A molecular phylogeny of the groupers of the subfamily Epinephelinae (Serranidae) with a revised classification of the Epinephelini

The phylogenetic relationships among the fishes in the perciform tribe Epinephelini (Serranidae) have long been poorly understood, in large part because of the numerous taxa that must be considered and the large, circumtropical distribution of the group. In this study, genetic data from two nuclear (Tmo-4C4 and histone H3) and two mitochondrial (16S and 12S) genes were gathered from 155 serranid and acanthomorph species as a means of developing a phylogenetic hypothesis using both maximum-likelihood and -parsimony criteria. The maximum-parsimony analysis recovered 675 most parsimonious trees of length 5703 steps (CI = 0.2523, HI = 0.7477, RI = 0.6582), and the maximum-likelihood analysis recovered 1 tree at −lnLikelihood = 28279.58341. These phylogenetic hypotheses are discussed in light of previous morphological evidence to evaluate the evolutionary history of the group and their implications for the currently recognized taxonomy. Our results question the monophyly of the Serranidae, as well as the genera Cephalopholis, Epinephelus, and Mycteroperca as currently defined. The Serranidae is monophyletic only with the exclusion of the genera Acanthistius and Niphon. We propose a revised classification of the tribe Epinephelini that reflects the hypothesized shared ancestry of the group and recognizes 11 genera: Alphestes, Cephalopholis, Dermatolepis, Epinephelus, Gonioplectrus, Hyporthodus (which is resurrected for 11 species of deep-bodied groupers), Mycteroperca (including 7 species heretofore allocated to Epinephelus), Plectropomus, Saloptia, Triso, and Variola.     

Molecular phylogenetic relationships of China Seas groupers based on cytochrome b gene fragment sequences

The classification and evolutionary relationships are important issues in the study of the groupers. Cytochrome b gene fragment of twenty-eight grouper species within six genera of subfamily Epinephelinae was amplified using PCR techniques and the sequences were analyzed to derive the phylogenetic relationships of the groupers from the China Seas. Genetic information indexes, including Kimura-2 parameter genetic distance and T _S/T _V ratios, were generated by using a variety of biology softwares. With Niphon spinosus, Pagrus major and Pagrus auriga as the designated outgroups, phylogenetic trees, which invoke additional homologous sequences of other Epinephelus fishes from GenBank, were constructed based on the neighbor-joining (NJ), maximum-parsimony (MP), maximum-likelihood (ML) and minimum-evolution (ME) methods. Several conclusions were drawn from the DNA sequences analysis: (1) genus Plectropomus, which was early diverged, is the most primitive group in the subfamily Epinephelinae; (2) genus Variola is more closely related to genus Cephalopolis than the other four genera; (3) genus Cephalopolis is a monophyletic group and more primitive than genus Epinephelus; (4) Promicrops lanceolatus and Cromileptes altivelis should be included in genus Epinephelus; (5) there exist two sister groups in genus Epinephelus. These authors contributed equally to this work.     

Molecular phylogenetic relationships of China Seas groupers based on cytochrome <Emphasis Type="Italic">b</Emphasis> gene fragment sequences

The classification and evolutionary relationships are important issues in the study of the groupers. Cytochrome b gene fragment of twenty-eight grouper species within six genera of subfamily Epinephelinae was amplified using PCR techniques and the sequences were analyzed to derive the phylogenetic relationships of the groupers from the China Seas. Genetic information indexes, including Kimura-2 parameter genetic distance and T _S/T _V ratios, were generated by using a variety of biology softwares. With Niphon spinosus, Pagrus major and Pagrus auriga as the designated outgroups, phylogenetic trees, which invoke additional homologous sequences of other Epinephelus fishes from GenBank, were constructed based on the neighbor-joining (NJ), maximum-parsimony (MP), maximum-likelihood (ML) and minimum-evolution (ME) methods. Several conclusions were drawn from the DNA sequences analysis: (1) genus Plectropomus, which was early diverged, is the most primitive group in the subfamily Epinephelinae; (2) genus Variola is more closely related to genus Cephalopolis than the other four genera; (3) genus Cephalopolis is a monophyletic group and more primitive than genus Epinephelus; (4) Promicrops lanceolatus and Cromileptes altivelis should be included in genus Epinephelus; (5) there exist two sister groups in genus Epinephelus.     

