Doubly uniparental transmission of mitochondrial DNA length variants in the mussel <Emphasis Type="Italic">Mytilus</Emphasis><Emphasis Type="Italic">trossulus</Emphasis>

Doubly uniparental inheritance of mitochondrial DNA (mtDNA) is an unusual feature found in marine mussels and a few other bivalve species. In addition to a mitochondrial genome (F) inherited through the female line, heteroplasmic individuals (males) contain a second highly diverged genome (M) that is inherited through the paternal line. The Baltic mussel Mytilus trossulus is characterized by the presence of two phylogenetically close female and male genomes. We examined M. trossulus sampled from the Gulf of Gdansk, southern Baltic. Somatic tissues and gametes were surveyed for the presence of different types of mtDNA. Length variants were identified using PCR (polymerase chain reaction) amplification of the mtDNA fragment containing the major noncoding region. Seventeen length variants present in homo- and heteroplasmic individuals were found in a sample of 343 individuals analyzed. Two length variants of the major noncoding region (PCR product lengths: 1520 and 1370 bp) were the most frequent. Length heteroplasmy was found in 46.8% of males, and was mostly caused by the presence of the short length variant (PCR product length: 1370 bp) of the major noncoding region. MtDNA variants were also detected by restriction analysis of a 1.3 kb segment of coding region (ND2-COIII) amplified by PCR. This study provides evidence that the short length variant is always transmitted to sperm and has taken over the role of the M genome. The remaining length variants were present in both males and females. Longer length variants were transmitted mainly through the female line. A possibility of much higher incidence of genome role reversals in Baltic M. trossulus, in comparison with other populations of mussels is discussed.     

Dynamics of pigment degradation by the copepodite stage of <Emphasis Type="Italic">Pseudodiaptomus</Emphasis><Emphasis Type="Italic">euryhalinus</Emphasis> feeding on <Emphasis Type="Italic">Tetraselmis</Emphasis><Emphasis Type="Italic">suecica</Emphasis>

Short-term (3 h) changes in concentration of chlorophylls and their derivatives in stage V Pseudodiaptomus euryhalinus and their fecal material were followed by HPLC during a 24 h experiment. Copepodites were fed with the prasinophyte Tetraselmis suecica. Intact chlorophyll a and b were found in animals and fecal material and had similar dynamics of accumulation over time. The extent of transformation of chlorophyll a and b to colorless compounds was different with chlorophyll a being more extensively degraded. Additionally, several chlorophyll derivatives (pheophytin and pyropheophytin-like pigments) were found. Pyropheophytin a was the most abundant followed by pheophytin b, pheophytin a, and pheophorbide a. Relative amounts of pheopigments were different in copepodites and fecal material, and pheophytin a, pheophorbide a, and pheophytin b concentrations were low and variable. The amount of ingested chlorophyll recovered as chlorophyll a and its derivatives in fecal and copepodite pools was generally low (<5%), with one exception occurring after 9 h, when it accounted for >70%. These data suggest individual pheopigments are produced at different rates and that chemical or enzymatic mechanisms in the gut of copepodites act on the two chlorophylls in different ways.     

Effects of substrate type on growth and mortality of blue mussels (<Emphasis Type="Italic">Mytilus</Emphasis><Emphasis Type="Italic">edulis</Emphasis>) exposed to the predator <Emphasis Type="Italic">Carcinus</Emphasis><Emphasis Type="Italic">maenas</Emphasis>

Structure and complexity of the substrate are important habitat characteristics for benthic epifauna. The specific growth and mortality rates and inducible defence characters on medium-sized blue mussels (Mytilus edulis L.) exposed to shore crabs (Carcinus maenas L.) were examined on three different substrate types in combined field and laboratory experiments. The experiments showed that complexity of the substrate increased blue mussel survival significantly, through a decrease in predation pressure. However, increased intraspecific competition for food on the complex substrate resulted in significantly lower growth rates of the mussels. Inducible defence characters were also influenced by substrate type. Blue mussels were more affected by predators on the structurally simple substrate, where they developed thicker shells and a larger posterior adductor muscle.     

