Recolonization and possible recovery of Burrowing Mayflies (Ephemeroptera: Ephemeridae: Hexagenia spp.) in Lake Erie of the Laurentian Great Lakes

Burrowing mayflies of the genus Hexagenia spp. were widely distributed (ca. 80% of sites) and abundant (ca. 160 nymphs/m²) in the western basin of Lake Erie of the Laurentian Great Lakes in 1929–1930, prior to a period of anoxia in the mid 1950s. Nymphs were absent or rare in the basin between 1961 and 1973–1975. In 1979–1991, nymphs were infrequently found (13–46% of sites) in low abundance (3–40 nymphs/m²) near shore (<7.5 km from shore), but were absent or rare offshore (0–7% of sites at 0–1 nymphs/m²). Increased abundance occurred offshore between 1991 (0% of sites) and 1993 (52% of sites at 7/m²). Annual sampling, beginning in 1995, indicates that nymphs increased in both nearshore and offshore waters. By 1997, nymphs were found throughout the lake (88% of sites) at a mean density 40-fold greater (392/m²) than that observed in 1993 (11/m²). In 1998, the distribution of nymphs remained the same as 1997 (88% of sites) but density declined 3-fold (392 to 134/m²). These data indicate that mayflies have recolonized sediments of western Lake Erie and that their abundance may be similar to levels observed before their disappearance in the mid 1950s. However, prior to the mid 1950s, densities were greater in offshore than nearshore waters, but between 1979 and 1998 greater densities occurred near shore than offshore. In addition, there were two areas in the 1990s where low densities consistently occurred. Therefore, recovery of nymphs in western Lake Erie may not have been complete in 1998. At present we do not know the cause for the sudden recolonization of nymphs in large portions of western Lake Erie. Undoubtedly, pollution-abatement programs contributed to improved conditions that would have ultimately led to mayfly recovery in the future. However, the explosive growth of the exotic zebra mussel, Dreissena polymorpha, undoubtedly diverted plankton foods to bottom substrates which could have increased the speed at which Hexagenia spp. nymphs recolonized sediments in western Lake Erie in the 1990s.     

Size-selective predation by roach (Rutilus rutilus) on zebra mussel (Dreissena polymorpha): field stuides

Summary Studies of predation by roach (Rutilus rutilus) on zebra mussel (Dreissena polymorpha) in a large, eutrophic lake showed that there was a clearly marked size threshold ( 160 mm SL) above which roach began to feed on mussels. Roach preying on various sizes of mussels selected them in proportions different from their abundance and accessibility in the habitat. The mean size of mussels ingested by roach of 220 mm and larger, which fed predominantly on Dreissena, closely followed the pattern expected for a constant ratio of mean prey size to mean predator mouth size = 0.59. To explain the size selection we applied an optimal foraging approach, based on the ability of different-sized fish to crush (cost) mussels of different sizes, and hence crushing resistance, and energy contents (benefit). We found that fish smaller than 160 mm, which showed no inclination to eat Dreissena, would only be able to take small mussels with a very high cost/benefit ratio. The real switch to Dreissena would be expected in fish of 230–240 mm that could take most of their prey from highly profitable, numerous, and easily accessible size classes while keeping the mean prey size at the optimal level relative to mean predator mouth size.     

Effects of an exotic bivalve mollusc on benthic invertebrates and food quality in the Ohio River

Effects of zebra mussels (Dreissena polymorpha) on populations of amphipods (Gammarus fasciatus) and prosobranch snails (Lithasia obovata) and on nutritional quality of benthic organic matter were examined in 20 artificial streams receiving Ohio River water and containing either mussels or small gravel. Twenty individually-marked snails were placed in each trough, and streams were allowed to colonize with other benthic species for 28 days.Dreissenids positively affected other benthic invertebrates in our stream channels. Compared to gravel channels, Gammarus biomass was significantly higher (P<0.01) in mussel channels, amphipod densities increased 300%, and snail growth rates were 50% greater. Food quality of fine benthic organic matter (FBOM) was greater in mussel channels (i.e. lower C:N), and FBOM was carbon depleted (lower ¹³C) but nitrogen enriched (higher ¹⁵N). Isotope data suggest that detrital FBOM was not the sole food source for snails and amphipods in our channels and that they were assimilating a higher quality portion of this BOM. The overall influence of dreissenids on particular benthic invertebrates may depend on the response and/or susceptibility of those species to biofouling, increased habitat heterogeneity, and changes in the quality and quantity of nutrients.     

