Effects of a rapidly increasing population of common carp on vegetative cover and waterfowl in a recently restored Midwestern shallow lake

Although the common carp (Cyprinus carpio), an invasive benthic fish from Eurasia, has long been strongly implicated in the disappearance of vegetative cover and reduced waterfowl abundance in North American shallow lakes, the details of this relationship are obscure. This study documented ecological changes in a recently restored shallow lake (Hennepin and Hopper Lakes, IL, USA) at a time that it was experiencing a large increase in its carp population. We estimated the abundance and biomass of carp 7 years after this lake had been restored and then back-calculated carp population size across time while examining changes in the lake’s plant and waterfowl communities. We found that the biomass of carp remained below ~30 kg/ha for 5 years following restoration, but then increased to ~100 kg/ha in the sixth year following a strong recruitment event. Although a carp biomass of <30 kg/ha had no discernible effects on vegetative cover (which exceeded 90%) or waterfowl (which exceeded 150,000 individuals during fall censuses), the increase to 100 kg/ha was associated with a ~50% decrease in both vegetative cover and waterfowl. A further increase in carp biomass to over 250 kg/ha during the seventh year coincided with a decrease in the vegetative cover to 17% of the lake’s surface and a decline in waterfowl use to ~10% of its original value. These data suggest that the common carp is extremely damaging to the ecological integrity of shallow lakes when its density exceeds ~100 kg/ha. Since the biomass of carp in Midwestern shallow lakes commonly exceeds this value by 3–4 times, it seems likely that carp are responsible for the large-scale habitat deterioration described in many of these ecosystems. Handling editor: J. Cambray     

Candidate gene microsatellite variation is associated with parasitism in wild bighorn sheep

The loss of genetic variation in host populations is thought to increase host susceptibility to parasites. However, few data exist to test this hypothesis in natural populations. Bighorn sheep (Ovis canadensis) populations occasionally suffer disease-induced population declines, allowing us to test for the associations between reduced genetic variation and parasitism in this species. Here, we show that individual mean heterozygosity for 15 microsatellite loci is associated with lungworm abundance (Protostrongylus spp.) in a small, recently bottlenecked population of bighorn sheep (linear regression, r2=0.339, p=0.007). This association remains significant for seven microsatellites located in genes (p=0.010), but not for eight neutral microsatellites (p=0.306). Furthermore, heterozygotes at three of four microsatellites located within disease-related genes had lower lungworm burdens. This study corroborates theoretical findings that increased parasitism and disease may be a consequence of reduced heterozygosity in wild populations, and that certain individual loci influence parasite resistance. The results illustrate the usefulness of using genomic information, strong candidate genes and non-invasive sampling for monitoring both genetic variation and fitness-related traits, such as parasite resistance, in natural populations.     

Propagation of the myxozoan parasite Myxobolus cerebralis by different geographic and genetic populations of Tubifex tubifex: An Oregon perspective

Tubifex tubifex are obligate invertebrate hosts in the life cycle of Myxobolus cerebralis, the myxozoan parasite that causes whirling disease in salmonid fishes. This exotic parasite is established to varying degrees across Oregon’s Columbia River system (Pacific Northwest, USA) and characteristics of local T. tubifex populations likely play a role in the pattern of disease occurrence. To better understand these patterns, we collected T. tubifex from three Oregon river basins (Willamette, Deschutes, and Grande Ronde), determined their genotype (mitochondrial 16S rDNA lineage and RAPD genotype) and exposed 10 different populations to M. cerebralis in the laboratory. Four mt lineages were identified: I, III, V and VI. Lineage III was found in all river basins but dominated both central and eastern sites. The RAPD assay further divided these lineages into geographic sub-populations; no RAPD genotype was common to all basins. There was a significant difference in prevalence of infection and level of parasite production among the populations we exposed to M. cerebralis that was attributed to genotypic composition. Only lineage III worms released actinospores and only populations dominated by this lineage amplified the parasite. These populations had the lowest survival, however, the lineage dominant before exposure remained dominant despite the high prevalence of infection. The distribution and infection dynamics of susceptible T. tubifex throughout Oregon may contribute to the differences in M. cerebralis occurrence; our studies further support the influence of oligochaete genotypes on the manifestation of whirling disease in salmonid populations.     

