Experimental evidence for direct nutrient assimilation by the lophophore of articulate brachiopods

The uptake of inorganic and non-nutritive organic molecules has been compared with uptake of nutritive molecules by the articulate brachiopod Terebratalia transversa (Sowerby). Only minimal uptake of Na₂ ¹⁴CO₃ and ¹⁴C-urea was observed, while ¹⁴C-glucose was concentrated extensively. After administration of a dilute solution of ¹⁴C-glucose over timed intervals, whole organ counts and autoradiographs showed that labelled material was accumulated along the exposed ciliated epidermal tissue of the lophophore and mantle and concentrated along the peritoneal lining of the coelom even before appearing in the gastrointestinal tract. The presence or absence of bacteria had little discernible effect upon extent and rate of uptake. The uptake experiments suggest that the lophophore not only creates an inhalent and exnalent current as is common in other filter-feeders, but also appears to be adapted for extraction of dilute nutrients in seawater. This ability of the lophophore to extract nutrients may help explain the evolutionary trend of the lengthening of the articulate lophophore and the reduction of the intestine to a short blind-ended gut.This work was supported by National Science Foundation Grant GB-20067.     

Patterns of shell repair in articulate brachiopods indicate size constitutes a refuge from predation

The cost of overcoming prey defenses relative to the value of internal tissues is a key criterion in predator/prey interactions. Optimal foraging theory predicts: (1) specific sizes of prey will result in the best returns to predators, and (2) there will often be a size at which the cost/benefit balance is low enough to effectively exclude predation. Data presented here on styles of repaired shell damage and size at which injury had been sustained was collected from samples of terebratulide brachiopods from the Antarctic Peninisula (Liothyrella uva), Falkland Islands (Magellania venosa and Terebratella dorsata) and Chile (M. venosa). The predominant form of damage on shells was indicative of predators attacking the valve margins. The modal size for repaired damage was more than 10 mm smaller than the modal size for the overall size distribution in each species and there were no repaired attacks in the largest size classes of any species. These data suggest that size forms a refuge from predation, as would be predicted by optimal foraging theory. The optimal sizes that predators appeared to attack vary between species, as do the sizes that provided a refuge from predation. High levels of multiple repairs (19% of the M. venosa population from the Falkland Islands sampled had 2 or more repairs) suggest that the mortality following attack is low, suggesting that many predators abandon their attacks.     

Genetic evidence for contrasting patterns of dispersal in solitary and colonial ascidians

In situ and in vitro observations indicate that brooding colonial ascidians commonly display limited larval dispersal, whilst the larvae of most solitary species are assumed to be widely dispersed. We used allozyme data to determine the population genetic consequences of reproduction and dispersal in a broadcast-spawning solitary ascidian and two brooding colonial species along the central and southern coast of New South Wales, Australia. We surveyed genetic variation at 2 to 9 variable loci for samples collected from 6 to 8 local populations of each of the stalked solitary species Pyura gibbosa gibbosa Heller, 1878; the social Stolonica australis Michaelsen, 1927 and the compound Botrylloides magnicoecum Hartmeyer, 1912. Samples from each local population displayed levels and patterns of genotypic diversity that were consistent with expectations for sexually-derived recruitment of both solitary zooids and separate colonies. However, we found clear differences in the structure of the populations of solitary and colonial species. Genotype frequencies within all nine samples of P. gibbosa gibbosa conformed to expectations for random mating (i.e. Hardy–Weinberg equilibria). Moreover, allele frequencies showed little variation among samples [mean standardised genetic variance (F _{S T} ) =0.002], which implies that local populations are strongly connected by larval dispersal. We estimate (via Wright's “island model”) that gene flow (N _e m) within this set of local populations is 125 effective migrants per generation, which is very similar to estimates obtained for other broadcast-spawning taxa in this region. In contrast, genotype frequencies within samples of both colonial species were characterised by large and statistically significant deficits of heterozygotes, consistent with expectations for highly limited dispersal of larvae or sperm. Moreover, local populations were highly differentiated (F _{S T} =0.201 and 0.202 for S. australis and B. magnicoecum, respectively) and N _e m was estimated to be ∼1.0 in each case. These values of F _{S T} and subsequent estimates of N _e m lie within the range of values reported for other New South Wales taxa with direct larval development, and imply that local populations are effectively closed to immigration. Received: 13 February 1997 / Accepted 18 July 1997     