Evidence of a spawning area of <Emphasis Type="Italic">Anguilla</Emphasis><Emphasis Type="Italic">marmorata</Emphasis> in the western North Pacific

Leptocephali of the tropical eel Anguilla marmorata have been consistently collected in the same area of the North Equatorial Current (NEC) in the western North Pacific during three consecutive cruises in June and July of 1991 (N=28) and 1994 (N=20), and July and September of 1995 (N=27), indicating that this is a spawning area of this species. These leptocephali were collected from 130°E to 142°E and 12°N to 20°N, to the west of the Mariana Islands, in 20 tows in 1991, in 13 tows in 1994 and in 17 tows in 1995, indicating a widespread presence, but a relatively low abundance. Six of these specimens (16.3-36.0 mm total length) from the 1995 cruise, which were of the typical size range of these leptocephali, were genetically confirmed to be A. marmorata in a previous study. The consistent presence of recently spawned A. marmorata leptocephali (9-20 mm) in all 3 years, suggests that the western region of the NEC is the spawning area of the northern population of A. marmorata that was identified in a recent population genetics study. These leptocephali would thus be transported westward by the NEC and then transported north into the Kuroshio Current and toward Taiwan and Japan, or south toward the southern Philippines and into the Celebes Sea by the Mindanao Current. Available evidence indicates that A. marmorata may have potentially year-round spawning, and the presence of a spawning area of this species in the same region as that of Anguilla japonica suggests that the northern population of A. marmorata has evolved a spawning migration from East Asia, the Philippines and the Celebes Sea region to the NEC area, but differs from A. japonica by having some individuals that recruit to more southern areas.     

Cardiac output during exposure to <Emphasis Type="Italic">Chattonella</Emphasis><Emphasis Type="Italic">marina</Emphasis> and environmental hypoxia in yellowtail (<Emphasis Type="Italic">Seriola</Emphasis><Emphasis Type="Italic">quinqueradiata</Emphasis>)

The experiments were undertaken to measure, for the first time, cardiac output in yellowtail (Seriola quinqueradiata) during exposure to a harmful red tide flagellate (Chattonella marina). The responses were compared with those during exposure to environmental hypoxia to evaluate the significance of the drop of arterial oxygen partial pressure (PaO₂) in the fish-kill mechanisms by C. marina. PaO₂ immediately decreased, whereas heart rate (HR) was maintained until shortly before death during exposure to C. marina. Suffocation developing during the exposure resulted from a decrease in blood oxygen content, but not from lowered blood flow to the tissue. Although exposure to both C. marina and hypoxia immediately decreased PaO₂, arterial oxygen content (CaO₂) and pH (pHa) were significantly lower, whereas HR and cardiac output (&Qdot;) remained significantly higher, for the C. marina-exposed fish than for hypoxia-exposed fish. Although the drop in PaO₂ appears to play a pivotal role in the mechanisms of fish death by C. marina, other physiological response(s) should also be considered.     

Distribution of the alien ctenophore <Emphasis Type="Italic">Mnemiopsis</Emphasis><Emphasis Type="Italic">leidyi</Emphasis> in the Caspian Sea in August 2001

In this study, spatial and vertical distributions of the invasive ctenophore Mnemiopsis leidyi in the Caspian Sea were evaluated by using data collected at 41 stations during the August 2001 cruise. A comparison of data from different depths revealed that M. leidyi were generally confined to surface waters. The maximum size of the ctenophore was only 41-45 mm, and the bulk of individuals (85.5%) were <10 mm in length. The average and maximum biomasses of M. leidyi were calculated as 120 and 351 g wet weight m^-2, respectively. Whilst highest biomasses were observed in the western and central Middle Caspian Sea, hot spot areas of reproduction were present along the coasts of the western Caspian Sea, with abundance values of up to 2285 ind. m^-2. The impact of such high densities of M. leidyi is expected to be significant for the pelagic ecosystem of the Caspian Sea.     

