Effects of host dietary fructose on experimentally stunted Moniliformis (Acanthocephala)

Investigating over-dispersion; Moniliformis (Acanthocephala) and rats

An analysis of the frequency distribution of numbers of Moniliformis dubius in rats of an outbred strain of Wistar origin (CFHB) and feeding ad libitum on Oxoid 41B diet, showed that over-dispersion occurred regardless of the age and sex of the rats and the infective dose given (12, 20 or 40 cystacanths/rat). Over-dispersion was also shown to be independent of variability in the age and sex of the cystacanths given. The analysis demonstrated that the over-dispersion declined as the course of the infection proceeded. As expected, parasite survival was found to be age-dependent with female worms living longer, on average, than males, and both male and female worms living longer in rats given 12 as opposed to 20 cystacanths. Possible mechanisms for generating the over-dispersion observed during this work are discussed and a tentative hypothesis, invoking host heterogeneity with regard to carbohydrate availability in the small intestine, is proposed for further experimental investigation.

Cryptic speciation and patterns of phenotypic variation of a highly variable acanthocephalan parasite

An investigation of a parasite species that is broadly host- and habitat-specific and exhibits alternative transmission strategies was undertaken to examine intraspecific variability and if it can be attributed to cryptic speciation or environmentally induced plasticity. Specimens of an acanthocephalan parasite, Leptorhynchoides thecatus, collected throughout North America were analysed phylogenetically using sequences of the cytochrome oxidase I gene and the internal transcribed spacer region. Variation in host use, habitat use, and transmission were examined in a phylogenetic context to determine if they were more likely phylogenetically based or due to environmental influences. Results indicated that most of the variation detected can be explained by the presence of cryptic species. The majority of these species have narrow host and microhabitat specificities although one species, which also may comprise a complex of species, exhibits broad host and habitat specificity. Alternate transmission pathways only occurred in two of the cryptic species and correlate with host use patterns. Taxa that mature in piscivorous piscine hosts use a paratenic fish host to bridge the trophic gap between their amphipod intermediate host and piscivorous definitive host. One potential example of environmentally induced variation was identified in three populations of these parasites, which differ on their abilities to infect different host species.

Parasite population biology and host nutrition: dietary fructose and Moniliformis (Acanthocephala)

Experiments were carried out to investigate the possible influence of host-dietary fructose concentration on the relationship between worm burden and the fecundity of Moniliformis dubius. Worm length was found to be dependent both on the fructose concentration of the host's diet and on worm burden. The number of free ovaries/female worm was found to increase linearly with increasing dietary fructose concentration but was independent of worm burden. The length of the ovaries increased with increasing dietary fructose concentration and decreased in response to increases in worm density. The magnitude of the density-dependent reduction in the volume of ovarian tissue/female was decreased in worms from rats fed on diets containing low concentrations of fructose. The numbers of eggs present in the body cavities of the female worms was found to be positively correlated with dietary fructose concentration. At 5 weeks post-infection, mature eggs (containing fully developed acanthor larvae) were found in the body cavities of female worms from rats whose diets contained 3 and 12% fructose, but not in those from rats whose diets contained 1 and 2% fructose (w/w). The experimental results are discussed in the wider context of the influence of host nutrition on parasite population biology.

Rat-dietary fructose and the intestinal distribution and growth of Moniliformis (Acanthocephala)

The numbers, distribution in the small intestine, sexual development and growth (dry weight) of 5-week-old Moniliformis dubius (Acanthocephala) were investigated experimentally in adult, female CFHB rats fed on theoretically isoenergetic diets containing known amounts of fructose in combination with either maize-oil fatty acids or maize oil and two concentrations of casein. There was no obvious development of M. dubius when there was no fructose in the host's diet. In contrast, estimated consumption by the host of as little as about 2 g of fructose during the 5-week infection period was accompanied by marked sexual dimorphism and weight gain in most of the M. dubius present. The dry weights of M. dubius of both sexes were positively correlated with fructose concentrations ranging from 0 to 2.5% (w/w) in the diets containing fatty acids. Significant, but not substantial, increases in M. dubius dry weight were observed as the dietary fructose concentration was raised to 12% (w/w). Similar trends were observed when the fructose was offered to the infected rats with maize oil, but in general, fructose added to the fatty-acid based diets supported most M. dubius growth. Differences in the distribution pattern of the worms in rats fed on the fatty-acid or maize-oil based diets were observed and their possible significance is discussed.