Niphon spinosus,a primitive Epinepheline serranid: Corroborative evidence from the larvae

The larvae ofNiphon spinosus are described based on seven specimens (4.2 mmNL–7.2 mmSL) collected in the East China Sea during October and November of 1980–1984. The morphology of these larvae, in particular the elongate third dorsal spine and the configuration of the developing anterior dorsal pterygiophore complex, corroborates the hypothesis thatNiphon is a member of the serranid subfamily Epinephelinae. Within the Epinephelinae larvalNiphon resemble most closely those of the tribe Epinephelini, but differ in several respects, such as the absence of serrations on the dorsal, pelvic and preopercular spines. Using outgroup comparison as a basis for character polarization, a character analysis demonstrates that it is most parsimonious to hypothesize thatNiphon is the sister group of all other epinepheline tribes rather than the sister group of the tribe Epinephelini.     

Morphological description of three marine ciliates (Ciliophora, Scuticociliatia), with establishment of a new genus and two new species

Three marine scuticociliates, Falcicyclidium fangi nov. gen., nov. spec., Falcicyclidium atractodes nov. spec., and Cristigera media Kahl, 1928 were investigated using live observation and silver impregnation methods. The genus Falcicyclidium is distinguished by the combination of: (i) dorsoventrally flattened body, (ii) hook-like (falciform) paroral membrane, (iii) anterior end of paroral membrane posterior to anterior end of membranelle 1, and (iv) multiple caudal cilia. Falcicyclidium fangi nov. spec., the type of the new genus, can be recognized by the combination of its large size, extremely dorsoventrally flattened (3:1) body, consistently 10 somatic kineties, and the broad, elongate buccal area occupying 60% of the body length. Falcicyclidium atractodes nov. spec. is mainly characterized by a unique spine projecting from both the anterior and posterior end. The uncommon form, Cristigera media is redescribed based on the population from Qingdao, the statistic data and additional features, especially the morphology of the living cells, are documented.     

Immunoreactivity of subunits of the (Na + K)-ATPase Cross-reactivity of the α,α+ and β forms in different organs and species

The immunologic cross-reactivity of the α and α+ forms of the large subunit and the β subunit of the (Na⁺ + K⁺)-ATPase from brain and kidney preparations was examined using rabbit antiserum prepared against the purified holo lamb kidney enzyme. As previously reported by Sweadner ((1979) J. Biol. Chem. 254, 6060–6067) phosphorylation of the large subunit of the (Na⁺ + K⁺)-ATPase in the presence of Na⁺, Mg²⁺, and [γ-³²P]ATP revealed that dog and, very likely, rat brain contain two forms of the large subunit (designated α and α+) while dog, rat, and lamb kidney contain only one form (α). The cross-reactivity of the α and α+ forms in these preparations was investigated by resolving the subunits by SDS-polyacrylamide gel electrophoresis. The separated polypeptides were transferred to unmodified nitrocellulose paper, and reacted with rabbit anti-lamb kidney serum, followed by detection of the antigen-antibody complex with ¹²⁵I-labeled protein A and autoradiography. By this method, the α and α+ forms of rat and dog brain, as well as the α form found in kidney, were shown to cross-react. In addition, membranes from human cerebral cortex were shown to contain two immunoreactive bands corresponding to the α and α+ forms of dog brain. In contrast, the brain of the insect Manduca sexta contains only one immunoreactive polypeptide with a molecular weight intermediate to the α and α+ forms of dog brain. The β subunit from lamb, dog and rat kidney and from dog and rat brain cross-reacts with anti-lamb kidney (Na⁺ + K⁺)-ATPase serum. The mobility of the β subunit from dog and rat brain on SDS-polyacrylamide electrophoresis gels is greater than the mobility of the β subunit from lamb, rat or dog kidney.     

