Evolution ofPeperomia (Piperaceae) in the Juan Fernandez Islands,Chile

Four species ofPeperomia (Piperaceae) occur in the Juan Fernandez Islands, Chile:P. berteroana, P. margaritifera, P. skottsbergii, andP. fernandeziana. The last species is found also in continental Chile, whereas the other three are endemic to the archipelago.Peperomia margaritifera is found only on the older island of Masatierra, whereasP. skottsbergii is confined to the younger island of Masafuera, andP. berteroana occurs on both islands. Phenetic analyses of mainland taxa suggest thatP. fernandeziana belongs to subg.Sphaerocarpidium whereas the endemic taxa form their own subg.Tildenidium connecting to subg.Tildenia. Cladistic analyses indicate thatP. margaritifera is the most primitive species in the archipelago and thatP. berteroana is the most derived, especially patristically. Chromosomally, the four species are all n = 22, which may be tetraploid on a base of x = 11. Sulfated flavones occur only inP. berteroana andP. skottsbergii, which are otherwise unknown for the family. Dispersal of propagules to the islands from the continent and between islands is believed to have been accomplished by birds.     

Evolutionary Patterns in Pearl Oysters of the Genus <Emphasis Type="Italic">Pinctada</Emphasis> (Bivalvia: Pteriidae)

Pearl oysters belonging to the genus Pinctada (Bivalvia: Pteriidae) are widely distributed between the Indo-Pacific and western Atlantic. The existence of both widely distributed and more restricted species makes this group a suitable model to study diversification patterns and prevailing modes of speciation. Phylogenies of eight out of the 11 currently recognised Pinctada species using mitochondrial (cox1) and nuclear (18S rRNA) data yielded two monophyletic groups that correspond to shell size and presence/absence of hinge teeth. Character trace of these morphological characters onto the molecular phylogeny revealed a strong correlation. Pinctada margaritifera appears polyphyletic with specimens from Mauritius grouping in a different clade from others of the French Polynesia and Japan. Hence, P. margaritifera might represent a species complex, and specimens from Mauritius could represent a different species. Regarding the putative species complex Pinctada fucata/Pinctada martensii/Pinctada radiata/Pinctada imbricata, our molecular analyses question the taxonomic validity of the morphological characters used to discriminate P. fucata and P. martensii that exhibited the lowest genetic divergence and are most likely conspecific as they clustered together. P. radiata and P. imbricata were recovered as monophyletic. The absence of overlapping distributions between sister lineages and the observed isolation by distance suggests that allopatry is the prevailing speciation mode in Pinctada. Bayesian dating analysis indicated a Miocene origin for the genus, which is consistent with the fossil record. The northward movement of the Australian plate throughout the Miocene played an important role in the diversification process within Pinctada.     

Species identity and phylogenetic relationship of the pearl oysters in Pinctada Röding, 1798 based on ITS sequence analysis

Analysis of ITS 1 and ITS 2 sequences in the pearl oysters Pinctada albina, Pinctada chemnitzi, Pinctada fucata, Pinctada fucata martensii, Pinctada imbricata, Pinctada margaritifera, Pinctada maxima, Pinctada nigra and Pinctada radiata was carried out. Homogeneity test of substitution patterns suggests that GC contents are highest in P. margaritifera and P. maxima and chromosomal rearrangements occurred in P. chemnitzi. These observations indicate that P. margaritifera and P. maxima are primitive species and P. chemnitzi is a recent species. Phylogenetic analysis shows that the pearl oysters studied constitute three clades with P. margaritifera and P. maxima forming the basal clade, congruent with results revealed by the substitution pattern test. The second clade consists of P. fucata, P. fucata martensii and P. imbricata. Low genetic distances among these taxa indicate that they may be conspecific. The remaining species make up the third clade and low genetic divergence between P. albina and P. nigra suggests that they may represent the same species. The ITS 1 sequence of P. radiata in GenBank is almost identical to that of P. chemnitzi determined in the present study and we suspect that the specimen used for the P. radiata sequence was misidentified.     

