Population genetics and systematics of theLeptasterias hexactis (Echinodermata: Asteroidea) species complex

Morphological characters and 14 enzyme loci were examined for 1 040 sea stars, currently recognized as forms ofLeptasterias hexactis, from Lynn Canal, Alaska, and Puget Sound, Washington, USA, between March 1988 and April 1989. Three morphologically and two genetically distinctLeptasterias forms were identified. The most common form found at both localities wasL. epichlora (Brandt)sensu Verrill.L. hexactis (Stimpson)sensu Verrill co-occurred withL. epichlora at all study sites and apparently hybridizes extensively withL. epichlora in the Puget Sound region, but rarely, if at all, in Alaska. The presumptive product of this hybridization morphologically resembledL. aequalis (Stimpson)sensu Fisher, and was conspicuously absent from Alaskan samples. Considerable genetic distance existed betweenL. epichlora andL. hexactis (Nei'sD=0.19±0.01) and moderate genetic differentiation occurred between populations of each species from Alaska and Washington (Weir and Cockerham'sF _RT =0.29±0.04 forL. epichlora and 0.21±0.15 forL. hexactis). A significant (p<0.05) deficiency in the proportion of heterozygous individuals was found compared to Hardy-Weinberg expectations (Wright's fixation index,F _ID=0.12±0.04 and 0.31±0.08 forL. epichlora andL. hexactis, respectively). However, mean observed heterozygosity for each species (0.09±0.03, 0.14±0.04 and 0.14±0.04 forL. epichlora, L. hexactis andL. aequalis, respectively) fell within the range of reported values for other asteroid species (ca. 0.04 to 0.37). The results of this study indicate that considerable genetic integrity is maintained betweenL. epichlora andL. hexactis, which warrants their recognition as distinct species despite their apparent hybridization in the Puget Sound region.     

Molecular phylogeny and zoogeography of marine sculpins in the genus Gymnocanthus (Teleostei; Cottidae) based on mitochondrial DNA sequences

Gymnocanthus is the most widely distributed genus in the family Cottidae, with six species distributed in the high-latitude area of northern hemisphere. To clarify the phylogenetic relationships and to estimate the divergence times of species in the genus, 2,548 bp of the partial sequences of the 12–16S rRNA, cytochrome oxidase subunit I and cytochrome b gene were analyzed. Our results suggest the monophyletic genus, which arose in the Aleutian Archipelago, divided into a shallow-water group and a deep-water group 8.1 million years ago (Ma). G. tricuspis of the shallow-water group firstly migrated from the Pacific to the Arctic Ocean 5.0 Ma when the Bering Strait first opened. A second migration occurred in the late Pliocene to early Pleistocene after which G. pistilliger and G. intermedius diverged 3.9 Ma. Our findings are discussed within an evolutionary and zoogeographic context.     

Clonal and solitary anemones (Anthopleura) of western North America: population genetics and systematics

Francis (1979) proposed that clonal and solitary forms of the anemone Anthopleura elegantissima are actually two species. In 1984 and 1985, samples from two to six California populations of all known forms and species of California Anthopleura were analyzed electrophoretically to determine their taxonomic relationships. Data from 14 enzymes and 18 loci, 17 of them polymorphic, show that the two forms of A. elegantissima are virtually identical electrophoretically, and there is no evidence of reduced gene flow between them. We conclude there are three species of Anthopleura in California: A. elegantissima (Brandt, 1835), A. xanthogrammica (Brandt, 1835) and A. artemisia (Dana, 1848). Genetic variation in the two species capable of asexual reproduction, A. elegantissima and A. artemisia, is extremely high, approximately 2.5 times that of the strictly sexual A. xanthogrammica.     