Mechanisms of range expansion in the intertidal brown alga <Emphasis Type="Italic">Fucus</Emphasis><Emphasis Type="Italic">serratus</Emphasis> in northern Spain

The intertidal brown alga Fucus serratus is naturally expanding its distributional range along the north shore of Spain. Shores being colonised by F. serratus harbour saturated algal communities, with almost no free space. Processes responsible for the successful expansion were investigated in a locality where the alga was experimentally introduced. After a short period, the number of F. serratus plants increased exponentially at a monthly intrinsic rate of 0.111. At early and intermediate stages of invasion, colonisation occurred by the growth of patches of the invader around the transplant points. F. serratus is a bad disperser, with most of propagules settling in near proximity to parent plants. Colonisation of manipulated and control areas was influenced by the proximity of propagule sources. Experimental removals of canopies, irrespective of whether the turf was removed or left intact, accelerated the expansion, as this component of the community had a negative influence on recruitment of both F. serratus and F. vesiculosus. The unmanipulated algal beds were, however, invasible, as some control quadrats close (<10 m) to F. serratus patches had a 100% cover of F. serratus at the end of the study. Prior or concurrent to increases of F. serratus, a decrease in cover of F. vesiculosus and other resident macroalgae was evident. No formal competition experiment was done but results suggest that F. serratus outcompetes F. vesiculosus and Bifurcaria bifurcata at mid-tidal levels. In scraped quadrats, in which both Fucus species recruited at large densities, F. serratus grew at a higher rate than F. vesiculosus and eventually monopolised the experimental surfaces.     

Development and biology of <Emphasis Type="Italic">Periphylla</Emphasis><Emphasis Type="Italic">periphylla</Emphasis> (Scyphozoa: Coronatae) in a Norwegian fjord

The globally distributed coronate scyphomedusa Periphylla periphylla (Peron and Lesueur, 1809) occurs in permanent and extremely high abundance in some Norwegian fjords. Studies on the species in Lurefjorden, 40 km north of Bergen, have revealed a holopelagic life cycle with direct development. We distinguished 14 successive developmental stages, characterised by size and morphology. Eggs and early stages are non-mobile, neutrally buoyant, and found mainly at intermediate depths. Rearing studies indicated a development time of 2-3 months from fertilisation to stage 9, when the medusa starts feeding and becomes motile. The fjord population usually shows a strong diel vertical migration, with aggregations at shallower depths during the night. The development includes a gradual increase in pigmentation (porphyrins), starting with the stomach, and thereafter extending to tentacles and the whole exumbrella. This pigment is photodegraded by natural light. Rearing experiments in the laboratory have shown a lethal effect of light. Here, development stops at stage 5. Pigments become visible in stage 7. Older medusae are severely damaged and killed within a few days by exposure to daylight. All stages of P. periphylla are bioluminescent, with this capacity increasing with growth, probably in connection with the development of the nervous net. The light reaction starts at the point of stimulation and spreads at two different speeds corresponding to the two nerve nets of the medusae. The coronal furrow has a central function in transmission of the reaction. It is hypothesised that the bioluminescence is used mainly as a warning to some potential predators, signalling that the porphyrin-containing medusa is unpalatable. P. periphylla has the same two categories of nematocysts as other coronates, with a total of six different types. Nematocyst abundance, distribution and morphology indicate their function. The giant euryteles (capsule up to 100 µm and tubule up to 1160 µm) are the largest ones known among Scyphozoa, and are unique in that this size increases during medusa development.     

Seasonal variation in the degree of heterospecific association of two syntopic hyraxes (<Emphasis Type="Italic">Heterohyrax</Emphasis><Emphasis Type="Italic">brucei </Emphasis>and <Emphasis Type="Italic">Procavia capensis</Emphasis>) exhibiting synchronous parturition

