The molecular ecology of echinostome trematodes: Elucidating the phylogenetics and transmission dynamics of a freshwater helminth parasite

This study explored the transmission dynamics of a parasite with a complex life cycle that exhibits varying degrees of host specificity at particular life stages. I focused on echinostome trematodes, which are a widely distributed, species-rich group of internal parasites that infect a wide array of hosts and are agents of disease in amphibians, birds, and mammals. The project utilized several molecular markers evolving at different rates as well as novel ecological approaches to determine the dynamics of parasite transmission. First, we utilized nuclear and mitochondrial DNA markers to clarify echinostome systematics and to understand patterns of morphology, host use and geographic distribution among several species groups. Second, we compared host colonization patterns in nature and the laboratory and suggested that although parasites are more compatible with certain host species in a laboratory, parasite-host encounter rates mask this compatibility in nature and therefore can be a significant determinant of infection. Third, we used microsatellite and mitochondrial markers to evince the colonization routes of larval parasites between the molluscan hosts (1st intermediate and second intermediate) in the parasite life cycle. We compared clonal diversity of infection for one parasite species, E. revolutum, as well as haplotype richness among echinostome species between first and second intermediate hosts. Compared to previous studies, low levels of clonal diversity were found in both types of hosts, however higher diversity was observed in second intermediate hosts. Similarly, echinostome haplotype richness was higher in second intermediate hosts as compared to first intermediate hosts. We suggest that low host vagility and low water flow contributed to lower levels of clonal diversity relative to other trematode-host systems. In addition, host recolonization and antagonistic parasite-parasite interactions may help to limit both clonal and haplotype diversity within simultaneous first and second intermediate hosts. Morphological similarity among echinostomes, especially the larval stages, demonstrates that a molecular ecology approach is essential to understanding their biology. This work will help clarify the role of echinostomes in amphibian decline, and provide disease epidemiology models with a better understanding of the role of intermediate hosts in the distribution and maintenance of parasite genetic diversity

The Role of Phylogeny and Ecology in Experimental Host Specificity: Inisights from a Eugregarine-Host System

The degree to which parasites use hosts is fundamental to host–parasite coevolution studies, yet difficult to assess and interpret in an evolutionary manner. Previous assessments of parasitism in eugregarine–host systems suggest high degrees of host specificity to particular host stages and host species; however, rarely have the evolutionary constraints on host specificity been studied experimentally. A series of experimental infections were conducted to determine the extent of host stadium specificity (larval vs. adult stage) and host specificity among 6 tenebrionid host species and 5 eugregarine parasite species. Eugregarines from all host species infected both the larva and adult stages of the host, and each parasite taxa colonized several host species (Tribolium spp. and Palorus subdepressus). Parasite infection patterns were not congruent with host phylogeny, suggesting that host phylogeny is not a significant predictor of host–parasite interactions in this system. However, the two host stages produced significantly different numbers of parasite propagules, indicating that ecological factors may be important determinants of host specificity in this host–parasite system. While field infections reflect extant natural infection patterns of parasites, experimental infections can demonstrate potential host–parasite interactions, which aids in identifying factors that may be significant in shaping future host–parasite interactions

\u3ci\u3eGregarina niphandrodes\u3c/i\u3e (Eugregarinorida: Septatorina): Oocyst Surface Architecture

The surface architecture of oocysts produced by Gregarina niphandrodes (Eugregarinorida) from Tenebrio molitor,/i\u3e adults (Coleoptera: Tenebrionidae) as revealed by scanning electron microscopy is reported. Gametocysts were allowed to dehisce on 15-mm, round cover glasses; the cover glasses with their oocysts chains were then mounted on stubs without further processing, and sputter-coated with 20-nm gold-palladium. Scanning electron microscopy was performed at 10-15 kV with a Hitachi 3000N SEM. Oocysts retained their characteristic shapes as reported in the original species description but showed longitudinal ridges of relatively uniform height, width, and spacing, in separate fields on either side of a central equatorial bulge in the oocysts. There was no ultrastructural evidence of an enclosing external sheath holding the oocysts in a chain. Oocyst ends were flared slightly, and the chain itself was twisted, with adjacent oocysts offset slightly from one another. This article now provides an additional set of structural characters potentially useful in gregarine systematics

New and Emended Descriptions of Gregarines from Flour Beetles (\u3ci\u3eTribolium\u3c/i\u3e spp. and \u3ci\u3ePalorus subdepressus\u3c/i\u3e: Coleoptera, Tenebrionidae)

The following new gregarine taxa are described from larvae of flour beetles (Coleoptera: Tenebrionidae): Awrygregarina billmani, n. gen., n. sp., from Tribolium brevicornis; Gregarina cloptoni, n. sp., from Tribolium freemani; Gregarina confusa, n. sp., from Tribolilum confusum; and Gregarina palori, n. sp., from Palorus subdepressus. In addition, the description of Gregarina minuta Ishii, 1914, from Tribolium castaneum, is emended. Scanning electron micrograph studies of these species’ oocysts reveal differences in surface architecture. The Gregarina species have oocysts with longitudinal ridges, visible with SEM, whereas Awrygregarina billmani oocysts have fine circumferential striations; surface architecture is the main feature distinguishing the two gregarine genera. Although parasites from adult beetles are not included in the descriptions, adults of all host species can be infected experimentally using oocysts from the new taxa