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     

Seasonal variation in some population parameters of Euchaeta species (copepoda: Calanoida)

Studies of the biology of oceanic copepods are few relative to those of coastal species. Females of the genus Euchaeta have spermatophores attached to the genital somite by the male and carry their broods of eggs attached to this somite, so defining the breeding season. Populations of E. norvegica in the fjordic environment of Loch Etive (collected between 1971 and 1974 and from 1978 to 1979), Scotland and in the marginal oceanic region of the Rockall Trough, northeastern Atlantic Ocean (collected between 1973 and 1976) and of a further eight species of Euchaeta in the Trough are examined. Seasonal changes in the incidence of egg masses and spermatophores attached to the females, sex ratio and population numbers are determined. Sampling errors in the estimation of these parameters are larger in the oceanic Rockall Trough. The Loch Etive populations of E. norvegica produce two generations per year with a proportion, variable between years, of the population producing a third generation. This species produces a single annual generation in the Rockall Trough as do E. acuta and E. pseudotonsa. Two generations per year are probably passed through by E. gracilis in the Trough while the large bathypelagic E. sarsi may produce a single generation in the autumn of every second year. The other bathypelagic species, E. barbata, E. scotti, E. abbreviata and E. longissima, breed continuously throughout the year and no estimate of their generation times is possible. Consequently, this approach to population analysis is useful where breeding is seasonal, but resolving generation time in bathypelagic crustaceans remains a problem.     

Lipid storage and composition in tropical surgeonfishes (Teleostei: Acanthuridae)

The lipid composition of tropical marine reef fishes is poorly known, despite their use as food by local human populations and recent interest in health-related benefits of fish lipids. We examined the composition of lipids from epaxial muscle, liver, and two storage sites [mesenteries surrounding the gut (intraperitoneal fat, IPFs) and retroperitoneal fat bodies (FBs) posterior to the peritoneal cavity] in three species of surgeonfishes from Ishigaki Island, Japan: Naso lituratus (Bloch and Schneider, 1801), Acanthurus lineatus (Linnaeus, 1758), and A. bariene (Lesson, 1830). Triacylglycerols dominated all samples of neutral lipid and constituted ≥ 99% of FBs and IPFs. Polar lipids generally contained large fractions of phosphatidylethanolamine and phosphatidylcholine. Quantified fatty acids ranged in length from C₁₄ to C₂₄. C₁₆ fatty acids prevailed (>35% of neutral fatty acids, >23% of polar fatty acids), although C₁₈ (>16 and >14%, respectively) and C₂₀ acids (>8 and >19%, respectively) were also common. Saturated fatty acids, dominated by palmitic acid (16:0), comprised 38.7 to 50.7% of acids from neutral lipids and 30.8 to 41.1% from polar lipids. The most common monounsaturated acids were 18:1n9 and 20:1n9. Polyunsaturated acids were prevalent in polar lipids (especially 20:4n6, 20:5n3, 22:2n3, 22:5n3, 22:5n6 and 22:6n3). Common polyunsaturated acids of neutral lipids were 18:2n6, 18:4n3, several n-3 and n-6 C₂₀ acids, 22:2n3 and 22:5n3. IPF and FB were almost identical across species, and lipids of fat bodies (IPFs, FBs) were more similar to those of muscle than those of liver for all three species. The FBs appear to constitute an accessory storage site, which overcomes constraints on lipid storage imposed by a small, inflexible abdominal cavity that contains both viscera and consistently voluminous gut contents. Fatty acid signatures indicate that largely overlooked epiphytic or epilithic diatoms contribute significantly to lipid acquisition. The combination of large quantities of both saturated and n-3 and other polyunsaturated fatty acids in surgeonfishes, in contrast to low saturates and high polyunsaturated acids in lipids of commercially important cool-water fishes, suggests that a study of dietary effects of fish lipids on human inhabitants of the tropics may be instructive insofar as human health and nutrition are concerned. Received: 16 March 1998 / Accepted: 6 August 1998     

Polymorphism in gigantobacterial symbionts in the guts of surgeonfish (Acanthuridae: Teleostei)

The morphology and partial cytology of a group of bacteria-related organisms from the guts of surgeonfish are described. These gigantobacteria symbionts are encountered in the guts of various species of this fish family throughout the Indo-Pacific region and the Red Sea. They have been tentatively grouped and placed in a “family”, Epulopiscidae, according to the first species described, Epulopiscium fishelsoni Montgomery and Pollak, 1988. In addition to a morphological comparison between the various forms from different species of surgeonfish, suggestions are presented with regard to their possible morphological diversification during evolutionary and host-species specificity. Received: 10 June 1998 / Accepted: 29 October 1998     

Histology and ultrastructure of the skin of Lepadichthys lineatus (Gobiesocidae: Teleostei)

The skin of the Red Sea clingfish Lepadichthys lineatus Briggs, 1966, which lives on shallow-water crinoids, consists of a continuous layer of giant mucus-producing cells. Upon stimulation, these cells are able, in seconds, to envelope the fish entirely with a thick layer of their secretion. The cells are 75 to 290 high, and are enveloped by septa of compressed epithelium. They rest on a strong collagenous layer, and extend to the skin surface, where they open. The nuclei of the giant cells are large, and irregularly shaped; their cytoplasm has a very extensive endoplasmic reticulum and undergoes deep structural changes during maturation. Their ability to produce large amounts of mucus seems to be an adaptive device to protect the fish from contact with the rough surface of the crinoid host.     