Adult rock hyrax (Procavia capensis) and bush hyrax (Heterohyrax brucei) allocate much of their surface activity to being vigilant for vertebrate predators. Individuals of the two species associate for thermoregulatory basking on rock outcrops (koppies) and, in the Matobo National Park, Zimbabwe, frequently constitute heterospecific groups that produce offspring synchronously. Exposure to predators during basking is thought to put a high premium on vigilance, particularly during the presence of dependent offspring in nurseries. We predicted, therefore, an increase in the association of the two species of hyraxes when offspring were present because this would lead to larger groups, thus enhancing the ability to detect predators. Koppie aggregations of hyraxes were classified as homospecific or heterospecific according to basking group composition. Heterospecific association increased when offspring were present, and heterospecific groups were larger than homospecific ones. Fifty-one percent of nurseries were heterospecific for adults/subadults. During the pre-weaning phase (<2 months after birth), 85% of P. capensis and 65% of H. brucei juveniles were in nurseries of heterospecific basking groups. Heterospecific groups had more offspring than homospecific groups. Juvenile mortality is most evident after young are weaned and heterospecific associations break down. Heterospecific aggregation, through increased group size, may result in a higher probability of avoiding predators, thereby reducing the vulnerability of young.     

Settlement of the wreckfish (<Emphasis Type="Italic">Polyprion</Emphasis><Emphasis Type="Italic">americanus</Emphasis>)

The wreckfish (Polyprion americanus) is a panoceanic, long-lived, deep-water demersal species, characterized by an extended pelagic juvenile phase associated with floating objects. In the present study morphometric data from 435 specimens collected from Greece (Crete), Italy (Ionian Sea) and the Atlantic coast of France from September 1999 to March 2001 were analyzed to estimate the settlement size of the species and associated changes in morphology. The fishery sample included specimens from both the pelagic and the demersal stage. Length-at-settlement (TL₅₀) and 95% confidence intervals were estimated by fitting a logistic function. Eleven morphometric characters were analyzed, and the existing inflection points, reflecting alterations in body shape, were defined: (1) iteratively, as the transition point, splitting the data set into two groups, for which the reduced major axis functions, between a character and total length, of the successive groups best fit (minimum sum of squares of residuals) the combined data set and (2) where the second derivative of the fitted third-order polynomial functions to morphometric ratios equaled zero. The main size range within which wreckfish settled was 56-65 cm, and the means of the inflection points defined by the two methods were 61 and 64 cm. These results indicate changes in functional morphology associated with settlement. The monitoring of wreckfish juveniles caught in the wild and kept individually in captivity showed changes in growth and food intake at approximately the estimated settlement length and suggested that temperature was the most likely factor triggering settlement.     

Life on a hot dry beach: behavioural,physiological, and ultrastructural adaptations of the littorinid gastropod <Emphasis Type="Italic">Cenchritis</Emphasis> (<Emphasis Type="Italic">Tectarius</Emphasis>) <Emphasis Type="Italic">muricatus</Emphasis>

The distribution and abundance of the littorinid gastropod Cenchritis (Tectarius) muricatus were determined on an exposed shore at Lee Stocking Island, Bahamas in July/August 1995 and June 1999. Activity patterns were observed on two occasions shortly before a hurricane passed near the island in 1995. C. muricatus extended from the low water mark to 3.6 m vertical height above it. Highest densities (20/m²) were found just above the high tide mark but the animal remained relatively abundant (8/m²) at the highest point. Small animals were only found at high shore levels. With the exception of animals very near to the water's edge C. muricatus was inactive by day and on dry nights. Many individuals of the high shore populations became active at night during periods of high humidity and rainfall, moving distances of up to 4 m overnight. At lower levels, extensive pairing and copulation was associated with these periods of rainfall. Abundance changed dramatically after the passage of the hurricane. At the level of maximum abundance numbers were reduced from 20/m² to 2.8/m². Long-term experimental studies of water loss rate and haemolymph concentration showed that both water loss rate and increase in haemolymph concentration are greatest in the early period of desiccation. The concentration of the blood after 20 weeks is 250% of the original and the water lost is of the order of 22.5%. After an initial increase there appears to be evidence of regulation of haemolymph concentration possibly by exchange with free water in the shell itself. The considerable reserve capacity in tolerance is no doubt in part due to the structure and functioning of the kidney. Adaptive features of the excretory system identified from ultrastructural examination include the replacement of podocyte-containing filtration chambers in the auricle by extracellular tubules permeating the walls of both auricle and ventricle, which suggests a reduction in the rate of primary urine formation. This is also indicated by a reduced surface area of the nephridial gland, which resorbs organic solutes from the urine. Excretory cells contain single large vacuoles in which arise large multi-layered concretions composed of phospholipids and calcium salts typical of prosobranchs in which excretory products may be stored for long periods.     