Predation by vertebrates and invertebrates on the seeds of five canopy tree species of an Amazonian forest

We studied the pre-germination loss of seeds to invertebrate and vertebrate seed predators of 5 species of Amazonian trees (Astrocaryum macrocalyx—Palmae; Bertholletia excelsa—Lecithydaceae; Calatola venezuelana—Icacinaceae; Dipteryx micrantha—Leguminosae (Papilionoidae); Hymenaea courbaril-Leguminosae (Caesalpinoidae)). These five species were selected from a large tree flora on several criteria. All possess large (3–10 cm) well-protected seeds that might plausibly be attractive to mammalian seed predators. The reproductive biology of three of the species, or close congeners, had been studied elsewhere in the Neotropics (Astrocaryum, Dipteryx, Hymenaea); one is important to the economy of southeastern Peru (Bertholletia); and one, despite large and apparently edible seeds, appeared to suffer no pre-germination loss to predators (Calatola). We conducted the research in mature forests in the Manu National Park of southeastern Peru where mammal densities are unperturbed by human activities. Densities of adult trees of the five species in our area range from very high (>30 per ha: Astrocaryum) to very low (1 per ha: Hymenaea).Loss of seeds to all causes, and to mammalian seed predators in particular, was determined for seeds placed in 2-square meter mammal exclosures and in open controls located at 10 m (near) and 50 m (far) from a large mature individual of the target species (with minor variations in the design for Astrocaryum and Calatola). The exclosures were of two types: impermeable—designed to exclude all mammals, but not invertebrate seed predators, and semipermeable—designed to admit small (<500 g), but not large mammals. Experimental and control plots were stocked with apparently viable seeds during the dry-wet transition period (October–November) and scored one year later.A significant distance effect (higher predation near vs far from a large conspecific adult) was found in only one of the species (Astrocaryum), the only one to be attacked with high frequency by invertebrate seed predators. The absence of any detectable distance effect attributable to mammals suggests that mammals, over the course of a year, thoroughly search the forest floor for seeds. Invertebrates may thus be responsible for most pre-germination distance (density) effects. With respect to the treatments, we found three qualitatively distinct results: seeds of three species (Astrocaryum, Bertholletia, Dipteryx) were significantly protected by the impermeable, but not semipermeable exclosures, implicating small mammals in seed loss; the seeds of one species (Hymenaea) were significantly protected by exclosures of both types, implicating large mammals; and the seeds of one species (Calatola) exhibited 100% survival, whether or not protected by exclosures.The importance of large mammals as seed predators is generally underestimated in these experiments because semipermeable exclosures may serve as foraging reserves for small mammals. Finally, we noted no relationship between the intensity of mammalian seed predation (as suggested by the survival of unprotected seeds) and the abundance of adults of the five species in the environment. The diversity of results obtained for the five species reveals that large-seeded tropical trees may display a wide range of demographic patterns, and points to the likely importance of post-germination bottlenecks in the population biology of many species, even those that may experience severe pre-germination seed loss.     

A new type of exterilium larva referable to Leptobrotula (Ophidiiformes: Ophidiidae: Neobythitinae) from tropical Indo-West Pacific

A new type of exterilium larvae referable to Leptobrotula (Ophidiiformes: Ophidiidae) is described on the basis of two specimens (20.7+mm and ca. 35.4mmSL) collected from the tropical Indo-Pacific. They are characterized, in particular, by several elongated anterior dorsal fin rays supported by the large dorsal pterygiophores and the exterilium gut bearing filamentous appendages along the ventral border. It is suggested from larval evidence that Leptobrotula forms a distinct lineage with Brotulotaenia and Lamprogrammus, which may be placed in an expanded Brotulonaeniinae.     

