Behavioural fever in the Senegalese grasshopper, Oedaleus senegalensis, and its implications for biological control using pathogens

1. Thermoregulatory behaviour of the Senegalese grasshopper, Oedaleus senegalensis (Krauss), was investigated in the field following a spray application of an oil-based formulation of Metarhizium flavoviride Gams and Rozsypal in Niger, West Africa.
2. Measurements of environmental temperature, wind speed and solar radiation were made in conjunction with measurements of internal body temperatures of grasshoppers from a control (unsprayed) and treated plot using microthermocouples and hand-held thermometers. Grasshoppers were monitored for 4 days from the third day after application.
3. Oedaleus senegalensis utilized a range of thermoregulatory behaviours to maximize body temperatures during periods of low insolation and ambient temperature, and to minimize excessive heat loading during the hottest periods. Preferred body temperature of uninfected grasshoppers was 39 °C, with a range from 24 °C in the early morning to a high of 46 °C during periods of high insolation and ambient temperature.
4. Infected grasshoppers altered their thermoregulatory behaviour and showed a behavioural fever response to the pathogen. Preferred body temperatures of infected individuals were raised to a new set point of ≈ 42 °C. This is believed to be the first evidence for a behavioural fever in response to a microbial infection for any natural population. In the present study, its effects appeared to provide little therapeutic advantage to hosts infected following application. Preliminary evidence from other studies, however, indicates that modifications to host thermoregulation could be a significant constraint to the pathogen and may limit its impact under certain conditions.     

THE EFFECTS OF SAMPLING BIAS ON PALAEOZOIC FAUNAS AND IMPLICATIONS FOR MACROEVOLUTIONARY STUDIES

Abstract:  Trilobites, a dominant component of marine faunas during the Cambrian and Ordovician and which survived until the end of the Permian (542–251 Ma) have been used in many macroevolutionary analyses. Here, we use a discovery curve to document the sampling history of trilobites, which we consider a proxy for Palaeozoic faunas in general. At higher taxonomic ranks, orders, suborders and superfamilies, the fossil record has been completely sampled, while the family rank also shows a high level of sampling completeness, having reached an asymptote in 1970. Importantly, this levelling-off occurred even though worker effort continued to increase. However, at genus level the sampling record is incomplete, indicating that families should not be used as a proxy for genera. There is little variation among the different subsets of generic data, with the sampling history of different stratigraphic periods and among different orders being very similar. However, there is noticeable variation among geographical regions, caused by variations in worker effort, and this could cause problems when comparing speciation and diversity patterns across faunal provinces. The role of synonyms on sampling history has had little effect.     

Retention time as a primary determinant of colour and light attenuation in two tropical Australian reservoirs

1. The light climates of Darwin River Reservoir (DRR) and Manton River Reservoir (MRR), in northern Australia, are compared for an 8-year period. The reservoirs are subject to the same wet/dry tropical climate and have similar catchment characteristics, but differ in their basin morphology, retention time and trophic status.
2. Median euphotic depths in DRR and MRR were 9.7 and 4.4 m, respectively. Seasonal variation in each reservoir's euphotic depth was best explained by colour, based on a stepwise linear regression. Turbidity was excluded from the two regressions, while chlorophyll a concentration was significant only for the MRR regression.
3. Both reservoirs showed the same seasonal pattern for colour. Wet season inflow increased reservoir colour, and was followed by a reduction in colour due to photodegradation and microbial decomposition of humic material, reaching a minimum before the next wet seasons inflow.
4. Although the colour of catchment run-off into both reservoirs was similar, MRR colour was two to three times greater than that measured in DRR. The higher colour and greater light attenuation of MRR is attributed primarily to its shorter retention time, and therefore shorter time for colour removal. Annual retention time accounted for 97% of the variability of average annual colour (measured as absorption at 440 nm), based on a linear regression of log₁₀ transformed data for both reservoirs.
5. Long retention times favour reduced colour, increasing water transparency, particularly in water bodies of low trophic state and inorganic turbidity.     