Trophic relationships between the larvae of two freshwater mussels and their fish hosts

Freshwater mussels of the order Unionoida have life cycles that include larval attachment to and later metamorphosis on suitable host fishes. Information on the trophic relationship between unionoid larvae and their host fishes is scarce. We investigated the trophic interaction between fish hosts and encysted larvae of two species of freshwater mussels, Margaritifera margaritifera and Unio crassus, using stable isotope analyses of larvae and juvenile mussels as well as of host fish gill and muscle tissues before and after infestation. Due to different life histories and durations of host‐encystment, mass and size increase in M. margaritifera during the host‐dependent phase were greater than those of U. crassus. δ¹³C and δ¹⁵N signatures of juvenile mussels approached isotopic signatures of fish tissues, indicating a parasitic relationship between mussels and their hosts. Shifts were more pronounced for M. margaritifera, which had a five‐fold longer host‐dependent phase than U. crassus. The results of this study suggest that stable isotope analyses are a valuable tool for characterizing trophic relationships and life history strategies in host–parasite systems. In the case of unionoid mussels, stable isotopic shifts of the larvae are indicative of the nutritional versus phoretic importance of the host.     

The food and growth of pelagic 0+ Alestes nurse (Characidae) from the Blue Nile,near Khartoum

The food, feeding habits and growth of 0+ Alestes nurse (Rüppel) from the Blue Nile near Khartoum, was investigated. 0+ A. nurse were observed to change their food from phytoplankton and small zooplankton during their pre-metamorphosis stages, to larger zooplankton (Daphnia spp., Chydorus sp.) and insects (larvae, pupae and imagines) during their post-metamorphosis stage.Their growth in length and weight was characterized by two distinct stanzas; during the first stanza, the fish increased in total length at a rate of 0.196 mm mm^–1 wk^–1, and in wet weight at a rate of 0.430 g g^–1 wk^–1. These rates were reduced during the second stanza to 0.046 mm mm^–1 and 0.080 g g^–1 wk^–1, respectively. The calculated value of the exponent b in their length-weight relationship suggested that their growth was allometric.     

Characterization of MRNP34, a novel methionine-rich nacre protein from the pearl oysters

Nacre of the Pinctada pearl oyster shells is composed of 98% CaCO₃ and 2% organic matrix. The relationship between the organic matrix and the mechanism of nacre formation currently constitutes the main focus regarding the biomineralization process. In this study, we isolated a new nacre matrix protein in P. margaritifera and P. maxima, we called Pmarg- and Pmax-MRNP34 (methionine-rich nacre protein). MRNP34 is a secreted hydrophobic protein, which is remarkably rich in methionine, and which is specifically localised in mineralizing the epithelium cells of the mantle and in the nacre matrix. The structure of this protein is drastically different from those of the other nacre proteins already described. This unusual methionine-rich protein is a new member in the growing list of low complexity domain containing proteins that are associated with biocalcifications. These observations offer new insights to the molecular mechanisms of biomineralization.     

Food and feeding habits of Labeo niloticus (Pisces,Cyprinidae) in Jebel Aulia Reservoir,Sudan

Basic knowledge on the feeding ecology of one of the common and commercially important fish species in Jebel Aulia Reservoir is provided.The structure of the feeding apparatus indicates that Labeo niloticus is a bottom feeder, depending on soft and decayed vegetation, organic debris and whatever small organisms found within. However, juveniles and fry are prone to explore all layers and depths of the river selectively for plankton. There is little evidence of seasonal selection of food. Changes in diet quality are governed by the availability of type of food. Variability of feeding activity is connected with climate and breeding season.     

Variability of Ribosomal DNA ITS-2 and Its Utility in Detecting Genetic Relatedness of Pearl Oyster

The objective of this study was to detect interspecific and intraspecific genetic variations of the second internal transcribed spacer of ribosomal DNA (ITS-2), and explore the feasibility of using it as a molecular marker phylogenetic analyses and species identification among pearl oysters. ITS-2 sequences of 6 pearl oysters were amplified via polymerase chain reaction. The amplified DNA fragments were about 500 bp, spanning the partial sequences of 5.8S and 28S rRNA genes. The GC contents of all species used in this study were higher than the AT contents. The variations of sequences involved substitutions as well as insertions/deletions and were mainly concentrated in spacer regions. Sequences of about 30-bp in spacer regions showed no variations among 5 Pincatda species. Intraindividual and intraspecific polymorphisms of ITS-2 sequences were detected in some species; the interspecific variability was significantly larger than the variability within species, and the variability at the genus level was higher than that at the species level. Both neighbor-joining and parsimony analyses of ITS-2 sequences revealed the distinguishable species boundary of 6 pearl oysters, and indicated that P. chemnitzi and P. nigra were the closely related species, as were P. maxima and P. margaritifera. The findings revealed that ITS-2 sequences could be an appropriate tool for phylogenetic study of pearl oysters.     

