Within-host dynamics of Trichinella spiralis predict persistent parasite transmission in rat populations

Trichinella spiralis is transmitted and maintained in both a domestic and sylvatic cycle, whereby rats contribute to the spread of T. spiralis from domestic to sylvatic animals and vice versa. As a model for T. spiralis transmission in wildlife, we studied the potential of rats to act as a reservoir species for T. spiralis, by assessing experimentally its within-host infection dynamics, and simulating the between-host dynamics by a Monte Carlo approach. The distribution of parasite burden in individual rats is mathematically defined by roots of the dose response equation intersecting with the diagonal. In simulated between-host dynamics, up to 10⁴ events of uninterrupted parasite transmission were observed. Histograms of parasite burdens per individual rat matched closely with the mixture of two gamma distributions, which were derived from the within-host infection dynamics. In conclusion, T. spiralis transmission persists in a population of rats when they cannibalize their own species. Rats should be included in the minimal set of wildlife species that maintain the life cycle of T. spiralis.     

Sarcoptes scabiei: Specific immune response to sarcoptic mange in the Iberian ibex Capra pyrenaica depends on previous exposure and sex

Host acquired immunity is a critical factor that conditions the survival of parasites. Nevertheless, there is a shortage of data concerning inter-individual immunological inequalities in wild mammals. Sarcoptic mange is a widespread parasitosis that severely affects mammals such as the Iberian ibex (Capra pyrenaica). Despite some work on the subject, the immune response to sarcoptic mange infestation is still a complex and poorly understood phenomenon. To improve knowledge of the host-Sarcoptes immunological interaction, 18 Iberian ibexes were experimentally infested. IgG levels were assessed using ELISA to test for potential factors determining the specific immune response to infestation. Previous exposure and sex appeared to affect the IgG response to infestation and our results suggest a sex-biased immunomodulation. We discuss the immunological pattern of host-Sarcoptes interactions and also suggest further lines of work that may improve the understanding of immunological interactions of host-Sarcoptes systems.     

The role of host sex in parasite dynamics: field experiments on the yellow-necked mouse Apodemus flavicollis

We investigated the role of host sex in parasite transmission and questioned: ‘Is host sex important in influencing the dynamics of infection in free living animal populations?’ We experimentally reduced the helminth community of either males or females in a yellow‐necked mice (Apodemus flavicollis) population using an anthelmintic, in replicated trapping areas, and subsequently monitored the prevalence and intensity of macroparasites in the untreated sex. We focussed on the dominant parasite Heligmosomoides polygyrus and found that reducing parasites in males caused a consistent reduction of parasitic intensity in females, estimated through faecal egg counts, but the removal of parasites in females had no significant influence on the parasites in males. This finding suggests that males are responsible for driving the parasite infection in the host population and females may play a relatively trivial role. The possible mechanisms promoting such patterns are discussed.     

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.     

A review of global diversity in avian haemosporidians (Plasmodium and Haemoproteus: Haemosporida): new insights from molecular data

Biogeographic patterns of parasite diversity are useful for determining how host–parasite interactions can influence speciation. However, variation in methodologies and sampling effort can skew diversity estimates. Avian haemosporidians are vector-transmitted blood parasites represented by over 1300 unique genetic lineages spread across over 40 countries. We used a global database of lineage distributions for two avian haemosporidian genera, Plasmodium and Haemoproteus, to test for congruence of diversity among haemosporidians and their avian hosts across 13 geographic regions. We demonstrated that avian haemosporidians exhibit similar diversity patterns to their avian hosts; however, specific patterns differ between genera. Haemoproteus spp. diversity estimates were significantly higher than those of Plasmodium spp. in all areas where the genera co-occurred, apart from the Plasmodium spp.-rich region of South America. The geographic distributions of parasite genera also differed, with Haemoproteus spp. absent from the majority of oceanic regions while Plasmodium spp. were cosmopolitan. These findings suggest fundamental differences in the way avian haemosporidians diverge and colonise new communities. Nevertheless, a review of the literature suggests that accurate estimates of avian haemosporidian diversity patterns are limited by (i) a concentration of sampling towards passerines from Europe and North America, (ii) a frequent failure to include microscopic techniques together with molecular screening and (iii) a paucity of studies investigating distributions across vector hosts.     

