Chytrid infections of Daphnia pulicaria: development, ecology, pathology and phylogeny of Polycaryum laeve

1. We combined ecological surveys, life table studies, microscopy and molecular sequencing to determine the development, ecology, pathology and phylogeny of Polycaryum laeve, an endoparasite of cladocerans. We report the first records of P. laeve from North America, where we have used a polymerase chain reaction primer and microscopic examination to confirm infections in 14 lakes. Infections are highly pathogenic and caused increased mortality, reduced growth, and reproductive castration in Daphnia pulicaria during life table studies. 2. Biweekly data from Allequash Lake (Wisconsin, U.S.A.) throughout 2003 indicated that fecundity and infection prevalence were inversely correlated. Infection prevalence was highest in late winter and early spring (up to 80%) and lowest during late summer. Epidemics were generally followed by sharp declines in host population density (up to 99%). 3. Within the haemocoel of its host, P. laeve forms thick‐walled sporangia, which occur systemically in later stages of infection. Fungal thalli associate closely with muscle fibres and connective tissue, leading to degeneration as the infection becomes advanced. Following death of the host, flagellated zoospores are released through an exit papilla on the sporangium. Based on the infection‐induced castration of the host and increases in infection prevalence with Daphnia size, we postulate that transmission is horizontal, but may be indirect through an additional host or free‐living stage. 4. Molecular and morphological data clearly indicate that P. laeve belongs in the fungal phylum Chytriodiomycota, order Blastocladiales. Based on ribosomal RNA gene sequences and morphological features, we transfer the genus Polycaryum from the Haplosporidia to the Chytridiomycota, and designate a lectotype and epitype for P. laeve. Considering the high prevalence of P. laeve infection within Daphnia populations, the frequency with which we detected infections among lakes, and the keystone importance of large‐bodied Daphnia in aquatic food webs, we suggest that P. laeve may exert a regulatory influence on Daphnia populations in lake ecosystems.     

A comparison,by sweep sampling,of the arthropod fauna of secondary vegetation in Michigan,England and Costa Rica

• 1 Six 800-sweep samples of English and Michigan (“old field”) secondary vegetation arthropods are compared with Costa Rican samples taken in the same way.
• 2 Parasitic Hymenoptera and spiders accounted for a larger proportion of the arthropod fauna in the mid-latitude than the tropical samples.
• 3 In one English field, the seasonal change in insect numbers was 88% of that recorded over all the seasonal and elevational changes examined in Costa Rica. Furthermore, the difference in the total dry weights of the arthropod fauna between December and July was similar to the difference found between the wet and dry seasons in tropical secondary vegetation (also similar to the difference between day and night values during the dry season).
• 4 Aphids and Psyllidae were far more abundant in the English site than in the Costa Rican mainland sites.
• 5 In mid-summer, the English field had far more arthropods in it than did any of the tropical sites sampled.

     

Soil nitrous oxide and methane fluxes are low from a bioenergy crop (canola) grown in a semi-arid climate

Understanding nitrous oxide (N₂O) and methane (CH₄) fluxes from agricultural soils in semi‐arid climates is necessary to fully assess greenhouse gas emissions from bioenergy cropping systems, and to improve our knowledge of global terrestrial gaseous exchange. Canola is grown globally as a feedstock for biodiesel production, however, resulting soil greenhouse gas fluxes are rarely reported for semi‐arid climates. We measured soil N₂O and CH₄ fluxes from a rain‐fed canola crop in a semi‐arid region of south‐western Australia for 1 year on a subdaily basis. The site included N fertilized (75 kg N ha^?1 yr^?1) and nonfertilized plots. Daily N₂O fluxes were low (?1.5 to 4.7 g N₂O‐N ha^?1 day^?1) and culminated in an annual loss of 128 g N₂O‐N ha^?1 (standard error, 12 g N₂O‐N ha^?1) from N fertilized soil and 80 g N₂O‐N ha^?1 (standard error, 11 g N₂O‐N ha^?1) from nonfertilized soil. Daily CH₄ fluxes were also low (?10.3 to 11.9 g CH₄‐C ha^?1 day^?1), and did not differ with treatments, with an average annual net emission of 6.7 g CH₄–C ha^?1 (standard error, 20 g CH₄–C ha^?1). Greatest daily N₂O fluxes occurred when the soil was fallow, and following a series of summer rainfall events. Summer rainfall increased soil water contents and available N, and occurred when soil temperatures were >25 °C, and when there was no active plant growth to compete with soil microorganisms for mineralized N; conditions known to promote N₂O production. The proportion of N fertilizer emitted as N₂O, after correction for emissions from the no N fertilizer treatment, was 0.06%; 17 times lower than IPCC default value for the application of synthetic N fertilizers to land (1.0%). Soil greenhouse gas fluxes from bioenergy crop production in semi‐arid regions are likely to have less influence on the net global warming potential of biofuel production than in temperate climates.     

