Effect of the snail Ilyanassa obsoleta (Say) on dynamics of the amphipod Corophium volutator (Pallas) on an intertidal mudflat

We investigated interactions between two dominant invertebrate species of intertidal soft-sediment environments of the northwest Atlantic, the mud snail Ilyanassa obsoleta and the burrowing amphipod Corophium volutator, on a mudflat of the upper Bay of Fundy, Canada. Distribution of I. obsoleta on the mudflat was highly patchy and negatively correlated with density of C. volutator. Manipulation of snail density in cages showed that I. obsoleta influences C. volutator; specifically, increasing density of snails reduced density, increased patchiness in distribution, decreased recapture rates and decreased immigration of C. volutator. Ilyanassa obsoleta seems to be affecting C. volutator through an influence on survival rate and emigration rate, although temporal variation in these effects was observed. Given that both I. obsoleta and C. volutator show a preference for tide pools, an important microhabitat on mudflats, snails might have a profound impact on C. volutator population dynamics.     

Effect of immersion at low tide on distribution and movement of the mud snail, Ilyanassa obsoleta (Say), in the upper Bay of Fundy, eastern Canada

Habitat heterogeneity often affects movement behaviours of animals, and consequently their spatial distribution. We evaluated the effect of immersion at low tide on the distribution, fine-scale movement patterns and daily movement patterns of the mud snail Ilyanassa obsoleta on a mudflat in the upper Bay of Fundy, Canada. Mud snails migrate onto intertidal mudflats in the summer, and our field survey showed that their density was higher inside tide pools relative to adjacent areas that are exposed at low tide. Using time-lapse videography, we evaluated the effect of snail size, snail density, and immersion at low tide on fine-scale movement patterns of I. obsoleta. Time until snails stopped moving and burrowed was unaffected by snail size, but snails at low and high densities burrowed somewhat faster than those at intermediate densities. Snail size and snail density had no detectable effect on displacement speed or linearity of displacement. Immersion affected snail movement: snails within tide pools delayed burrowing and traveled in more convoluted paths compared to those on exposed mud. Snails increased their turning angles within tide pools, which is probably the mechanism by which aggregations are formed. We also performed a mark-recapture experiment to compare daily movement patterns of snails released inside and outside tide pools. Snails released in tide pools moved shorter distances, but did not orient themselves differently than snails released outside tide pools. Both groups exhibited significant directionality, moving against the mean water current direction over 24 h. In sum, immersion at low tide affected the behaviour and spatial distribution of snails, resulting in snail aggregations within tide pools. These snail aggregations, in turn, may be a major factor influencing spatial dynamics on mudflats, including causing changes in distribution patterns of the burrowing amphipod Corophium volutator, a dominant inhabitant and key species in the food web of mudflats.     

Differential emigration causes aggregation of the amphipod Corophium volutator (Pallas) in tide pools on mudflats of the upper Bay of Fundy, Canada

We investigated mechanisms responsible for the formation of spatial patterns in a dominant macro-invertebrate, the burrowing amphipod Corophium volutator, in relation to tide pools on intertidal mudflats of the upper Bay of Fundy, Canada. A field survey of 3 different mudflats showed that density of C. volutator at low tide was consistently higher inside than outside tide pools, and a manipulative field experiment indicated that C. volutator selected tide pools over the adjacent emerged areas. Differential survival in immersed and emerged areas at low tide did not explain the observed pattern, because short-term survival of amphipods was not affected by immersion at low tide. As well, immigration rates of C. volutator into immersed and emerged areas at low tide were similar after one day, so preferential settlement did not explain aggregation of amphipods. However, marked C. volutator departed from experimental areas that were immersed at low tide at a slower rate compared to emerged experimental areas. Thus, formation of the spatial pattern observed in the field (higher densities inside tide pools) is likely the result of an effect of immersion at low tide on proportion of individuals emigrating from an area every day.     