Filtering impacts of larval and sessile zebra mussels (Dreissena polymorpha) in western Lake Erie

Summary We assessed the feeding biology of veliger larvae of the introduced zebra mussel (Dreissena polymorpha Pallas) in laboratory experiments using inert microspheres as food analogues. Mean clearance rate on 2.87-m beads ranged between 247 and 420 L veliger^–1 day^–1. Clearance rate was unrelated to bead concentration up to 100 beads L^–1, but was positively correlated with veliger shell length. Clearance rates of Dreissena veligers are within the range of those reported for marine bivalve veligers of similar size and for herbivorous Great Lakes microzooplankton, but are orders of magnitude lower than those of settled, conspecific adults. The impact of settled zebra mussel grazing activities on phytoplankton stocks may be up to 1162 times greater than that exerted by veliger populations in western Lake Erie. Based on 1990 size-frequency distributions and associated literature-derived clearance rates, reef-associated Dreissena populations in western Lake Erie (mean depth 7 m) possess a tremendous potential to filter the water column (up to 132 m³ m^–2 day^–1) and redirect energy from pelagic to benthic foodwebs. Preliminary analyses indicate that chlorophyll a concentration is strongly depleted (<1 g L^–1) above Dreissena beds in western Lake Erie.     

Filtering Impacts of an Introduced Bivalve (Dreissena polymorpha) in a Shallow Lake: Application of a Hydrodynamic Model

Nonindigenous species may exert strong effects on ecosystem structure and function. The zebra mussel (Dreissena polymorpha) has been attributed with profound changes in invaded ecosystems across eastern North America. We explored vertical profiles of water flow velocity and chlorophyll a concentration in western Lake Erie, over rocky substrates encrusted with Dreissena, to assess the extent to which mussels influence coupling between benthic and pelagic regions of the lake. Flow velocity was always low at surveyed sites (less than or equal to 2.9 cm s^-1) and declined in direct proximity to the lakebed. Mean chlorophyll a concentration was also low (less than 5μg L^-1) at all sites and depths. Chlorophyll a concentration was positively correlated with distance above lakebed and was lowest (0.3μg L^-1) directly adjacent to the lakebed. Spatial patterns of zooplankton grazers could not explain observed vertical gradients in chlorophyll concentration. Hydrodynamic modeling revealed that filtering effects of Dreissena in a nonstratified, shallow basin depend mainly on upstream chlorophyll concentration, intensity of turbulent diffusion, feeding efficiency of the mussel colony, and the distance downstream from the leading edge of the mussel colony. In contrast to widespread perceptions that molluscs reduce phytoplankton concentration only adjacent to the lakebed, modeling scenarios indicated that depletion occurs throughout the water column. Depletion was, however, inversely proportional to distance above the lakebed. Simulation results are consistent with field-based observations made in shallow water habitats populated by large Dreissena populations in the Great Lakes and elsewhere. Results from this study indicate that zebra mussels strongly enhance coupling between pelagic and benthic regions in shallow lakes. Enhanced coupling between these regions explains, in part, high population densities of Dreissena and of many benthic invertebrates in ecosystems invaded by zebra mussels. Received 14 July 1998; accepted 25 March 1999.     

Tooth development in vitro in two teleost fish,the cichlid <Emphasis Type="Italic">Hemichromis bimaculatus</Emphasis> and the cyprinid <Emphasis Type="Italic">Danio rerio</Emphasis>

A technique for organotypic in vitro culture with serum-free medium was tested for its appropriateness to mimic normal odontogenesis in the cichlid fish Hemichromis bimaculatus and the zebrafish Danio rerio. Serial semithin sections were observed by light microscopy to collect data on tooth patterning and transmission electron microscopy was used to compare cellular and extracellular features of tooth germs developing in vitro with the situation in vivo. Head explants of H. bimaculatus from 120 h post-fertilization (hPF) to 8.5 days post-fertilization (dPF) and of zebrafish from 45 hPF to 79 hPF and adults kept in culture for 3, 4 or 7 days revealed that tooth germs developed in vitro from explants in which the buccal or pharyngeal epithelium was apparently undifferentiated and, when present at the time of explantation, they continued their development up to a stage of attachment. In addition, the medium allowed the morphogenesis and cytodifferentiation of the tooth germs similar to that observed in vivo and the establishment of a dental pattern (place and order of tooth appearance and of attachment) that mimicked that in vivo. Organotypic culture in serum-free conditions thus provides us with the means of studying epithelial-mesenchymal interactions during tooth development in teleost fish and of analysing the genetic control of either mandibular or pharyngeal tooth development and replacement in these polyphyodont species. Importantly, it allows heads from embryonically lethal (zebrafish) mutants or from early lethal knockdown experiments to develop beyond the point at which the embryos normally die. Such organotypic culture in serum-free conditions could therefore become a powerful tool in developmental studies and open new perspectives for craniofacial research.The in vitro infrastructure at the Ghent laboratory was financed through a grant of the Bijzonder Onderzoeksfonds of Ghent University (BOF: 01102995) and a Krediet aan navorsers (no. 31513695) of the Fonds voor Wetenschappelijk onderzoek (FWO-Vlaanderen). This study also benefitted from an exchange program between the Centre National de Recherche Scientifique (CNRS) and the Ministerie van de Vlaamse Gemeenschap. Research performed by C. Van der heyden was partly financed through a specialization grant of the Flemish Institute for the Advancement of Scientific-Technological Research in Industry (IWT).     

