Applications of microarthropod life-history tactics in nature management and ecotoxicology

Examples of the practical use of microarthropod life-history tactics in nature management and ecotoxicology were selected. A key to the tactics was developed to facilitate the use of the life-history tactics. Examples of the microarthropod distribution over these tacties were selected from a forest, a grassland, and a salt marsh. The process of decomposition of grass leaves in litterbags was described using life-history tactic diagrams. The effects of various disturbances were described in terms of shifts in the distribution of life-history tactics of species. Irregular unpredictable disturbances lead to an increased representation of phoresy tactics. Regular disturbances lead to an increased representation of synchronization tactics. Permanent and persistent pollution, finally, leads to an increased representation of tactics with thelytokous reproduction. The consequences of the latter for ecotoxicology were examined. It was concluded that microarthropod life-history tactics meet the criteria described, permitting comparisons between effects of management measures and pollution in different biotopes and countries.     

Life-history tactics of soil microarthropods

A sound basis for defining life-history tactics was obtained by reviewing life-history traits. This involved an explanation of the ecological implications of thelytoky (automictic or apomictic), arrhenotoky, amphitoky, sexual reproduction, semelparity, iteroparity, seasonal iteroparity, and the relationship between semelparity and juvenile development. Several forms of synchronization of life cycles with environmental conditions were classified, ranging from the ability to overcome harsh seasonal conditions to obligate diapause dormancy. Ecologically, this involves adaptations to environmental conditions ranging from irregularly occurring and unpredictable events to regularly occurring and predictable conditions. Dispersal traits were grouped as directional migration (phoresy) and undirectional migration (anemochory). Distinctions were made between facultative and obligate phoresy and between carrier-specific and carrier-unspecific phoresy. A multi-dimensional system of tactics was outlined, based on well-defined underived traits. This system was compared with one- and two-dimensional schemes described by MacArthur and Wilson (1967), Grime (1977), and Southwood (1977) and with the multi-dimensional system described by Stearns (1976). For each tactic, relationships with the main biotopes in which it occurs were defined. Examples of species showing certain tactics were selected from the taxonomic orders of microarthropods. The generality of the traits for various groups of organisms and of the classification of life-history tactics developed was explored.     

Trace metals in roof runoff

In this paper we present the concentration of heavy metals (Cd, Cu, Pb, Zn) in runoff from five different roofs (tar felt, pantiles, asbestos cement, Zn sheet, gravel) during two rainfall events. The heavy metal load of roof runoff is assessed and the different processes influencing the fate of heavy metals on roof surfaces and in roof runoff are discussed. The extent of contamination with heavy metals of runoff from different roofing material has the following sequence: zinc sheet>tar felt>pantiles>asbestos cement>gravel. The hazard of infiltration of roof runoff with respect to heavy metals is discussed by comparison with concentrations in rain.     

Rapid increase in clusters of presynaptic proteins at onset of long-lasting potentiation

A change in the efficiency of synaptic communication between neurons is thought to underlie learning. Consistent with recent studies of such changes, we find that long-lasting potentiation of synaptic transmission between cultured hippocampal neurons is accompanied by an increase in the number of clusters of postsynaptic glutamate receptors containing the subunit GluR1. In addition, potentiation is accompanied by a rapid and long-lasting increase in the number of clusters of the presynaptic protein synaptophysin and the number of sites at which synaptophysin and GluR1 are colocalized. These results suggest that potentiation involves rapid coordinate changes in the distribution of proteins in the presynaptic neuron as well as the postsynaptic neuron.     

Assessment of protective efficacy of live and killed vaccines based on a non-encapsulated mutant of Streptococcus suis serotype 2.

The protective efficacy of a live and killed non-encapsulated isogenic mutant of Streptococcus suis serotype 2 was determined in pigs, and compared with the efficacy of the capsulated wild-type strain. SPF pigs were vaccinated twice intramuscularly at 4 and 7 weeks of age with a dose of 1 x 10(9) formalin-killed CFU of the wild-type (WT-BAC), formalin-killed non-encapsulated mutant (CM-BAC) or live non-encapsulated mutant (CM-LIVE) strain. After 2 weeks, vaccinated pigs and non-vaccinated controls were challenged intravenously with 1 x 10(7) CFU of the homologous, wild-type S. suis serotype 2 strain. Protection was evaluated by clinical, bacteriological, serological and post-mortem examinations. All pigs vaccinated with WT-BAC were completely protected against challenge with the homologous serotype. Pigs vaccinated with CM-BAC were partially protected. Although all pigs vaccinated with CM-BAC survived the challenge, four out of five pigs developed clinical signs of disease for several days. Compared to the WT-BAC and CM-BAC, the CM-LIVE vaccine was less protective. Two out of five pigs vaccinated with CM-LIVE died in the course of the experiment and all of them developed specific clinical signs of disease for several days. The protective efficacy of the vaccines could be associated with serum antibody titers. Antibody titers against cells of wild-type and non-encapsulated mutant strains as well as against muramidase-released proteins (MRP) were high in pigs vaccinated with WT-BAC and CM-BAC. Pigs vaccinated with CM-LIVE showed lower antibody titers. Antibody titers against purified capsular polysaccharides (CPS) of S. suis serotype 2 were only found in pigs vaccinated with WT-BAC. These findings indicate that CPS and other bacterial components of WT-BAC are probably essential for full protection against homologous challenge.     