Foraging by the mud snail, Ilyanassa obsoleta (Say), modulates spatial variation in benthic community structure

We investigated the foraging behavior of the mud snail, Ilyanassa obsoleta, and its consequences for macrobenthic community structure on mud flats on Long Island, NY, USA. Field sampling demonstrated strong spatial heterogeneity in the population densities of I. obsoleta. We experimentally tested three hypotheses: (i) I. obsoleta are strongly attracted to areas with high levels of detritus; (ii) local abundances of deposit-feeding annelids are limited by detritus; and (iii) the foraging activities of I. obsoleta negatively affects annelid assemblages. We manipulated the density of mud snails using inclusion fences and the levels of detritus using dried Ulva. Results showed that high densities of I. obsoleta were attracted to areas enriched with Ulva detritus. In addition, high densities of snails negatively affected abundances of annelids, with the opportunistic species, Capitella spp. and Paranais litoralis, being most affected. The addition of Ulva detritus had more specific effects on annelid assemblages. Only Capitella spp. showed a significant positive response, although previous evidence has demonstrated that higher experimental detrital inputs stimulated growth of other species of annelids and microphytobenthos. In an experimental treatment with enhanced detritus and low densities of snails, we found population abundances of opportunistic annelids (up to 200,000 m⁻²) substantially larger than has ever been recorded in 5 years of sampling. Because mud snails in natural areas actively search, locate and exploit areas with enhanced detritus and their foraging negatively affects abundances of opportunistic worms, I. obsoleta probably controls the upper limits of annelid abundance in the field. Foraging behavior of I. obsoleta therefore modulates spatial variation in benthic community structure in an environment where limiting resources are patchily distributed.     

Effects of substrate on interactions between juvenile sea scallops (Placopecten magellanicus Gmelin) and predatory sea stars (Asterias vulgaris Verrill) and rock crabs (Cancer irroratus Say)

We investigated the effect of substrate (glass bottom, sand, granule, pebble) on predation of juvenile sea scallops (Placopecten magellanicus) by sea stars (Asterias vulgaris) and rock crabs (Cancer irroratus) at two prey sizes (11-15 mm and 24-28 mm shell height), and two prey densities (10 and 30 scallops per aquarium) in laboratory experiments. Specifically, we quantified predation rate and underlying behaviours (proportion of time a predator spent searching for and handling prey, encounter rate between predators and prey, and various outcomes of encounters). We detected a significant gradual effect of particle size of natural substrates on sea star predation: specifically, predation rate on and encounter rate with small scallops tended to decrease with increasing particle size (being highest for sand, intermediate for granule, and lowest for pebble). Substrate type did not significantly affect predation rates or behaviours of sea stars preying on large scallops or of rock crabs preying on either scallop size classes. Other factors, such as prey size and density, were important in the scallop-sea star and scallop-rock crab systems. For example, predation rate by sea stars and crabs and certain sea star behaviours (e.g. probability of consuming scallops upon capture) were significantly higher with small scallops than with large scallops. As well, in interactions between small scallops and sea stars, predation rate and encounter rate increased with prey density, and the proportion of time sea stars spent searching was higher at low prey density than high prey density. Thus, substrate type may be a minor factor determining predation risk of seeded scallops during enhancement operations; prey size and prey density may play a more important role. However, substrate type still needs to be considered when choosing a site for scallop enhancement, as it may affect other scallop behaviours (such as movement).     

The distribution of mallophaga on the domestic pigeon (Columba livia)

The distribution of Hohorstiella lata, Colpocephalum turbinatum, Campanulotes bidentatus compar, and Comlumbicola columbae on domestic pigeons were determined. Each species laid its eggs on a different part of the body but all fed on the fluffy part of the body feathers. H. lata also fed on blood, and C. turbinatum on its own eggs and nymphs. Reduction of the efficiency of preening led to an increase in the number of lice and more widespread distribution of nymphs and adults but not to a rapid change in the distribution of eggs. It is suggested that preening has played a major selective role, and that the morphological and behavioural adaptions of the lice are to ensure that they and their eggs survive this type of predation.     

