Feeding ecology of three predacious aquatic insects and two fish in a riffle of the Speed River,Ontario

The food habits of two fish (Etheostoma flabellare and Rhinichthys atratulus) and three predacious aquatic insects (Nigronia serricornis, Paragnetina media and Agnetina capitata) were examined for one year in a riffle of the Speed River, Ontario. Adult E. flabellare fed primarily on net-spinning caddisflies whereas juvenile E. flabellare relied heavily on chironomids. Rhinichthys atratulus had a more varied diet composed of chironomids, Antocha larvae (Tipulidae) and net-spinning caddisflies. Two of the aquatic insect predators consumed large numbers of net-spinning caddisflies; however, P. media contained large percentages of Hydropsyche and Cheumatopsyche whereas N. serricornis fed primarily on non-hydropsychid net-spinners. The diet of A. capitata was composed largely of chironomids and mayflies. Schoener's diet overlap index () suggested that large E. flabellare and P. media had similar diets; however, E. flabellare ingested much larger prey than P. media. Adult E. flabellare contained a significantly greater proportion of larger prey items in comparison with benthic samples whereas similar comparisons with other predators showed no selection for larger prey. These data demonstrate that E. flabellare was size selective given the range of prey sizes available whereas the other predators were not. Also, there was little dietary overlap among the fish and invertebrate predators suggesting a partitioning of resources.     

Seasonal colour and antipredator behaviour in Etheostoma (Percidae)

This study examined how colour varies across season and sex in the fantail darter Etheostoma flabellare and the banded darter Etheostoma zonale. Etheostoma flabellare has male‐only parental care and exhibited slight sexual dimorphism in overall colour, with no discernible effect of season on colour; whereas E. zonale does not have parental care and exhibited substantial sexual dimorphism in colour, but only in the breeding season. Additionally, antipredator behaviour of E. zonale was compared between males that were fully coloured during the breeding season and males that were partially coloured at that time, but the effects of colour and season were not consistent across males.     

The impact of temperature regimes on development,dormancy breaking and germination of dwarf shrub seeds from arctic,alpine and boreal sites

It has been suggested that the infrequent sexual reproduction of arctic dwarf shrubs might be related to the harsh environmental conditions in which they live. If this is the case, then increases in temperature resulting from global climate change might drastically affect regeneration of arctic species. We examined whether recruitment of Empetrum nigrum ssp. hermaphroditum and Vaccinium uliginosum (hereafter E. nigrum and V. uliginosum) was affected by temperature during three reproductive stages: seed development, dormancy breakage and germination. Seeds were collected from an arctic, an alpine (only E. nigrum) and a boreal site with different climates; stored at different winter temperatures and incubated for germination at different temperatures. Seeds of V. uliginosum developed in the boreal region had a higher percentage germination than did seeds developed in the Arctic. In contrast, seeds of E. nigrum from the arctic site had a higher or similar percentage germination than did seeds from the alpine and boreal sites. Increased winter temperatures had no significant effect on resulting germination percentage of E. nigrum. However, V. uliginosum seeds from the arctic site suffered increased fungal attack (and thus decreased germination) when they were stratified under high winter temperatures. Seeds of both species increased germination with increased incubation temperatures. Our results suggest that both species would increase their germination in response to warmer summers. Longer summers might also favour the slow-germinating E. nigrum. However, increased winter temperatures might increase mortality due to fungal attack in V. uliginosum ecotypes that are not adapted to mild winters.     

Reproductive isolation between two darter species is enhanced and asymmetric in sympatry

Robust reproductive isolation was found between the rainbow darter Etheostoma caeruleum and the orangethroat darter Etheostoma spectabile, as more offspring were produced when conspecific males and females were crossed as compared with heterospecific crosses. Furthermore, fewer eggs resulted from heterospecific crosses involving sympatric E. spectabile females than those using allopatric E. spectabile females, while a similar pattern was not observed in heterospecific crosses using E. caeruleum females. These results suggest that reinforcement, i.e. selection for pre‐zygotic reproductive barriers driven by reduced hybrid fitness, may have contributed to the evolution and maintenance of reproductive barriers between these potentially hybridizing species in sympatry.     