Effect of the snail Ilyanassa obsoleta (Say) on dynamics of the amphipod Corophium volutator (Pallas) on an intertidal mudflat

We investigated interactions between two dominant invertebrate species of intertidal soft-sediment environments of the northwest Atlantic, the mud snail Ilyanassa obsoleta and the burrowing amphipod Corophium volutator, on a mudflat of the upper Bay of Fundy, Canada. Distribution of I. obsoleta on the mudflat was highly patchy and negatively correlated with density of C. volutator. Manipulation of snail density in cages showed that I. obsoleta influences C. volutator; specifically, increasing density of snails reduced density, increased patchiness in distribution, decreased recapture rates and decreased immigration of C. volutator. Ilyanassa obsoleta seems to be affecting C. volutator through an influence on survival rate and emigration rate, although temporal variation in these effects was observed. Given that both I. obsoleta and C. volutator show a preference for tide pools, an important microhabitat on mudflats, snails might have a profound impact on C. volutator population dynamics.     

Migration, site selection, and development of Ornithodiplostomum sp. metacercariae (Digenea: Strigeoidea) in fathead minnows (Pimephales promelas)

The metacercarial stage of trematodes is typically considered an encysted, developmentally quiescent, resting stage. Yet the metacercariae of some species of strigeoid trematode undergo extravagant development within specific tissues of their second intermediate host. Our understanding of patterns of migration, site selection and development of these types of metacercariae is known for only a few species. In this study, we characterize the invasion and development of Ornithodiplostomum sp. metacercariae in their second intermediate host, the fathead minnow, Pimephales promelas. Diplostomules completed their migration into the abdominal cavity between 15 min and 48 h p.i. Most diplostomules migrated along muscular and connective tissue then penetrated the peritoneal lining of the abdominal cavity en route to the liver or pancreas. Alternatively, some diplostomules migrated within the host’s circulatory system, including the heart and arteries of the hepatic portal system. Metacercarial development in the liver and pancreas involved distinct growth, encystment and consolidation phases. Metacercarial volume increased 15-fold between 48 h and 4 weeks p.i., presumably due to absorptive and/or ingestive feeding activities within host tissues. By 2 weeks p.i., metacercariae were enveloped within a cyst wall and they were found loosely attached to the surfaces of internal tissues or unattached within the body cavity. These results emphasize the complex nature of metacercarial migration and growth and demonstrate that their growth and encystment phases occur within different habitats within their intermediate hosts.     

New evidence for the involvement of Paracartia grani (Copepoda,Calanoida) in the life cycle of Marteilia refringens (Paramyxea)

The dynamics of the protozoan parasite Marteilia refringens was studied in Thau lagoon, an important French shellfish site, for 1 year in three potential hosts: the Mediterranean mussel Mytilus galloprovincialis (Mytiliidae), the grooved carpet shell Ruditapes decussatus (Veneriidae) and the copepod Paracartia grani (Acartiidae). Parasite DNA was detected by PCR in R. decussatus. In situ hybridisation showed necrotic cells of M. refringens in the digestive epithelia of some R. decussatus suggesting the non-involvement of this species in the parasite life cycle. In contrast, the detection of M. refringens in mussels using PCR appeared bimodal with two peaks in spring and autumn. Histological observations of PCR-positive mussels revealed the presence of different parasite stages including mature sporangia in spring and autumn. These results suggest that the parasite has two cycles per year in the Thau lagoon and that mussels release parasites into the water column during these two periods. Moreover, PCR detection of the parasite in the copepodid stages of P. grani between June and November supports the hypothesis of the transmission of the parasite from mussels to copepods and conversely. In situ hybridisation performed on copepodites showed labeling in some sections. Unusual M. refringens cells were observed in the digestive tract and the gonad from the third copepodid stage, suggesting that the parasite could infect a copepod by ingestion and be released through the gonad. This hypothesis is supported by the PCR detection of parasite DNA in copepod eggs from PCR-positive females, which suggests that eggs could contribute to the parasite spreading in the water and could allow overwintering of M. refringens. Finally, in order to understand the interactions between mussels and copepods, mussel retention efficiency (number of copepods retained by a mussel) was measured for all P. grani developmental stages. Results showed that all copepod stages could contribute to the transmission of the parasite, especially eggs and nauplii which were retained by up to 90%.     