Seasonal changes in the digestive enzyme levels of the amphipod Corophium volutator (Pallas) in relation to diet

The diet of the amphipod Corophium volutator (Pallas) living on extensive intertidal mud flats in the Bay of Fundy, eastern Canada, was investigated by direct and indirect methods. Microscopic observation of gut contents revealed macrophyte detritus but few diatom frustules. Laboratory cultures showed good survival on a diet of benthic diatoms, while on a diet of Spartina detritus survival was poor, although significantly better than the survival of starved animals. The ratios of gut enzyme activities, amylase to protease and amylase to laminarinase, changed markedly with the season. In summer the ratio was similar to that of animals cultured on a diet of benthic diatoms; in spring it resembled that of animals cultured on Spartina detritus, while in winter it was similar to that of starved animals. It is concluded that in summer, rapid growth is made possible by feeding on benthic diatoms, while Spartina detritus is an inferior food source which aids survival at other times of the year.     

Reproductive costs of the symbiotic hydroid Hydractinia symbiolongicarpus (Buss and Yund) to its host hermit crab Pagurus longicarpus (Say)

Studies on the interaction between the hermit crab Pagurus longicarpus and its symbiotic hydroid Hydractinia symbiolongicarpus have focused on positive effects of hydroids on their host hermit crabs (e.g., protection from predators). Yet, these benefits may be balanced with reproductive costs, which are rarely studied. Results from field observations, laboratory trials, and a mesocosm experiment indicate that female hermit crabs in hydroid-colonized shells exhibit depressed ovigery, smaller clutch sizes, and increased clutch failure relative to females in bare shells. Frequent switching between bare and hydroid-colonized shells may alleviate negative effects when the density of hydroids in the environment is low, but at high densities Hydractinia may significantly impact hermit crab reproduction.     

Septal pore complex morphology in the Agaricomycotina (Basidiomycota) with emphasis on the Cantharellales and Hymenochaetales

The ultrastructure of septa and septum-associated septal pore caps are important taxonomic markers in the Agaricomycotina (Basidiomycota, Fungi). The septal pore caps covering the typical basidiomycetous dolipore septum are divided into three main phenotypically recognized morphotypes: vesicular-tubular (including the vesicular, sacculate, tubular, ampulliform, and globular morphotypes), imperforate, and perforate. Until recently, the septal pore cap-type reflected the higher-order relationships within the Agaricomycotina. However, the new classification of Fungi resulted in many changes including revision of existing and addition of new orders. Therefore, the septal pore cap ultrastructure of more than 325 species as reported in literature was related to this new classification. In addition, the septal pore cap ultrastructures of Rickenella fibula and Cantharellus formosus were examined by transmission electron microscopy. Both fungi have dolipore septa associated with perforate septal pore caps. These results combined with data from the literature show that the septal pore cap-type within orders of the Agaricomycotina is generally monomorphic, except for the Cantharellales and Hymenochaetales.It appears from the fungal phylogeny combined with the septal pore cap ultrastructure that the vesicular-tubular and the imperforate type both may have arisen from endoplasmic reticulum. Thereafter, the imperforate type eventually gave rise to the perforate septal pore cap-type.     

Effects of juvenile non-indigenous Carcinus maenas on the growth and condition of juvenile Cancer irroratus

The Atlantic rock crab, Cancer irroratus, is a commercially fished species and a critical prey item for the American lobster, Homarus americanus, in Atlantic Canada. The recent invasion of European green crab, Carcinus maenas, may have significant effects on the growth and condition of native C. irroratus, because both species overlap spatially and temporally and have similar habitat and dietary requirements. To examine such potential effects, we measured the growth of juvenile C. irroratus in the presence of juvenile C. maenas over a period of 4 months (growing season), under the following species combinations: (1) one C. irroratus (10-25 mm CW); (2) two C. irroratus (10-25 mm CW); (3) one C. irroratus (10-25 mm CW) and one C. maenas (10-15 mm CW). Morphological measurements included pre- and post-molt carapace width, chela height, abdomen width (mm), weight (g), and estimates of molt increment (%) and intermolt duration (days). Analysis of the hepatopancreas for % lipid content at the end of the experiment provided an estimate of physiological condition. The effect of the presence of C. maenas on the growth of C. irroratus shifted from negative to positive, when C. irroratus reached CW of 19-22 mm and gained a presumably significant size advantage over C. maenas. The positive effect resulted from increased energy intake through crab consumption. In the absence of crab consumption, the presence of a second crab (conspecific or C. maenas) had no effect on growth. C. irroratus consumed crabs more frequently when the second individual was a green crab than a conspecific. Consumption of C. maenas had a pronounced effect on the growth rate of C. irroratus, resulting in shorter intermolt periods and larger percent molt increments than in the presence of a conspecific. Therefore, the presence of juvenile C. maenas does not appear to have a prolonged negative effect on the growth of C. irroratus; rather, it may provide an additional food item as rock crabs grow, as long as encounters between the two species occur at high enough rates.     