Living on the bottom: Kinematics of benthic station‐holding in darter fishes (Percidae: Etheostomatinae)

Darters represent a substantial radiation of freshwater fishes that live in close association with the substrate in North American streams and rivers. A key feature of any darter species is therefore its ability to stay in place or to “hold station” in flowing water. Here, we quantify the station‐holding performance of two morphologically divergent darter species, the fantail darter Etheostoma flabellare and the Missouri saddled darter Etheostoma tetrazonum. We also characterize the primary kinematic responses of the two species when holding station in flow speeds ranging from 4 to 56 cm s^?1 in a flow tank on either plexiglas or small rock substrate. We then present a series of hypotheses about the potential hydrodynamic and functional consequences of the observed postural changes and the links among morphology, posture, and station‐holding performance. On both substrates, E. tetrazonum was able to hold station at higher flow speeds than E. flabellare. On rocks, E. tetrazonum slipped at an average speed of 55.7 cm s^?1 whereas E. flabellare slipped at 40.2 cm s^?1. On plexiglas, E. tetrazonum slipped at an average speed of 24.7 cm s^?1 whereas E. flabellare slipped at 23.1 cm s^?1. We measured body and fin positions of the two species from individual frames of high‐speed video while holding station on rocks and plexiglas. We found that on both substrates, the two species generally exhibited similar kinematic responses to increasing flow: the head was lowered and angled downward, the back became more arched, and the median and caudal fin rays contracted as water flow speed increased. The ventral halves of the pectoral fins were also expanded and the dorsal halves contracted. These changes in posture and fin position likely increase negative lift forces thereby increasing substrate contact forces and reducing the probability of downstream slip. J. Morphol., 2010. © 2009 Wiley‐Liss, Inc.     

In vitro studies on the effects of fungicides on beneficial fungi of peach twig mycoflora

In vitro studies were carried out to investigate a possible integrated use of chemical and biological means to control the peach twig blight pathogen,Monilinia laxa. Three fungal antagonists ofM. laxa (Penicillium purpurogenum, Penicillium frequentans andEpicoccum nigrum) and six fungicides (vinclozolin, iprodione, thiram, captan, benomyl and thiophanate-methyl) were used in the study. Sensitivity of the fungal isolates to the fungicides was determined in vitro by calculating ED50 values. Benomyl and thiophanate-methyl were the most fungitoxic compounds and captan was the least fungitoxic.M. laxa andP. purpurogenum were the most sensitive to all chemicals tested, whileE. nigrum andP. frequentans presented bigger differences in their sensitivity to chemicals compared toM. laxa. E. nigrum was consistently less sensitive to benomyl (ED50=2.26 ppm), thiophanate-methyl (ED50=9.61 ppm) and vinclozolin (ED50=3.89 ppm) than the other fungi.P. frequentans was less sensitive to captan, vinclozolin, iprodione, thiophanate-methyl and thiram thanM. laxa (8, 7, 5, 4 and 2 times respectively). These results suggest thatE. nigrum andP. frequentans could be successfully used in an integrated control programme that combines biological and chemical methods.     

Amidohydrolase activity,soil N status,and the invasive crucifer Lepidium latifolium

Wetlands and riparian habitats in the western United States are being invaded by the exotic crucifer Lepidium latifolium (perennial pepperweed, tall whitetop). It was hypothesized that L. latifolium was an effective competitor due to its ability to make available and take up more nitrogen than vegetation it is replacing. The hypothesis was tested by comparing amidohydrolase activities, available soil N, 30 day aerobic N-mineralization rates, and plant uptake of N in paired L. latifolium invaded and non-invaded plots occupied by Elytrigia elongata (tall wheatgrass). Attributes were measured by date (June 1998, September 1998, April 1999, and May 2000) and by soil depth (0–15, 15–30, 30–50, and 50–86 cm). Lepidium latifolium invaded sites had significantly (p 0.05) greater urease, amidase, glutaminase, and asparaginase activities than sites occupied by E. elongata for most dates and soil depths. In addition, despite far greater uptake of N per unit area, L. latifolium sites still had significantly greater available N and N-mineralization potentials than E. elongata for most dates and depths. In general, enzyme activities significantly correlated with available soil N, with a stronger relationship for sites invaded by L. latifolium. There were few significant linear correlations of enzyme activities with net N mineralization potentials for L. latifolium sites, but many for sites occupied by E. elongata. These data support the working hypothesis.     

