Ultrastructure of post-fertilization development in the red alga Scinaia articulata (Galaxauraceae,Nemaliales, Rhodophyta)

The ultrastructure of the carposporophyte and carposporogenesis is described for the red alga Scinaia articulata Setch. After fertilization, the trichogyne disappears, and the pericarp develops to form a thick protective tissue that surrounds the carposporophyte. The hypogynous cell cuts off both one-celled and two-celled sterile branches. Patches of chromatin are frequently observed in evaginations of the nuclear envelope, which appear to produce vesicles in the cytoplasm of the cell of the sterile branch. Large gonimoblast lobes extend from the carpogonium and cleave to form gonimoblast initials. Subsequently, a fusion cell is formed from fusions of the carpogonium, the hypogynous cell and the basal cell of the carpogonial branch. The mature carposporophyte comprises the fusion cell that is connected to the sterile branch cells, gonimoblast cells and carpospores and is surrounded by extensive mucilage. Young carpospores possess a large nucleus and proplastids with a peripheral thylakoid, but they have few dictyosomes and starch granules and are indistinguishable from gonimoblast cells. Subsequently, dictyosomes are formed, which produce vesicles with an electron-dense granule, which indicates an initiation of wall deposition. Thylakoid formation coincides with incipient starch granule deposition. The nuclear envelope produces fibrous vacuoles and concentric membrane bodies. Carpospores are interconnected by pit connections with two cap layers. Dictyosome activity increases, resulting in the production of vesicles, which either continue to deposit wall material or coalesce to form fibrous vacuoles. The final stage of carposporogenesis is characterized by the massive production of cored vesicles from curved dictyosomes. Mature carpospores are uninucleate and contain fully developed chloroplasts, numerous cored vesicles, numerous starch granules and fibrous vacuoles. The mature carpospore is surrounded by a wall layer and a separating layer, but a carposporangial wall is lacking.     

Changes in epibiotic burden during the intermolt of Daphnia determined by hypodermal retraction stages

We calibrated four stages of hypodermal retraction and cuticle regeneration with five stages of parthenogenetic egg development in Daphnia. Using the hypodermal retraction stages, we found that epibiotic burden increased with elapsed intermolt time for juvenile, male, and female Daphnia bearing parthenogenetic or ephippial eggs. The rate of increase of burden was similar for adult females of two Daphnia species and for males and females of D. pulex. Rate of increase of burden was similar between juvenile and adult females of D. galeata mendotae and D. pulex.     

Intralineage variation in the pattern ofrbcL nucleotide substitution

Variation in chloroplastrbcL sequences was studied in representative species of four different lineages: the tribeRubieae (Rubiaceae), and the generaDrosera (Droseraceae),Nothofagus (Nothofagaceae) andIlex (Aquifoliaceae). Each lineage has its particular non-overlapping set ofrbcL polymorphic sites, indicating that common unconstrainedrbcL sites are not shared. Large differences in the rate and pattern of nucleotide substitution are observed among the four lineages. The genusIlex has the lowest rate of substitution, the lowest transition/transversion ratio, the lowest synonymous/replacement ratio and the lowest number of substitutions at the third codon position. An apparent relationship of these measures to the age of the lineages is observed. The A + T content and codon use among the four lineages are very similar and, apparently, cannot account for the observed differences in patterns of nucleotide substitution. However, the A + T content of the two bases immediately flanking the polymorphic sites is higher inIlex than in the other lineages. This could be correlated with the transversion/transition bias observed inIlex. The particularly low synonymous/replacement ratio found inIlex could also be explained by the small population sizes of species in this genus.     

Consequences of mixed species infestation on the searching behavior and parasitism success of a larval parasitoid

When two herbivore pest species are potential hosts of a single parasitoid species, two questions arise. Firstly, which host is preferable for mass rearing in terms of later parasitoid performance, and secondly, how do parasitoids perform in mixed herbivore situations after colony establishment? We tested Hyssopus pallidus, a gregarious parasitoid of two major pests of apple, Cydia (Grapholita) molesta and Cydia pomonella, before and after landing on apples infested by one of the two Cydia species. Pre-alighting host preference was tested in a Y-tube olfactometer setup, and parasitism success in a contact bioassay. To gain information on parasitoid performance throughout the growing season, different fruit growth stages were used. Irrespective of the host they had developed on, the parasitoids showed similar olfactory preferences when given a dual choice between infested and healthy fruits, and they did not discriminate between fruits infested by C. molesta and C. pomonella. Responsiveness was generally high, especially late in the season close to harvest. Both hosts are parasitized regardless of the host the parasitoid female had developed on, and no differences in parasitism rates or number of offspring were noted for the two hosts offered. Results were consistent for all apple growth stages tested. In conclusion, mass rearing of this parasitoid can be carried out on either host, without limiting the future efficacy of the bio-control agent. Similarly, established colonies are expected to develop further on both hosts without any bias in host preference.     