Habitat Shift in Invading Species: Zebra and Quagga Mussel Population Characteristics on Shallow Soft Substrates

Unexpected habitat innovations among invading species are illustrated by the expansion of dreissenid mussels across sedimentary environments in shallow water unlike the hard substrates where they are conventionally known. In this note, records of population characteristics of invading zebra (Dreissena polymorpha) and quagga (Dreissena bugensis) mussels from 1994 through 1998 are reported from shallow (less than 20m) sedimentary habitats in western Lake Erie. Haphazard SCUBA collections of these invading species indicated that combined densities of zebra and quagga mussels ranged from 0 to 32,500 individuals per square meter between 1994 and 1998, with D. polymorpha comprising 75–100% of the assemblages. These mixed mussel populations, which were attached by byssal threads to each other and underlying sand-grain sediments, had size–frequency distributions that were typical of colonizing populations on hard substrates. Moreover, the presence of two mussel cohorts within the 1994 samples indicated that these species began expanding onto soft substrates not later than 1992, within 4 years of their initial invasion in western Lake Erie. Such historical data provide baselines for interpreting adaptive innovations, ecological interactions and habitat shifts among the two invading dreissenid mussel species in North America.     

On the dynamics of the stocks of blue mussels (Mytilus edulis L.) in the Danish Wadden Sea

As biological basis for the monitoring programme for the commercially exploited stock(s) of mussels (Mytilus edulis L.) in the Danish Wadden Sea, samples of mussels have been collected regularly since 1986, both from sub-tidal and inter-tidal mussel beds. These samples are the basis for the estimation of total biomass. They also provide data on size frequency distributions, which have been analysed for cohort identification resulting in length at age data, which again have been used for estimating parameters (L and K) for the von Bertalanffy growth equation (VBGE) as well as mortality parameters. By applying these in the Beverton & Holt model, estimates of average biomass and annual production (P) of the mussels have been obtained together with possible fisheries yields from the beds. The growth and mortality parameters and the figures for annual production and P/B are compared with figures from other investigations. These analyses have been the basis for annual assessments of the mussel stocks, which again are used in the current management of mussel fishery in the Danish Wadden Sea.     

The distribution of Heterotrissocladius oliveri Saether (Diptera: Chironomidae) in Lake Michigan

Fifty one chironomid species were identified from 504 samples collected at depths ranging 8 to 267 m in Lake Michigan, U.S.A. Heterotrissocladius oliveri Saether occurred in 32% of these samples and had an average abundance of 22 m^–2 which was similar to other estimates from the Great Lakes. Maximum average lake-wide density was at 30 to 60 m (41 m^–2). At depths 60 m, H. oliveri was the dominant chironomid species comprising 75% of total Chironomidae. The substrate preference of H. oliveri differed within each depth regime considered: at 30–60 m, 2–3 ; at 60–120 m, 3–5 , 7–9 ; and at 120–180 m, 6–8 . Abundance was notably reduced at all depths in substrates characterized as medium silt (5–6 ). On a lake-wide basis, the distribution pattern suggested H. oliveri was most numerous from 30 to 60 m along the southwestern, eastern, and northern shorelines and at 60–120 m depths along the southern and eastern shorelines. Increased abundance in the South Basin was concurrent with evidence of increased sedimentation at 60 to 100 m. However, in several other areas of the lake, high densities were associated with medium to very fine sands relatively free of silts and clays. This observation suggested occurrence of H. oliveri was minimally affected by sediment type.Widely variable, but generally elevated water temperatures likely prevent H. oliveri from establishing a substantial population density at depths < 30 m. With increased depth, temperature fluctuation is negligible and food is more stable, though the source is variable. Factors limiting abundance of H. oliveri at depths 30 m were related to decreased food supply due to distance from shore, food sources of lower value (clays), and, most importantly, to reproductive replenishment.Although still oligotrophic in nature, high density occurrences in both high and low sedimentation areas of the lake suggest the trophic indicator status of H. oliveri might be broader than previously thought.     

