Structure of the pinworm (Oxyurida: Nematoda) guild in the hindgut of the American cockroach, Periplaneta americana

Microhabitat distributions and species interactions of ectoparasites on the gills of cichlid fish in Lake Victoria, Tanzania

Heterogeneous exposure to parasites may contribute to host species differentiation. Hosts often harbour multiple parasite species which may interact and thus modify each other's effects on host fitness. Antagonistic or synergistic interactions between parasites may be detectable as niche segregation within hosts. Consequently, the within-host distribution of different parasite taxa may constitute an important axis of infection variation among host populations and species. We investigated the microhabitat distributions and species interactions of gill parasites (four genera) infecting 14 sympatric cichlid species in Lake Victoria, Tanzania. We found that the two most abundant ectoparasite genera (the monogenean Cichlidogyrus spp. and the copepod Lamproglena monodi) were non-randomly distributed across the host gills and their spatial distribution differed between host species. This may indicate microhabitat selection by the parasites and cryptic differences in the host-parasite interaction among host species. Relationships among ectoparasite genera were synergistic: the abundances of Cichlidogyrus spp. and the copepods L. monodi and Ergasilus lamellifer tended to be positively correlated. In contrast, relationships among morphospecies of Cichlidogyrus were antagonistic: the abundances of morphospecies were negatively correlated. Together with niche overlap, this suggests competition among morphospecies of Cichlidogyrus. We also assessed the reproductive activity of the copepod species (the proportion of individuals carrying egg clutches), as it may be affected by the presence of other parasites and provide another indicator of the species specificity of the host-parasite relationship. Copepod reproductive activity did not differ between host species and was not associated with the presence or abundance of other parasites, suggesting that these are generalist parasites, thriving in all cichlid species examined from Lake Victoria.

Ecological release in lizard endoparasites from the Atlantic Forest, northeast of the Neotropical Region

We compared lizard endoparasite assemblages between the Atlantic Forest and naturally isolated forest enclaves to test the ecological release hypothesis, which predicts that host specificity should be lower (large niche breadth) and parasite abundance should be greater for parasites from isolated forest enclaves (poor assemblages) than for parasites from the coastal Atlantic Forest (rich assemblages). Parasite richness per specimen showed no difference between the isolated and non-isolated areas. Parasite abundance did not differ between the isolated and non-isolated areas but showed a positive relationship with parasite richness considering all areas (isolated and non-isolated). Furthermore, host specificity was positively related to parasite richness. Considering that host specificity is inversely proportional to the host range infected by a parasite, our results indicate that in assemblages with greater parasite richness, parasites tend to infect a smaller range of hosts than do those in simple assemblages. In summary, our study partially supports the ecological release hypothesis: in assemblages with greater parasite richness, lizard parasites from Atlantic Forest are able to increase their parasite abundance (per host), possibly through facilitated infection; however, the amplitude of infected hosts only expands in poor assemblages (lower parasite richness).

Complex and Diverse Drivers of Parasite Loads in a Cosmopolitan Insect

The goal of parasite epidemiologists is to understand the factors that determine host infection levels. Potential infection determinants exist at many scales, including spatial and temporal environmental variation, among-host differences, and interactions between symbionts infecting the same host. All of these factors can impact levels of parasitism, but frequently only a subset is considered in any host-parasite system. We examined several potential determinants of pinworm infection in wild Australian cockroaches (Periplaneta australasiae) from multiple biological scales: (1) habitat; (2) season; (3) cockroach body size, developmental stage, and sex; and (4) interactions between 2 pinworm species (Leidynema appendiculata and Thelastoma sp.). Over 1 yr, we collected 239 cockroaches from 2 separate rooms in an Illinois greenhouse. We used generalized linear mixed-effects models (GLMMs) to evaluate simultaneously the influence of these factors on pinworm abundance, and nearly all had significant effects. Overall, the abundance of L. appendiculata was greater than Thelastoma sp., but the relative abundance of the 2 species was reversed in each room (i.e., a taxon × habitat effect). Abundance varied over 4 trapping seasons and increased with cockroach size. Adult cockroaches had more pinworms than nymphs, and there was also a significant taxon × stage effect: adult cockroaches had fewer pinworms than expected for their larger size, and this reduction was greater in Thelastoma sp. than in L. appendiculata. Cockroach sex had no effect on infection. Although females had more worms than males, this difference could be explained by the larger size of females. Finally, after controlling for all other potential determinants of infection, we found a strong negative association between Thelastoma sp. and L. appendiculata; cockroaches tended to be infected with either 1 pinworm species or the other. Our work underscores the importance of measuring potential determinants of infection from as many scales as possible. Such approaches are necessary to unravel the complexities of host-parasite interactions.