Age, distribution and abundance of viable resting eggs of Acartia pacifica (Copepoda: Calanoida) in Xiamen Bay, China

The distribution and abundance of viable resting eggs of copepod Acartia pacifica in Xiamen Bay, China, were determined in the laboratory by the presence of nauplii hatched from the sediments. Sediment cores to a depth of 30 cm, sliced at 1.0 cm intervals, showed that most viable resting eggs of A. pacifica occurred near the sediment surface (0-5 cm), and the number of viable eggs sharply decreased with depth of the sediment, although resting eggs remained viable as deep as 23 cm. ²¹⁰Pb analyses of the sediments indicated that the maximum age of viable eggs of A. pacifica was 20.5 years and the mean egg age was 4.3 years. The egg mortality of A. pacifica in the sediment was 0.1408 year⁻¹, or 85.92% annual egg survival, calculated by regressing ln(egg density) on the age of the sediment. The horizontal distribution of viable resting eggs ranged from 2.27×10³ to 3.85×10⁵ m⁻², with a mean value of 9.49×10⁴ m⁻². Regressions between viable eggs of A. pacifica and all fine-fraction particle size classes (at 2 μm intervals) were not significant. The accumulation of viable resting eggs that can persist for an extended period of time provided evidence for the existence of an egg bank of A. pacifica in the seabed of Xiamen Bay.     

Implications of a fluctuating fish predator guild on behavior, distribution, and abundance of a shared prey species: the grass shrimp Palaemonetes pugio

In some systems, the identity of a prey species' dominant predator(s) may not be constant over time. In cases in which a prey species exhibits different responses to various predator species, such changes in predator identity may have population-wide consequences. Our goals were to determine (1) whether mortality of and refuge use by the grass shrimp, Palaemonetes pugio, were predator-specific, and (2) how effects of prey size and habitat interacted with predator type. Striped bass (Morone saxatilis) exerted twice as much predation pressure as mummichog (Fundulus heteroclitus), although not equally as great on large (female) and small (male) shrimp. Mummichog, which fed preferentially on large shrimp, forced a partitioning of habitat between the two shrimp size classes. In contrast, large and small shrimp occupied similar habitats when subjected to striped bass, which fed on both size classes equally. Refuge use of grass shrimp depended on predator type. In the presence of mummichog, which occupied shallower depths in the water column than striped bass, shrimp stayed deep and close to structural habitat. Striped bass, which were deeper, caused shrimp to move high in the water column away from structural habitat. When both predators were present, shrimp distribution was similar to that when only striped bass were present, striped bass predation rate was enhanced, and overall mortality was higher than with either predator alone. Results suggest that at times when mummichogs are the dominant predators, large (female) shrimp experience higher predation than small (male) shrimp and are physically separated from their potential mates. When striped bass are more abundant, male and female shrimp may share a similar, shallow, less structure-oriented distribution and be subjected to higher mortality. When both predators are present, mortality rates may be higher still. This predator-, size-, and habitat-specificity of grass shrimp behavior suggests significant population and distribution consequences of fluctuating predator guilds and fluctuating cover of structural habitats in the field.     