Interactions of antimicrobial peptides with Leishmania and trypanosomes and their functional role in host parasitism

Antimicrobial peptides (AMPs) are multifunctional components of the innate systems of both insect and mammalian hosts of the pathogenic trypanosomatids Leishmania and Trypanosoma species. Structurally diverse AMPs from a wide range of organisms have in vitro activity against these parasites acting mainly to disrupt surface-membranes. In some cases AMPs also localize intracellularly to affect calcium levels, mitochondrial function and induce autophagy, necrosis and apoptosis. In this review we discuss the work done in the area of AMP interactions with trypanosomatid protozoa, propose potential targets of AMP activity at the cellular level and discuss how AMPs might influence parasite growth and differentiation in their hosts to determine the outcome of natural infection.     

The genetics and evolution of obligate reproductive parasitism in Trichogramma pretiosum infected with parthenogenesis-inducing Wolbachia

Parthenogenesis-inducing (PI) Wolbachia belong to a class of intracellular symbionts that distort the offspring sex ratio of their hosts toward a female bias. In many PI Wolbachia-infected species sex ratio distortion has reached its ultimate expression-fixation of infection and all-female populations. This is only possible with thelytokous PI symbionts as they provide an alternative form of reproduction and remove the requirement for males and sexual reproduction. Many populations fixed for PI Wolbachia infection have lost the ability to reproduce sexually, even when cured of the infection. We examine one such population in the species Trichogramma pretiosum. Through a series of backcrossing experiments with an uninfected Trichogramma pretiosum population we were able to show that the genetic basis for the loss of female sexual function could be explained by a dominant nuclear effect. Male sexual function had not been completely lost, though some deterioration of male sexual function was also evident when males from the infected population (created through antibiotic curing of infected females) were mated to uninfected females. We discuss the dynamics of sex ratio selection in PI Wolbachia-infected populations and the evolution of non-fertilizing mutations.     

Intraspecific queen parasitism in a highly eusocial bee

Insect societies are well-known for their advanced cooperation, but their colonies are also vulnerable to reproductive parasitism. Here, we present a novel example of an intraspecific social parasitism in a highly eusocial bee, the stingless bee Melipona scutellaris. In particular, we provide genetic evidence which shows that, upon loss of the mother queen, many colonies are invaded by unrelated queens that fly in from unrelated hives nearby. The reasons for the occurrence of this surprising form of social parasitism may be linked to the fact that unlike honeybees, Melipona bees produce new queens in great excess of colony needs, and that this exerts much greater selection on queens to seek alternative reproductive options, such as by taking over other nests. Overall, our results are the first to demonstrate that queens in highly eusocial bees can found colonies not only via supersedure or swarming, but also by infiltrating and taking over other unrelated nests.     

Effect of Gregarina sp. parasitism on the susceptibility of Blattella germanica to some control agents

Gregarines are enteric parasites of invertebrates but little is known about the negative effects of this parasitism on host species. The present study evaluates the influence of the parasitism of Gregarina sp. on the survival of Blattella germanica and methods for elimination of gregarine infection in laboratory rearing systems. Insects were dissected and the infection was detected in 80% of a sample of 50 adults. Diseased cockroaches had swollen abdomens, slower movement at high incidences of the protozoan, and short antennas. Dead cockroaches showed darkened body and putrid smell, indicating septicaemia. Infected insects were more susceptible than healthy cockroaches when treated with Metarhizium anisopliae and triflumuron.     

Minor effects of two elicitors of insect and pathogen resistance on volatile emissions and parasitism of Spodoptera frugiperda in Mexican maize fields

Synthetic elicitors can be used to induce resistance in plants against pathogens and arthropod herbivores. Such compounds may also change the emission of herbivore-induced plant volatiles, which serve as important cues for parasitic wasps to locate their hosts. Therefore, the use of elicitors in the field may affect biological control of insect pests. To test this, we treated maize seedlings growing in a subtropical field in Mexico with methyl jasmonate (MeJA), an elicitor of defense responses against many insects, and benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), an elicitor of resistance against certain pathogens. Volatile emission, herbivore infestation, pathogen infection, and plant performance (growth and grain yield) of treated and untreated maize plants were measured. Application of BTH slightly reduced volatile emission in maize, while MeJA increased the emission compared to control treatments. Despite the apparent changes in volatile emissions, the elicitor application did not consistently affect infestation by Spodoptera frugiperda larvae, the main insect pest found on the maize seedlings, and had only marginal effects on parasitism rates. Similarly, there were no treatment effects on infestation by other herbivores and pathogens. Results for the six replications that stretched over one summer and one winter season were highly variable, with parasitism rates and the species composition of the parasitoids differing significantly between seasons. This variability, as well as the severe biotic and abiotic stresses on young seedlings might explain why we measured only slight effects of elicitor application on pest incidence and biological control in this specific field study. Indeed, an additional field experiment under milder and more standardized conditions revealed that BTH induced significant resistance against Bipolaris maydis, a major pathogen in the experimental maize fields. Similar affects can be expected for herbivory and parasitism rates.     

