Coexistence of natural enemies in a multitrophic host–parasitoid system

Abstract.  1. This study explored the temporal and spatial aspects of coexistence over many generations in a multispecies host–parasitoid assemblage.
2. The long-term interaction between the cabbage root fly, Delia radicum (Diptera: Anthomyiidae), and two of its natural enemies, Trybliographa rapae (Hymenoptera: Fitigidae) and Aleochara bilineata (Coleoptera: Staphylinidae), in a cultivated field at Silwood Park over 19 years was explored.
3. Although time series showed that the populations were regulated, the impact of the natural enemies was highly variable. Within-year determinants showed that the spatial response of the specialist parasitoid, T. rapae , was predominantly independent of host density while A. bilineata acted simply as a randomly foraging generalist parasitoid.
4. These findings are compared and contrasted with an earlier investigation of the same system when only the first 9 years of the time series were available. This study demonstrated the potential of long-term field studies for exploring hypotheses on population regulation, persistence, and coexistence.     

Effects of chronic antidepressant treatments on 5-HT and NA transporters in rat brain: an autoradiographic study

Tricyclic antidepressants and serotonin (5-HT) uptake inhibitors rapidly block uptake sites, or transporters; however, their therapeutic effects are only seen after 2-3 weeks of treatment. Thus, direct blockade of 5-HT and noradrenaline (NA) transporters cannot account entirely for their clinical efficacy, and other long-term changes may be involved. Adult Sprague-Dawley rats were treated for 21 days with daily injections of either desipramine, trimipramine, fluoxetine, or venlafaxine; a fifth group that was used as a control, received daily saline injections. Identified cortical areas, hippocampal divisions and nuclei raphe dorsalis, raphe medialis and locus coeruleus were examined by quantitative autoradiography using either [3H]citalopram to label 5-HT transporters, or [3H]nisoxetine for NA uptake sites. Increases in [3H]nisoxetine binding were found in the cingulate, frontal, parietal, agranular insular, entorhinal and perirhinal cortices as well as in the hippocampal divisions CA1, CA3, dentate gyrus and subiculum, and in nucleus raphe dorsalis of trimipramine-treated animals compared to the control rats. Also, densities of NA transporters decreased in temporal cortex, CA2 and nucleus raphe dorsalis in fluoxetine-treated rats as compared to the controls. Also, there was a decrease in NA transporters in the locus coeruleus of the desipramine-treated animals as compared to the densities measured in the control group. Chronic treatment with desipramine or trimipramine, which do not directly inhibit 5-HT uptake, compared to fluoxetine and venlafaxine, lead to increases in 5-HT transporter densities in cingulate, agranular insular and perirhinal cortices. The present study shows differential region-specific effects of antidepressants on 5-HT and NA transporters, leading to distinct consequences in forebrain areas.     

RFLP-based maps of the homoeologous group-6 chromosomes of wheat and their application in the tagging of Pm12, a powdery mildew resistance gene transferred from Aegilops speltoides to wheat

Genetic maps of the homoeologous group-6 chromosomes of bread wheat, Triticum aestivum, have been constructed spanning 103 cM on 6A, 90 cM on 6B and 124 cM on 6D. These maps were transferred to a Chinese Spring (CS) x line #31 cross to locate a dominant powdery mildew resistance gene, Pm12, introgressed into line #31 from Aegilops speltoides. Pm12 was shown to lie on the short arm of translocation chromosome 6BS-6SS.6SL in line #31, but could not be mapped more precisely due to the lack of recombination between the 6S Ae. speltoides segment and chromosome 6B. Possible strategies to reduce the size of the alien segment, which probably encompasses the complete long arm and more than 82% of the short arm of chromosome 6B, are discussed.     

Effect of probenecid on 5-hydroxyindoleacetic acid in cisternal cerebrospinal fluid of rats with portacaval anastomosis

Portal-systemic encephalopathy (PSE) is characterized by a neuropsychiatric disorder progressing through personality changes, to stupor and coma. Previous studies have revealed alterations of serotonin and of its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in brain tissue and CSF in experimental (rat) and human PSE. Increased brain 5-HIAA concentrations could result from its decreased removal rather than to increased serotonin metabolism. In order to evaluate this possibility, CSF 5-HIAA concentrations were measured using an indwelling cisterna magna catheter technique at various times following end-to-side portacaval anastomosis in rats (the most widely used animal model of PSE) treated with probenecid, a competitive inhibitor that blocks the active transport of acid metabolites out of the brain and CSF. Following portacaval anastomosis and probenecid treatment, CSF concentrations of 5-HIAA were increased to a greater extent than in sham-operated controls. When data were expressed as per-cent baseline values, the relative increase of CSF 5-HIAA in portacaval shunted rats following probenecid treatment was not significantly different from sham-operated controls. These findings confirm that increased 5-HIAA in the CNS in experimental PSE results from increased 5HT metabolism or turnover and that the probenecid-sensitive acid metabolite carrier is intact in PSE.     

