On the environment of Polymorphus minutus (Acanthocephala) in ducks

The activation of cystacanths of Polymorphus minutus (Acanthocephala) in vitro

The factors responsible for stimulating activation of cystacanths of Polymorphus minutus in vitro have been investigated. Under the conditions used, the optimum temperature for activation was found to be 42–44 °C, at a pH of 7·0. A marked enhancement of activation rate was observed after preincubation in a 1 mM solution of sodium taurocholate and in solutions of sodium cholate, sodium glycocholate or sodium deoxycholate. This apparent effect of bile salts has been compared with that of other detergents, and a significant enhancement of activation rate above control was observed with saponin and sodium fusidate. Trypsin did not affect the rate of activation, and some inhibition occurred with lipase. The osmotic pressure of the surrounding medium has an effect on activation, the rate of which varies inversely with osmolarity. The conditions for activation in vitro are compared with those of the physicochemical environment in vivo.

Recruitment, population structure, and habitat selection of Corynosoma australe (Acanthocephala) in South American fur seals, Arctocephalus australis, from Uruguay

We analysed recruitment, population structure, and intestinal distribution of Corynosoma australe Johnston, 1937 in 27 South American fur seals, Arctocephalus australis (Zimmerman, 1783), collected in two Uruguayan localities during 1990 and 1991. Only heavy infections of C. australe were found in all intestines. High transmission rates might result from the massive concentration of fur seals in the study area and the ecological ubiquity of C. australe. Intestinal length (IL) accounted, through a cubic relationship, for most of the variation (74%) in parasite intensity. IL3 also predicted the percentage of juvenile females among hosts (an indicator of recruitment rate) better than intensity or host body size. Intestinal size might be a suitable surrogate of host metabolic rate, the potential factor influencing intensity. The percentages of females and gravid females significantly increased along the intestine, and the distribution of juvenile females, gravid females, and males significantly covaried after controlling for intensity effects. These patterns suggest that worms migrate towards the lower jejunum and ileum while they mature, copulate, and reproduce. Males and gravid females shifted their distribution anteriad, and gravid females expanded their distribution, with intensity. These patterns might result from recruitment dynamics, intraspecific competition, or both. We do not know why males, gravid females, and juvenile females respond differently to these factors.

Experimental investigation of physiological factors that may influence microhabitat specificity exhibited by Leptorhynchoides thecatus (Acanthocephala) in green sunfish (Lepomis cyanellus)

Representatives of Leptorhynchoides thecatus (Acanthocephala) inhabit ceca of green sunfish but cannot survive in the anterior intestine. The influence of elevated cecal protein concentrations, pH, and amounts of lumenal materials on the microhabitat specificity of L. thecatus was investigated. An attempt was made to alter the distribution of worms in starved fish, in fish of which cecal pH was reduced, and in fish of which intestinal protein concentration was elevated. Protein concentration and pH showed no effect on worm distribution. Starving hosts had no effect on worm number or distribution but resulted in retardation of worm growth and development, providing a mechanism by which worms may overwinter and by which peak egg production may coincide with abundance of the amphipod intermediate host. None of the factors investigated is solely responsible for the microhabitat specificity of L. thecatus. It is suggested that helminth site specificity is characterized by long histories of adaptation to specific habitats with many physiological adaptations being facilitated synergistically. Maximization of sexual congress may exert an important selective pressure favoring this establishment of microhabitat specificity.

Observations on the establishment of Polymorphus minutus (Acanthocephala) in the intestines of domestic ducks

No external signs of activation of cystacanths in the alimentary tract were observed until 25 min after oral ingestion. Peak percentage evagination was observed after 60 min. Activation and establishment of cystacanths were never found in the ventriculus or anterior to it, but several crushed specimens were found in the ventriculus, which is a mechanical hazard to the parasite. Infections established by cannulation at the yolk-stalk are greater than infections produced by ingested parasites; thus the ventricular environment does not need to be experienced by the freed cystacanth for activation to take place.

Studies on the distribution and site location of Nippostrongylus brasiliensis within the small intestine of laboratory rats

The distribution ofN. brasiliensiswithin the small intestine of rats, following a primary infection, is described.

The fourth stage larvae were found to inhabit the sections later parasitized by the adult population.

Both the larval and adult worms were found to be confined to the anterior half of the small intestine. This aggregation is believed to be under the influence of stimuli (factor(s) 1), present in the lumen of the host gut.

The adult worms also clumped within the already confined worm population. This behaviour is thought to be due to intrinsic behaviour patterns of the worm, sexual attraction and thigmokinesis.

Larval and adult worms were surgically transferred to points, at varying distance from the ‘normally’ inhabited region, in the small intestine of fresh recipient rats. The resulting migratory behaviour of the worms was studied.

The worm populations resulting from both the larval and the adult transfers showed the ability to recognize that they were in the wrong position of the small intestine and to be able to orientate, migrate and locate the ‘normal’ site.