Molecular genetic evidence for probable reticulate speciation in the coral genus Madracis from a Caribbean fringing reef slope

For many corals, the existence of morphologically distinct yet sympatric populations/species implies reproductive isolation. Conversely, the presence of many intermediate and overlapping morphologies combined with synchronous, mass spawning suggests incomplete reproductive isolation. In Madracis (Scleractinia: Astrocoeniina: Pocilloporidae), high levels of morphological plasticity among the five most commonly recognized species (M. mirabilis, M. senaria, M. decactis, M. formosa and M. pharensis) on Caribbean reefs led us to question species boundaries. Phylogenetic relationships were investigated at the intra-individual, inter-individual and inter-specific levels using the ITS1-5.8S-ITS2 region (ca. 613 bp) of the ribosomal DNA cistron. Inter-specific divergence was ca. 6%, while intra-individual and intra-specific divergences ranged from 0% to 4.9% and 3.3% to 3.5%, respectively. M. senaria and M. mirabilis formed monophyletic groups. M. formosa, M. decactis and M. pharensis formed a paraphyletic complex. High levels of intra-individual and intra-specific ITS polymorphism in the decactis-formosa-pharensis cluster may be the result of very recent speciation within the clade (i.e. maintenance of ancestral polymorphism and incomplete lineage sorting), or the result of repeated introgressive hybridization among the three taxa. Polymorphism parsimony of 89 sites, including nine that showed additivity, revealed a phylogenetic topology more consistent with inter-taxal hybridization. Results are discussed in terms of weak reproductive barriers, and phylogenetic fission and fusion under Veron's model of reticulate speciation in corals. Ecological studies involving Madracis should consider M. decactis, M. formosa and M. pharensis as a complex.     

Extinction, recolonization, and dispersal through time in a planktonic crustacean

Dormant propagule banks are important reservoirs of biological and genetic diversity of local communities and populations and provide buffering mechanisms against extinction. Although dormant stages of various plant and animal species are known to remain viable for decades and even centuries, little is known about the effective influence of recolonization from such old sources on the genetic continuity of intermittent populations under natural conditions. Using recent and old dormant eggs recovered from a dated lake sediment core in Kenya, we traced the genetic composition of a local population of the planktonic crustacean Daphnia barbata through a sequence of extinction and recolonization events. This was combined with a phylogeographic and population-genetic survey of regional populations. Four successive populations, fully separated in time, inhabited Lake Naivasha from ca. 1330 to 1570 AD, from ca. 1610 to 1720 AD, from ca. 1840 to 1940 AD, and from 1995 to the present (2001 AD). Our results strongly indicate genetic continuity between the 1840-1940 and 1995-2001 populations, which are separated in time by at least 50 years, and close genetic relatedness of them both to the 1330-1580 population. A software tool (Colonize) was developed to find the most likely source population of the refounded 1995-2001 population and to test the number of colonists involved in the recolonization event. The results confirmed that the 1995-2001 population most probably developed out of a limited number of surviving local dormant eggs from the previous population, rather than out of individuals from regional (central and southern Kenya) or more distant (Ethiopia, Zimbabwe) populations that may have immigrated to Lake Naivasha through passive dispersal. These results emphasize the importance of prolonged dormancy for the natural long-term dynamics of crustacean zooplankton in fluctuating environments and suggest an important role of old local dormant egg banks in aquatic habitat restoration.     

Genetic evidence for cryptic speciation in allopatric populations of two cosmopolitan species of the calcareous sponge genusClathrina

Many sponge species are considered to be cosmopolitan. However, the systematics of marine sponges are very difficult because of the paucity of taxonomically useful characters, and hence the apparently cosmopolitan nature of many species may be simply a consequence of this. In this paper, geographically distant populations of two pairs of cosmopolitan calcareous sponges of the genusClathrina were compared genetically.C. clathrus andC. cerebrum were collected by SCUBA diving between January and March 1989 from two localities: the Mediterranean Sea at La Vesse, near Marseille, Frances, at 9 to 12 m depth, and from the South West Atlantic at Arraial do Cabo, about 200 km east of Rio de Janeiro, at 2 to 10 m depth. Very high levels of gene divergence were found between the allegedly conspecific populations. The levels of genetic identity,I, observed are so low (I=0.128 and 0.287) that the populations clearly cannot be considered conspecific. New species names ofC. aurea sp. nov. andC. brasiliensis sp. nov. are therefore assigned to the southwest Atlantic counterparts ofC. clathrus andC. cerebrum, respectively. It is concluded that, at least for the species studied, and probably for many other species in taxonomically difficult groups, the actual distributions of single species may be far more geographically restricted than is generally assumed.     