Interacting effects of temperature and salinity on Bonamia sp. parasitism in the Asian oyster Crassostrea ariakensis

The proposition to introduce the Asian oyster Crassostrea ariakensis to the mid-Atlantic region of the USA is being considered with caution, particularly after the discovery of a novel microcell haplosporidian parasite, Bonamia sp., in North Carolina. Although this parasite was found to be pathogenic in C. ariakensis under warm euhaline conditions, its persistence in C. ariakensis exposed to various temperature and salinity combinations remained unresolved. In this laboratory experiment, we tested the influence of temperature in combination with a wide range of salinities (10, 20 and 30 psu) on Bonamia sp. Temperature was either changed from warm (>20 °C) to cold (6 °C for 6 weeks) and back to warm or maintained constant and warm. Warm temperature was associated with higher host mortality than cold temperature, suggesting that temperature influenced Bonamia sp. pathogenicity. The effect of salinity was revealed under warm temperature with highest mortality levels observed in infected C. ariakensis exposed to 30 psu. When temperature was increased following low-temperature exposure, Bonamia sp. was not detected; however sub-optimal experimental conditions may have contributed to this result, making it difficult to draw conclusions regarding the reemergence of the parasite after low-temperature exposure. Although the overwintering of Bonamia sp. in C. ariakensis will need to be further investigated, the results presented here suggest that Bonamia sp. may be able to persist in C. ariakensis under a combination of low temperature and meso- to euhaline salinities.     

寄主大小及寄生顺序对蝇蛹佣小蜂寄生策略的影响

寄主大小模型认为寄生蜂后代性比与寄主大小相关,寄生蜂倾向于在大寄主上产出更多雌性后代,在小寄主上产出更多雄性后代.探讨了以家蝇蛹为寄主时,蝇蛹佣小蜂后代产量和性比变化;单次寄生情况下,寄主大小及寄生顺序对寄生蜂后代性比等影响.结果表明,蝇蛹佣小蜂的产卵期为(8.93±3.34)d,单头雌蜂能产雌性后代(34.11±16.34)头和雄性后代(11.04±8.87)头,且雄性百分比为0.24±0.11.随成蜂日龄的增大,寄生蜂产生雄性后代的比率显著增加.蝇蛹佣小蜂在寄生家蝇蛹时,会优先选择寄生个体较大的蛹;在单次寄生的情况下,蝇蛹佣小蜂倾向于在较大的家蝇蛹内产出更多的雌性后代.     

The maintenance of hybrids by parasitism in a freshwater snail

Hybrids have often been labelled evolutionary dead-ends due to their lower fertility and viability. However, there is growing awareness that hybridisation between different species may play a constructive role in animal evolution as a means to create variability. Thus, hybridisation and introgression may contribute to adaptive evolution, for example with regards to natural antagonists (parasites, predators, competitors) and adaptation to local environmental conditions. Here we investigated whether parasite intensity contributes to the continuous recreation of hybrids in 74 natural populations of Melanopsis, a complex of freshwater snails with three species. We also examined, under laboratory conditions, whether hybrids and their parental taxa differ in their tolerance of low and high temperatures and salinity levels. Infections were consistently less prevalent in males than in females, and lower in snails from deeper habitats. Infection prevalence in hybrids was significantly lower than in the parental taxa. Low hybrid infection rates could not be explained by sediment type, snail density or geographic distribution of the sampling sites. Interestingly, infected hybrid snails did not show signs of parasite-induced gigantism, whereas all parental taxa did. We found that hybrids mostly coped with extreme temperatures and salinity levels as well as their parental taxa did. Taken together, our results suggest that Melanopsis hybrids perform better in the presence of parasites and environmental stress. This may explain the widespread and long-term occurrence of Melanopsis hybrids as evidenced by paleontological and biogeographic data. Hybridisation may be an adaptive host strategy, reducing infection rates and resisting gigantism.     

