Ameliorating Effect of Chloride on Nitrite Toxicity to Freshwater Invertebrates with Different Physiology: a Comparative Study Between Amphipods and Planarians

High nitrite concentrations in freshwater ecosystems may cause toxicity to aquatic animals. These living organisms can take nitrite up from water through their chloride cells, subsequently suffering oxidation of their respiratory pigments (hemoglobin, hemocyanin). Because NO2¿ and Cl¿ ions compete for the same active transport site, elevated chloride concentrations in the aquatic environment have the potential of reducing nitrite toxicity. Although this ameliorating effect is well documented in fish, it has been largely ignored in wild freshwater invertebrates. The aim of this study was to compare the ameliorating effect of chloride on nitrite toxicity to two species of freshwater invertebrates differing in physiology: Eulimnogammarus toletanus (amphipods) and Polycelis felina (planarians). The former species presents gills (with chloride cells) and respiratory pigments, whereas in the latter species these are absent. Test animals were exposed in triplicate for 168 h to a single nitrite concentration (5 ppm NO2-N for E. toletanus and 100 ppm NO2-N for P. felina) at four different environmental chloride concentrations (27.8, 58.3, 85.3, and 108.0 ppm Cl¿). The number of dead animals and the number of affected individuals (i.e., number of dead plus inactive invertebrates) were monitored every day. LT50 (lethal time) and ET50 (effective time) were estimated for each species and each chloride concentration. LT50 and ET50 values increased with increases in the environmental chloride concentration, mainly in amphipods. Results clearly show that the ameliorating effect of chloride on nitrite toxicity was more significant in amphipods than in planarians, likely because of the absence of gills (with chloride cells) and respiratory pigments in P. felina. Additionally, this comparative study indicates that the ecological risk assessment of nitrite in freshwater ecosystems should take into account not only the most sensitive and key species in the communities, but also chloride levels in the aquatic environmen

Frost Hardiness of Iraqi Wheat genotypes

Frost hardiness level in winter cereals is especially temperature dependent. The low temperature which kills 50% of plants (LT50) is considered to be a standard indicator of frost hardiness level of plant. Frost hardiness is considered the most important parameter for the field survival which is the ultimate measure of winter-hardiness of a cultivar. This study aimed to determine the genetic level of frost hardiness of five Middle Eastern varieties (Abu-Ghraib, Fatah, IPA 95, IPA 99, and Sham 6) in comparison to the European cultivar (Claire). All of the Middle Eastern varieties tested showed very similar LT50’s in the nonacclimated state, whilst when of acclimated they responded in different ways to freezing temperatures. Abu-Ghraib and Claire showed more tolerance than the other cultivars

Embryonic Heat Shock and its Effect on Larval and Adult Performance in Drosophila melanogaster

Drosophila melanogaster live across a wide latitudinal range, thus resulting in divergence in thermal adaptation between populations. Despite differences in thermal tolerances, the effects of an embryonic thermal stress on development have not been studied. The goal of this experiment was to determine the effects of a brief embryonic heat shock on larval and adult performance in tropical versus temperate genotypes of D. melanogaster. Larval and adult performance were measured through pupation height and walking speed, respectively. I predicted that as embryonic thermal shock temperature increased, performance values would decrease, showing a physiological cost in response to the heat shock. Additionally, I expected that the tropical genotype would exhibit less of a plastic response to the thermal shock compared to the temperate genotype due to having a higher embryonic thermal tolerance. In response to increasing embryonic shock temperature, performance values decreased similarly in both genotypes. Given the tropical flies only walked at a slightly faster pace, it can be concluded that the thermal shocks resulted in a comparable plastic response in both genotypes. With global temperature rising and an increasing number of days reaching thermal extremes, these results suggest a possible decrease in survival and performance of D. melanogaster in the natural environment. Although there is a possibility of natural selection resulting in a less severe plastic response to embryonic thermal stress, based on these data, there may not be significant phenotypic variation among populations of this species on which natural selection can act

Elucidation of the Photorhabdus temperata Genome and Generation of a Transposon Mutant Library To Identify Motility Mutants Altered in Pathogenesis