Differences in feeding ecology among three co-occurring species of wrasse (Teleostei: Labridae) on rocky reefs of temperate Australia

The foraging behaviours and dietary compositions of three co-occurring labrids (Ophthalmolepis lineolatus, Notolabrus gymnogenis and Pictilabrus laticlavius), which are conspicuous on rocky reefs in temperate south-eastern Australia, were investigated between 2003 and 2005. SCUBA observations at two locations showed that the feeding intensity, and hence the associated effects of these fishes on rocky reef invertebrate prey, was temporally consistent. Relative differences in the contributions of ingested prey and use of different feeding microhabitats demonstrated that the feeding ecology differed significantly among the three species. Thus, O. lineolatus fed on proportionately higher volumes of polychaetes, polyplacophorans, marginellid gastropods (especially Austroginella sp.), bivalves and echinoids, which were sighted opportunistically in a wide selection of microhabitats, but particularly in sand/rubble. Ambush hunting was used regularly by smaller N. gymnogenis and all sizes of P. laticlavius to forage on amphipods, small decapods and small gastropods at algal bases or fronds and Diopatra dentata tubes. Amphipods were similarly important in the diet of smaller O. lineolatus. Larger N. gymnogenis foraged opportunistically over an increased reef area and made greater use of microhabitats that offered minimal prey refuge (e.g. sand/rubble, bare rock/steel) from which common prey, in particular decapods, were obtained. The significant intra- and inter-specific differences in dietary compositions, allied with differences in the use of feeding microhabitats, would facilitate co-occurrence of these three conspicuous species and contribute to maintaining high richness of labrid species in reef systems. Echinoids were regularly consumed by each species but they made a moderate contribution to the diet of only O. lineolatus, which suggests that only one of the three labrids is likely to play a significant role in regulation of echinoid densities in these rocky reef habitats. However, the broad diets and diverse forging strategies employed by these labrid species imply that they have a system-wide influence on invertebrate prey on rocky reefs.     

A molecular phylogeny of the Patellogastropoda (Mollusca: Gastropoda)

Phylogenetic analyses of partial 18S rDNA sequences from species representing all living families of the order Patellogastropoda, most other major gastropod groups (Cocculiniformia, Neritopsina, Vetigastropoda, Caenogastropoda, Heterobranchia, but not Neomphalina), and two additional classes of the phylum Mollusca (Cephalopoda, Polyplacophora) confirm that Patellogastropoda comprises a robust clade with high statistical support. The sequences are characterized by the presence of several insertions and deletions that are unique to, and ubiquitous among, patellogastropods. However, this portion of the 18S gene is insufficiently informative to provide robust support for the monophyly of Gastropoda, or to address the division of the Gastropoda into the subclasses Eogastropoda (= Patellogastropoda + hypothetical coiled ancestors) and Orthogastropoda. These sequence data invariably group Patellogastropoda in a weakly supported clade with cocculiniform limpets, despite greater sequence divergences between Patellogastropoda and “Cocculiniformia” than between the Patellogastropoda and Orthogastropoda. Partial 18S sequences support the inclusion of the family Neolepetopsidae within the superfamily Acmaeoidea, and refute its previously hypothesized position as sister group to the remaining living Patellogastropoda. This region of the 18S rDNA gene diverges at widely differing rates, spanning an order of magnitude among patellogastropod lineages, and therefore does not provide meaningful resolution of the relationships among higher taxa of patellogastropods. Data from one or more genes that evolve more uniformly and more rapidly than the 18S rDNA gene (possibly one or more of the mitochondrial genes) seem more likely to be informative about relationships within Patellogastropoda. Received: 5 February 1999 / Accepted: 16 May 2000     

