A checklist of parasites recorded on sticklebacks (Actinopterygii: Gasterosteidae) from Poland

Hybridization between two cestode species and its consequences for intermediate host range

Background

Many parasites show an extraordinary degree of host specificity, even though a narrow range of host species reduces the likelihood of successful transmission. In this study, we evaluate the genetic basis of host specificity and transmission success of experimental F₁ hybrids from two closely related tapeworm species (Schistocephalus solidus and S. pungitii), both highly specific to their respective vertebrate second intermediate hosts (three- and nine-spined sticklebacks, respectively).

Methods

We used an in vitro breeding system to hybridize Schistocephalus solidus and S. pungitii; hybridization rate was quantified using microsatellite markers. We measured several fitness relevant traits in pure lines of the parental parasite species as well as in their hybrids: hatching rates, infection rates in the copepod first host, and infection rates and growth in the two species of stickleback second hosts.

Results

We show that the parasites can hybridize in the in vitro system, although the proportion of self-fertilized offspring was higher in the heterospecific breeding pairs than in the control pure parental species. Hybrids have a lower hatching rate, but do not show any disadvantages in infection of copepods. In fish, hybrids were able to infect both stickleback species with equal frequency, whereas the pure lines were only able to infect their normal host species.

Conclusions

Although not yet documented in nature, our study shows that hybridization in Schistocephalus spp. is in principle possible and that, in respect to their expanded host range, the hybrids are fitter. Further studies are needed to find the reason for the maintenance of the species boundaries in wild populations.

Tissue responses of Clarias gariepinus (Catfish) to experimental Eimeria subepithelialis infection

Coccidial infection is a common feature in most African fishes. As a result of the chronic nature of the disease in fish, mortality is gradual (Kim and Paperna, 1993a) and is often overlooked in most farms, with losses becoming evident only at the end of the production cycle. This study evaluates the tissue responses of Clarias gariepinus (Catfish) in an experimental infection with Eimeria subepithelialis using 200 laboratory-bred Juveniles. Four groups (A, B, C and D) of 50 Juveniles each were preconditioned for 2 weeks. Groups A and B were infected per os with 200 E. subepithelialis sporocysts per juvenile, while groups C and D served as uninfected controls. At the onset of demonstrable oocysts in liver and spleen tissues, groups B and C were treated for a week in Amprolium(R) dip (0.6 mg/L) at the rate of 1 h a day. Five fish from each group were culled at intervals of 3 days to study the tissue responses to infection. At gross pathological level, intestinal and testicular congestion, splenomegaly and hepatomegaly were the common features of the infection. Histological lesions in the infected and treated group (group B) were confined to the small intestine while extra-intestinal lesions were seen in the infected and untreated fish (group A). The presence of pathological lesions in tissues, following experimental infection of C. gariepinus with E. subepithelialis sporocysts, indicated that the parasite is pathogenic to the catfish. Contrary to coccidiosis of terrestrial animals, sporulation of oocysts in piscine coccidiosis appeared to occur endogenously within the host. The use of Amprolium in the control of piscine coccidiosis is effective only when used early in the course of the infection, prior to onset of clinical signs. Proper certification of brooder and replacement stock, improved plane of nutrition and adequate stocking density are recommended aquacultural practices that may minimize the incidence of visceral coccidiosis in cultured fish.

The unique Morgue ubiquitination protein is conserved in a diverse but restricted set of invertebrates

Drosophila Morgue is a unique ubiquitination protein that facilitates programmed cell death and associates with DIAP1, a critical cell death inhibitor with E3 ubiquitin ligase activity. Morgue possesses a unique combination of functional domains typically associated with distinct types of ubiquitination enzymes. This includes an F box characteristic of the substrate-binding subunit in Skp, Cullin, and F box (SCF)-type ubiquitin E3 ligase complexes and a variant ubiquitin E2 conjugase domain where the active site cysteine is replaced by a glycine. Morgue also contains a single C4-type zinc finger motif. This architecture suggests potentially novel ubiquitination activities for Morgue. In this study, we address the evolutionary origins of this distinctive protein utilizing a combination of bioinformatics and molecular biology approaches. We find that Morgue exhibits widespread but restricted phylogenetic distribution among metazoans. Morgue proteins were identified in a wide range of Protostome phyla, including Arthropoda, Annelida, Mollusca, Nematoda, and Platyhelminthes. However, with one potential exception, Morgue was not detected in Deuterostomes, including Chordates, Hemichordates, or Echinoderms. Morgue was also not found in Ctenophora, Cnidaria, Placozoa, or Porifera. Characterization of Morgue sequences within specific animal lineages suggests that gene deletion or acquisition has occurred during divergence of nematodes and that at least one arachnid expresses an atypical form of Morgue consisting only of the variant E2 conjugase domain. Analysis of the organization of several morgue genes suggests that exon-shuffling events have contributed to the evolution of the Morgue protein. These results suggest that Morgue mediates conserved and distinctive ubiquitination functions in specific cell death pathways.