Elektronenmikroskopische Untersuchungen am Pinealorgan von Passer domesticus

Zusammenfassung Das Pinealorgan von Passer domesticus enthält Zellen mit innengliedartigem mitochondrienreichen Stift, der eine bulböse Zilie mit 9+0 Zilienfibrillen entsendet. Randzipfel solcher Zilien, die vielfach in Gruppen anzutreffen sind, können sich in etwa 200 Å starke Lamellen fortsetzen. Konzentrische und wirbeiförmige Lamellenzüge, die von mehreren solchen Zilien ausgehen, bilden im Lumen markscheidenartige oder auch ungeordnete Membranenkomplexe. Ein direkter Zusammenhang mit Zilien konnte nur bei einem Teil dieser Lamellenkörper ermittelt werden. Der Bauplan der bulbösen Zilien entspricht den frühen Entwicklungsstadien des Photorezeptoren-Außengliedes. Es fehlen aber die für die letzteren so charakteristischen Membraninvaginationen; die Lamellenkomplexe der Vogelepiphyse haben eine ektopische Lage zur bulbösen Zilie. Oft finden sich an den Lamellenkörpern Degenerationszeichen. Diese degenerativ veränderten Strukturen erinnern an die Gebilde, die in den pinealen Lichtsinnesorganen der niederen Vertebraten aus zerfallenden Außengliedplättchen hervorgehen. Im Vergleich zu voll differenzierten pinealen Sinneszellen erscheinen die rezeptorenähnlichen Pinealocyten von P. domesticus rudimentär. Definitive funktionelle Schlüsse sind aus solchen morphologischen Vergleichen aber nicht möglich. Im Epiphysenstiel von P. domesticus verlaufen kräftige Nervenbahnen, die im Material dieser Studie ausschließlich aus marklosen Nervenfasern (Durchmesser 0,12–1,5 m) bestehen. Diese Faserzüge sind von autonomen Nervenstämmchen zu unterscheiden, die perivasculär die bindegewebige Hülle des Pinealorgans durchsetzen und stellenweise an das Parenchym vordringen. Im Pinealorgan von P. domesticus findet sich auch ein Pinealocytentyp mit 800–1200 Å großen granulierten Vesikeln, die im Golgi-Apparat dieser Zellen entstehen. Die elektronenmikroskopischen und neurohistologischen Befunde werden mit Hinweis auf verhaltensphysiologische (Gaston und Menaker) und elektrophysiologische (Ralph und Dawson) Ergebnisse diskutiert. Da das Pinealorgan von P. domesticus nach Menaker eine zentrale Komponente der biologischen Uhr beherbergt, sind Fragen nach einem sensorischen Eigenapparat und nach der sekretorischen Aktivität dieses Organs besonders aktuell.

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Electron microscopic studies of the pineal organ in Passer domesticus

Summary The pineal organ of Passer domesticus contains cells with an inner segment, rich in mitochondria, from which a bulbous 9+0 type cilium originates. These cilia are often grouped together and may form 200 Å thick lamellae. Concentric or irregular whorl-like lamellar complexes arise from a number of such cilia. The structure of the bulbous cilia corresponds to that of early developmental stages of the photoreceptor outer segment. The characteristic membrane invaginations of the retinal cones are absent in the bulbous cilia of the avian pineal organ; the lamellar complexes have a position ectopic to the cilia. Signs of degeneration are present at the lamellar bodies. The degenerated forms resemble structures that arise from disintegrating outer segment plates in the pineal photoreceptor cells of lower vertebrates. The receptor-like pinealocytes of P. domesticus appear rudimentary when compared with the fully differentiated pineal sensory cells. Definitive functional interpretations are not possible from such morphological comparisons. In the pineal stalk of P. domesticus, nerve tracts are present consisting of unmyelinated fibers of 0.12–1.50 m diameter. These nerve tracts differ from autonomic nerves that traverse perivascularly the connective tissue of the pineal capsule and in places enter the pineal organ. In the pineal organ of P. domesticus, a cell type is also found containing 800–1,200 Å diameter granular vesicles which originate in the Golgi complex. The electron microscopic and neurohistological findings are discussed with reference to experiments by Gaston and Menaker (i.e. the effect of pinealectomy on the circadian locomotor rhythm of P. domesticus) and to electrophysiological results of Ralph and Dawson. Since, according to Menaker, the pineal organ of P. domesticus is a crucial component of the endogenous time-measuring system, questions concerning the presence of a sensory apparatus and secretory activity in this organ assume a special significance.

Eine kurze Zusammenfassung der Ergebnisse wurde im Seminar on Hypothalamic and Endocrine Functions in Birds, Tokio (19.–24. Mai 1969), vorgetragen.     

A quantitative method for separating reaction components of CMP-sialic acid: Lactosylceramide sialyltransferase using Sep Pak C18 cartridges