Planktonic larval duration of one hundred species of Pacific and Atlantic damselfishes (Pomacentridae)

The plankton larval duration for 100 species of Pacific and Atlantic damselfishes was estimated from daily growth increments on the otolith of juvenile fish collected at various localities between July 1987 and September 1988. For newly-settled fishes, larval duration was determined by counting the entire number of increments present on the otolith, while for older juveniles estimates were made by counting the number of increments between the center of the otolith and a mark corresponding to settlement. We document the development of otolith formation during the period when eggs are incubated on the reef and show that daily increments are only accreted after larvae hatch and enter the planktonic phase. The planktonic larval duration for damselfish is shorter and less variable, both between and within species, compared to other groups of reef fishes such as wrasses and surgeonfishes. Larval duration ranged from 12 to 39 d. Average duration between species ranged from 13.1 to 35.2 d. The time spent in the plankton was not significantly correlated with geographic distribution when evaluated among species, however, genera with confined regional distribution have a shorter mean larval life than do widely distributed genera. Size at settlement was positively correlated with time spent in the plankton among species, but a significant correlation between these variables was only evident within one of ten species. The low variance in planktonic larval duration within species indicates that most damselfish are unable to delay metamorphosis following competency. This inability to postpone settlement limits the potential for dispersal, especially when dispersal time between suitable habitats is greater than about 30 d.     

Mitochondrial DNA sequence variation in deep-sea bamboo coral (Keratoisidinae) species in the southwest and northwest Pacific Ocean

The Keratoisidinae are a poorly known, but phenotypically diverse group of deepwater corals. Recent developments in deepwater trawling in the southwest Pacific have provided many more specimens of bamboo corals. Two sub-regions of the mitochondrial genome were sequenced to test genetic relationships among specimens collected over a wide geographical range (27–50° S): a sub-region of the large-subunit rRNA (16S rRNA), characterized by a highly variable insertion/deletion (INDEL#2) region; and a non-coding region between COII and COI. Based on DNA haplotypes, 14 species of Keratoisidinae were recognized among 88 specimens from deep water in the southwest Pacific Ocean. The common haplotypes also appeared in specimens collected in the northwest Pacific Ocean and may indicate that some bamboo coral species are widespread in the Pacific, or that the mitochondrial markers are insensitive to recent speciation events. Many specimens were taken from flat bottom areas and, contrary to assumptions, the bamboo corals are not endemic to seamounts. The closure of some seamounts to trawling will protect bamboo corals from extinction, but not from local depletion.Communicated by M.S. Johnson, Crawley     

Sexual maturity and hermaphroditism of the red porgy Pagrus pagrus (Teleostei: Sparidae)

Gonadal changes related to sexual maturity were examined by histology in reared populations of the red porgy Pagrus pagrus L., aged 0.5 to 6.5 years. More than 50% of red porgies were mature at the age of 4 years although some individuals were already mature at the age of 3, as indicated by changes in the gonadosomatic index, plasma levels of vitellogenin, 17β-estradiol and testosterone in females and males. Sex frequency distribution analysis in relation to the age and histological analysis of the gonads indicated the presence of males originated from the sex change of adult functional females. P. pagrus is a protogynous species. Some females had not changed sex up to the age of 6.5 years. Received: 16 July 1998 / Accepted: 29 April 1999     

Social organization and sexual pattern in the Mediterranean parrotfish Sparisoma cretense (Teleostei: Scaridae)

We examined the social organization and reproductive pattern of a population of Sparisoma cretense L. at Lampedusa Island (Italy). During the breeding season (July to September) individuals occur either in territorial or in non-territorial groups, which quantitatively differ with respect to use of space, sex-ratio and sexual activity. Territorial groups consist of one male plus one to three females, whereas in non-territorial groups as many as 54 fish share a common area. Among non-territorial groups, variations, in both sex-ratio and behavior, suggest they could represent either feeding aggregations or reproductive aggregations. Spawning, always in pairs, occurs daily in a short period of time before dusk and has been observed only in territorial groups. Group spawning has never been observed, but another alternative mating tactic, streaking on pair spawning, was recorded. In the non-breeding season fish do not aggregate in organized social units. Histological examination of gonads showed that adults are larger than 12 cm total length. Females have an asynchronous ovary, typical of species spawning several times during the breeding season. Males show secondary testes, indicating that their gonads develop ovaries as juveniles, which are later redifferentiated into functional testes. Histological and demographic data seem to indicate that, as in other species of this genus, prematurational sex-change occurs. The sexual pattern appears to be essentially gonochoristic, but the potential for sex-change is not excluded. Received: 5 January 1999 / Accepted: 22 June 1999     