Effects of intercropping white cabbage with clovers on pest infestation and yield

During two consecutive years the effects of intercropping fresh market white cabbage with two species of clover on pest populations and yield were studied. White cabbage cv. Minicole was intercropped withTrifolium repens (white clover) andTrifolium subterraneum (subterranean clover) as compared to the monocrop. During the season observations were made on pest population developments, especially ofMamestra brassicae L. (cabbage moth),Brevicoryne brassicae L. (cabbage aphid),Delia brassicae L. (cabbage root fly), and evaluation of caterpillar feeding injury. At harvest the yield in quantity and quality was determined to be able to assess the gross financial result. Intercropping effects in terms of suppression of oviposition and larval populations of various pests were found. Although no pesticides were used and competition reduced the weight, the quality of the intercropped cabbages lead to a better financial result compared to the monocropped cabbage crop. The results are discussed in the perspective of the practical implications in the context of IPM.     

Seasonality and toxigenicity ofVibrio cholerae non-01 isolated from different components of pond ecosystems of Dhaka City,Bangladesh

Diarrhoea due toVibrio cholerae non-01 is common in Bangladesh. Four hundred and eighty samples, including plants, water, phytoplankton and sediment, were collected from five ponds in Dhaka every 15 days for one year.V. cholerae non-01 was isolated from 181 (38%) of the samples. Two peaks were evident: one in April and the other in August/September. Forty-three (23%) of the 181 isolates were examined for toxigenicity and 19% were cytotoxic to Y1 adrenal cells. This study provides evidence of the likely infectious nature of some ponds and may have relevance to the epidemiology of diarrhoea caused byV. cholerae non-01 in Bangladesh.     

Trophic interactions involving mysid shrimps (Mysidacea) in the near-bottom habitat in the Baltic Sea

In a six month mesocosm tank experiment, hypotheses were tested concerning the role of benthopelagic mysid shrimps (Mysidacea) in the near-bottom food web of the Bothnian Sea, in the northern Baltic Sea. The first hypothesis tested was that the mysids interact, through predation, with benthic deposit-feeding Monoporeia affinis amphipods. A second hypothesis tested was that the sediment type is important for the overwintering success of the mysids. Changes in abundance and mass were recorded for M. affinis and mysids when separate and when coexisting, in two sediment types differing in organic content (food level); soft muddy clay (rich) and fine sand (poor). Despite the fact that newborn M. affinis offspring, a plausible target for predation by mysids, were present in substantial numbers in the tanks, no consistent evidence for any interaction between these taxa was found. The biomass of mysids was slightly higher in the muddy clay than in the sand tanks, and the mechanism behind this substrate effect is discussed. A third hypothesis, that the mysids interact with near-bottom zooplankton, was investigated. The tanks were continually supplied with in situ near-bottom sea-water containing a semi-natural assemblage of near-bottom plankton. As a result of mysid predation, tanks with mysids had lower abundance and biomass of cyclopoid copepods than tanks without mysids. Thus, the major interaction found was predation on near-bottom zooplankton by mysids and it is suggested that this interaction could potentially be an important food link, especially during periods with low food availability in the pelagic system.     

Evolutionary pattern of the gtwin retrotransposon in the Drosophila melanogaster subgroup

The gtwin retrotransposon was recently discovered in the Drosophila melanogaster genome and it is evolutionarily closer to gypsy endogenous retrovirus. This study has identified gtwin homologous sequences in the genome of D. simulans, D. sechellia, D. erecta and D. yakuba by performing homology searches against the public genome database of Drosophila species. The phylogenetic analyses of the gtwin env gene sequences of these species have shown some incongruities with the host species phylogeny, suggesting some horizontal transfer events for this retroelement. Moreover, we reported the existence of DNA sequences putatively encoding full-length Env proteins in the genomes of Drosophila species other than D. melanogaster. The results suggest that the gtwin element may be an infectious retrovirus able to invade the genome of new species, supporting the gtwin evolutionary picture shown in this work.     