A rapid procedure is described for the separation of CMP-sialic acid:lactosylceramide sialyltransferase reaction components using Sep Pak C₁₈ cartridges. The quantitative separation of the more polar nucleotide sugar, CMP-sialic acid, and its free acid from the less polar G_M3-ganglioside is simple and rapid relative to previously described methods. Recovery of G_M3 is optimized by the addition of phosphatidylcholine to the reaction mixture prior to the chromatographic step. Using rat liver Golgi membranes as a source of CMP-sialic acid: lactosylceramide sialyltransferase activity (G_M3 synthase; ST-1), the transfer of [¹⁴C] sialic acid from CMP-[¹⁴C] sialic acid to lactosylceramide can be quantified by this assay. The procedure is reliable and may be applicable to the isolation of ganglioside products in otherin vitro glycosyltransferase assays.Abbreviations G_M3 G_M3-ganglioside - II³NeuAc-LacCer NeuAc2-3Gal1-4Glc1-1Cer - G_D1a G_D1a-ganglioside, IV³NeuAc, II³NeuAc-GgOse₄Cer, NeuAc2-3Gal1-3GalNac1-4(NeuAc2-3)Gal1-4Glc1-1Cer - G_D3 G_D3-ganglioside, II³(NeuAc)₂LacCer, NeuAc2-8NeuAc2-3Gal1-4Glc1-1Cer - GgOse₄Cer asialo-G_M1 Gal1-3GalNAc1-4Gal1-4Glc1-1Cer - FucG_MI fucosyl-G_MI-ganglioside, Fuc1-2Gal1-3GalNAc1-4Gal1-4 Glc1-1Cer - ST-1 G_M3 synthase, CMP-sialic acid:lactosylceramide sialyltransferase - LacCer lactosylceramide, Gal1-4Glc1-1Cer - CMP-NeuAc cytidine 5-monophospho-N-acetylneuraminic acid - PC phosphatidylcholine - PMSF phenylmethylsulfonyl fluoride     

Differential location of regulatory and nonregulatory trehalases inCandida utilis cells

The isolation of vacuoles by density gradient centrifugation of protoplast lysates fromCandida utilis cells showed a high specific activity for nonregulatory trehalase in vacuoles whereas the regulatory trehalase activatable by phosphorylation behaves as a cytoplasmic enzyme. The vacuolar trehalase is a glycoprotein that can be precipitated by Con A-Sepharose. Treatment of this enzyme with endo H reduced its reactivity with the lectin without loss of enzyme activity and decreased its apparent molecular weight by gel filtration.Abbreviations cAMP adenosine 3, 5-cyclic monophosphate - Con A Concanavalin A - CP buffer 10mM sodium citrate-phosphate pH 6.8 - endo H endo--N-acetyl glucosaminidase H - PMSF phenyl-methyl-sulphonylfluoride - PNPG p-nitrophenyl--glucoside - PNPP p-nitrophenyl-phosphate     

Fouling mussels (Dreissena spp.) colonize soft sediments in Lake Erie and facilitate benthic invertebrates

• 1 We conducted survey and transplant studies to determine whether colonization and residency on soft sediments by introduced, fouling mussels (Dreissena polymorpha and D. bugensis) were affected by physical disturbance, and whether Dreissena presence in turn influenced the diversity and population densities of other benthic invertebrates. Surveys revealed that colony density was typically higher at moderate depths than at shallower and greater ones. However, the largest, midsummer colonies and greatest coverage of sediments by mussels occurred at deeper sites.
• 2 Disturbance of transplanted colonies varied by depth and colony size, with deeper and larger colonies experiencing the lowest destruction rates. Colony destruction rate was positively correlated with current velocity adjacent to the lakebed.
• 3 Absence of mussel colonies at shallow sites was not determined by recruitment or substrate limitation, as recruit density was higher and sediment characteristics more suitable for postveliger settlement at shallow than at deeper sites. Rather, seasonal storms have much stronger effects in shallow than in deep water.
• 4 Mussel residency on soft sediment has profound effects on invertebrate biodiversity. Invertebrate species (taxon) richness and total abundance were positively correlated with mussel colony area. Mussel‐sediment habitat supported between 462 and 703% more taxa, and between 202 and 335% more individuals (exclusive of Dreissena) than adjacent soft‐sediment lacking mussels.
• 5 Results from this study illustrate that physical disturbance directly limits the distribution of mussels on soft sediments, and the diversity and abundance of other benthic invertebrates in consequence.

     

Suppression of microzooplankton by zebra mussels: importance of mussel size

1. The zebra mussel (Dreissena polymorpha) is amongst the most recent species to invade the Great Lakes. We explored the suppressive capabilities of mussels 6–22-mm in size on Lake St Clair microzooplankton (< 240)μm) in laboratory experiments. 2. Absolute suppression of rotifers and Dreissena veliger larvae was proportional to mussel shell length for individuals larger than 10 mm; larger zooplankton, mainly copepod nauplii and Cladocera, were not affected. Mussel clearance rates on rotifers generally exceeded those on veligers, although rates for both increased with increasing mussel size. Rotifer-based clearance rates of large (22 mm) mussels approached published values for phytoplankton food. 3. Most zooplankton taxa, particularly rotifers, declined significantly in western Lake Erie during the late 1980s concomitant with the establishment and population growth of zebra mussels in the basin. Densities of some taxa subsequently increased, although rotifers and copepod nauplii densities remained suppressed through 1993. Available evidence indicates that direct suppression by Dreissena coupled with food limitation provides the most parsimonious explanation for these patterns.     