The systematics and evolution of pinworms (Nematoda: Oxyurida: Thelastomatoidea) from invertebrates

The nematode order Oxyurida is unique in including species for which definitive host ranges are broad and may include vertebrate or invertebrate hosts. The superfamily Thelastomatoidea is a highly diverse assemblage of oxyurids occurring in cockroaches, diplopods, hydrophilid beetles, passalid beetles, several other coleopteran larvae, mole crickets, and, with few representative species documented, other arthropod hosts. Published research and revision of the Thelastomatoidea, particularly in the 1980s and 1990s, provided several interesting hypotheses on the systematics and evolution of this group. In this review, these hypotheses are examined in the context of recent advances in taxonomy, discovery of additional species diversity and distribution, and preliminary phylogenetic hypotheses that have been proposed. There continues to remain a paucity of phylogenetic data that explore the phylogenetic relationships of the Thelastomatoidea and their relationships to vertebrate-parasitizing pinworms. A combination of mitochondrial and nuclear DNA sequences for representative species across all of the major lineages will be important for more robust phylogenetic hypotheses. Much broader geographical and host taxon sampling is necessary to determine true diversity of the Thelastomatoidea. Modern approaches to species descriptions, such as improvements in light and scanning electron microscopy and the use of molecular approaches to matching male and female nematodes, can also be applied to improve our understanding of the evolution of these fascinating parasites.

A comprehensive analysis of the biogeography of the thelastomatoid pinworms from Australian burrowing cockroaches (Blaberidae: Geoscapheinae, Panesthiinae): no evidence of coevolution

We report 21 thelastomatoid species parasitizing 31 described and 5 undescribed geoscapheine and panesthiine cockroaches, representing all but 1 of the known species of these subfamilies in Australia. The nematodes have 3 distinct patterns of host distribution: dominant, moderate and rare. The 4 dominant species, Cordonicola gibsoni, Leidynemella fusiformis, Travassosinema jaidenae and Aoruroides queenslandensis, are highly prevalent, found in nearly all host species examined, and broadly distributed. The 8 moderate species have lower prevalences but are still widely distributed. Many of these species are more common in one host subfamily than the other. The remaining 9 rare species have highly restricted host and geographical distributions. Six of the 21 species are exclusive to geoscapheines, 5 to panesthiines and 10 are shared. These patterns suggest that most of the reported thelastomatoid species are generalists rather than specialists, that host-specificity within this group is low and that co-evolutionary speciation has had little, if any, impact on structuring the thelastomatoid fauna of Australian burrowing cockroaches. In a broader context, this study provides the first comprehensive examination of the role of coevolutionary speciation and host specificity in regulating the distribution of pinworms in arthropods.

Molecular characterization of Thelastomatoidea (Nematoda: Oxyurida) from cockroaches in Australia

A molecular approach was used to genetically characterize 5 species (Aoruroides queenslandensis, Blattophila sphaerolaima, Cordonicola gibsoni, Desmicola ornata and Leidynemella fusiformis) belonging to the superfamily Thelastomatoidea (Nematoda: Oxyurida), a group of pinworms that parasitizes terrestrial arthropods. The D3 domain of the large subunit of nuclear ribosomal RNA (LSU) was sequenced for individual specimens, and the analysis of the sequence data allowed the genetic relationships of the 5 species to be studied. The sequence variation in the D3 domain within individual species (0-1.8%) was significantly less than the differences among species (4.3-12.4%). Phylogenetic analyses, using maximum parsimony, maximum likelihood, and neighbour-joining, tree-building methods, established relationships among the 5 species of Thelastomatoidea and Oxyuris equi (a species of the order Oxyurida). The molecular approach employed provides the prospect for developing DNA tools for the specific identification of the Thelastomatoidea, irrespective of developmental stage and sex, as a basis for systematic, ecological and/or population genetic investigations of members within this superfamily.