Landscape history, fragmentation, and patch occupancy: models for a forest bird with limited dispersal.

We developed and tested patch occupancy models for an endemic understory bird with limited dispersal ability, the Chucao Tapaculo (Scelorchilus rubecula), in two South American temperate rain forest landscapes that differed in levels and duration of forest loss. We assessed cover changes since 1961 in each landscape and surveyed patches for Chucao Tapaculo occupancy. We then developed incidence-based predictive models independently for each landscape and tested each model reciprocally in the alternative study area. We thereby assessed the domain of model applicability and identified those predictor variables with general effects and those that varied between the two landscapes. The two models were consistent regarding variable selection, and predictive accuracy of each model was high in the landscape where training data were collected. However, the models differed substantially in the magnitudes of effects related to patch size, with larger unoccupied patches observed in the landscape with the more advanced stage of fragmentation. Due to this discrepancy, each model performed poorly when applied to the alternative landscape, potentially reflecting the contrasting stages of habitat loss. Although it was impossible to dissociate effects of level and duration of forest loss, we viewed the landscapes as representing two extremes along a continuum of fragmentation, providing insights into potential trajectories for portions of the biome where deforestation is occurring. Further, our data suggest that static equilibrium models developed from distribution patterns in recently fragmented landscapes may overestimate persistence when used as a forecasting tool, or when extrapolated to alternative landscapes where fragmentation is more advanced. Thus, we suggest that landscapes used as standards for model building should be selected with caution. We recommend that distribution patterns be obtained from landscapes where fragmentation is advanced, preferably with histories of fragmentation long enough that time-delayed extinctions already would have occurred.     

Phylogeographic patterns of the mysid Mesopodopsis slabberi (Crustacea, Mysida) in Western Europe: evidence for high molecular diversity and cryptic speciation

The phylogeographic patterns among populations of Mesopodopsis slabberi (Crustacea, Mysida), an ecological important mysid species of marine and estuarine habitats, were analysed by means of DNA sequencing of a fragment of the mitochondrial cytochrome c oxidase subunit I (COI) and the 16S ribosomal RNA genes. Samples of M. slabberi collected from five Atlantic and two Western Mediterranean populations were investigated. Very high levels of within-population molecular diversity were observed in all samples (mean h=0.807 and π=0.0083), with exception of the Mediterranean Ebro population which contained only one haplotype. Differentiation among populations was high, and a clear phylogeographic break was observed between the Atlantic and Mediterranean populations. Moreover, a strong differentiation was detected between both populations in the Western Mediterranean Sea (Alicante and Ebro delta), while two divergent lineages occurred in sympatry within the Atlantic Mondego estuary. The high congruence between both the COI and 16S rRNA sequence data, the reciprocal monophyly of the different mitochondrial clades and the levels of nucleotide divergence between them suggest the presence of a complex of cryptic species within M. slabberi. Estimations of divergence time between the different mitochondrial lineages indicate that a split occurred during the late Miocene/early Pliocene. Such a divergence could be concordant with vicariant events during sea-level drops within the Mediterranean region at that time. However, within the Mediterranean Sea, the potential of divergence through ecological diversification cannot be ruled out.     

Mitochondrial DNA sequence variation in spiny lobsters: population expansion,panmixia, and divergence

To investigate population differentiation in a comparative and historical context, segments of the mitochondrial cytochrome c oxidase subunit I gene and the control region were sequenced in Panulirus argus from nine sites along approximately 1,500 km of the Northern Caribbean Sea (n = 326) and analyzed with respect to available panulirid data. A mismatch analysis and Fu’s F _S test uncovered a signature of historical population expansion around the time of the Last Glacial Maximum. Significant population structure was not detected in the area. The data supported a hypothesis of panmixia resulting from ongoing larval transport by ocean currents and historical population expansion. Despite high intraspecific divergence levels at COI within Panulirus argus and several other Panulirus species, genetic species identification through DNA barcoding was feasible using either a modified distance threshold or a character-based approach.     