Meiotic studies ofElymus nutans andE. jacquemontii (Poaceae,Triticeae) and their hybrids withPseudoroegneria spicata and seventeenElymus species

Hybridizations ofElymus nutans andE. jacquemontii were carried out with one species ofPseudoroegneria (S genome), and 20Elymus species, each containing either of the SH, SY, SYH, or SYW genomes. Chromosome configurations were analysed at metaphase I of the two target taxa and their interspecific hybrids. It is concluded that (i)E. nutans is an allohexaploid containing the SYH genomes, andE. jacquemontii is an allotetraploid having the SY genomes; (ii) the genomic affinity is associated with the geographic distance between the species studied; (iii) minor genomic structural rearrangements have occurred within the hexaploid taxon ofE. nutans.     

Adrenergic regulation of ion transport by primary cultures of canine tracheal epithelium: Cellular electrophysiology

Summary We examined the effect of adrenergic agents on the cellular electrical properties of primary cultures of canine tracheal epithelium. Both isoproterenol and epinephrine stimulated Cl secretion, as evidenced by an increase in transepithelial voltage and a fall in transepithelial resistance. Moreover, both agents appear to increase the conductance of apical and basolateral membranes. However, the pattern of response was different. Isoproterenol initially depolarized apical voltage _a and decreased the fractional resistance of the apical membranef _R. These changes are consistent with an initial increase in apical Cl conductance. In contrast, epinephrine acutely hyperpolarized _a and increasedf _R, changes consistent with an initial increase in basolateral K conductance. Following the acute effect of epinephrine, _a depolarized andf _R decreased to values not significantly different from those observed with isoproterenol. The acute increase in basolateral K conductance produced by epinephrine appeared to result from stimulation of adrenergic receptors because it was reproduced by addition of the agonist phenylephrine, and blocked by the antagonist phentolamine. The ability of prazosin but not yohimbine to block the acute epinephrine-induced increase in K permeability indicates the presence of ₁ adrenergic receptors. The acute adrenergic-induced increase in basolateral K conductance may be mediated by an increase in cell Ca because the response was mimicked by addition of the Ca ionophore A23187. In contrast, the response to isoproterenol was similar to that observed with addition of 8-bromo-cAMP and theophylline. These results indicate that both and adrenergic agents mediate the ion transport processes in canine tracheal epithelium. adrenergic agents have their primary effect on the apical Cl conductance, probably via an increase in cAMP. adrenergic agents exert their primary effect on the basolateral K conductance, possibly via an increase in cell Ca.     

Epiphytic Refugium: Are Two Species of Invading Freshwater Bivalves Partitioning Spatial Resources?

Enumeration of benthic (bottom dwelling) and epiphytic (attached to plants) zebra and quagga mussels (Dreissena polymorpha and D. bugensis, respectively) at Lake Erie near-shore sites in fall of 2000 revealed an unexpected prevalence of the zebra mussel on submerged plants. Even at Buffalo, New York, USA, where benthic dreissenids have been 92–100% quagga mussel since 1996, zebra mussels constituted 30–61% of epiphytes numerically. This may reflect a partitioning of settling space consistent with interspecific competition. A seasonal epiphytic refugium might allow the zebra mussel to persist even where the benthos is almost exclusively quagga mussel. This revised version was published online in July 2006 with corrections to the Cover Date.     

Experimentelle Analyse des Orientierungsverhaltens der Eilarve von Aleochara curtula Goeze (Coleoptera: Staphylinidae) am Wirt