Results of testing the comparatory method: The curvature of the shell valve frontal section is inappropriate as a systematic character for the freshwater pearl mussel of the genus Margaritifera

This paper continues a discussion on the number of pearl mussel species of the genus Margaritifera in northern Europe. A biometric study of 1711 pearl mussel Margaritifera margaritifera shells from 15 rivers in Russia and Latvia (basins of the White and Baltic seas) has been conducted. All the examined samples fall into two groups: the northern group (with the shells more flattened on average, f. margaritifera) and the southern one (with more convex shells, f. elongata); the boundary between these groups is at 63° N. Analysis of intrapopulation variation has shown that the samples contain individuals that correspond to f. margaritifera, f. elongata, and f. borealis. However, any hiatus between these forms is absent in all the samples, and individuals belonging to two intermediate forms are rather frequent. The hypothesis on the species specificity of the shell valve frontal section has not been confirmed based on examination of large shell samples. The pearl mussels inhabiting rivers of Northern Europe belong to a single species, M. margaritifera.     

Drainage-independent genetic structure and high genetic diversity of endangered freshwater pearl mussels (<Emphasis Type="Italic">Margaritifera margaritifera</Emphasis>) in northern Europe

Freshwater pearl mussels (Margaritifera margaritifera) are among the most critically threatened bivalve molluscs worldwide. An understanding of spatial patterns of genetic diversity is crucial for the development of integrative conservation strategies. We used microsatellites to study the genetic diversity and differentiation of 14 populations of M. margaritifera in central Sweden, an area which was described as a major secondary contact zone in postglacial colonisation for other species. Genetic diversity of Swedish pearl mussel populations was much greater than in central and southern Europe but similar to the genetic diversity observed in the northeastern portion of their European range. Genetic differentiation among populations was pronounced but to a large extent independent from present-day drainage systems. The complex patterns of genetic diversity and differentiation in pearl mussel seem to be strongly influenced by the species’ high degree of specialisation and extraordinary life history strategy which involves facultative hermaphrodism and an obligatory encystment stage on a host fish. Genetic drift effects and anthropogenic disturbances resulting in reduction of population size and loss of connectivity are less pronounced in northern pearl mussel populations compared to those in central and southern Europe.     

The Mendelian inheritance of rare flesh and shell colour variants in the black‐lipped pearl oyster (Pinctada margaritifera)

Pinctada margaritifera is French Polynesia's most economically important aquaculture species. This pearl oyster has the specific ability to produce cultured pearls with a very wide range of colours, depending on the colour phenotypes of donor oysters used. Its aquaculture is still based on natural spat collection from wild stocks. We investigated three rare colour variants of P. margaritifera – orange flesh, and red and white shell colour phenotypes – in comparison with the wild‐type black flesh and shell commonly found in this species. The study aimed to assess the geographic distribution and genetic basis of these colour variants. Colour frequencies were evaluated during transfer and graft processes of pearl oyster seed captured at collector stations. Among the collection locations studied, Mangareva Island showed the highest rate of the orange flesh phenotype, whereas Takaroa and Takume atolls had relatively high rates of red and white shell phenotypes respectively. Broodstocks were made of these rare colour variants, and crosses were performed to produce first‐ and second‐generation progenies to investigate segregation. The results were consistent with Mendelian ratios and suggest a distinct model with no co‐dominance: (i) a two‐allele model for flesh trait, whereby the orange allele is recessive to the black fleshed type, and (ii) a three‐allele model for shell trait, whereby the black wild‐type allele is dominant to the red coloration, which is dominant to the white shell. Furthermore, the proposed model provides the basis for producing selected donor pearl oyster lines through hatchery propagation.     

Population density and age structure of the freshwater pearl mussel, Margaritifera margaritifera, in two Iberian rivers

1. The European freshwater pearl mussel, Margaritifera margaritifera (Bivalvia: Unionoida), is one of the most threatened mussels. The Iberian populations of this species are considered peripheral because their distinct characters such as growth rate and longevity, and require development of effective conservation strategies. 2. We assessed population density and age structure of pearl mussels in two Galician rivers (Eo and Masma in north‐west Spain). Four sampling sites were selected in each river to cover stretches of 100 m. The mean density of mussels in each of these sampling transects was estimated using the adaptive sampling technique, given that mussels occur at low densities and are highly aggregated in these rivers. 3. Age structure was inferred for each population using length–age keys. The empty shells encountered during sampling were used to determine the length of the specimens at different ages (years), together with length‐at‐age data from shells previously analysed for computing growth rates from the same rivers. Water samples from both rivers were analysed for typical physicochemical parameters. 4. Mean densities were very variable, even within the same river (from 0.27 to 6.55 m^?2 in the River Eo and from 0.98 to 2.38 m^?2 in the River Masma). Individuals in the 0‐ to 5‐year age class were scarce in both rivers. 5. Margaritifera margaritifera showed a preference for the strip of river bed within 1.5 m from the river bank and avoided sites at greater distances. The species also showed a preference for sites with more than 80% tree cover and avoided sites with <50% cover. 6. Iberian populations exhibit the highest growth rate, together with the lowest maximum age and maximum length known for M. margaritifera. Detailed knowledge about these peripheral Iberian populations will contribute to developing strategies for conservation and management of this endangered species.     