Biochemical genetic variation and evidence of speciation in Chthamalus barnacles of the tropical eastern Pacific Ocean

Gene-enzyme variation was studied electrophoretically within and between barnacle populations of the genus Chthamalus from 8 intertidal stations from central California to the Pacific coast of Panamá. Horizontal starch-gel electrophoresis separated and resolved 18 enzymes from 512 individual barnacles. A maximum of 25 gene-enzyme systems was interpretable from the resulting zymograms. Electrophoretic phenotypes and patterns of phenotypic variation generally conformed with those observed in other organisms. The amount of genetic variation within barnacle populations varied; average heterozygosity, for example, ranged from a low of 3.4% in a Mexican population of the C. fissus group to a high of 10.4% in C. anisopoma from the Gulf of California. Observed and expected average heterozygosities agreed in all population samples, indicating that these species are outbreeding. In contrast to the prediction stemming from a hypothesis that trophic stability regulates the amount of genetic variation in marine species, average heterozygosity tends to be positively correlated with latitude. Data from these and other barnacle species may support a hybrid environmental heterogeneity-trophic diversity model recently proposed to explain genetic variation in decapod crustaceans. Juxtaposition of individuals from different localities revealed numerous genetic differences among populations of the C. fissus group. At least three partially sympatric sibling species are separated by genetic distances as large as those observed between the C. fissus group and the distinct species C. dalli and C. anisopoma. A cladistic analysis places C. anisopoma close to the Mexican and Panamanian sibling species, with C. fissus from San Diego and C. dalli successively farther removed.     

Explaining long-distance dispersal: effects of dispersal distance on survival and growth in a stream salamander

Long-distance dispersal (LDD) may contribute disproportionately to range expansions, the creation of new evolutionary lineages, and species persistence in human-dominated landscapes. However, because data on the individual consequences of dispersal distance are extremely limited, we have little insight on how LDD is maintained in natural populations. I used six years of spatially explicit capture-mark-recapture (CMR) data to test the prediction that individual performance increases with dispersal distance in the stream salamander Gyrinophilus porphyriticus. Dispersal distance was total distance moved along the 1-km study stream, ranging from 0 to 565 m. To quantify individual performance, I used CMR estimates of survival and individual growth rates based on change in body length. Survival and growth rates increased significantly with dispersal distance. These relationships were not confounded by pre-dispersal body condition or by ecological gradients along the stream. Individual benefits of LDD were likely caused by an increase in the upper limit of settlement site quality with dispersal distance. My results do not support the view that the fitness consequences of LDD are unpredictable and instead suggest that consistent evolutionary mechanisms may explain the prevalence of LDD in nature. They also highlight the value of direct CMR data for understanding the individual consequences of variation in dispersal distance and how that variation is maintained in natural populations.     

Oxygen- and carbon-isotope analyses of the articulate brachiopodLaqueus californianus: a recorder of environmental changes in the subeuphotic zone

This study is the first systematic attempt to use oxygen and carbon isotopes in modern brachiopods to investigate seasonality and growth rates. A comparison of oxygen-isotope analyses of shells of living specimens ofLaqueus californianus dredged from 80 and 130 m off Santa Catalina Island, California, to available hydrographie data indicates that this articulate brachiopod secretes its shell in or close to oxygen isotopic equilibrium with ambient seawater. Periodic oxygen-isotope depletions appear to result from El Nino events. Unexpectedly low ¹³C values associated with the 1983 El Nino may be explained by increased bacterial activity or organic loading into the Southern California Bight associated with these warm-water pulses. Growth rates determined from annual cycles in ¹⁸O records are variable, but generally average between 2 and 3 mm yr^–1 for mature individuals. Because of the longevity ofL. californianus,¹⁸O profiles provide high-resolution seasonal temperature records spanning one to two decades. Our data suggest that oxygen isotopes in brachiopod shells can be utilized as monitors of environmental change in the subeuphotic zone.     