Complex trait differentiation between host-populations of the pea aphid Acyrthosiphon pisum (Harris): implications for the evolution of ecological specialisation

Variation in traits affecting preference for, and performance on, new habitats is a key factor in the initiation of ecological specialisation and adaptive speciation. However, habitat and resource use also involves other traits whose influence on ecological and genetic divergence remains poorly understood. In the present study, we investigated the extent of variation of life-history traits among sympatric populations of the pea aphid Acyrthosiphon pisum , which shows several host races that are specialised on various plants of the family Fabaceae plants and is an established model for ecological speciation. First, we assessed the community structure of microbial partners within host populations of the pea aphid. The effect of these microbes on host fitness is uncertain, although there is growing evidence that they may modulate various important adaptive traits of their host such as plant utilisation and resistance against natural enemies. Second, we performed a multivariate analysis on several ecologically relevant features of host populations recorded in the present and previous studies (including microbial composition, colour morph, reproductive mode, and male dispersal phenotype), enabling the identification of correlations between phenotypic traits. We discuss the ecological significance of these associations of traits in relation to the habitat characteristics of pea aphid populations, and their consequences for the evolution of ecological specialisation and sympatric speciation.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 718–727.     

Respiration Rate and Mitochondrial Oxidase Activity in Arum Spadix

1. Mitochondria prepared from young Arum spadix oxidise succinicand -ketoglutaric acids at about 300µl. O₂/hr./g. wetwt. but as the spadix ages the activity of the mitochondriaincreases more than tenfold. The increase results from a smallrise in the quantity of mitochondrial nitrogen brought downin the centrifuge and a larger rise in oxidase activity permg. mitochondrial nitrogen. 2. The rate of respiration of spadix slices has been measuredunder conditions in which it is not limited by slow diffusionof oxygen. Slices of young spadix respire at about 1,000–2,000µl. O₂/hr/g. but as the inflorescence opens the rate soarsto 20,000µl. O₂/hr/g. and the spadix becomes warm. 3. Cytochrome oxidase was assayed in mitochondria treated withdigitonin. There is at all times enough cytochrome oxidase toaccount for the rates of oxidation of succinate and -ketoglutarate;and enough to account for the relatively slow respiration ofthe young spadix slices but not for the fastest respirationof the mature spadix. 4. The respiration of spadix slices is found, in contradictionto an earlier report, to be sensitive to malonate.     

Carbon dynamics in an ultra-oligotrophic epishelf lake (Beaver Lake, Antarctica) in summer

1. Microbial plankton dynamics in an ultra‐oligotrophic epishelf lake (Beaver Lake, Antarctica) were investigated over an austral summer (December 2002 to January 2003). The aim was to characterise carbon cycling in an environmentally extreme lake. 2. The lake had an unusual temperature profile with peak temperatures of 1.3–1.9 °C between 20 and 25 m. Photosynthetically active radiation penetrated to the lake bottom (110 m) on occasions. The ice cover underwent marked thinning and melting during the study period. 3. Chlorophyll a concentrations were consistently low, usually below 1 μg L^?1, with highest concentrations close to the lake bottom, where the photosynthetic elements showed strong autofluorescence. Mean photosynthetic nanoflagellates ranged between 34.9 × 10⁴ L^?1 ± 33.5 (23rd December) and 130.9 × 10⁴ L^?1 ± 112.3 (4th December). Highest photosynthetic activity was usually recorded below 25 m. Rates of carbon fixation varied between 0.089 μg C L^?1 h^?1 ± 0.002 and 0.579 μg C L^?1 h^?1 ± 0.156. Primary production was limited by low temperature and orthophosphate availability. 4. Mean bacterial concentration throughout the water column ranged between 9.3 × 10⁷ L^?1 ± 1.2 (23rd December) and 14.0 × 10⁷ L^?1 ± 1.8 (28th January). Bacterial production was low, less than 10% of primary production and ranged between 2.1 ng C L^?1 h^?1 ± 0.8 and 12 ng C L^?1 h^?1 ± 0.9. Highest rates coincided with times of highest primary production. On occasion dissolved organic carbon (DOC) concentrations dropped to 20 μg L^?1, probably below accurate limits of detection, suggesting that carbon substratum and phosphorus may have limited bacterial growth. 5. Heterotrophic nanoflagellates varied significantly over the summer from a mean of 26.6 × 10⁴ L^?1 ± 14.2 (23rd December) to 133.8 × 10⁴ L^?1 ± 33.5 (14th December). They imposed a significant grazing impact on the bacterioplankton, removing in excess of 100% of bacterial production in December. 6. The total organic carbon pool [DOC and particulate organic carbon (POC)] was below 600 μg L^?1. The ratio of DOC : POC ranged between 0.44 : 1 and 2.8 : 1 in the upper 40 m of the water column, and 1.8 : 1 and 3.7 : 1 in the lower waters. The microbial plankton contributed 1–29% of POC, thus detrital POC made up the largest fraction of the POC pool. 7. Beaver Lake is an extreme lacustrine ecosystem where heterotrophic processes occasionally appear to be carbon limited. Significant summer ice‐melt, not seen in a previous opportunistic sampling, may be having an impact on the carbon cycle.     