Osteological development of the vertebral column and of the fins in Diplodus sargus (Teleostei: Perciformes: Sparidae)

The osteological development of vertebral column and fins in white sea bream, Diplodus sargus (Linnaeus, 1758) was studied. Vertebral ontogeny started at 5.7 mm total length (TL, post-fixation), with the formation of the first cartilaginous neural and haemal arches, and was completed by the full attainment of dorsal ribs (20.8 mm TL). The formation of vertebral centra occurred between 7.3 and 9.4 mm TL, but was fully completed only after the development of post- and pre-zygapophyses (26.0 mm TL). Pectoral supports were the first fin elements that started to develop (3.8 mm TL), followed by those of the caudal fin (5.2 mm TL), dorsal and anal fins (6.7 mm TL), and then by those of the pelvic fin (9.5 mm TL). The caudal fin of D. sargus was the first to develop fin rays and attain the full count of lepidotrichia (5.6-7.8 mm TL), but the last to attain the full count of dermatotrichia (7.9-16.0 mm TL). The next fins starting to present rays were the pectoral (6.5 mm TL) and the dorsal and anal fins (7.5 mm TL), while the pelvic fins were the last (11.5 mm TL). Following the caudal lepidotrichia (7.8 mm TL), the anal (10.5 mm TL), dorsal (12.0 mm TL), pectoral (11.4 mm TL) and pelvic fins (12.5 mm TL) were the next with fully completed ray counts. Finally, fin meristics were fully developed with the caudal dermatotrichia. The results are discussed in comparison with the fin and vertebral ontogeny of other teleosts.     

Duration of the planktonic larval stage of one hundred species of Pacific and Atlantic wrasses (family Labridae)

The planktonic larval durations of a preliminary sample of one hundred species of wrasses from both the Pacific and Atlantic Oceans were estimated with the use of the daily otolith-increment aging-technique. Larval durations were determined by counting the number of daily increments between the center of the otolith and the mark corresponding to settlement. The duration of the planktonic larval phase of wrasses appears to be extremely variable between species, ranging from 15 d in Diproctacanthus xanthurus to 121 d in a specimen of Thalassoma ballieui. Larval durations within species were also variable, especially in species with relatively long durations. Congeners tended to have similar larval durations and similar otolith-increment characteristics. Hawaiian and Eastern Pacific species had longer larval durations than their Caribbean or Western Pacific congeners. Similarly, Hawaiian populations had significantly longer larval durations than their Western Pacific conspecifics. The implications of these findings for biogeographical studies are discussed.     

Population genetics of the northern Pacific seastar Asterias amurensis (Echinodermata: Asteriidae): allozyme differentiation among Japanese,Russian, and recently introduced Tasmanian populations

The northern Pacific seastar Asterias amurensis Lütken was recently introduced to Tasmanian waters, possibly through ballast water discharged from ocean-going vessels. Three Tasmanian populations and seven native populations from Japan and eastern Russia were examined in 1994 for variation at 22 allozyme loci. There was significant spatial heterogeneity in gene frequencies among the native populations, especially for the ocus APK ^*, where G _ST was a very high 0.47. The Tasmanian populations could not be separated genetically from one another, suggesting they have a common origin from a single introduction. The average heterozygosity per locus of the Tasmanian populations (0.116 to 0.127, mean 0.123) was 30 to 40% less than that of the native populations (0.177 to 0.216, mean 0.192), suggesting that colonisation of Tasmanian waters was accompanied by a population-size bottle-neck. The Tasmanian seastars were genetically more closely related to the two populations from central Japan (Suruga and Tokyo Bays) than to populations from Vladivostok, northern Japan (Yoichi, Nemuro and Mutsu Bays) or southern Japan (Ariake Sea). However, there were significant differences between the populations from Tasmania and central Japan, which may be attributable to founder effects or may mean that the true source of the Tasmanian introduction has yet to be identified.