Zusammenfassung Es wurde das Orientierungsverhalten der Eilarve des raubparasitischen Staphyliniden, Aleochara curtula Goeze, an dem Wirt, dem Puparium von Calliphora erythrocephala Meig., untersucht. I. Das Phänomen des gerichteten Wirtsbefalls 1. Die A. curtula-Eilarve nagt die Eingangsöffnung unabhängig von der Körperlage des Wirtes im Boden innerhalb eines ringförmigen Vorzugsbereiches am Pupariumhinterende. 2. Die morphologische Ventralhälfte dieses Vorzugsbereiches wird häufiger mit Eingangsöffnungen belegt (Ventralattraktivität). 3. Die Schwerkraft selbst oder ein anderer in Richtung Schwerkraft wirkender Faktor hat einen Einfluß auf die Verteilung der Eingangsöffnungen innerhalb des Vorzugsbereiches. 4. Der Vorzugsbereich von A. curtula lag bei den geprüften Wirtsarten stets am Pupariumhinterende. Die verschiedene Lage der Vorzugsbereiche von A. curtula und A. bilineata am gleichen Wirt läßt auf artspezifische Unterschiede im Orientierungsverhalten schließen. 5. Die Eilarven von A. curtula vollführt am Hinterende des Pupariums Orientierungsläufe, die von Stigma-Besuchen unterbrochen werden. II. Analyse des gerichteten Wirtsbefalles 1. Das abdominale Stigmenpaar des Wirtes dient der Larve als Orientierungsmarke. Nach Verschluß dieser Stigmen werden die Eingangsöffnungen nicht mehr am Hinterende, sondern am Vorderende des Wirtes in der Nähe des prothorakalen Stigmenpaares genagt. Nach Verschluß beider Stigmenpaare streut der Befall über die gesamte Wirtsoberfläohe. 2. Die Stigmen am Wirt sind Austrittspforten eines flüchtigen, mit organischen Lösungsmitteln extrahierbaren Stoffes, von dem die Larven angelockt werden. 3. Für den experimentell verursachten ungerichteten Befall der Wirtsoberfläche sind sowohl chemische als auch mechanische Faktoren verantwortlich: a) Der Rückgang der Befallsquote auf 40% bei absolut duftlosen Puparienhülsen und das Vorkommen von unvollendeten Eingangsöffnungen ist auf Fehlen anlockender Stoffe zurückzuführen. b) Parasitierungsversuche mit verschieden geformten Paraffinattrappen zeigen, daß für den Restbefall der duftlosen Puparienhülsen die Krümmung der Oberfläche verantwortlich ist. 4. Nach Ausschalten der Krümmung orientieren sich die Larven nach einem in eine plane Membran eingelassenen, normal duftenden Hinterstigma und nagen innerhalb eines ringförmigen Vorzugsbereiches ihre Eingangsöffnungen durch die Membran. Die Auslösbarkeit dieser Handlung steigt mit dem Larvenalter vom 1. bis zum 4. Tag von 26 auf 67%. Wird den Larven außer dem Stigma noch eine gekrümmte Oberfläche geboten, erhöht sich die Befallsrate von l Tag alten Larven auf 72%. 5. Parasitierungsversuche an experimentell veränderten Puparien beweisen, daß die Krümmung der Wirtsoberfläche in die Orientierungshandlung als richtende Reize mit einbezogen werden. Damit erklärt sich die stärkere Bevorzugung der Ventralhälfte (Ventralattraktivität); denn zwischen dieser und dem dorsal liegendem abdominalen Stigmenpaar hat die Krümmung ihr Maximum. 6. Hypothesen zur Erklärung des mittleren Abstandes zwischen Duftquelle Stigma und Eingangsöffnung sind experimentell geprüft worden: a) Versuche mit Luftströmungen, künstlich erweiterten oder stufenweise verengten Abdominalstigmen ergaben keinen eindeutigen Hinweis für eine Orientierung der Larven nach einem Konzentrationsoptimum des Duftstoffes. b) Die Annahme, daß die Larven mit Hilfe ihrer Körperlänge den Abstand festlegen, konnte durch Amputation von Abdominalsegmenten der Larven widerlegt werden. c) Das Bewegungsverhalten der Larven wird durch einmaligen kurzen Kontakt mit dem Wirt umgestimmt. Das Muster dieser Suchbewegungen ändert sich charakteristisch je länger der Aufenthalt auf dem Wirt dauerte. Es wird vermutet, daß in diesen starren Bewegungsabfolgen Elemente enthalten sind, die den Abstand erklären könnten. III. Diskussion 1. Beobachtungen und experimentelle Befunde werden zu einer Vorstellung verknüpft, die den Ablauf der Orientierungshandlung der A. curtula-Eilarve am Wirt erklären kann. 2. Diskutiert werden Hinweise, die für den arterhaltenden Wert dieser Orientierungshandlung sprechen, und Möglichkeiten, einen Einblick in die Stammesgeschichte des Orientierungsverhaltens am Wirt bei der Gattung Aleochara zu erhalten.

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Experimental analysis of orientation behaviour of the Aleochara curtula goeze egg larva (Coleoptera: Staphylinidae) on the host