Behavioral adaptations of the cubozoan medusa <Emphasis Type="Italic">Tripedalia cystophora</Emphasis> for feeding on copepod (<Emphasis Type="Italic">Dioithona oculata</Emphasis>) swarms

The cubozoan medusa Tripedalia cystophora preys on dense swarms of the copepod Dioithona oculata in the mangrove prop-root habitat of Puerto Rico. The copepod swarms form in shafts of sunlight that penetrate the mangrove canopy during the day. T. cystophora are found primarily within the same illuminated areas, feeding heavily on the dense swarms of copepods. Laboratory studies were conducted to examine the behavioral adaptations of T. cystophora that allow them to remain within these dense copepod swarms. In the presence of vertical light shafts, T. cystophora showed both a significant change in swimming speed and a significant increase in turning rate. T. cystophora turn abruptly when they leave a vertical shaft of light and quickly re-enter. The presence or absence of copepod prey, either in swarms or dispersed, had no significant effect on T. cystophora swimming speed or turning behavior. Feeding rates of T. cystophora on the copepod D. oculata increase rapidly with copepod density, and maximum rates are not achieved until the high densities associated with swarms are reached. It seems doubtful that these small medusae could survive without their ability to encounter and exploit these dense swarms of copepods.     

<Emphasis Type="Italic">Semibalanus</Emphasis><Emphasis Type="Italic">balanoides</Emphasis> in winter and spring: larval concentration,settlement, and substrate occupancy

This study measured the progression from pelagic larvae to juvenile barnacles, and examined whether recruitment of barnacles, Semibalanus balanoides Linnaeus, at two intertidal sites in contrasting hydrodynamic regimes was determined by pre-settlement or post-settlement processes. The two sites were 1.5 km apart in the vicinity of Woods Hole, Mass., USA. Quantitative plankton samples were taken twice weekly from December 1997 to May 1998 at a nearby site as an estimate of nearshore larval abundance. The presence of S. balanoides nauplii was noted, and cyprids were enumerated and measured. Larval settlement at the two sites [Gansett Point, Buzzards Bay (GP) and Little Harbor, Vineyard Sound (LH)] was estimated from examination of replicate settlement plates exposed for 2 or 3 days throughout the settlement season, and from replicate plots on marked rock quadrats at each site. On both plates and rocks settled cyprids and metamorphs were enumerated. Space occupancy on unmanipulated rock quadrats by all stages from cyprids to adult barnacles was also examined. Settlement occurred from 2 January to 20 May, and major settlement peaks coincided with peaks in pelagic cyprid concentration at LH, but not at GP. Space occupied by juvenile barnacles was close to zero up until late February despite substantial settlement prior to that. At LH, juvenile barnacle cover was zero at the end of the observations; all settlement failed. Almost 100% of settled cyprids failed to metamorphose within 2 days from late January to late March. Then the proportion metamorphosing increased sharply coinciding with a sudden increase of 3°C in water temperature. Observed site differences in space occupancy by juvenile barnacles suggest that while cyprid supply is a necessary condition for barnacle settlement, other factors affecting metamorphosis of settled cyprids and early juvenile mortality determine recruitment.     

Competition,fluctuating asymmetry and sperm transfer in male gryllid crickets (<Emphasis Type="Italic">Gryllus bimaculatus</Emphasis> and <Emphasis Type="Italic">Gryllodes sigillatus</Emphasis>)

