Equations for describing growth of the schistosome host snail Biomphalaria glabrata.

Biomphalaria glabrata and Stagnicola palustris were raised in aquaria under crowded and uncrowded conditions. Measurements of greatest shell diameter were taken at regular intervals. Von Bertalanffy and logistic growth curves were fitted by least squares and maximum likelihood methods. The resulting parameter estimates produced better fits for the logistic equation than for the von Bertalanffy equation.

Altered feeding response as a cause for the altered heartbeat rate and locomotor activity of Schistosoma mansoni-infected biomphalaria glabrata.

Biomphalaria glabrata infected with Schistosoma mansoni for 33 days fed more often than uninfected snails. Whereas uninfected snails had nocturnal increases in feeding, snails with a 33-day-old infection of S. mansoni fed as often during the day as in the night. Using direct observation and film analysis, we found that feeding increased the heartbeat rate and locomotor activity of B. glabrata. When snails were allowed to feed ad lib., infected snails had higher heartbeat rates than uninfected snails both during the day (P less than 0.01) and the night (P less than 0.001). However, when the snails were deprived of food for 24 hr, infected snails had slightly higher heartbeat rates than uninfected snails only during the day (P less than 0.05). There was no difference between the heartbeat rates of feeding, infected snails and the heartbeat rates of uninfected snails that were starved for 8 hr, and then allowed to feed. Uninfected snails had nocturnal increases in heartbeat rate regardless of feeding schedule, but infected snails had greater nighttime heartbeat rate than daytime heartbeat rate only when they were not allowed to feed. Infected snails had less nocturnal locomotor activity than uninfected snails when feeding, but there was no difference between the locomotor activity of infected and uninfected snails when the snails were deprived of food for 24 hr. Absence of food also resulted in an increased nighttime to daytime ratio of locomotor activity of infected snails. These results suggest that the increased heartbeat rate and altered rhythms of heartbeat rate and locomotor activity in B. glabrata infected with S. mansoni for 33 days were caused by the altered feeding response of these snails.

Effects of alterations in the heartbeat rate and locomotor activity of Schistosoma mansoni-infected Biomphalaria glabrata on cercarial emergence.

During a 27-hr period of food deprivation, Biomphalaria glabrata infected with Schistosoma mansoni had lower heartbeat rates and locomotor activities than did controls that were feeding ad lib. However, there was no difference between the cercarial emergence from control and experimental snails either before, during, or after the period of food deprivation. No correlation was found between the locomotor activity of the snail and the number of cercariae emerging from the snail in continuous light. Our results indicated that the emergence of S. mansoni cercariae from B. glabrata was not affected by the heartbeat rate or locomotor activity of the snail. The factors controlling the rhythm of S. mansoni cercarial emergence from B. glabrata may be independent of the snail.

Descriptive statistics of swimming behavior of Schistosoma mansoni miracidia in artificial pond water.

Timed-exposure, dark-field photography was used to characterize the swimming behavior of Schistosoma mansoni miracidia in artificial pond water. Histograms and descriptive statistics were determined for helical swimming amplitude and wavelength, linear speed, turning frequency, and turning angle. Turning frequency could not be distinguished from a Poisson distribution so that turning appeared to occur randomly. Amplitude and wavelength showed no correlation. Faster miracidia exhibited less helical pattern while swimming. The effects of vertical movement of miracidia and of miracidial concentration were determined to be minimal.