The entomopathogenic nematode Heterorhabditis bacteriophora forms a specific mutualistic association with its bacterial partner Photorhabdus temperata. The microbial symbiont is required for nematode growth and development, and symbiont recognition is strain specific. The aim of this study was to sequence the genome of P. temperata and identify genes that plays a role in the pathogenesis of the Photorhabdus-Heterorhabditis symbiosis. A draft genome sequence of P. temperata strain NC19 was generated. The 5.2-Mb genome was organized into 17 scaffolds and contained 4,808 coding sequences (CDS). A genetic approach was also pursued to identify mutants with altered motility. A bank of 10,000 P. temperata transposon mutants was generated and screened for altered motility patterns. Five classes of motility mutants were identified: (i) nonmotile mutants, (ii) mutants with defective or aberrant swimming motility, (iii) mutant swimmers that do not require NaCl or KCl, (iv) hyperswimmer mutants that swim at an accelerated rate, and (v) hyperswarmer mutants that are able to swarm on the surface of 1.25% agar. The transposon insertion sites for these mutants were identified and used to investigate other physiological properties, including insect pathogenesis. The motility-defective mutant P13-7 had an insertion in the RNase II gene and showed reduced virulence and production of extracellular factors. Genetic complementation of this mutant restored wild-type activity. These results demonstrate a role for RNA turnover in insect pathogenesis and other physiological functions

Influence of Temperature on the Physiology and Virulence of the Insect Pathogen Serratia sp. Strain SCBI

The physiology of a newly recognized Serratia species, termed South African Caenorhabditis briggsae Isolate (SCBI), which is both a nematode mutualist and an insect pathogen, was investigated and compared to that of Serratia marcescens Db11, a broad-host-range pathogen. The two Serratia strains had comparable levels of virulence for Manduca sexta and similar cytotoxic activity patterns, but motility and lipase and hemolytic activities differed significantly between them

Could natural selection change the geographic range limits of light brown apple moth (Lepidoptera, Tortricidae) in North America?

We artificially selected for increased freeze tolerance in the invasive light brown apple moth. Our results suggest that, by not accounting for adaptation to cold, current models of potential geographic distributions could underestimate the areas at risk of exposure to this species

The Effect of Repeated Low Temperature on Eggs of the Alfalfa Weevil (Coleoptera: Curculionidae)

Three ages of alfalfa weevil, Hypera postica (Gyllenhal) eggs were exposed to repeated exposures of -15 and -20°C. Fresh-laid eggs were quite susceptible and 3- and 5day old eggs were relatively resistant to -15\u27C, but all ages of eggs showed considerable susceptibility to -20°C, with an average LT50 of 2.2 days. Comparison of this data with similar studies utilizing constant low temperature exposures showed the effect to be independent of temporal interruptions

Tolerance to air exposure of the New Zealand mudsnail Potamopyrgus antipodarum (Hydrobiidae, Mollusca) as a prerequisite to survival in overland translocations

Spreading throughout a new ecosystem is the last step of an exotic species to become invasive. In the case of invasive aquatic molluscs, tolerance to air exposure is one of the main mechanisms allowing overland translocation and spreading. The mudsnail Potamopyrgus antipodarum (Hydrobiidae, Mollusca) is native to New Zealand but it has spread worldwide, invading ecosystems in Europe, Australia, America and Asia. The aim of our study is to assess mudsnail tolerance to air exposure, which may contribute to the successful overland translocation of this species. We conducted a laboratory experiment with four levels of air exposure (9, 18, 24 and 36 hours in a controlled climatic chamber). Snails were placed for 60 seconds in a laboratory paper filter to remove surface snail water. Then they were placed back in empty vessels during the four periods of air exposure, except the control group, which was immediately returned to water. At the end of each period of air exposure all vessels were filled with water and the cumulative mortality was monitored after 24, 96, 168 and 264 hours of rehydration. The calculated Lethal Times (i.e. the time of air exposure (in hours) necessary to cause the death of 50% (LT50) or 99% (LT99) of the population) and their 95% confidence limits at 24, 96, 168 and 264 hours were 28.1 (25.2–31.9), 26.9 (24.2–30.1), 25.9 (23.4–28.9) and 25.9 (23.4–28.9) hours, respectively for LT50, and 49.6 (42.7–63.3), 45.6 (39.9–56.5), 43.2 (38.0–53.0) and 43.2 (38.0–53.0) hours, respectively for LT99. Therefore an air exposure time over 43 hours caused the death of all studied individuals during all monitoring periods. Extending the monitoring period beyond 24 hours did not significantly change lethal times. Therefore, we recommend exposing fishing tools or boats at open air during at least 53 hours as a low cost measure to control mudsnail spread in early stages of invasion