was similar for 1978–1979 and 1979–1980. The ranking of areas was again similar for 1980–1984 when mortality rates were determined from an additional census in June 1984. Average further life-expectancy of mature fish based on mortality rates varied from 1 yr in one study area to 5 to 13 yr in a different area.     

Molecular phylogeny of Ostracoda (Crustacea) inferred from 18S ribosomal DNA sequences: implication for its origin and diversification

Nucleotide sequences for the 18S rDNA of 17 ostracod species, representing 4 extant orders and 12 superfamilies, were determined and compared with known sequences of other crustaceans. Resulting molecular phylogenetic trees based on maximum-likelihood, maximum-parsimony, and neighbor-joining methods consistently indicated that the Podocopida plus Platycopida forms a monophyletic group, but did not indicate monophyly of the Ostracoda consisting of the four orders, Podocopida, Platycopida, Kirkbyocopida, and Myodocopida. The tree topology and the crustacean fossil record suggest that the lineage of podocopidans and platycopidans, that of kirkbyocopidans, and that of myodocopidans should have separately been established already in the Cambrian, although there is no ostracod fossil record in that time period. Close relationships between the Bythocytheroidea and Cytheroidea and among the Macrocypridoidea, Pontocypridoidea, and Cypridoidea can safely be postulated, but other relationships among podocopidan and platycopidan superfamilies could not be resolved from the 18S rDNA data. The polychotomous relationship among five lineages of the podocopidan and platycopidan superfamilies, i.e. Cytherelloidea, Bairdioidea, Darwinuloidea, Bythocytheroidea plus Cytheroidea, and Macrocypridoidea plus Pontocypridoidea plus Cypridoidea, suggests that common ancestors of those lineages diverged from each other rapidly in short intervals in the early Paleozoic.     

Population biology and life strategies of Chlorophthalmus agassizii Bonaparte, 1840 (Pisces: Osteichthyes) in the Mediterranean Sea

The population biology and life strategies of Chlorophthalmus agassizii were studied in the Ionian Sea (eastern–central Mediterranean) using the data collected during the experimental trawl surveys carried out from 1995 to 2000. Depth-related trends of both density and size were found. With depth the former decreased while the latter increased. A typical bigger–deeper phenomenon was detected: young-of-the-year individuals occur on the shelf during autumn–winter months and move towards bathyal bottoms as they grow. The sampled population was made up of several size–age groups. The maximum age of 8 years was identified by means of otolith readings. The Von Bertalanffy growth parameters were estimated from the age–length key (L _∞=189.04±5.401 mm; k=0.24±0.021; t _o=−1.20±0.132; φ′=3.94) and modal progression analysis (L _∞=218.33±18.397 mm; k=0.164±0.028; t _o=−1.694±0.171; φ′=3.89). Reproduction of this monoecious fish was observed during summer–early autumn. Considering the female portion of the gonad, the size at attainment of 50% maturity was 115 mm TL. The corresponding age is within the third year of life. The simultaneous occurrence of oocytes in different development stages was shown in the ovary. Both the asynchronous ovary and oocyte size distribution indicate that C. agassizii spawns more than once during a reproductive season (batch spawner). Functional fecundity (on average 3,018 hydrated oocytes) was between 37 and 69% of the absolute fecundity and increased significantly with the individual size. Since adult specimens are mostly distributed on the slope, eggs and larvae develop in epipelagic waters and migrate in-shore where juvenile forms recruit on the shelf. Juveniles migrate ontogenetically towards deeper bottoms and after 2–3 years start to reproduce annually within a life span greater than 10 years.