Comparison of parasitism by Cotesia glomerata with bacterial infection and wounding in Pieris brassicae: induction of new haemolymph polypeptides and changes in humoral immune response

In Pieris brassicae, parasitism by Cotesia glomerata and bacterial infection are differentiated with respect to haemolymph protein arrays, and production or suppression of antibacterial agents. Bacteriolytic activity in haemolymph from parasitized larvae was slightly, but significantly, higher 24h post-treatment than that of untreated and wounded controls. Micrococcus lysodeikticus- or lipopolysaccharide-(LPS) injected insects exhibited an 11-fold greater response than those parasitized. At 24h post-treatment, antibacterial activity against Escherichia coli was observed in haemolymph from all but untreated larvae. Injection of Grace's medium, M. lysodeikticus or LPS, caused a greater than threefold response than parasitization or wounding. The protein banding patterns of parasitized hosts did not correspond to those of the other treatments. Two parasitoid-induced proteins (38 and 128 kDa) were examined. Both were found in parasitized insects, not in those wounded, injected with Grace's medium, M. lysodeikticus or LPS. Neither protein was bacteriolytic or bacteriostatic in inhibition zone assays.     

Neglected and emerging fungal infections: review of hyalohyphomycosis by Paecilomyces lilacinus focusing in disease burden, in vitro antifungal susceptibility and management

Paecilomyces lilacinus is an emerging pathogenic fungus that can cause different clinical manifestations ranging from cutaneous and sub-cutaneous infections to severe oculomycosis. This review discusses infections caused by P. lilacinus, as well as their symptoms and correlates of immune responses, morphological characteristics of the fungus, therapies, in vitro susceptibility tests, laboratory diagnosis and the experimental models available.     

The host range of the male-killing symbiont Arsenophonus nasoniae in filth fly parasitioids

The Son-killer bacterium, Arsenophonus nasoniae, infects Nasonia vitripennis (Hymenoptera: Pteromalidae), a parasitic wasp that attacks filth flies. This gammaproteobacterium kills a substantial amount of male embryos produced by an infected female. Aside from male death, the bacterium does not measurably affect the host, and how it is maintained in the host population is unknown. Interestingly, this bacterial symbiont can be transmitted both vertically (from mother to offspring) and horizontally (to unrelated Nasonia wasps developing in the same fly host). This latter mode may allow the bacterium to spread throughout the ecological community of filth flies and their parasitoids, and to colonize novel species, as well as permit its long-term persistence.We tested 11 species of filth flies and 25 species of their associated parasitoids (representing 28 populations from 16 countries) using diagnostic PCR to assess the bacterium’s actual host range. In addition to 16S rRNA, two loci were targeted: the housekeeping gene infB, and a sequence with high homology to a DNA polymerase gene from a lysogenic phage previously identified from other insect symbionts. We identified infections of A. nasoniae in four species of parasitoids, representing three taxonomic families. Highly similar phage sequences were also identified in three of the four species. These results identify the symbiont as a generalist, rather than a specialist restricted solely to species of Nasonia, and also that horizontal transmission may play an important role in its maintenance.     

Disparate infection patterns of Ceratomyxa shasta (Myxozoa) in rainbow trout (Oncorhynchus mykiss) and Chinook salmon (Oncorhynchus tshawytscha) correlate with internal transcribed spacer-1 sequence variation in the parasite

Ceratomyxa shasta is a virulent myxosporean parasite of salmon and trout in the Pacific Northwest of North America. The parasite is endemic in the Klamath River, Oregon/California, where a series of dams prevent movement of fish hosts between the upper and lower parts of the basin. Ceratomyxa shasta exhibits a range of infection patterns in different fish species above and below the dams. We hypothesised that the variations in infection and disease are indicators that different strains of the parasite exist, each with distinct host associations. Accordingly, we sought to identify strain-specific genetic markers in the ssrRNA and internal transcribed spacer region 1 (ITS-1). We examined 46 C. shasta isolates from water samples and two fish hosts, from June 2007 field exposures at upper and lower Klamath River sites with similarly high parasite densities. We found 100% of non-native rainbow trout became infected and died at both locations. In contrast, mortality in native Chinook salmon was <10% in the upper basin, compared with up to 40% in the lower basin. Parasite ssrRNA sequences were identical from all fish. However, ITS-1 sequences contained multiple polymorphic loci and a trinucleotide repeat (ATC)_0-3 from which we defined four genotypes: 0, I, II and III. Non-native rainbow trout at both sites were infected with genotype II and with a low level of genotype III. Chinook salmon in the upper basin had genotypes II and III, whereas in the lower basin genotype I predominated. Genotype I was not detected in water from the upper basin, a finding consistent with the lack of anadromous Chinook salmon there. Genotype O was only detected in water from the upper basin. Resolution of C. shasta into sympatric, host-specific genotypes has implications for taxonomy, monitoring and management of this significant parasite.