Ontogenetic changes and sexual dimorphism in the mandible of adult woolly mammoths (Mammuthus primigenius)

Morphometric studies are a fundamental tool in paleontology to answer taxonomic, functional and evolutionary questions. In particular, appropriate functional interpretation often requires consideration of ontogenetic changes in the structures studied. The woolly mammoth (Mammuthus primigenius) is one of the most representative large mammal species of the Eurasian Pleistocene. Available ontogenetic studies on woolly mammoth mandible have focused on the first ontogenetic stages of the mandible development up to 4-5 years and have suggested that the symphysial process is sexually dimorphic. In the present work, we studied ontogenetic changes and sexual dimorphism in 45 mandibles from subadult and adult stages (8-56 African Elephant Years). Our results show positive correlations among almost all the morphometric variables measured, as well as an increase of mandible size with age. This increase does not differ among the variables examined, although the highest values are related with the symphysis height and the opening of the horizontal branches, and the lower ones with the greatest length (dimension), which implies the increase in the relative mandible width and height throughout the individual life. Sexual dimorphism in the mandible is at best slight, and the symphysial process is not diagnostic for sexing purposes. In addition, differences in age were an important confounding factor to assess sexual dimorphism and should be considered in future uses of sexual dimorphism assessment techniques.     

Intercontinental effect on sexual shape dimorphism and allometric relationships in the beetle pest Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae)

Hind wing shape variation was examined in 686 adult Diabrotica virgifera virgifera collected from maize plants in Europe and the USA Corn Belt, using geometric morphometric techniques. Sexual dimorphism at an Intercontinental scale was assessed using canonical variates analysis, a multivariate statistical method used to find the shape characters that best distinguish among groups of specimens. Our results showed that each of the populations of D. v. virgifera investigated in this study showed high levels of sex based hind wing shape dimorphism. In particular a stronger and more obvious pattern of hind wing shape variation was found in the USA than in Europe. These results support previous studies on D. v. virgifera wing shape that show that female D. v. virgifera have more elongated wings than males. These differences raise the question of whether sexual dimorphism may be modulated by natural selection.     

Lifelong dynamics of human CD4CD25 regulatory T cells: Insights from in vivo data and mathematical modeling

Despite their limited proliferation capacity, regulatory T cells (T_regs) constitute a population maintained over the entire lifetime of a human organism. The means by which T_regs sustain a stable pool in vivo are controversial. Using a mathematical model, we address this issue by evaluating several biological scenarios of the origins and the proliferation capacity of two subsets of T_regs: precursor CD4⁺CD25⁺CD45RO⁻ and mature CD4⁺CD25⁺CD45RO⁺ cells. The lifelong dynamics of T_regs are described by a set of ordinary differential equations, driven by a stochastic process representing the major immune reactions involving these cells. The model dynamics are validated using data from human donors of different ages. Analysis of the data led to the identification of two properties of the dynamics: (1) the equilibrium in the CD4⁺CD25⁺FoxP3⁺T_regs population is maintained over both precursor and mature T_regs pools together, and (2) the ratio between precursor and mature T_regs is inverted in the early years of adulthood. Then, using the model, we identified three biologically relevant scenarios that have the above properties: (1) the unique source of mature T_regs is the antigen-driven differentiation of precursors that acquire the mature profile in the periphery and the proliferation of T_regs is essential for the development and the maintenance of the pool; there exist other sources of mature T_regs, such as (2) a homeostatic density-dependent regulation or (3) thymus- or effector-derived T_regs, and in both cases, antigen-induced proliferation is not necessary for the development of a stable pool of T_regs. This is the first time that a mathematical model built to describe the in vivo dynamics of regulatory T cells is validated using human data. The application of this model provides an invaluable tool in estimating the amount of regulatory T cells as a function of time in the blood of patients that received a solid organ transplant or are suffering from an autoimmune disease.     