Food preference of Sancassania polyphyllae (Acari: Acaridae): living entomopathogenic nematodes or insect tissues?

Sancassania polyphyllae (Acari: Acaridae) adult female mites will feed on insect cadavers and infective juveniles (IJs) of entomopathogenic nematodes. Our objective was to determine whether S. polyphyllae has a food preference when offered a choice between tissues of Polyphylla fullo (Coleoptera: Scarabaeidae) or Galleria mellonella (Lepidoptera: Pyralidae), or IJs of Steinernema feltiae (Rhabditida: Steinernematidae) or IJs of Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae). When offered a choice between no food and one of the different food sources, P. fullo, G. mellonella or S. feltiae IJs, S. polyphyllae had a significant preference for food sources compared to no food. When it was offered either no food or H. bacteriophora, there was no significant difference in the mite distribution. When offered two different food choices, P. fullo or G. mellonella, P. fullo or S. feltiae, and P. fullo or H. bacteriophora, the mite showed significant preferences for P. fullo larvae. In S. feltiae vs. G. mellonella and S. feltiae vs. H. bacteriophora experiments, S. polyphyllae showed significant a preference for S. feltiae. In three-choice experiments, S. polyphyllae had a preference for P. fullo, followed by S. feltiae, G. mellonella and H. bacteriophora, respectively. Our data confirm, in part, our hypothesis that when offered different food choices, this mite species prefers tissues of its phoretic host, P. fullo over lepidopteran host tissues or living IJs. Based on these laboratory data, H. bacteriophora should be used as a biological control agent against P. fullo over a Steinernema species.     

Influence of the filamentous cyanobacterium Planktothrix agardhii on population growth and reproductive pattern of the rotifer Brachionus calyciflorus

The population dynamics of B. calyciflorus was investigated using a green alga, Monoraphidium minutum, and a blue-green alga Planktothrix agardhii as food sources, separately and as mixtures. Growth rate (r), egg ratio (ER), and juvenile development time (D _j ) were measured in the laboratory and mortality rate and embryonic development time (D _E ) were calculated. With M. minutum, Brachionus showed a typical growth curve (Monod-kinetics) dependent on food concentration. In contrast B. calyciflorus did not grow well on P. agardhii. With all food concentrations the measured growth rates were about r=0. At low food concentrations r was low with both food types, but the ER of B. calyciflorus was significantly higher with P. agardhii as food source. Furthermore the relative egg volume of females carrying one egg was higher with Planktothrix than with Monoraphidium. An addition of P. agardhii to M. minutum led to increasing growth rates. Highest growth rates were found with complementary food sources. High food concentrations of M. minutum shortened the juvenile development (D _J ) time, but D _j was uneffected by different P. agardhii food concentrations. A mixture of both algae did not shorten D _j compared with M. minutum as single food. The calculated D _E was not effected by different food qualities but the calculated mortality was nearly 3 times higher with P. agardhii as food.     

Temperature and the effects of elemental food quality on Daphnia

1. We examined the responses of two species of Daphnia to changes in food phosphorus (P) content, with animals reared at three different water temperatures. Specifically, we measured mass‐specific growth rate (MSGR), body P content and respiration rate of Daphnia magna and Daphnia pulex acclimatised to 10, 17.5 and 25 °C and fed food carbon : phosphorus (C : P) ratios of either 150 or 500. 2. The responses of these three physiological variables to temperature–food quality interactions were species‐specific. There was a significant interactive effect of temperature and food quality on D. magna, as the greatest proportional effect of food quality on growth was observed at 10 °C and reductions in body P because of low food P content were relatively greater at 25 °C. These effects may reflect the temperature dependence of mechanisms that reduce elemental constraints associated with food quality in D. magna. By contrast, there were no interactive effects between food quality and temperature on MSGR, body P or mass‐specific respiration of D. pulex. 3. It thus appears that temperature can alter food quality effects on Daphnia but the nature of these alterations depends upon the daphniid species and its thermal adaptability. Significant temperature–food quality interactions will complicate efforts to understand zooplankton nutrition in nature and warrant future consideration.     