First report of the Asian seaweed <Emphasis Type="Italic">Sargassum filicinum</Emphasis> Harvey (Fucales) in California,USA

We report the occurrence of the brown seaweed Sargassum filicinum Harvey in southern California. Sargassum filicinum is native to Japan and Korea. It is monoecious, a trait that increases its chance of establishment. In October 2003, Sargassum filicinum was collected in Long Beach Harbor. In April 2006, we discovered three populations of this species on the leeward west end of Santa Catalina Island. Many of the individuals were large, reproductive and senescent; a few were small, young but precociously reproductive. We compared the sequences of the mitochondrial cox3 gene for 6 individuals from the 3 sites at Catalina with 3 samples from 3 sites in the Seto Inland Sea, Japan region. The 9 sequences (469 bp in length) were identical. Sargassum filicinum may have been introduced through shipping to Long Beach; it may have spread to Catalina via pleasure boats from the mainland.     

Taxonomic study of the genusMyagropsis (Cystoseiraceae,Phaeophyta)

The generic names of the brown algaeMyagropsis, Cystoseira andCystophyllum have been used in Japan, Korea and China for a small group of seaweeds whose limits have not been clearly understood. Studies on the development of the eggs and subsequent germlings show that substantial differences occur betweenCystoseira andMyagropsis. Myagropsis Kützing is distinguished fromCystoseira C. Agardh by the following characteristics: (1) the tongue cell is undivided during development of the conceptacle; (2) paraphyses are projected from the conceptacle ostiole and become entangled; (3) during development, oospore germlings are mixed among paraphyses projecting from the ostiole; (4) oospores are large, with eight nuclei at maturity; (5) thirty-two primary rhizoids are produced on the germlings; and (6) the thallus is bilateral in organization. The shape and size of vesicles, their formation, and the presence of cryptostomata have been used as specific characters, but their use cannot be continued. It is concluded that the genusMyagropsis is monotypic, with a single species,M. myagroides (Turner) Fensholt. The status of this species is also discussed.     

New species ofAcremonium, Cylindrocarpon andVerticillium from soil in the Bonin (Ogasawara) Islands, Japan

Three new soil fungi from the Bonin (Ogasawara) Islands, Japan are described:Acremonium macroclavatum, characterized by large clavate guttulate conidia;Cylindrocarpon boninense, characterized by 3–7-septate clavate macroconidia, terminal or intercalary chlamydospores, rarely produced unicellular clavate microconidia; andVerticillium hahajimaense, characterized by conidial heads bearing cylindrical conidia, and catenulate chlamydospores.     

Ultrastruktur und systematische Bedeutung des Pollens beiBocageopsis,Ephedranthus, Malmea undUnonopsis (Annonaceae)

The four genera investigated show solitary sulcate pollen grains. The structure and sculpture of the sporoderm is very similar inBocageopsis andUnonopsis, and supports the close relationship of both genera; their flower morphology also is very similar. In contrast, the sporoderm ofEphedranthus, and especially that ofMalmea, is different in some characters and suggests more remote relationships; this is also confirmed by differences in flower morphology. Within this group of genera a distinct exine progression can be recognized from non-columellate (Malmea) to granular (Unonopsis guatterioides), further to somewhat irregularly (Bocageopsis, someUnonopsis species), and finally to very regularly columellate (Ephedranthus). The sculpture of the tectum varies from a reticulum with large lumina (Malmea) to one with small performations (Ephedranthus). Within theAnnonaceae the genusMalmea is among the most primitive in respect to pollen structure. The sulcus of the four genera is very large and runs over 1/3 of the pollen grain. It is characterized by a reduction of the exine and a bulgy thickening of the intine.