Summary There is an investigation of the behaviour of directed attack by the newly hatched larva of the roveparasitic beetle, Aleochara curtula Goeze, on his host, the puparium of the muscid, Calliphora erythrocephala Meig. I. The Phenomenon of Directed Host Attack 1. Independent of the host position in soil, the egg larva of Aleochara curtula gnaws the entry hole within a ringlike preference region at the posterior end of the puparium. 2. The morphological ventralhalf of this preference region is more often attacked (Ventralattractivity). 3. The force of gravity or another factor, which is effecting in direction of the gravity, has an influence on the distribution of the entry holes within the preference region. 4. In all proved host species the preference region of A. curtula lies at the posterior end of the puparium. At the same host the different positions of the preference regions of A. curtula and A. bilineata depend consequently on species-specific differences in the behaviour. 5. Orientation runs, which are interrupted by visits at a stigma, are carried out by the egg larva of A. curtula. II. Analysis of Directed Host Attack 1. The abdominal pair of the stigmata of the host serves the larva for a mark for finding the preference region. After covering these stigmata, the entry holes are gnawed no more at the posterior end of the host but at the anterior end near the prothoracal pair of stigmata. After covering both pairs of stigmata, the attack distributes all over the host surface. 2. The host stigmata are points of emergence for a volatile product. It is extractable with organic solvents and attractive for the larvae. 3. Chemical as well as mechanical factors are responsible for the experimental caused diffused attacks of the host surface. a) The diminution of the attack quote to 40% in absolutely odourless puparia pods and the appearance of unfinished entry holes are traceable missing of attractive substances. b) Experiments with differently formed host models of paraffine show, that the curvature of the surface is responsible for residual attacks to the odourless puparia pods. 4. After elimination of the curvature the larvae are able to a orientation to a normal scenting stigma, which is inserted in a plane membrane. They gnaw their entry holes into the membrane round the stigma within a ring-like preference region. Dependency to the age of the larvae from first till fourth day the response to this situation rises from 26 to 67%. Offering the larvae the curvature of the surface besides the stigma the attack quote of one day old larvae rises to 72%. 5. The distribution of the entry holes in experimentally altered puparia demonstrate, that the curvature of the host surface is a directing stimulus in the orientation behaviour. This accounts for the stronger preference of the ventralhalf (Ventralattractivity); because in normal puparia the curvature is maximal between the dorsal stigmata and the ventralhalf. 6. Hypotheses to explain the middle distance between scent mark stigma and entry hole are proved by experiments: a) Experiments with air, artificially widened or gradually narrowed abdominal stigmata don't point to orientation of the larvae by a maximal concentration of aromatic substance. b) The assumption, that the larvae would make use of their length to fix the distance could be disproved by amputation of abdominal segments. c) A change of larval locomotion is stimulated by a short contact with the host. The pattern of this searching actions changes characteristically with the duration of the contact. It is supposed, that these stereotyped actions contain elements, which could explain the distance. III. Discussion 1. Observations and experimental results are connected to an opinion, which could explain the termination of orientation behaviour of the A. curtula egg larva on its host. 2. Indications are discussed, which confirm a biological importance of this orientation action. Further are discussed prospects, which could give insight into the phylogeny of the orientation behaviour on the host in the genus Aleochara.

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Habilitationsschrift der Naturwissenschaftlichen Fakultät der Universität Würzburg.     

Antifouling activity of seaweed extracts on the green alga Enteromorpha prolifera and the mussel Mytilus edulis

Twenty-seven species of common seaweeds from the coast of Korea havebeen screened for antifouling activity. The seaweed extracts were tested inlaboratory assays against the marine fouling green alga Enteromorphaprolifera and the blue mussel Mytilus edulis. Tissue growth, sporesettlement, zygote formation and germlings of the E. prolifera wereinhibited by methanol extracts of the seaweed Ishige sinicola (= I. foliacea) and Sargassum horneri. Spore settlement was stronglyinhibited by using extract concentrations as low as 30 g mL^-1with I. sinicola and 120 g mL^-1 with S. horneri. The repulsive activity of the foot of the mussel was completely inhibited bymethanol extracts of I. sinicola and Scytosiphon lomentaria atconcentrations of 40 g per 10 L drop supplied to eachmussel. These extracts also showed strong antifouling activities onlarval settlement with, respectively, no or only 6% of the spat settlingwhen a test concentration of 0.8 mg mL^-1 was used. This work isthe first stage towards the development of novel antifouling agents frommarine macroalgae.     

The surf zone: a semi-permeable barrier to onshore recruitment of invertebrate larvae?

The supply of larvae to the shore is important for population replenishment and intertidal community dynamics but its variability at most scales is not well understood. We tested the relationship between nearshore mussel larval abundance and intertidal settlement rates over several years at multiple spatiotemporal scales in Oregon and New Zealand. Abundance of competent larvae nearshore and intertidal recruitment rates were simultaneously quantified using collectors mounted at different depths on moorings 50-1100 m from shore, and at adjacent rocky intertidal sites. Total mussel larval abundance and oceanographic conditions were also measured in some locations. At all scales, abundance of nearshore mussel larvae was unrelated to intertidal recruitment rates. In the intertidal, patterns of mussel recruitment were persistent in space, with sites of consistently high or low recruitment. In contrast, nearshore competent larval abundance showed generally similar abundances among sites except for a high, and spatially-inconsistent, variability in Oregon during 1998 only. On moorings, recruitment tended to be greater on midwater collectors than shallower or deeper. Finally, on moorings larval abundance in traps and recruitment on collectors was unrelated. These results suggest that (1) among sites, the size of the nearshore larval pool is relatively uniform while onshore recruitment varies and is unrelated to larval abundance, (2) temporal variability in nearshore larval availability is not strongly expressed onshore, (3) vertical stratification of competent larvae nearshore is strong and may influence transport and recruitment, and (4) within-coast variability in onshore recruitment is strongly driven by processes occurring locally within the surf zone that need to be studied to understand coastal recruitment dynamics.