三峡蓄水以来葛洲坝下中华鲟产卵场河床质特征变化

中华鲟是国家一级保护水生动物,是产底层产粘性卵鱼类。河床质构成了中华鲟受精卵和早期胚胎发育的物理环境,其变化可能直接影响中华鲟自然繁殖的规模和效果。基于水声学和水下视频技术对葛洲坝下现存唯一已知中华鲟自然产卵场的河床质特征进行了连续观测,对三峡水库蓄水以来中华鲟自然产卵场的河床质特征变化进行了研究。水声学分析结果显示,2004-2012年间,中华鲟产卵场区域内河床硬度未有明显变化,但粗糙度显著增加 (P < 0.05)。对产卵位点的河床质特征分析表明,下产卵区的硬度增加(2012年显著高于2008和2004年 (P < 0.05)),上产卵区硬度呈明显下降趋势(2004年显著高于2008和2012年(P < 0.05));上产卵区的河床粗糙度均呈不显著上升趋势(P > 0.05);下产卵场区的河床粗糙度呈显著上升趋势(P < 0.05)。水下视频观测结果显示,三峡蓄水导致的水体含沙量明显减少,对河床的冲刷日益明显,表现在产卵场江段沉积细砂和粗砂区域面积显著减少,河床卵石缝隙充塞度明显下降 (P < 0.05)。下产卵区在2007-2012年视频观察过程中发现河床卵石缝隙充分暴露,几乎没有任何细砂或粗砂填充,与上产卵区河床卵石缝隙充塞度特征明显不同。长期观测表明,2004-2012年期间中华鲟自然产卵位点发生了明显的改变,2004-2007年均发生在下产卵区,而2008-2012年均发生在上产卵区,自然繁殖规模和效果也明显下降。综合分析显示,中华鲟产卵场河床质特征的变化可能是导致中华鲟自然产卵位点的改变和迁移的原因,进而影响中华鲟自然产卵场的繁殖适合度,影响中华鲟自然繁殖的规模和效果。对三峡蓄水清水下泄的生态影响评估以及中华鲟自然产卵场的改良或修复有重要借鉴意义。     

Evaluation of Epicoccum nigrum for growth, morphology and production of natural colorants in liquid media and on a solid rice medium

Four nonpathogenic and nontoxigenic Epicoccum nigrum strains were evaluated for their growth, morphology and pigment producing ability in three complex and one defined liquid media. Epicoccum nigrum IBT 41028 produced pigments in all the four media tested with a maximum pigment of 3.68 AU at 410 nm in M1 medium (unoptimized) containing 5 g/l yeast autolysate. The color hue of the crude pigment extracts ranged from 74 to 102 exhibiting dark orange to green-yellow color. Pelleted morphology was shown to have a positive influence on the pigment production by E. nigrum strain IBT 41028 in the liquid media, and the use of Bis-tris buffer was found to diminish or reduce the pellet formation. Since Monascus is a well known pigment producer on rice. Pigment producing ability of E. nigrum IBT 41028 was tested on rice and compared to liquid media with Monascus ruber IBT 7904 as control. Though, both genera preferred rice but E. nigrum produced 4.6 folds higher pigment in the liquid unoptimized fermentation medium compared to M. ruber. Solid phase extraction and subsequently HPLC-DAD analysis of the crude pigment extracts showed qualitative as well as quantitative variation in the pigment composition under solid and liquid cultivations.     

Incomplete behavioural isolation and asymmetric female preference in darter sister species (Percidae: Etheostoma)

In this study, female preferences and behavioural isolation were estimated in a pair of allopatric sister species, Etheostoma duryi and Etheostoma flavum. Dichotomous mate preference trials were conducted to determine whether females prefer to associate with conspecific over heterospecific males and free‐spawning assays were conducted to determine whether those preferences translated into behavioural isolation. Dichotomous mate choice trials revealed asymmetric female preference, as female E. flavum preferred conspecific males, whereas female E. duryi showed no preference. Free‐spawning assays indicated that behavioural isolation remains incomplete between E. duryi and E. flavum (I_B = 0·19). In addition to female mating preferences, male behaviour also appeared to influence mating outcomes as male E. flavum consistently courted conspecific females more often in free‐spawning assays whereas male E. duryi did not. The data therefore suggest that despite marked divergence in male nuptial colour, divergence in female preferences between these species may not be sufficient to maintain species boundaries upon secondary contact. These results contrast with similar work in a sympatric darter species pair and may be explained by considering the contributions of reinforcement and differences in colour pattern as well as colour value.     