Effects of diet quality on performance and nutrient regulation in an omnivorous katydid

1. Omnivores by definition eat both plants and animals. However, little is known about how diet macronutrient content affects omnivore performance, or the extent to which they can regulate macronutrient intake. We assessed these questions using the salt marsh katydid, Conocephalus spartinae Fox (Tettigoniidae). 2. In our first experiment we used artificial diets with different protein–carbohydrate ratios to assess the effects of diet quality on survival, growth, and lipid accumulation. We found that diets with a high protein–carbohydrate ratio negatively affected Conocephalus survival. Among surviving individuals growth was not significantly different across the treatments, but lipid content decreased significantly as the protein–carbohydrate ratio of diets increased. 3. In a second experiment we explored the ability of Conocephalus to regulate their protein–carbohydrate intake. Results revealed that Conocephalus did not feed randomly when presented with two nutritionally complementary foods. A detailed analysis of their protein–carbohydrate intake revealed selection for a protein‐biased diet, but a lack of tight regulate of protein–carbohydrate intake. 4. We discuss how key macronutrients can limit omnivores, and how nutritional flexibility may enable omnivores to persist in nutritionally heterogeneous environments.     

Faecal case architecture in the gibbosus species group of Neochlamisus Karren, 1972 (Coleoptera: Chrysomelidae: Cryptocephalinae: Chlamisini)

Constructions composed of faeces are rare in insects, but occur in certain leaf-beetle clades. Members of the subfamily Cryptocephalinae share a complex behavioural and morphological synapomorphy, involving portable faecal cases that house the immature stages. A maternally initiated egg case is expanded and enlarged through four larval stadia, then sealed to provide a pupal chamber from which adults eventually emerge. We analyse and compare faecal-case architecture in ten taxa of the cryptocephaline genus Neochlamisus , and assess structural variation within a life cycle, between different 'host forms' of Neochlamisus bebbianae , and among species. These cases proved to be comprised primarily of faeces, with plant trichomes representing the only common secondary component. General architectural trends reflected variation in shape, faecal texture, and the incorporation and density of trichomes. Deviations of the Neochlamisus case from a simple geometrical gnomon reflect the changing body size of the animal, differential application of faeces, and shifts in the orientation of the carriage of the case. Neochlamisus cases are presumably energetically costly to produce, carry, and maintain, and some adaptive hypotheses of case evolution are proposed. Additionally, literature on case morphology in other camptosomates is reviewed.  © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society , 2008, 152 , 315–351.     

Predictive Model of Habitat Suitability for the Marbled Murrelet in Western Washington

Abstract: The marbled murrelet (Brachyramphus marmoratus) is a small Pacific seabird with a breeding range that extends from the Aleutian Islands to central California. Throughout most of its breeding range, it uses mature and old-growth coniferous forests as nesting habitat. Although most murrelets seem to nest within 60 km of the coast, occupied nesting habitat has been identified as far as 84 km from the ocean in Washington state. Due to the extensive inland distances within which birds are known to breed, the area requiring surveys to identify breeding sites can be enormous. Therefore, the standard 2-year survey protocol can be expensive and time-consuming for forest management agencies and companies to administer. We developed a logistic regression model to determine whether a suite of forest structural characteristics could be used to reliably predict occupancy of a forest patch by marbled murrelets. We tested the performance of the final model using cross-validation procedures and a sample of independent sites. We used 50 sites surveyed for marbled murrelets to estimate the model, and 48 independent sites were available to test model performance. All 50 sites were on private forestland owned by Rayonier located in the western lowlands of Olympic Peninsula within the Sitka spruce and western hemlock transition zones. We sampled forest habitat at each site, and we collected information on 15 explanatory variables. The best-fitting logistic regression model contained variables that measured number of canopy layers (P<0.001, approx. F test) and mistletoe (Arceuthobium sp.) abundance (P = 0.031, approx. F test). The model misclassified 2 of 33 (94% correct) unoccupied sites as occupied using a classification cut-off (c) of c=0.25. In the other direction, under cross-validation the final model misclassified 2 of 17 (88% correct) occupied sites as unoccupied. On a test of the model against an independent sample, using a classification cut-off value of c = 0.25, the final model correctly classified 36 of 48 sites (75% correct). The final model misclassified 3 of 31 occupied sites as unoccupied (90% correct). Use of predictive models could greatly reduce the amount of forest that requires surveys by screening out those sites with little probability of use and by focusing remaining effort on higher probability sites, resulting in a higher likelihood of identifying occupied sites and thereby more efficiently conserving marbled murrelet nesting habitat.     