Differential growth of the barnacle Notobalanus flosculus (Archaeobalanidae) onto artificial and live substrates in the Beagle Channel, Argentina

In the Beagle Channel, southern South America (ca. 55°S 67°W), about 20% of false king crabs (Paralomis granulosa) >80 mm carapace length are fouled with the barnacle Notobalanus flosculus. To evaluate differences in growth rates of barnacles attached to artificial and live substrates, clay tiles were anchored as collectors to the bottom at two different sites in the Beagle Channel in September 1996: in Ushuaia harbour (low currents and high levels of suspended matter) and around the Bridges Islands (strong currents and low level of suspended matter). Another set of collectors was deployed at the same sites in October 1998 to collect barnacles for histological studies. Tiles were removed from each place, approximately, on a monthly basis. Carapaces of P. granulosa with the epizoic N. flosculus were sampled between November 1996 and 1997, and between March 1998 and September 1999, to study sexual maturation of barnacles. Growth of barnacles was compared between the collectors and P. granulosa carapaces following a qualitative approach. A sexual maturity scale was defined, based on the stage of development of the female reproductive apparatus of N. flosculus. Growth rate of barnacles was highest in the harbour, intermediate on P. granulosa, and lowest around the Bridges Islands. Presence of oocytes was registered only in epizoic barnacles, suggesting that at least a proportion of these individuals is able to spawn on the carapaces. The potential advantages of settling on a living substrate, namely increased availability of food particles and decreased predation risks are discussed.     

The infestation and dispersion patterns of Carcinonemertes spp. (Nemertea) on their crab hosts

Seasonal changes in the infestation and dispersion patterns of egg predatory nemerteans on their crab hosts were analyzed. Marked differences in the seasonal patterns of infestation were noted between worm species, yet, common patterns in the aggregation of the worms were found. Worm aggregation increased at the onset of the reproductive seasons of the hosts, and at the nadirs of the reproductive seasons for those hosts with year round breeding. The aggregation patterns of two worm species fluctuated with the physical environment of their estuarine hosts. Salinity changes as a result of seasonal rains may have caused changes in the underlying dispersion patterns of Carcinonemertes epialti on Hemiarapsus oregonensis, and C. mitsukurii on Portunus pelagicus. Lastly, the embryogenic cycle of the host species was significant in shaping the infestation and aggregation patterns of C. epialti on Cancer anthonyi and C. regicides on Paralithodes camtschaticus. Worm immigration and emigration were linked to crab embryogenesis and directly influenced the dispersion patterns of the worms.     

Seasonality Pattern of Biomass Accumulation in a Drifting Furcellaria Lumbricalis Community in the Waters of the West Estonian Archipelago, Baltic Sea

A free-floating, loose form of Furcellaria lumbricalis (Huds.) Lamour is rare in the Baltic Sea area. Kassari Bay, situated in the West Estonian Archipelago Sea area contains the largest known community of this kind. Here the free-floating mixed Furcellaria lumbricalis-Coccotylus truncatus (Paela) M. J. Wynne et J. N. Heine community inhabits sandy bottom, covering up to 120 km². Commercial exploitation of the community started in 1966 and has led to regular monitoring surveys for the quantification of the commercial resource. The aim of the present study was to determine the potential growth rates of the two community-forming species as well as to test different environmental factors affecting their growth. Results showed that the highest growth rates were measured in shallower depths (4 m) for both species. The seasonal growth pattern was also very similar for both species, showing the highest growth rates during the beginning of summer. Incubation of both species in another sea area with apparently similar basic environmental conditions (the northern part of the Gulf of Riga, Kõiguste Bay) resulted in significantly lower growth rates during the whole incubation period.     

Seasonality of macrophytes and interaction with flow in a New Zealand lowland stream