     

Molecular cloning and characterization of novel isoforms of potato ADP-glucose pyrophosphorylase

ADP-glucose pyrophosphorylase (AGPase) is one of the major enzymes involved in starch biosynthesis in higher plants. We report here the molecular cloning of two cDNAs encoding so far uncharacterized isoforms (AGP S2 and AGP S3) of the potato enzyme. Sequence analysis shows that the two polypeptides are more homologous to previously identified large subunit polypeptides from potato and other plant species than to small subunit isoforms. This observation suggests that AGP S2 and AGP S3 represent novel large subunit polypeptides. agpS2 is expressed in several tissues of the potato plant, including leaves and tubers. Expression was stronger in sink leaves than in source leaves, indicating developmental regulation. In leaves, agpS2 expression was induced 2- to 3-fold by exogenous sucrose; therefore, agpS2 represents a new sucrose-responsive gene of starch metabolism. Expression of agpS3 was restricted to tubers: no agpS3 expression could be seen in leaves of different developmental stages, or when leaves were incubated in sucrose. Therefore, agpS3 represents the only AGPase gene so far characterized from potato, which is not expressed in leaves. Conversely, all four AGPase isoforms known from potato are expressed in tubers.     

Characterization of β-1,3-galactosyl-<Emphasis Type="Italic">N</Emphasis>-acetylhexosamine phosphorylase from <Emphasis Type="Italic">Propionibacterium acnes</Emphasis>

Homologs of the β-1,3-galactosyl-N-acetylhexosamine phosphorylase (GalHexNAcP) gene (gnpA) were cloned from the genomic DNA of Propionibacterium acnes JCM6425 and P. acnes JCM6473, showing 99.9% and 97.9% nucleotide sequence identity, respectively, with the ppa0083 gene from the genome-sequenced P. acnes KPA171202. No gnpA gene was detected in the genomic DNA of type strain P. acnes ATCC25746. The recombinant enzyme from P. acnes JCM6425 (GnpA) showed approximately 70 times higher specific activity of phosphorolysis on galacto-N-biose (Galβ1→3GalNAc, GNB) than that on lacto-N-biose I (Galβ1→3GlcNAc). K _m value for GnpA on GNB was high, but GnpA did not exhibit activity on any derivatives of GNB examined. These results indicate that GnpA is GalHexNAcP which should be classified as galacto-N-biose phosphorylase. The large k _cat value of GnpA on GalNAc suggests that GnpA would be a useful catalyst for the synthesis of GNB.     

Larval host plant affects fitness consequences of egg size variation in the seed beetle Stator limbatus

Egg size variation often has large effects on the fitness of progeny in insects. However, many studies have been unable to detect an advantage of developing from large eggs, suggesting that egg size variation has implications for offspring performance only under adverse conditions, such as during larval competition, periods of starvation, desiccation, or when larvae feed on low-quality resources. We test this hypothesis by examining the consequences of egg size variation for survivorship and development of a seed-feeding insect, Stator limbatus, on both a low-quality (Cercidium floridum) and a high-quality (Acacia greggii) host plant. Our results are consistent with the hypothesis. S. limbatus larval performance was affected by egg size only when developing on the poor-quality host (C. floridum); larvae from large eggs survived better on C. floridum than those from small eggs, while there was no evidence of an effect of egg size on progeny development time, body weight, or survivorship when larvae developed on A. greggii. These results indicate intense selection for large eggs within C. floridum-associated populations, but not in A. greggii-associated populations, so that egg size is predicted to vary among populations associated with different hosts. Our results also support this hypothesis; females from a C. floridum-associated population (Scottsdale) laid larger eggs than females from an A. greggii-associated population (Black Canyon City).     