Embryonic and larval development of brown trout, Salmo trutta L.: exposure to trace metal mixtures in soft water

Freshly fertilized ova of brown trout, Salmo trutta L., were exposed to all possible mixtures of Al (6000 nmol 1¹), Cu (80 nmol 1⁻¹), Pb (50 nmol 1⁻¹) and Zn (300 nmol 1 ¹). In a separate experiment, newly hatched brown trout yolk-sac fry were exposed to Mn (1500 nmol 1⁻¹), Fe (2500 nmol 1 ¹), Ni (200 nmol 1⁻¹) or Cd (4 nmol 1 ¹), separately, and in mixtures with either Al or Cu. Both experiments were conducted in flowing, artificial softwater media nominally at pH 5.6 [Ca] 20 μmol 1 ¹ and 10° C.
Mortalities were high in fry subjected to treatments which contained both Al and Cu (31–72%), and to the Cu + Fe treatment (78%) compared with those from the other trace metal mixtures (0–22%). In all the treatments tested, fry exposed to trace metal mixtures containing Al and/or Cu had reduced whole body Ca, Na and K content, and seriously impaired skeletal calcification. Whole body Mg content was variable. In trace metal mixtures which contained Cu but not Al, the effects on fry survival and whole body mineral content were in general more deleterious than the corresponding mixtures but with Al present rather than Cu. The presence of Pb and/or Zn in mixtures with Al and/or Cu had a slight ameliorative effect in terms both of fry survival and whole body mineral content.     

Climate-based models of spatial patterns of species richness in Egypt's butterfly and mammal fauna

Aim  Identifying areas of high species richness is an important goal of conservation biogeography. In this study we compared alternative methods for generating climate-based estimates of spatial patterns of butterfly and mammal species richness.
Location  Egypt.
Methods  Data on the occurrence of butterflies and mammals in Egypt were taken from an electronic database compiled from museum records and the literature. Using M axent , species distribution models were built with these data and with variables describing climate and habitat. Species richness predictions were made by summing distribution models for individual species and by modelling observed species richness directly using the same environmental variables.
Results  Estimates of species richness from both methods correlated positively with each other and with observed species richness. Protected areas had higher species richness (both predicted and actual) than unprotected areas.
Main conclusions  Our results suggest that climate-based models of species richness could provide a rapid method for selecting potential areas for protection and thus have important implications for biodiversity conservation.     

Embryonic and larval development of brown trout, Salmo trutta L.: exposure to aluminium, copper, lead or zinc in soft, acid water

Freshly fertilized ova, eyed ova and yolk-sac fry of brown trout, Salmo trutta L., were exposed to each of four trace metals (aluminium: 6000 nmol l^?1; copper: 80 nmol l^?1; lead: 50 nmol l^?1; zinc: 300 nmol l^?1) while held in flowing artificial soft-water media maintained at pH 4.5 or 5.6 and [Ca] 20 or 200 μmol l^?1. In continuous exposure from fertilization, survival of ova was severely affected at pH 4.5 and [Ca] 20 μmol l^?1, regardless of the presence of Cu, Pb or Zn; Al reduced embryonic mortality and improved hatching success. High ambient [Ca] at pH 4.5 increased egg survival. At ‘swim-up’, surviving fry exposed to Al or Pb had lower whole body Ca, Na and K content, irrespective of pH or ambient [Ca]. Cu reduced whole body Ca and K content at pH 5.6 and [Ca] 200 μmol^?1, and whole body Ca, Na and K content in the other media. Zn reduced whole body mineral content at pH 5.6 and [Ca] 20 μmol l^?1. Whole body Mg content was reduced by all trace metals at pH 5.6 and [Ca] 20 μmol l^?1, and by Cu at pH 5.6 and [Ca] 200 μmol l^?1. Al and Cu impaired skeletal calcification at pH 5.6 at both ambient [Ca]; Pb only at [Ca] 20 μmol I^?1. Zn enhanced calcification at pH 4.5 and [Ca] 200 μmol l^?1. In the absence of trace metals, low pH reduced body Ca, Na, K content and skeletal calcification at [Ca] 200 μmol l^?1. The uptake of Ca, Na and K, measured at regular intervals from hatching was impaired to the same extent by all treatments at pH 4.5, irrespective of ambient [Ca] or trace metal presence. At pH 5.6, irrespective of ambient [Ca], Al, Cu and Pb impaired Ca and K uptake. The rate of Na uptake was reduced by Al and Cu. Al-treated yolk-sac fry, exposed to low ambient [Ca] from 200–300° days post-hatch, suffered high mortalities regardless of pH. Ca, Na and K uptake was impaired by all treatments at pH 4.5, and by Al and Cu at pH 5.6 in a similar exposure period. The development of the early stages of brown trout in the presence of trace metals is discussed in relation to recruitment failure in areas of soft, acid water.     

Community response to experimental soil disturbance in a midsuccessional,abandoned pasture

To determine whether soil disturbance by digging and burrowing mammals altered community structure and the rate of succession in a midsuccessional abandoned pasture, species richness, composition and relative abundance were monitored over a two year period both on and off artificially created earth mounds (100, 900, 8100 cm²). Mean species richness increased by up to two species per small mound (100 cm²) and by up to four species per large mound (8100 cm²). However, increased species richness was evident for less than two years. Initially, up to sixteen of the twenty species present occurred more often on earth mounds than off mounds, with two of these species found only on large mounds (8100 cm²). After two years, there was little or no significant difference in species composition and relative frequency on and off earth mounds. Experimental soil disturbance temporarily altered community structure simply by increasing space available for colonization since light, nutrient and water supply did not increase significantly on mounds. Soil disturbance can increase species richness and change species' relative frequency in disturbances as small as 100 cm² but such changes were likely too small and short lived to alter permanently the structure and rate of succession in the abandoned pasture studied here.