Influence of Limnological Conditions on Clostridium Botulinum Type E Presence in Eastern Lake Erie Sediments (Great Lakes, USA)

Avian and fish botulism outbreaks have been recorded since 1999 in eastern Lake Erie. These outbreaks are caused by Clostridium botulinum type E, a toxin-producing bacteria that is found in anoxic substrates rich in organic material. We studied the environmental conditions present in eastern Lake Erie during 2002, a year when several botulism outbreaks were observed. We also tested for the presence of C. botulinum type E in lake sediments. Samples were taken at six stations from two sites of different depths in the Dunkirk (New York, USA) area. The depth of the sampling sites influenced physico-chemical and biological processes in the sediments. We used the quantitative polymerase chain reaction (Q-PCR) to quantify the levels of C. botulinum type E in the samples. Sediment samples contained a patchy distribution of type E spore concentrations (from not detectable to 5520 DNA copies/mg). Samples of benthic invertebrates tested positive for C. botulinum type E spores in tissues (Gammarus 2028 DNA copies/mg, oligochaetes 428 DNA copies/mg, chironomids 148 DNA copies/mg and dreissenid mussels 715 DNA copies/mg). Principal components analysis (PCA) from inshore stations indicated that a decrease in dissolved oxygen, pH and redox potential near the sediment was associated to an increase in specific conductance and the type E toxin gene in sediments. We also found that C. botulinum type E spores are present in sediments at different depths and at different times through the ice-free season.     

Cadmium accumulation in relation to organic acids in leaves of Solanum nigrum L. as a newly found cadmium hyperaccumulator

The influence of various cadmium concentrations on organic acid levels in leaves of the Cd hyperaccumulator, Solanum nigrum L. and a closely related species, Solanum melongena L., were investigated. In particular, the relationship of organic acids with Cd accumulation in the two plants was investigated. The results showed that Cd accumulation in the shoots of S. nigrum was significantly higher than that of S. melongena. The accumulation of Cd in the leaves of S. nigrum ranged from 2.0 to 167.8 μg g⁻¹ dry weight (DW), but only from 1.2 to 64.0 μg g⁻¹ DW in S. melongena. Solanum melongena was considerably less tolerant to Cd than S. nigrum. Approximately 20% of the total Cd in S. nigrum leaves was water-soluble, suggesting that some accumulated Cd was associated with water-soluble compounds such as organic acids. Malic acid in the leaves of S. nigrum was the most abundant organic acid [up to 115.6–145.7 μmol g⁻¹ fresh weight (FW)], but this acid was not significantly affected by the Cd concentration in soil. However, the level of malic acid in S. melongena plants was much lower, only 16.3–75.4 μmol g⁻¹ FW. The significant positive correlations between total Cd and water-soluble Cd concentrations and both acetic and citric acid concentrations in the leaves of S. nigrum were observed. In contrast, there was no correlation between concentrations of the two acids and Cd concentrations in the leaves of S. melongena. These results indicated that acetic and citric acids in the leaves of S. nigrum might be related to its Cd hyperaccumulation.     

Vesicular-arbuscular mycorrhizal fungi in coastal dune plant communities II. Spore formation ofGlomus spp. predominates under geographically separated patches ofElymus mollis

Five study sites in Japan with pure patches ofElymus mollis near to the shoreline were chosen. Abundance of spore formation ofGlomus spp. underE. mollis patches were studied at four sites to understand the factors determining the development of VA mycorrhizal fungal communities at the edge of coastal sand dune vegetation. At each study site, eight soil samples from two soil depths were collected four times (three times for Niigata) during a year. Spores ofGlomus spp. predominated at every site, but species composition ofGlomus spp. differed from site to site. In a further experiment to measure the soil depth of the highest spore densities underE. mollis, the highest density was found at depths where rhizomes ofE. mollis were present.Contribution No. 119, Laboratories of Plant Pathology and Mycology, Institute of Agriculture and Forestry, University of Tsukuba.     