Sperm competition theory predicts that ejaculate expenditure by males should increase with the risk of competition from rivals. The tendency to modulate expenditure, however, may reflect various constraints acting on different individuals. We test this idea here by looking at the effects of competition and fluctuating asymmetry (FA) in two species of gryllid cricket. Male Gryllus bimaculatus and Gryllodes sigillatus modulated the sperm content of their spermatophores in relation to both apparent competition and FA in limb size. Males of both species increased the amount of sperm transferred when an apparent male competitor was present, sperm number increasing regardless of the species of apparent competitor in G. bimaculatus, but significantly more with a conspecific competitor in G. sigillatus. In addition, the relative size of the spermatophylax in G. sigillatus increased in the presence of apparent competition, while spermatophore transfer time decreased in G. bimaculatus. Sperm number showed opposite relationships with limb asymmetry in the two species, decreasing with increasing asymmetry in males in G. sigillatus, but increasing with asymmetry in both males and females in G. bimaculatus. G. bimaculatus, but not G. sigillatus, also transferred more sperm when paired with a larger female. Relationships between reproductive measures and limb asymmetry were significant only when competitors were present in G. bimaculatus, but were significant regardless of competition in G. sigillatus. The differences may reflect the additional burden of producing a spermatophylax in G. sigillatus.     

Nematode assemblages from <Emphasis Type="Italic">Avicennia</Emphasis><Emphasis Type="Italic">marina</Emphasis> leaf litter in a temperate mangrove forest in south-eastern Australia

Meiofauna from Avicennia marina leaf litter in a temperate mangrove forest was enumerated, and the nematode assemblages compared on the bases of leaf colour (used as a guide to leaf age) and shore horizon where samples were collected. Twenty-one putative nematode species were collected from 48 leaf litter samples. Univariate analyses indicated that neither the colour of the leaf nor the shore horizon significantly affected abundance of nematodes. However, of the four (2Ƕ) treatment groups, rarefaction curves revealed highest diversity on brown leaves from under the shade of the tree canopy (H'=0.751ǂ.126 SE, n=17). Species diversity of leaf litter nematodes was lower in this temperate mangrove system than reported from tropical mangrove studies. ANOSIM tests confirmed a significant effect of shore horizon on nematode assemblages. The dominant feeding group among nematodes was non-selective deposit feeders (7/21 species, but 77% of all nematodes). Epigrowth grazers were represented by 8/21 species of nematodes, but only 19% of the total number. Excised leaves became skeletonised by about 15 weeks. Shorter temporal scales of life cycles of nematodes compared with leaf degradation, and the dynamic nature of epibiontic assemblages, probably explain the similar assemblage structure on yellow and brown leaves.     

Effects of chemical cues on orientation of blue crab, <Emphasis Type="Italic">Callinectes</Emphasis><Emphasis Type="Italic">sapidus</Emphasis>, megalopae in flow: implications for location of nursery areas

Megalopae (postlarvae) of the blue crab Callinectes sapidus Rathbun use flood-tide transport (FTT) for movement into and up estuaries. Since they settle around the time of slack water at the end of flood tide during FTT, it was predicted that orientation toward primary nursery areas of aquatic vegetation occurs at this time. This study tested the hypotheses that megalopae locate nursery areas by swimming upstream in the presence of chemical odors from potential nursery areas and avoid adverse microhabitats by swimming downstream when predator or adverse environmental odors are present. Megalopae were tested in a flume where they were exposed to the sequence of cues mediating FTT (i.e. 2 psu increase in salinity followed by an increase and a decrease in current speed and turbulence). The flume contained odor water either from the developmental area (offshore water), nursery area vegetation (seagrass, Zostera marina; salt marsh cord grass, Spartina alterniflora), predators (fiddler crab, Uca pugilator; mud crab, Panopeus herbstii; grass shrimp, Palaemonetes pugio), or chemicals associated with adverse environments (ammonium). Vertical positions of premolt and intermolt megalopae were similar in water devoid of estuarine chemical cues (offshore water) and water containing seagrass odor. Upstream swimming behavior (orientation) of intermolt megalopae was also similar in these waters. However, there was an ontogenetic behavioral change, as the proportion of premolt megalopae oriented upstream generally increased as the concentration of seagrass and salt marsh cord grass odor increased and as current speed decreased. Upstream orientation of premolt megalopae in response to seagrass odor decreased significantly (i.e. downstream swimming increased) in the presence of odor from U. pugilator, P. pugio, and ammonium, but not from P. herbstii. Thus, the hypothesis was supported. These results suggest premolt megalopae orient toward nursery areas by swimming upstream in response to odors from aquatic vegetation as current speeds decrease at the end of nocturnal flood tides. Moreover, these results also indicate that megalopae may discriminate among microhabitats and avoid adverse settlement habitat, as orientation toward nursery areas is reversed by predator odors and ammonium.     