Heavy metal speciation,leaching and toxicity status of a tropical rain-fed river Damodar,India

Speciations of metals were assessed in a tropical rain-fed river, flowing through the highly economically important part of the India. The pattern of distribution of heavy metals (Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn) were evaluated in water and sediment along with mineralogical characterization, changes with different water quality parameters and their respective health hazard to the local population along the Damodar River basin during pre-monsoon and post-monsoon seasons. The outcome of the speciation analysis using MINTEQ indicated that free metal ions, carbonate, chloride and sulfate ions were predominantly in anionic inorganic fractions, while in cationic inorganic fractions metal loads were negligible. Metals loads were higher in sediment phase than in the aqueous phase. The estimated values of I_geo in river sediment during both the seasons showed that most of the metals were found in the I_geo class 0–1 which represents unpolluted to moderately polluted sediment status. The result of partition coefficient indicated the strong retention capability of Cr, Pb, Co and Mn, while Cd, Zn, Cu and Ni have resilient mobility capacity. The mineralogical analysis of sediment samples indicated that in Damodar River, quartz, kaolinite and calcite minerals were dominantly present. The hazard index values of Cd, Co and Cr were >?1 in river water, which suggested potential health risk for the children. A combination of pragmatic, computational and statistical relationship between ionic species and fractions of metals represented a strong persuasion for identifying the alikeness among the different sites of the river.     

Krill evolution and the Antarctic ocean currents: evidence of vicariant speciation as inferred by molecular data

The phylogenetic relationships of the Antarctic krill Euphausia superba, the key species in the Antarctic food web, and other Antarctic and sub-Antarctic cuphausiids have been investigated using the 16S ribosomal mitochondrial gene. The phylogenetic reconstructions indicated that the Antarctic species form a monophyletic clade separated by the non-Antarctic species. The results revealed a large genetic divergence between the Antarctic (E. superba and E. crystallorophias) and sub-Antarctic species (E. vallentini). The time of separation between these species, estimated from the molecular data, is around 20 million years ago, which is comparable with the geological time of the formation of a circum-Antarctic water circulation and the Antarctic Polar Frontal Zone. The euphausiid molecular phylogeny therefore represents evidence for vicariant speciation.     

Seasonal distribution and speciation of mercury in a gold mining area,north-west province,South Africa

The seasonal speciation of mercury (Hg) was determined in water, soil, and sediments from watersheds located in the North-West province of South Africa. The study area is known to have a long history of mining activities which also include the recovery of gold from old tailings. Both inorganic (IHg) and methyl mercury (MHg) were detected at high concentrations (up to 8480 μg IHg kg^?1 and 13 μg MHg kg^?1) in surface sediments during dry season. A considerable remobilization of Hg from bottom sediments was observed in water from dry to wet season as well as the migration of Hg away from pollution sources due to seasonal influences. Hg in sediments mostly has been speciated as Hg⁰. Enhancement of Hg methylation occurred mainly in deeper sediments at regions corresponding to the lowest redox potential, higher pH, and enrichment of IHg. Hg values in borehole waters were very high (up to 3310 ng L^?1) suggesting a serious contamination of the site groundwater which needs to be addressed urgently in order to minimize further impact that affects the Vaal River and other water systems located nearby.     

An assessment of sampling,preservation, and analytical procedures for arsenic speciation in potentially contaminated waters

This study was undertaken to ascertain optimal methods of sampling, preserving, separating, and analyzing arsenic species in potentially contaminated waters. Arsenic species are readily transformed in nature by slight changes in conditions. Each species has a different toxicity and mobility. The conventional field sampling method using filters of 0.45 μm in size could overestimate the dissolved arsenic concentrations, as passing suspended particles that can act as a sink or source of arsenic depending on the site condition. For arsenic species in neutral pH and iron-poor waters, the precipitation can be stable for up to 3 days without any treatment, but for longer periods, a preservative, such as phosphoric acid, is required. Also, the analytical procedure must be selected carefully because the levels and hydride generation efficiencies of arsenic in different species can vary, even for the same amount of arsenic. For arsenic speciation in samples that also include organic species, a hybrid high-performance liquid chromatography (HPLC) column and inductively coupled plasma mass spectrometry (ICP-MS) gave the best resolution and lowest detection limits. However, the procedure using a solid phase extraction (SPE) cartridge can be used economically and conveniently for analyzing samples containing only inorganic arsenic species, such as groundwater, especially that related to mine activity.     