Nudibranch-sponge feeding dynamics: Benefits of symbiont-containing sponge to Archidoris montereyensis (Cooper, 1862) and recovery of nudibranch feeding scars by Halichondria panicea (Pallas, 1766)

Selected interactions between the encrusting sponge Halichondria panicea and its primary predator, the dorid nudibranch Archidoris montereyensis, were investigated in a high-latitude rocky intertidal community spatially dominated by H. panicea. Feeding experiments were conducted in which A. montereyensis pairs were provided with sponge containing symbiotic zoochlorellae or sponge in which the zoochlorellae population had been reduced or removed by shading. Nudibranchs consuming H. panicea with symbiotic zoochlorellae had higher feeding, growth, and egg production rates than individuals eating aposymbiotic sponge. We simulated A. montereyensis predation on H. panicea by creating typically sized feeding grooves in the sponge. H. panicea's response was high linear growth rates into the experimental feeding grooves, generally recovering most of the groove area within 4 weeks. Overall, the sponge's rapid response to tissue damage minimizes grazing impacts and substrate loss and reduces susceptibility to wave removal.     

Systematics and evolution of the genus Torrubiella (Hypocreales, Ascomycota)

Torrubiella is a genus of arthropod-pathogenic fungi that primarily attacks spiders and scale insects. Based on the morphology of the perithecia, asci, and ascospores, it is classified in Clavicipitaceae s. lat. (Hypocreales), and is considered a close relative of Cordyceps s. 1., which was recently reclassified into three families (Clavicipitaceae s. str., Cordycipitaceae, Ophiocordycipitaceae) and four genera (Cordyceps s. str, Elaphocordyceps, Metacordyceps, and Ophiocordyceps). Torrubiella is distinguished morphologically from Cordyceps s. lat. mainly by the production of superficial perithecia and the absence of a well-developed stipitate stroma. To test and refine evolutionary hypotheses regarding the placement of Torrubiella and its relationship to Cordyceps s. lat., a multi-gene phylogeny was constructed by conducting ML and Bayesian analyses. The monophyly of Torrubiella was rejected by these analyses with species of the genus present in Clavicipitaceae, Cordycipitaceae, and Ophiocordycipitaceae, and often intermixed among species of Cordyceps s. lat. The morphological characters traditionally used to define the genus are, therefore, not phylogenetically informative, with the stipitate stromata being gained and/or lost several times among clavicipitaceous fungi. Two new genera (Conoideocrella, Orbiocrella) are proposed to accommodate two separate lineages of torrubielloid fungi in the Clavicipitaceae s. str. In addition, one species is reclassified in Cordyceps s. str. and three are reclassified in Ophiocordyceps. The phylogenetic importance of anamorphic genera, host affiliation, and stipitate stromata is discussed.     

Phylogenetic reassessment of Hyaloscyphaceae sensu lato (Helotiales, Leotiomycetes) based on multigene analyses

Hyaloscyphaceae is the largest family in Helotiales, Leotiomycetes. It is mainly characterized by minute apothecia with well-differentiated hairs, but its taxonomic delimitation and infrafamilial classification remain ambiguous. This study performed molecular phylogenetic analyses using multiple genes including the ITS-5.8S rDNA, the D1–D2 region of large subunit of rDNA, RNA polymerase II subunit 2, and the mitochondrial small subunit. The primary objective was to evaluate the phylogenetic utility of morphological characters traditionally used in the taxonomy of Hyaloscyphaceae through reassessment of the monophyly of this family and its genera. The phylogenetic analyses inferred Hyaloscyphaceae as being a heterogeneous assemblage of a diverse group of fungi and not supported as monophyletic. Among the three tribes of Hyaloscyphaceae only Lachneae formed a monophyletic lineage. The presence of hairs is rejected as a synapomorphy, since morphologically diversified hairs have originated independently during the evolution of Helotiales. The true- and false-subiculum in Arachnopezizeae are hypothesized to have evolved through different evolutionary processes; the true-subiculum is likely the product of a single evolutionary origin, while the false-subiculum is hypothesized to have originated multiple times. Since Hyaloscyphaceae sensu lato was not resolved as monophyletic, Hyaloscyphaceae sensu stricto is redefined and only applied to the genus Hyaloscypha.     