Cover crop identity determines root fungal community and arbuscular mycorrhiza colonization in following main crops

Cover crops (CC) can promote nutrient retention and recycling for main crops yet may also promote soilborne pathogens or suppress beneficial root symbionts such as arbuscular mycorrhizal fungi (AMF). We investigated how root fungal communities of main crop are affected by preceding CC monocultures and mixtures and by main crop identity. We expected that AMF abundance and diversity in main crops are promoted by AM-host CC, and suppressed by non-AM-host CC, and that mixtures of CC species can promote beneficial and suppress pathogenic root fungi. Our full-factorial field experiment comprised crop rotation in sand soil with different CC treatments (monocultures of radish [AM non-host], ryegrass, clover, vetch [AM hosts], mixtures of radish + vetch, ryegrass + clover and fallow) and two main crops (oat and endive). At peak crop growth, we investigated the root fungal communities in the main crops using microscopy and high throughput sequencing (Illumina MiSeq). Cover crop identity was of prime importance and CC legacy overruled main crop identity in determining root fungal communities in main crops. Compared with fallow, CC with ryegrass increased AMF colonization and richness in both main crops and of non-AMF in oat. Legacies of ryegrass, ryegrass + clover and vetch resulted in distinct root fungal communities in the main crops, while the legacy of CC with radish were similar to the legacy of fallow. Root fungal community in crops after clover had highest abundance of representative fungal pathogens in contrast with the other CC treatments that resulted in fungal communities where pathogens were scarce. Oppositely to expected, CC mixtures did not enhance fungal symbionts or suppressed pathogens. Overall, fungal communities in roots of the main crops in our field experiment were determined by the preceding CC species in monoculture, rather than by the CC AMF preference or functional group. This research highlights that the choice of CC determines the root fungal community in main crop which may influence crop quality.     

Genetic differences in root mass of Lolium perenne varieties under field conditions

Although grasses have dense rooting systems, nutrient uptake and productivity can be increased, and N-leaching reduced, if rooting is further improved. The variation in root mass of 16 varieties of Lolium perenne was studied under field conditions in two experiments on sandy soil in The Netherlands. The chosen varieties differed in genetic and aboveground characteristics such as ploidy, productivity and grass cover. Root dry matter (RDM) was measured in the 0–8, 8–16 and 16–24 cm soil layers. In summary, we found that RDM of perennial ryegrass differed significantly between varieties under field conditions. These differences were not linked to grass yield, which indicates that it is possible to select perennial ryegrass varieties that combine high aboveground productivity with high RDM. In the first experiment, which was managed by cutting, diploid varieties had higher RDM than tetraploid varieties. Grand mean RDM in the second experiment, which was managed by cutting as well as grazing, was lower than in the first experiment. In this experiment, total RDM was not influenced by ploidy but by grass cover type: high grass cover types had higher RDM. Differences in management between the two experiments possibly explain the differences in RDM and in the influence of chosen characteristics on RDM. Considering challenges in the areas of climate change, water availability, pollution and soil degradation, grass varieties with improved root systems could significantly contribute to a more efficient use of nutrients and water, erosion control, soil improvement and carbon sequestration.     

A growth comparison among three commercial tilapia species in a biofloc system

Despite a worldwide boom in tilapia aquaculture, South Africa has failed to follow suit, resulting in a small, very much undeveloped local industry. Much of the justification for this reality lies on the inadequacy of the species used and the stringent legislation preventing the use of the Nile tilapia, Oreochromis niloticus. With momentum gained in recent years, the local industry lobbying for the legalization of the O. niloticus has made great progress and its use in certain systems has recently been facilitated. This study was conducted to compare the growth performance between the indigenous Mozambique tilapia, Oreochromis mossambicus, another African alternative gaining momentum in Zambia, the Three Spot tilapia, Oreochromis andersonii, and the globally reputable O. niloticus. The study was conducted in a biofloc technology (BFT) system, showing great potential as an environmentally friendly technology. The trial was run for 10 weeks with 60 fish/tank stocked into four repeats tanks per species. Fish were sampled on six occasions with a regression fitted to the mass data. Oreochromis niloticus showed a significantly higher growth rate with an average daily gain of 0.693 ± 0.018 g/day and the lowest feed conversion ratio (FCR) of 1.01 ± 0.05, followed by O. mossambicus with average daily gain of 0.405 ± 0.025 g/day and FCR of 2.24 ± 0.16, and then O. andersonii with an average daily gain of 0.185 ± 0.025 g/day and an FCR of 2.53 ± 0.28, respectively. From this study, O. niloticus therefore appears to be the most adequate species for use in BFT systems in South Africa.     

The perception of veterinary herd health management by Dutch dairy farmers and its current status in the Netherlands: a survey

The importance of veterinary herd health management (VHHM) is increasing in both dairy farming and veterinary practice. Little is known, however, about how VHHM is perceived by farmers in terms of structure, content and satisfaction. In 2007 a questionnaire, containing questions about these three items was therefore sent to 800 Dutch dairy farmers. Farmers received two questionnaires, one for participants in VHHM and one for non-participants, allowing them to choose the appropriate one. Results were summarized and statistically analyzed. Farmers who were participating in VHHM had better farm performance. They were satisfied with the way VHHM was executed on their farm. However, there were some pressure points. Goal setting and evaluation was still not a regular part of VHHM, even though it is said to be effective in literature. Time spent on VHHM not visible to the farmer was often not charged or not clearly specified on the bill. The differences in opinions between participants and non-participants of VHHM indicated a lack of communication and/or product differentiation. Satisfaction with the way VHHM was executed on the farm had no significant influence on 305-day production. There was, however, some influence on calving interval and bulk milk somatic cell count (BMSCC).