The benthic invertebrates of the Salton Sea: distribution and seasonal dynamics

The Salton Sea, California's largest inland water body, is an athalassic saline lake with an invertebrate fauna dominated by marine species. The distribution and seasonal dynamics of the benthic macroinvertebrate populations of the Salton Sea were investigated during 1999 in the first survey of the benthos since 1956. Invertebrates were sampled from sediments at depths of 2–12 m, shallow water rocky substrates, and littoral barnacle shell substrates. The macroinvertebrates of the Salton Sea consist of a few invasive, euryhaline species, several of which thrive on different substrates. The principal infaunal organisms are the polychaetes Neanthes succinea Frey & Leuckart and Streblospio benedicti Webster, and the oligochaetes Thalassodrilides gurwitschi Cook, T. belli Hrabe, and an enchytraeid. All but Neanthes are new records for the Sea. Benthic crustacean species are the amphipods Gammarus mucronatus Say, Corophium louisianum Shoemaker, and the barnacle Balanus amphitrite Darwin. Neanthes succinea is the dominant infaunal species on the Sea bottom at depths of 2–12 m. Area-weighted estimates of N. succinea standing stock in September and November 1999 were two orders of magnitude lower than biomass estimated in the same months in 1956. During 1999, population density varied spatially and temporally. Abundance declined greatly in offshore sediments at depths >2 m during spring and summer due to decreasing oxygen levels at the sediment surface, eventually resulting in the absence of Neanthes from all offshore sites >2 m between July and November. In contrast, on shoreline rocky substrate, Neanthes persisted year round, and biomass density increased nearly one order of magnitude between January and November. The rocky shoreline had the highest numbers of invertebrates per unit area, exceeding those reported by other published sources for Neanthes, Gammarus mucronatus, Corophium louisianum, and Balanus amphitrite in marine coastal habitats. The rocky shoreline habitat is highly productive, and is an important refuge during periods of seasonal anoxia for Neanthes and for the other invertebrates that also serve as prey for fish and birds.     

Early development of johnny darter,Etheostoma nigrum,and fantail darter,E. flabellare,with a discussion of its ecological and evolutionary aspects

Synopsis Fantail darters,Etheostoma flabellare, have larger eggs with greater yolk volume than johnny darters,E. nigrum, and have a longer embryo period. This longer embryo period is associated with accelerated finfold differentiation, producing a larger, better formed individual at the onset of exogenous feeding. Developmental differences among these two species and the rainbow darter,Etheostoma caeruleum, primarily in timing of ontogenetic events, are described in detail. These differences in timing are considered largely early developmental phenomena as they affect embryos, larvae, and aievins but apparently not juveniles or adults. Demographic aspects of early life history were assessed using data from studies of Ontario streams. Differences in early survival among species appear to play an important role in recruitment of mature females, but cannot be attributed to parental care or egg size differences.     

Host suitability of two biotypes of Bemisia tabaci on some common weeds

Significant differences in some reproductive parameters of the B and Q biotypes of Bemisia tabaci (Gennadius) with regard to four species of winter weeds were determined in a no-choice assay. The highest fecundity (eggs) and fertility (pupae and adults) were obtained with Malva parviflora L. as host, followed by Capsella bursa-pastoris L., Brassica kaber (DC) and Lactuca serriola L. The percentage of adult emergence (from egg to adult) was significantly higher (P < 0.001) with M. parviflora, C. bursa-pastoris and B. kaber than with L. serriola. Except on L. serriola, the mean values of the reproductive parameters for the Q-biotype were significantly (P < 0.05) greater than those for the B-biotype. On the other hand, in choice experiments with summer weeds, both B- and Q-biotypes preferred Datura stramonium L. and Solanum nigrum L. to Amaranthus retroflexus L., Chenopodium album L. and Echinochloa crus-galli L. Significantly more males and females, and more pupae and empty pupal cases per plant were found on D. stramonium than on S. nigrum. Adult abundance on A. retroflexus, C. album and E. crus-galli plants was very low. At a constant temperature of 26 ± 1°C, the Q-biotype developed significantly faster than the B-biotype on S. nigrum and D. stramonium. Both biotypes required, for this development, significantly more days on D. stramonium than on S. nigrum. These results suggest that it is important to suppress the growth of M. parviflora, C. bursa-pastoris, B. kaber, D. stramonium and S. nigrum in order to avoid the risk of further expansion of whitefly populations where these weeds and both B- an Q-biotypes are present.     