Mycobiota associated with the ambrosia beetle Scolytodes unipunctatus (Coleoptera: Curculionidae, Scolytinae)

Ambrosia beetles (Coleoptera: Scolytinae) are associated with strictly entomochoric and mutualistic fungi. We studied the mycobiota associated with Scolytodes unipunctatus, ambrosia beetles that infest Cecropia trees in Central America. Isolates were characterized using morphology and rDNA sequences (ITS region, LSU, and SSU rDNA). Four species are described here: Raffaelea scolytodis sp. nov. (Ophiostomatales), Gondwanamyces scolytodis sp. nov., Custingophora cecropiae sp. nov., and Graphium sp. (Microascales). The genus Custingophora is emended to include Knoxdaviesia anamorphs of Gondwanamyces based on uniformity of DNA sequences and phenotype.     

短期淹水培养对水稻土中地杆菌和厌氧粘细菌丰度的影响

模拟水稻土淹水过程,采用Real-time PCR技术测度了不同水稻土中地杆菌(Geobacteraceae spp.)和厌氧粘细菌(Anaeromyxobacter spp.)在不同淹水时期16S rDNA拷贝数的变化,比较了地杆菌和厌氧粘细菌丰度与培养过程中微生物Fe (Ⅲ)还原的关系。结果表明,在4类稻作区采集的水稻土样品中,Fe (Ⅲ)还原潜势有明显的区别,表现出由北向南逐渐降低的趋势。从淹水12 h的地杆菌和厌氧粘细菌拷贝数变化看出,采自浙江和天津的水稻土样品对淹水过程具有高度敏感性,而采自吉林和广西的水稻土样品对淹水响应不敏感。在17 d的短期淹水培养中,地杆菌丰度明显高于厌氧粘细菌,表明地杆菌对水稻土中铁还原的贡献大于厌氧粘细菌。地杆菌和厌氧粘细菌拷贝数总体上表现出在11 d 时达到峰值,17 d时显著下降。吉林水稻土中地杆菌丰度在5 d时达到38.3%,与其最大铁还原速率到达时间(T_Vmax)为4.07 d相对应,表明地杆菌对其铁还原过程具有重要贡献。四川水稻土中地杆菌和厌氧粘细菌丰度均较低,暗示其他兼性铁还原菌对其铁还原的作用值得重视。     

Real-time PCR detection of Holophagae (Acidobacteria) and Verrucomicrobia subdivision 1 groups in bulk and leek (Allium porrum) rhizosphere soils

In the light of the poor culturability of Acidobacteria and Verrucomicrobia species, group-specific real-time (qPCR) systems were developed based on the 16S rRNA gene sequences from culturable representatives of both groups. The number of DNA targets from three different groups, i.e. Holophagae (Acidobacteria group 8) and Luteolibacter/Prosthecobacter and unclassified Verrucomicrobiaceae subdivision 1, was determined in DNA extracts from different leek (Allium porrum) rhizosphere soil compartments and from bulk soil with the aim to determine the distribution of the three bacterial groups in the plant-soil ecosystem. The specificity of the designed primers was evaluated in three steps. First, in silico tests were performed which demonstrated that all designed primers 100% matched with database sequences of their respective groups, whereas lower matches with other non-target bacterial groups were found. Second, PCR amplification with the different primer sets was performed on genomic DNA extracts from target and from non-target bacteria. This test demonstrated specificity of the designed primers for the target groups, as single amplicons of expected sizes were found only for the target bacteria. Third, the qPCR systems were tested for specific amplifications from soil DNA extracts and 48 amplicons from each primer system were sequenced. All sequences were > 97% similar to database sequences of the respective target groups. Estimated cell numbers based on Holophagae-, Luteolibacter/Prosthecobacter- and unclassified Verrucomicrobiaceae subdivision 1-specific qPCRs from leek rhizosphere compartments and bulk soils demonstrated higher preference for one or both rhizosphere compartments above bulk soil for all three bacterial groups.