The Crown Pearl: a draft genome assembly of the European freshwater pearl mussel Margaritifera margaritifera (Linnaeus, 1758)

Since historical times, the inherent human fascination with pearls turned the freshwater pearl mussel Margaritifera margaritifera (Linnaeus, 1758) into a highly valuable cultural and economic resource. Although pearl harvesting in M. margaritifera is nowadays residual, other human threats have aggravated the species conservation status, especially in Europe. This mussel presents a myriad of rare biological features, e.g. high longevity coupled with low senescence and Doubly Uniparental Inheritance of mitochondrial DNA, for which the underlying molecular mechanisms are poorly known. Here, the first draft genome assembly of M. margaritifera was produced using a combination of Illumina Paired-end and Mate-pair approaches. The genome assembly was 2.4 Gb long, possessing 105,185 scaffolds and a scaffold N50 length of 288,726 bp. The ab initio gene prediction allowed the identification of 35,119 protein-coding genes. This genome represents an essential resource for studying this species’ unique biological and evolutionary features and ultimately will help to develop new tools to promote its conservation.     

Respiration Rate and Species-Specific Lifespan in Freshwater Bivalves of Margaritiferidae and Unionidae Families

We studied changes in the respiration rate in five species of freshwater bivalves as a function of animal age and size. The species-specific lifespan was calculated on the basis of the obtained data: Rubner's constant (Ru) and lifespan at standard temperature 20°C (T ₂₀). The longest and shortest lifespan among the studied mollusks was specific for the pearl mussel Margaritifera margaritifera(Ru= 37 kJ and T ₂₀= 36 years) and the freshwater mussel Anodonta anatina(Ru= 8 kJ and T ₂₀= 8 years), respectively.     

Development of microsatellite markers for the endangered freshwater pearl mussel Margaritifera margaritifera L. (Bivalvia: Unionoidea)

Freshwater pearl mussels (Margaritifera margaritifera L.) are among the most critically endangered freshwater invertebrates. We describe the isolation and characterization of the first microsatellite markers for this species, which were obtained by screening 4900 recombinant clones from two genomic libraries. Thirteen loci revealed polymorphisms as demonstrated on 42 tested individuals from four river drainages. Allelic richness ranged from two to 12 alleles and averaged 6.8 alleles per locus with heterozygosity levels varying from 0 to 0.850 for observed heterozygosity (H_O) and from 0.174 to 0.850 for expected heterozygosity (H_E). Deficiency of heterozygous genotypes was observed in eight of 13 loci.     

Permanent swamp vegetation of the Upper Nile

This paper describes vegetation in the nothern Sudd area of the Sudan. A visit by boat was made in April 1978 along the White Nile from Malakal to Lake No; to the inflow regions of the Bahr el Jebel, the Bahr el Zeraf and to the Bahr el Ghazal. Only the vegetation along the fringe of the rivers was observed as plants were tall and dense and it was not possible to penetrate into the inner swamps.The outer edge of the vegetation was fringed by extensive mats of free-floating Eichhornia crassipes which was easily dislodged and formed floating islands to be carried downstream. The main rivers, excluding the Bahr el Ghazal, were too deep and turbid to support beds of submerged species but plants such as Ceratophyllum demersum could be found amongst floating plants. Vossia cuspidata usually produced a broad zone to the landward of Eichhornia. It dominated the shallow water with a floating raft of stems growing out from the shore over the water surface. Massive stands of Cyperus papyrus and/or Phragmites karka, over 5 metres tall, dominated the vegetation behind and sometimes excluded the Vossia zone. The papyrus could form dense, floating rafts of rhizomes at the water's edge, but Phragmites always remained firmly rooted to the bottom. Floating papyrus and Vossia would become detached from the main beds and drifted downstream with Eichhornia.Creepers were common amongst papyrus but less common amongst Phragmites where the vegetation was generally more dense. Large stands of Typa domingensis were observed behind the fringe vegetation.The vegetation of the Bahr el Ghazal, in marked contrast to the rest, was stunted, and reasons for this are suggested. Species diversity was greater and the less turbid waters allowed considerable development of floating-leaved and submerged species.Estimates of fresh weights and heights of dominant vegetation types were attained but methods were very laborious and alternative ways have been suggested. The fresh weight of Eichhornia from a one metre square quadrat in the White Nile was around 70 kg. The shoots of Phragmites weighed 18.5 kg and Cyperus papyrus, 11.0 kg m^–2.