Global phylogeography of the fissiparous sea-star genus <Emphasis Type="Italic">Coscinasterias</Emphasis>

The fissiparous starfish genus Coscinasterias (Verrill) is represented in shallow waters around many of the world's continents. This wide distribution could be explained by dispersal, vicariance, or translocation associated with shipping, and represents an excellent system for marine biogeographic research. We conducted a global phylogeographic analysis of 42 Coscinasterias mtDNA cytochrome oxidase 1 sequences (15 haplotypes) from 18 sites, including representatives of all four recognised species. Phylogenetic analysis yielded a robust phylogeny, with strong support for the monophyly of the genus (90% bootstrap support) and of each separate species (99-100%). Haplotypes exhibited strong phylogeographic structure, with robust mtDNA clades often associated with distinct land masses. A general lack of genetic differentiation within sites may reflect fissiparity. However, shared haplotypes over larger distances (e.g. across Japan), and the presence of related haplotypes on adjacent land masses (e.g. Tasmania, New Zealand; 1.6-1.8%) suggest that long-distance dispersal is an important biogeographical process for Coscinasterias. The 4.0-4.4% divergence between Japanese and South African sister groups may relate to transequatorial dispersal around the onset of the Pleistocene. Divergent Atlantic and Mediterranean populations of C. tenuispina (maximum 1.5%) may deserve subspecific recognition, and high divergences within Australian C. muricata (maximum 8.0%) suggest a species complex.     

Sexual and asexual reproduction of <Emphasis Type="Italic">Coscinasterias</Emphasis><Emphasis Type="Italic">tenuispina</Emphasis> (Echinodermata: Asteroidea) from Rio de Janeiro,Brazil

An intertidal population of the fissiparous sea star Coscinasterias tenuispina (Lamarck, 1816) was sampled over a 1 year period at Ponta de Itaipu, Niterói, Rio de Janeiro. Gonadal indices revealed an annual reproductive cycle. Spawning occurred in the late winter and early spring between August and November. Pyloric caecal indices did not show a clear annual cycle or a reciprocal relationship with gonadal indices. The population appears to be sustained only by fission, as only males were found. Fission occurred throughout the year, but was most frequent in the winter (July, August and September). Incidence of fission was correlated with the occurrence of the extremely low tides during daytime that exposes many specimens to air. Austral winter tides are low by day and high by night, while the austral summer tides are low by night and high by day. The most extreme annual deviation in seawater temperature is about 5°C. Larval recruitment seems to be negligible, since very small individuals were not found.     

Effect of oxygen concentration on metabolism and locomotory activity of <Emphasis Type="Italic">Moina</Emphasis><Emphasis Type="Italic">micrura</Emphasis> (Cladocera) cultured under hypo- and normoxia

The influence of oxygen concentration on total and basal metabolism, scope of activity, drag force and duration of jerks, time spent swimming and energy cost of locomotion in Moina micrura Hellich females cultured under hypo- and normoxia was investigated. Scope of activity (Q_l) of hemoglobin-rich red individuals (M_a) acclimated to hypoxia depended less upon oxygen concentration than that of non-acclimated, pale individuals (M_na). Within the range 10-0.3 mg O₂ l^-1 Q_l decreased 4.4-fold in M_a and 62.5-fold in M_na. In both M_a and M_na the integral drag force of antenna fell from 0.22ǂ.07 to 0.12ǂ.04 dyn (1 dyn=1·10^-5 N), the duration of jerks increased from 0.06ǂ.01 to 0.1ǂ.02 s in the range from ~2.0 mg O₂ l^-1 to sublethal oxygen concentrations. At 0.7-0.8 mg O₂ l^-1 M_na stopped filtration and increased time spent swimming. In contrast, even under more severe hypoxia (~0.2 mg O₂ l^-1), M_a maintained their filtering activity using energy (up to 80% of total metabolism) achieved due to increased oxygen capacity of the blood. Separating locomotion and feeding functions, M. micrura can spend less energy for swimming and use its energy budget more plastically under changing environmental conditions.