Dissolved carbon leaching from soil is a crucial component of the net ecosystem carbon balance

Estimates of carbon leaching losses from different land use systems are few and their contribution to the net ecosystem carbon balance is uncertain. We investigated leaching of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and dissolved methane (CH₄), at forests, grasslands, and croplands across Europe. Biogenic contributions to DIC were estimated by means of its δ¹³C signature. Leaching of biogenic DIC was 8.3±4.9 g m^?2 yr^?1 for forests, 24.1±7.2 g m^?2 yr^?1 for grasslands, and 14.6±4.8 g m^?2 yr^?1 for croplands. DOC leaching equalled 3.5±1.3 g m^?2 yr^?1 for forests, 5.3±2.0 g m^?2 yr^?1 for grasslands, and 4.1±1.3 g m^?2 yr^?1 for croplands. The average flux of total biogenic carbon across land use systems was 19.4±4.0 g C m^?2 yr^?1. Production of DOC in topsoils was positively related to their C/N ratio and DOC retention in subsoils was inversely related to the ratio of organic carbon to iron plus aluminium (hydr)oxides. Partial pressures of CO₂ in soil air and soil pH determined DIC concentrations and fluxes, but soil solutions were often supersaturated with DIC relative to soil air CO₂. Leaching losses of biogenic carbon (DOC plus biogenic DIC) from grasslands equalled 5–98% (median: 22%) of net ecosystem exchange (NEE) plus carbon inputs with fertilization minus carbon removal with harvest. Carbon leaching increased the net losses from cropland soils by 24–105% (median: 25%). For the majority of forest sites, leaching hardly affected actual net ecosystem carbon balances because of the small solubility of CO₂ in acidic forest soil solutions and large NEE. Leaching of CH₄ proved to be insignificant compared with other fluxes of carbon. Overall, our results show that leaching losses are particularly important for the carbon balance of agricultural systems.     

Carbon Dioxide Production in Early Anaerobiosis

1. Slices of swede tissue placed under nitrogen produce carbondioxide and ethanol in equal amounts after an initial phaselasting about 1.5 hours. During this initial phase some 2 µM./g.fr. wt. of extra carbon dioxide is produced. The productionof such extra carbon dioxide is not affected by iodoacetate,fluoride, or arsenite which inhibit glycolysis or by dinitrophenolwhich stimulates glycolysis. Slices incubated in air in thepresence of cyanide also produce extra carbon dioxide. 2. A second extra burst of carbon dioxide can be induced aftersome hours of anaerobiosis by treating slices with methyleneblue, DPN, or TPN, or as a result of a short air experience. 3. Experiments with labelled sugars support the view that theextra carbon dioxide originates ultimately from carbohydrate,being released, it is proposed, in the oxidative decarboxylationof either pyruvate or 6-phosphogluconate. Carbon dioxide productionthen continues so long as oxidants are available in the cell,finally coming to a standstill when cell components reach theirreduced states.