Enhancing male sexual success in a lekking fly (Anastrepha suspensa Diptera: Tephritidae) through a juvenile hormone analog has no effect on adult mortality

While defending lek-territories, male Anastrepha suspensa (Loew) produce chemical, acoustic and visual courtship signals. In the laboratory and under semi-natural conditions, topical application of the juvenile hormone analog methoprene doubles pheromone production and subsequently doubles sexual success. However, sexual signals and interactions are likely to be physiologically expensive and so result in higher male mortality. Comparison of males kept in isolation for 35 days, but provided daily with a potential mate or a rival male, revealed that both male- and female-interactors shortened focal-male lifespan. In addition, focal males were either treated with methoprene or not, then either provided with protein in their sucrose-based diet or not. Protein proved to similarly double sexual success and also resulted in longer male life spans in all of the interactor-categories. However, there was no evidence that methoprene induced hypersexuality resulted in higher rates of mortality, i.e., the longevity of males treated with methoprene did not significantly differ from untreated males in the same interactor/diet categories. This apparent lack of costs to a putatively sexually selected signal is unexpected but presents an opportunity to increase the sexual competence of sterile flies with few consequences to their survival following mass-release.     

Leishmania (Viannia) panamensis: An in vitro assay using the expression of GFP for screening of antileishmanial drug

Promastigotes of Leishmania (Viannia) panamensis were successfully transfected with p6.5-egfp to express green fluorescent protein. The transfectants remained infective to macrophages, providing an in vitro model for screening antileishmanial drugs. This was demonstrated by flow cytometry of macrophage-associated GFP after exposure of infected cultures to known antileishmanial drugs, i.e. amphotericin B and glucantime^®. Fluorescence of GFP diminished progressively from infected cells with increasing drug concentrations used in both cases. The availability of this fluorescent assay for infection of macrophages by L. (V.) panamensis facilitates drug discovery program for the Viannia species, which differ significantly from those of the Leishmania subgenus.     

Causes of secondary sexual differences in plants — Evidence from extreme leaf dimorphism in Leucadendron (Proteaceae)

In extreme cases leaves in male plants of the dioecious genus Leucadendron (Proteaceae) are up to an order of magnitude smaller than female leaves. This secondary sexual dimorphism (SSD) in leaf size has previously been suggested to be due to intra-male sexual selection, leading to an increase in male allocation to reproduction in dimorphic species. After critically evaluating previous data provided to support this hypothesis, I suggest on both theoretical grounds and on re-analysis that this argument is unlikely and unsupported. Leaf size dimorphism could theoretically evolve directly due to disruptive ecological selection between genders, leading to niche dimorphism either within or between habitats. I test this ecological causation hypothesis by providing data on specific leaf area (sla) and water use efficiency (δ ¹³C) of leaves from males and females of several Leucadendron species. Results confirm the expectation of minimal gender differences. I argue that leaf dimorphism is a consequence of selection on flower size and architecture.     

Microdajus tchesunovi sp. n. (Tantulocarida, Microdajidae) - A new crustacean parasite of from the White Sea

A new species of Tantulocarida, Microdajus tchesunovi sp. n., was found on tanaid host, Typhlotanais sp. of the family Nototanaidae, collected from silty sediment in the Kandalaksha Bay in the White Sea. Several tantulus larvae, developing males at different stages of metamorphosis, and early stages of parthenogenetic females were found attached to different sites of their hosts. Ultrastructure of the new species was studied with SEM. Microdajus tchesunovi sp. n. can be easily distinguished from other species of the genus Microdajus Greve by the presence of a pair of longitudinal dorsal lamellae at the anterior end of the cephalon. It is also characterized by the presence of an endopod seta on the sixth thoracopod and the absence of thoracopodal endites. A morphological comparison of species of the family Microdajidae is presented in tabular form.     

Spatial and temporal factors affecting parasite genotypes encountered by hosts: Empirical data from American dog ticks (Dermacentor variabilis) parasitising raccoons (Procyon lotor)