Somatic hybridization of an atrazine resistant biotype of Solanum nigrum with Solanum tuberosum

Summary Representative regenerated clonal plants from protoplast fusion of Solanum tuberosum L. and an atrazine resistant biotype of S. nigrum L. were studied to ascertain which plastomes each clone contained. DNA was isolated from fractionated chloroplasts, restricted with DNAases XHO-1, BGL-1, PVU-2 and BAM-H1, and the fragments separated by agarose gel electrophoresis for comparison. No difference could be found between resistant and susceptible biotypes of S. nigrum with all four enzymes. XHO-1, BGL-1, BAM-H1 differentiated between S. nigrum and S. tuberosum. All atrazine resistant regenerants, despite plant morphology, had the plastid DNA pattern of S. nigrum while all sensitive ones resembled S. tuberosum, even the subclone 38S having a S. nigrum morphology and chromosome number.     

Migratory behaviour of adult pikeperch (Stizostedion lucioperca) in a lowland river

The behaviour of radio-tagged adult pikeperch (Stizostedion lucioperca (L.)) from two areas in the Danish River Gudenaa were recorded prior to, and during the spawning period. Eight of 13 tagged fish in the lower reaches of the river were located throughout the whole study. Five of these fish moved upstream to various sites in the river prior to spawning, which occurred from late April to June. The three remaining fish moved to the fjord. These movements were interpreted as a spawning migration, and it is suggested that the lower reaches of the River Gudenaa constitute an over-wintering area for pikeperch, which use different spawning areas. Ten pikeperch caught just downstream of an impassable hydropower plant were radio-tagged and translocated upstream of the dam to a reservoir. Within a week, half of the fish moved to a lake situated more than 30 km upstream the reservoir. This behaviour is hypothesised to be a homing response. The study reveals that the pikeperch is a highly mobile species with a complicated migration pattern, even in relatively small river systems.     

RAPD fingerprinting of blackcurrant (Ribes nigrum L.) cultivars

Ribes nigrum germplasm was screened for random amplified polymorphic DNA (RAPD) markers. Fiftyfour markers were identified which generated individual fingerprints for each of 21 cultivars. Genetic variation within R. nigrum germplasm, as detected by RAPDs, demonstrated that the genetic basis for improvement of blackcurrant is narrower than would be expected by the analysis of parentage.     

Predation of Northern Pike (Esox lucius L.) Eggs: A Possible Cause of Regionally Poor Recruitment in the Baltic Sea

Northern pike (Esox lucius) spawning habitat and egg mortality were studied in three spawning areas in 2001 along the Swedish coast of the Baltic proper: the Blekinge Archipelago, Kalmar Sound and coastal freshwater streams. Spawning peaked during the last week of April in streams, at temperatures ranging from 7.7 to 8.9 °C and during the first week of May in brackish waters, at temperatures ranging from 8.9 to 13.8 °C. Spawning occurred in shallow waters, at depths between 0.2–1.5 m, but generally most of the spawn was found in the shallowest areas. In streams, eggs were mainly attached to emersed vegetation, while in brackish sites pike eggs were well scattered among flooded emersed plants, submersed plants and filamentous algae. Mean egg density varied between 469–1829 m^–2 with the lowest density observed in Kalmar Sound. The calculated egg loss occurring from approximately one day after spawning to one day before hatching ranged from 41±7% in coastal streams to 67±6% in the Blekinge Archipelago and 100% in Kalmar Sound. The significant removal of eggs from spawning sites in Kalmar Sound and Blekinge was most likely due to predation from several fish species. In situ observations and stomach analyses suggested that many pike eggs in Kalmar Sound were lost to the three-spined stickleback (Gasterosteus aculeatus), a species that presently dominate the littoral small fish community. This study therefore suggests that egg predation by sticklebacks and other fishes may be a possible cause of the reported poor recruitment of coastal pike populations in the Kalmar Sound region.