Infrapopulation sizes of co-occurring trematodes in the snail Ilyanassa obsoleta

This study addresses the infrapopulation sizes of 2 larval trematode species Himasthla quissetensis and Zoogonus rubellus as they co-occur within their estuarine snail host Ilyanassa obsoleta. Rediae of H. quissetensis and sporocysts of Z rubellus were counted in snails singly infected with each parasite and in snails infected with both. Comparisons of the counts indicate that infrapopulations of H. quissetensis were unaffected by co-occurrence with Z rubellus. However, Z. rubellus infrapopulations were reduced when co-occurring with H. quissetensis. It is proposed that this situation does not result from an interspecific interaction between parasite species. Although this double infection is relatively frequent in certain snail populations, it is contended that these trematode species do not co-occur often enough to evolve responses to one another. However, the host environment must be encountered in each life cycle, and both trematode species must be adapted to use it. On this basis, whatever happens when these 2 species occupy the same host is based on adaptations of the parasites to the host. It is proposed that these parasites are adapted to self-limit their infrapopulations in the snail host. They can, thus, preserve and use the host for many years and thereby enhance total cercarial transmission (fitness). Infrapopulation sizes would be determined by host resource levels, which, among other factors, would be influenced by the presence of multiple parasite species. In single infections, by far the most common situation, host resource levels would be set by the nutritional status or age (size) of the host (or both). The reduced infrapopulation sizes of Z rubellus on co-occurrence suggest that this trematode is more sensitive to host resource levels than is H. quissetensis.

Significance of methanogenic symbionts for development of the American cockroach, Periplaneta americana

The effects of suppression of methanogenesis with a drug, 2-bromoethanesulfonic acid (BES), on the hindgut ecosystem and development of the cockroach Periplaneta americana fed either low or high fiber diet were evaluated by measuring methane production, volatile fatty acids (VFA) concentrations in the hindgut, cockroach weight gain and development time (the length of nymphal period). Methane production and VFA concentrations in the hindgut of cockroaches fed high fiber diet were significantly higher than those fed low fiber diet. Although BES treatment greatly reduced methane production, VFA concentrations in the hindgut, cockroach weight gain and development time were not significantly altered. These results indicate that methanogenic microbes are not essential for keeping low hydrogen pressure in the hindgut lumen, and normal cockroach development.

Evolutionary patterns in life histories of Oxyurida

The Oxyurida comprises some 850 known species that occur in the intestine of arthropods and vertebrates (one species in annelids). Important arthropod hosts include Diplopoda, Blattodea, Gryllotalpoidea, Passalidae, Scarabaeida and Hydrophilidae. The major vertebrate hosts are lizards, tortoises, primates, rodents and lagomorphs. An underlying characteristic of the group is haplodiploid reproduction and like many haplodiploid groups, pinworms tend to have life histories that involve high levels of inbreeding. Unlike Strongylida, Ascaridida and Spirurida, which have diversified in tissue site and life cycle as well as hosts, pinworms show little variation in these features and have radiated only across host groups. Two explanations are advanced for this. Haplodiploidy and its concomitant inbreeding may act to canalise evolutionary change, although diverse groups such as the Hymenoptera belie this. Alternatively, Strongylida, Ascaridida and Spirurida are presumed to have arisen from skin-penetrating ancestors that were forced to undergo a tissue migration before reaching their primitive tissue site, the gut. This migration demanded they adapt to a variety of tissue sites and thus acted as a preadaptation to further diversification. The Oxyurida, in contrast, probably arose using oral contaminative transmission. The lack of exposure to other tissue sites may therefore have relegated pinworms to their position in the posterior gut.