The American dog tick (Dermacentor variabilis) is an important vector of numerous pathogens of humans and animals. In this study, we analysed population genetic patterns in D. variabilis at scales of the host individual (infrapopulation) and population (component population) to elucidate fine-scale spatial and temporal factors influencing transmission dynamics. We genotyped D. variabilis collected from raccoons (Procyon lotor) trapped in two habitat patches (located in Indiana, USA) which were spatially proximate (5.9 km) and limited in size (10.48 Ha and 25.47 Ha, respectively). Despite the fine spatial sampling scale, our analyses revealed significant genetic differentiation amongst component populations and infrapopulations (within each component population), indicating a non-random pattern of encountering tick genotypes by raccoons at both scales evaluated. We found evidence for male-biased dispersal in the ticks themselves (in one component population) and an age-bias in spatial scales at which raccoons encountered ticks in the environment. At the scale of the component population, our analyses revealed that raccoons encountered ticks from a limited number of D. variabilis family groups, likely due to high reproductive variance amongst individual ticks. Finally, we found evidence for a temporal effect with raccoons encountering ticks in the environment as “clumps” of related individuals. While the genetic structure of parasite populations are increasingly being investigated at small spatial scales (e.g. the infrapopulation), our data reveal that genetic structuring can originate at scales below that of the infrapopulation, due to the interaction between temporal and biological factors affecting the encounter of parasites by individual hosts. Ultimately, our data indicate that genetic structure in parasites must be viewed as a consequence of both spatial and temporal variance in host-parasite interactions, which in turn are driven by demographic factors related to both the host and parasite.     

Serum testosterone,progesterone, and estradiol concentrations and sexual maturation in spotted seals (Phoca largha)

Spotted seals (Phoca largha) are ice-breeding phocid found in eight different breeding colonies all over the world. They exhibit a seasonal breeding pattern, with annual and synchronous cycles; however, little is known about their reproductive endocrinology. In this study, we measured serum testosterone, progesterone, and 17β-estradiol concentrations in captive spotted seals (simple number: female n = 68; male n = 89) throughout a full reproductive cycle. Males that were older than 4 years had significant testosterone fluctuations and were, therefore, classified as sexually mature. These animals show significant seasonal changes in testosterone levels, with average peak concentrations of 10.81 ± 9.57 nmol/L (±SD) from November to February, compared with mean concentrations of 1.42 ± 3.09 nmol/L throughout the remainder of the year. Females that reported a significant variation in progesterone concentrations and were older than 4 years were considered to be sexually mature. In these females, progesterone levels increased in February, remained elevated for 7 months with a mean value of 37.39 ± 17.03 nmol/L, and then dropped to 0.74 ± 0.54 nmol/L. Serum 17β-estradiol levels were also found to be significantly increased in January, remained so for 8 months (15.80 ± 14.15 ng/L), and then declined after August (7.77 ± 6.78 ng/L). In seals, mating typically occurs in February and March, 1 month after the observed peaks in testosterone and estradiol concentrations and corresponding to the increase in progesterone. A moderate positive correlation between testosterone and progesterone concentrations in sexually mature males was also observed (Spearman rho, r = 0.63, P < 0.01). In sexually immature females, progesterone and estradiol concentrations were found to be significantly lower than those in mature females. Finally, the observed patterns of estradiol and progesterone in sexually mature females suggest that embryonic diapause or successful implantation occurs in August.     

Septal pore complex morphology in the Agaricomycotina (Basidiomycota) with emphasis on the Cantharellales and Hymenochaetales

The ultrastructure of septa and septum-associated septal pore caps are important taxonomic markers in the Agaricomycotina (Basidiomycota, Fungi). The septal pore caps covering the typical basidiomycetous dolipore septum are divided into three main phenotypically recognized morphotypes: vesicular-tubular (including the vesicular, sacculate, tubular, ampulliform, and globular morphotypes), imperforate, and perforate. Until recently, the septal pore cap-type reflected the higher-order relationships within the Agaricomycotina. However, the new classification of Fungi resulted in many changes including revision of existing and addition of new orders. Therefore, the septal pore cap ultrastructure of more than 325 species as reported in literature was related to this new classification. In addition, the septal pore cap ultrastructures of Rickenella fibula and Cantharellus formosus were examined by transmission electron microscopy. Both fungi have dolipore septa associated with perforate septal pore caps. These results combined with data from the literature show that the septal pore cap-type within orders of the Agaricomycotina is generally monomorphic, except for the Cantharellales and Hymenochaetales.It appears from the fungal phylogeny combined with the septal pore cap ultrastructure that the vesicular-tubular and the imperforate type both may have arisen from endoplasmic reticulum. Thereafter, the imperforate type eventually gave rise to the perforate septal pore cap-type.