Introduced submerged macrophytes have come to dominate many shallow water bodies in New Zealand, and are a common component of many lowland streams. We investigated the seasonal variation of macrophyte abundance, its influence on flow and channel volume, and the implications of this on stream habitat and functioning in Whakapipi Stream, a typical lowland stream draining a predominantly agricultural catchment.Abundance of macrophytes over the summer was primarily controlled by the phenological cycles of the two dominant species. Mean minimum total macrophyte biomass (36 g m^–2) and cover (7%) occurred in winter (June and August, respectively), and mean maximum biomass (324 g m^–2), and cover (79%) occurred in late summer (March and February respectively). Egeria densa comprised the majority of both cover and biomass during the study period, except early summer (December) when Potamogeton crispus was prevalent in the shallow stream reaches.Macrophyte beds had a major impact on summer stream velocities, reducing average velocities by an estimated 41%. Stream cross-sectional area was maintained at relatively stable levels similar to that recorded over winter, when stream discharge was in the order of seven times greater. The mean velocity distribution coefficient (), and Manning's roughness coefficient (n) were dependent on and displayed a positive linear relationship with macrophyte abundance. The velocity distribution coefficient is recommended as a better indicator of macrophyte effects on velocity in natural streams, as it does not assume uniform velocity, channel depth and slope within the stream reach.Our study shows that submerged macrophytes play an important structuring role within the stream during the summer period, where macrophyte beds act as semi-permeable dams, retarding flow velocities and increasing stream depth and cross-sectional area. This promotes habitat heterogeneity by creating a greater range of flow velocity variation, and also provides large stable low-flow areas. Other likely ecosystem effects resulting from macrophyte/velocity interactions include increased sedimentation, potential for nutrient processing and increased primary production, both by macrophytes and attached epiphyton. The complex architecture of submerged macrophytes and their influence on stream flow may also provide an increased diversity of habitat for other aquatic biota. We propose that management of degraded lowland streams such as the Whakapipi Stream to maintain stretches with moderate quantities of submerged macrophytes interspersed with shaded areas would optimise stream health during low summer flows.     

Chronic effects of cadmium on two species of mysid shrimp:Mysidopsis bahia andMysidopsis bigelowi

Two species of mysid shrimp, the sub-tropicalMysidopsis bahia and the northern temperateMysidopsis bigelowi, were exposed simultaneously to cadmium (as CdCl₂) in a continuous-flow bioassay system to determine the effect on survival and reproductive success. Temperature and salinity were maintained at 21 ± 1°C and 30,respectively. The 96-h LC50 was 110 µg ^–1 for both species. The 23-day life cycle LC50 forM. bahia was 19.5 µg ^–1 and forM. bigelowi the 27-day LC-50 was 14.8 µg ^–1. At 10 µg ^–1 a series of morphological aberrations were observed in both species at the onset of sexual maturity. Carapace malformations apparently prevented molting after the release of the initial brood and resulted in death of brooding females. As a result, although the initial reproductive rate at this concentration was successful, successive broods could not be produced. For both species in this study the no observed effect concentration was 5.1 µg ^–1; the effect concentration was 10.0 µg ^–1. Mechanisms were postulated in this study to explain the effect of cadmium on the molting process and on calcification and enzymatic reactions of osmosis.Contribution No. 257 of the U.S. Environmental Protection Agency.Contribution No. 257 of the U.S. Environmental Protection Agency.     

Aplysia punctata added to list of laboratory-cultured Aplysia

The marine opisthobranch molluscAplysia punctata was cultured at the Laboratoire de Biologie Marine in Concarneau, France.A. punctata veligers settled and underwent metamorphosis on the algaLomentaria articulata, but not onUlva spp., Palmaria marina, Laminaria spp. andFucus spp.Research supported by grants from The Arts Foundation and the Lerner Fund for Marine Research of the American Museum of Natural History. We wish to thank Director Yves Legal, College de France for his support and cooperation.     

Birth Seasonality in Alouatta caraya in Northern Argentina

Given appropriate ecological and social conditions, natural selection should favor individuals that can concentrate their reproductive events to a particular time of the year that offers high opportunities for infant survivorship. Previous studies on births in Alouatta caraya in Northern Argentina revealed the existence of a peak during the dry season—a period with scarcity of food resources—in mainland gallery forest (G. E. Zunino, Extra 133: 1–10, 1996). The time of conception and the period of independence of the offspring are positively correlated with precipitation, temperature and availability of food. Offspring became independent from their mothers when the availability of resources was high, and conception coincided with the peak of fruit production. Our goal was to examine patterns of birth seasonality in Alouatta caraya in flooded forest on an island in Northern Argentina for comparison with the mainland population. Both sites are at similar latitudes, but differ in forest type. The results indicate that the availability of new and mature leaves is more consistent throughout the year in the flooded forest (p<0.05); however, there was no difference in the availability of fleshy fruits between sites (p>0.05). The pattern of births differed between the gallery forest and the flooded forest (2-way Anova, p<0.001). In the flooded forest births occurred throughout the year, which supports the contentions that howlers do not have a fixed birth season and that the observed variation in the timing of births appears to represent a facultative behavioral response to changes in food availability.     