Behaviour that influences dispersal and connectivity in the small,young larvae of a reef fish

Determining the scale of larval dispersal and population connectivity in demersal fishes is a major challenge in marine ecology. Historically, considerations of larval dispersal have ignored the possible contributions of larval behaviour, but we show here that even young, small larvae have swimming, orientation and vertical positioning capabilities that can strongly influence dispersal outcomes. Using young (11–15 days), relatively poorly developed (8–10 mm), larvae of the pomacentrid damselfish, Amblyglyphidodon curacao (identified using mitochondrial DNA), we studied behaviour relevant to dispersal in the laboratory and sea on windward and leeward sides of Lizard Island, Great Barrier Reef. Behaviour varied little with size over the narrow size range examined. Critical speed was 27.5 ± 1.0 cm s⁻¹ (30.9 BL s⁻¹), and in situ speed was 13.6 ± 0.6 cm s⁻¹. Fastest individuals were 44.6 and 25.0 cm s⁻¹, for critical and in situ speeds, respectively. In situ speed was about 50% of critical speed and equalled mean current speed. Unfed larvae swam 172 ± 29 h at 8–10 cm s⁻¹ (52.0 ± 8.6 km), and lost 25% wet weight over that time. Vertical distribution differed between locations: modal depth was 2.5–5.0 and 10.0–12.5 m at leeward and windward sites, respectively. Over 80% of 71 larvae observed in situ had directional swimming trajectories. Larvae avoided NW bearings, with an overall mean SE swimming direction, regardless of the direction to nearest settlement habitat. Larvae made smaller changes between sequential bearings of swimming direction when swimming SE than in other directions, making it more likely they would continue to swim SE. When swimming NW, 62% of turns were left (more than in other directions), which would quickly result in swimming direction changing away from NW. This demonstrates the larvae knew the direction in which they were swimming and provides insight into how they achieved SE swimming direction. Although the cues used for orientation are unclear, some possibilities seemingly can be eliminated. Thus, A. curacao larvae near Lizard Island, on average swam into the average current at a speed equivalent to it, could do this for many hours, and chose different depths in different locations. These behaviours will strongly influence dispersal, and are similar to behaviour of other settlement-stage pomacentrid larvae that are older and larger.     

北京市凉水河污灌区土壤重金属累积和形态分析

采用野外定点连续采样和室内分析相结合的方法,对北京市凉水河污灌区土壤中Cu、Zn、Cr、Pb、Ni等重金属在土壤中的累积及其化学形态进行了系统研究.结果表明,①凉水河污灌区土壤中重金属的质量分数均高于北京地区的土壤背景值,特别是Cu和Pb分别达到北京市土壤环境背景值的3.47倍和4.53倍,凉水河污灌区土壤已经发生明显的重金属累积.②土壤重金属元素之间相关分析表明研究地区存在重金属复合污染,土壤有机质与土壤重金属显著相关表明污灌可能是导致土壤重金属富集的重要原因;土壤各理化性质与土壤重金属相关性表现不一致,土壤重金属富集与迁移的影响因素复杂多样.③Tessier连续提取法测定土壤5种重金属的形态分布规律均为:残渣态>铁锰结合态>有机结合态>碳酸盐结合态>可交换态,铁锰结合态含量较高与污水中铁锰含量较高具有一定的关系;凉水河污灌区重金属潜在迁移能力顺序为:Cu>Zn>Pb>Ni>Cr.④综合分析各土壤重金属富集状况、形态分布及其生态毒性,Cu和Pb是凉水河污灌区土壤中需要优先控制的重金属.     

A mathematical model for dispersal of an annual plant population with a seed bank

In order to describe the spatial dispersion of a population of annual plants with a seed bank, we have formulated a delay integrodifference equation model. The plant population growth is considered as being dependent on the density of seedlings that spring from seeds of the two previous years. We have analyzed the effects of the seed bank on the total population size, on the population spatial distribution as well as on the population velocity of invasion. It is showed that the seed bank can significantly alter the dynamics of annual plants, since it can have both a stabilizing and a destabilizing effect on the total population and can also homogenize the spatial distribution of the plants.