A novel transposon-like structure carries the genes for pyocin AP41, a Pseudomonas aeruginosa bacteriocin with a DNase domain homology to E2 group colicins

Summary The genetic determinant for pyocin AP41, a bacteriocin produced by Pseudomonas aeruginosa, has been cloned. The determinant is located on the chromosome flanked by a pair of inverted repeats, forming a transposon-like structure (TnAP41). TnAP41 possesses some features characteristic of the Tn3 family of transposons. Based on a comparison with the structure of the corresponding region of the chromosome of a nonproducer strain, we propose that P. aeruginosa has acquired pyocinogeny by the transposition of TnAP41 into the chromosome. The determinant comprises two ORFs encoding the protein subunits responsible for the killing action (the large component) and immunity (the small component). Amino acid sequences of the C-terminus of the large component (the deoxyribonuclease domain) and the immunity protein show remarkable homology to those of E2 group colicins, suggesting that these bacteriocins, which are produced by distantly related species, have originated from a common ancestor.     

Molecular characterization of multiple cDNA clones for ADP-glucose pyrophosphorylase from Arabidopsis thaliana

PCR amplification of cDNA prepared from poly(A)⁺ RNA from aerial parts of Arabidopsis thaliana, using degenerate nucleotide primers based on conserved regions between the large and small subunits of ADP-glucose pyrophosphorylase (AGP), yielded four different cDNAs of ca. 550 nucleotides each. Based on derived amino acid sequences, the identities between the clones varied from 49 to 69%. Sequence comparison to previously published cDNAs for AGP from various species and tissues has revealed that three of the amplified cDNAs (ApL1, ApL2 and ApL3) correspond to the large subunit of AGP, and one cDNA (ApS) encodes the small subunit of AGP. Both ApL1 and ApS were subsequently found to be present in a cDNA library made from Arabidopsis leaves. All four PCR products are encoded by single genes, as found by genomic Southern analysis.     

Endothelial heparan sulphate: Compositional analysis and comparison of chains from different proteoglycan populations

From cultures of human umbilical vein endothelial cells incubated with³H-glucosamine or³⁵S-sulphate, we have purified three heparan sulphate proteoglycans: 1) a low density (1.31 g/ml) proteoglycan from the cell extract, 2) a low density proteoglycan from the medium, and 3) a high density (>1.4 g/ml) proteoglycan from the medium. The disaccharide composition of heparan sulphate chains from the low density proteoglycan of the medium was examined, using specific chemical and enzymic degradations followed by gel chromatography and strong anion exchange HPLC. Chains released from each of the different proteoglycan populations were then compared by gel chromatography and gradient polyacrylamide gel electrophoresis before and after various specific degradations. The results indicate that heparan sulphate from human endothelial cells are large polymers (MW>50,000) of low overall sulphation (32–35%N-sulphated glucosamine and an N/O-linked sulphate ratio of 2.0) with rare and solitary heparin-like disaccharides. Heparan sulphate from the different proteoglycan populations appeared to have similar structure except that chains from the high density fraction were larger polymers.Abbreviations HSPG heparan sulphate proteoglycan - DSPG dermatan sulphate proteoglycan - GlcNAc(6S) N-acetylglucosamine 6-sulphate - GlcNAc6R glucosamine with either-OH or-OSO₃ at C-6 - GlcNR glucosamine with either-SO₃ or-COCH₃ as N-substituent - GlcNSO₃ N-sulphated glucosamine - GlcNSO₃(3S) N-sulphated glucosamine 3-sulphate - GlcA d-glucuronic acid - IdoA l-iduronic acid - IdoA(2S) iduronic acid 2-sulphate - HexA hexuronic acid - DHexA hexuronic acid with a 4,5-double bond - Xyl xylose - SAX strong anion exchange - d.p. degree of polymerization (a disaccharide has d.p.=1 etc) - AUFS absorbance units full scale The codes used for proteoglycans denote in turn: C 2, low-density (1.35–1.28 g/ml) HSPG from the cell extract; M 1a, high density (>1.4 g/ml) HSPG fraction from the spent medium; M 2a, low-density (1.31 g/ml) HSPG from the spent medium [6].     