The effect ofAcremonium coenophialum on the growth and nematode infestation of tall fescue

The presence of the endophytic fungusAcremonium coenophialum Morgan-Jones et Gams in tall fescue (Festuca arundinacea Schreb.) induces toxicity when this grass is grazed by cattle; however, there is evidence that removing the endophyte reduces the stand vigor and longevity of fescue. A field trial was conducted to determine the effects of water supply and the presence of the endophytic fungus on plant growth, drought tolerance, and soil nematode populations in Kentucky 31 tall fescue. The design included two factors, level of endophyte infection (0 and 75%) and irrigation regime (none, low, and high). Where water deficits occurred, herbage yield and leaf area were lower, and percentage dead tissue and canopy minus air temperature were greater in endophyte-free compared with endophyte-infected fescue. Soil populations ofPratylenchus scribneri andTylenchorhynchus acutus were substantially higher in the noninfected than in the endophyte-infected plots. The endophyte apparently confers drought tolerance to Kentucky 31 tall fescue, and this effect may be at least partially mediated through enhanced resistance to soil-borne nematodes.Published with the approval of the Director of the Ark. Agric. Exp. Stn.     

Seasonality and controls of phytoplankton productivity in the middle Cape Fear River, USA

Our 1 year study was aimed at assessing seasonal patterns and controls on phytoplankton primary production (PPR) and biomass (chlorophyll a) in a fourth order section of the middle Cape Fear River in North Carolina, USA, and to determine the impact of three low-head lock and dam (LD) structures on these variables within the 70 km study reach of this coastal river. Mean concentrations of NO₃ ⁻–N, NH₄ ⁺–N and soluble reactive phosphorus (SRP) averaged 52.9, 6.0, and 3.6 μmol l⁻¹ in monthly sampling, while the average light attenuation coefficient was 2.4 m⁻¹. The average euphotic depth was 2.1 m. Nutrient concentrations and attenuation coefficients were not significantly different above versus below each LD, or along the entire study reach. Significantly higher concentrations of dissolved O₂ below versus above each LD were attributed to re-aeration during spillway transit. No seasonal pattern in physicochemical properties was apparent. Phytoplankton chlorophyll a concentrations ranged from <1 to 36 μg l⁻¹, while rates of primary production ranged from 18 to 2,580 mg C m⁻² day⁻¹, with values for both variables peaking in the spring and early summer. Chlorophyll a and primary productivity values were consistently higher above versus below each LD in May and June suggesting a seasonal effect, but values were otherwise similar such that overall means were not significantly different. Several factors point to light as the primary control on phytoplankton in the middle Cape Fear River: high nutrient concentrations; a low ratio of euphotic : mixing depth (0.46); progressive increases in chlorophyll a and radiocarbon uptake in all treatments in quarterly nutrient enrichment bioassays conducted at levels of irradiance elevated relative to in situ river values; and consistently low quarterly values of (maximum rate of chlorophyll-normalized C uptake; ≤3.7 mg C mg chl a⁻¹ h⁻¹) and I _k (light saturation parameter; ≤104 μmol photons m⁻² s⁻¹) for photosynthetic light–response (P–I) curves. Handling editor: L. Naselli-Flores     

Cytochrome d expression and regulation pattern in free-living Rhizobium phaseoli

The respiratory system of Rhizobium phaseoli CFN42 in free-living cultures was studied. Cytochromes b, c, o and aa ₃ were found in fast growing cells cultured under forced aeration. Stationary aerobic cells, and semianaerobically grown cells showed decreased levels of cytochromes c, aa ₃ and o, concomitant with a significant increase of b type cytochromes and the synthesis of a new cytochrome, tentatively identified as cytochrome d. Cell membranes with the highest content of cytochrome d (semianaerobically grown cells) showed the highest respiratory activities with NADH, succinate, malate or ascorbate-TMPD (N,N,N,N-tetramethyl p-phenylendiamine). In the presence of either of the above electron donors, cytochrome d was clearly reduced. NADH dependent respiration in membranes of fast growing cells (no cytochrome d detected) was abolished by 25 M KCN. This inhibitor concentration caused only 15–20% inhibition in membranes of semianaerobically grown cells (cyt d present). Moreover, in the presence of 1–5 mM KCN, the oxidation of cyt d and a b type cytochromes was spectrally detected. It is suggested that cyt d is a functional cytochrome in the respiratory system of free-living Rhizobia, probably acting as terminal oxidase.