Breeding status, contaminant burden and helminth parasites of Northern Fulmars Fulmarus glacialis from the Canadian high Arctic

We studied the relationship between contaminant concentrations in livers, endohelminth prevalence and physiological indices of chronic stress (spleen size, heterophil/lymphocyte ratios) in Northern Fulmars Fulmarus glacialis collected during the breeding season in Nunavut, Canada. No blood parasites were found, similar to reports for other petrel species elsewhere. However, 54% of Fulmars had gastrointestinal helminths, principally cestodes (52% prevalence, mean intensity of 11 worms), nematodes (34% prevalence, 3.6 worms) and acanthocephalans (3%, eight worms). Both prevalence and intensity of helminth infections were lower for Arctic Fulmars than for Fulmars and other petrels found in southern parts of the species' range. Spleen size was not significantly related to either contaminant concentration or presence of parasites, suggesting that Fulmar health was generally unaffected by contaminant and parasite levels at the colony. However, we cannot rule out the possibility that Fulmars with higher parasitaemias or contaminant loads were in poorer condition and did not attend the breeding colony.     

The taxonomy, biogeography and host plant relationships of jumping plant-lice (Hemiptera: Psyllidae) associated with creosote bushes (Larrea spp., Zygophyllaceae)

Abstract.  The Neotropical genus Panisopelma (Psyllidae: Aphalaroidinae) is revised and its internal phylogeny analysed. The constituent species, including five new ones, are described and illustrated. Keys are provided for the adults and the last instar larvae. Eight species are associated with creosote bushes ( Larrea , Zygophyllaceae): five with L. nitida and three with L. divaricata . There is evidence that another three species, the larvae of which are unknown, also develop on L. divaricata . Seven species are restricted to Argentina, one to Bolivia and three to Chile. The cladistic analysis based on male, female and larval morphological characters yielded a single most-parsimonious tree. The species associated with L. nitida form a monophyletic clade, those on L. divaricata , by contrast, are paraphyletic. One clade with three species is restricted to Argentina, but three clades each contain a species from Argentina and Chile. Although a close association exists between Panisopelma and Larrea , there is no evidence for cospeciation, but rather an initial shift from an unknown host to L. divaricata and a second shift from L. divaricata to L. nitida . In three species pairs of Panisopelma , the distribution patterns suggest geographical vicariance between Argentina and Chile.     

Is realised connectivity among populations of aquatic fauna predictable from potential connectivity?

1. Effective management of aquatic fauna requires knowledge of the ways in which populations in different catchments and sub‐catchments are connected. A powerful way to estimate this is using genetic markers, which provide information on the average amount of genetic connectivity among populations over generations. Although many studies of genetic connectivity have appeared in the literature, there are innumerable species that have not been studied. 2. This study explores whether it is possible to make broad generalisations about population connectivity, based on readily available information in the form of species life history and architecture of the aquatic habitat. 3. A number of models have been proposed to explain the pattern of connectivity shown by aquatic species with different life‐history characteristics, for example, the stream hierarchy model, Isolation by Distance, the Death Valley Model, the headwater model and panmixia. 4. In this study, we propose a dichotomous key to assign species to different models of potential connectivity. The key is based on a few very simple questions about the life history of the species and the geographical arrangement of study sites. We then assessed the performance of the key with 109 data sets of Australian fish and macroinvertebrates, using genetic data to provide an estimate of realised connectivity. 5. The realised connectivity fitted the proposed potential connectivity model in over 70% of cases, and we suggest this might be a useful initial approach for managers where empirical data are lacking.