Electrophoretic and immunological comparisons of chloroplast and prokaryotic ribosomal proteins reveal that certain families of large subunit proteins are evolutionarily conserved

Summary Antibodies to individual chloroplast ribosomal (r-)proteins ofChlamydomonas reinhardtii synthesized in either the chloroplast or the cytoplasm were used to examine the relatedness ofChlamydomonas r-proteins to r-proteins from the spinach (Spinacia oleracea) chloroplast,Escherichia coli, and the cyanobacteriumAnabaena 7120. In addition,³⁵S-labeled chloroplast r-proteins from large and small subunits ofC. reinhardtii were coelectrophoresed on 2-D gels with unlabeled r-proteins from similar subunits of spinach chloroplasts,E. coli, andAnabaena to compare their size and net charge. Comigrating protein pairs were not always immunologically related, whereas immunologically related r-protein pairs often did not comigrate but differed only slightly in charge and molecular weight. In constrast, when³⁵S-labeled chloroplast r-proteins from large and small subunits of a closely related speciesC. smithii were coelectrophoresed with unlabeledC. reinhardtii chloroplast r-proteins, only one pair of proteins from each subunit showed a net displacement in mobility.Analysis of immunoblots of one-dimensional SDS and two-dimensional urea/SDS gels of large and small subunit r-proteins from these species revealed more antigenic conservation among the four species of large subunit r-proteins than small subunit r-proteins.Anabaena r-proteins showed the greatest immunological similarity toC. reinhardtii chloroplast r-proteins. In general, antisera made against chloroplast-synthesized r-proteins inC. reinhardtii showed much higher levels of cross-reactivity with r-proteins fromAnabaena, spinach, andE. coli than did antisera to cytoplasmically synthesized r-proteins. All spinach r-proteins that cross-reacted with antisera to chloroplast-synthesized r-proteins ofC. reinhardtii are known to be made in the chloroplast (Dorne et al. 1984b). FourE. coli r-proteins encoded by the S10 operon (L2, S3, L16, and L23) were found to be conserved immunologically among the four species. Two of the large subunit r-proteins, L2 and L16, are essential for peptidyltransferase activity. The third (L23) and two otherE. coli large subunit r-proteins (L5 and L27) that have immunological equivalents among the four species are functionally related to but not essential for peptidyltransferase activity.     

Impact of Holoshestes heterodon Eigenmann (Pisces: Characidae) on the plankton community of a subtropical reservoir: the importance of predation by Chaoborus larvae

We analyzed the effects of planktivorous Holeshestes heterodon Eigenmann (Characidae) predation on the plankton community of a small subtropical reservoir, using four enclosures (volume about 17.5 m³), open to the sediment, established in the littoral zone. Two enclosures were stocked with fish (mean TL 5.7 cm), at a density of about 4–5 fish m^–3 (approx. 8 g m^–3), whereas two remained fishless. The experiment lasted a little longer than one month. In the fish enclosures, most Crustacea and Chaoborus larvae remained scarce, probably as a result of visually selective fish predation. In both fishless enclosures, Chaoborus larvae became abundant. However, in only one of these did large individuals become relatively numerous; this discrepancy in the demographic structure of the Chaoborus populations between the two fishless enclosures is unexplained. Only in the fishless enclosure without appreciable numbers of large Chaoborus did densities of Crustacea increase greatly. It is suggested that in the enclosure containing large Chaoborus individuals, crustacean populations were prevented from developing due to predation pressure, while the small Chaoborus larvae of the other enclosure could not readily consume these prey. Rotifers were low in abundance in the absence of fish, probably as a consequence of Chaoborus predation. Phytoplankton density increased in all four enclosures, due probably to the lack of water flow. Only in the fishless enclosure with high densities of crustaceans did phytoplankton abundance decrease markedly at the end of the experiment, perhaps because of grazing losses.