Effect of temperature changes on the cercarial-shedding rate of two trematodes

Abstract

ABSTRACT. Since temperature is a key condition in the initiation of cercarial emergence, the objective of the work reported here was to evaluate the eff ect of that variable on the shedding of two morphologic and taxonomic types of cercariae. Bioassays were accordingly performed with snails naturally infected with either monostome or pleurolophocercous cercariae because those two cercarial types were found to be the most prevalent in the environment under study. The snails were placed in 6-ml circular plastic dishes with soft plastic stoppers containing 3 ml of reconstituted water and then sequentially exposed for 24 h to a 14:10-h light:dark cycle at 20, 25, or 30 °C. The data were analyzed at a signifi cance level of p <0.05 by means of the InfoStat program. The optimum temperature for cercarial emergence was typically in the range of 25 °C and decreased signifi cantly at 30 °C. We observed no signifi cant diff erence in the number of cercariae emerging between the two morphologic types.KEYWORDS. Parasites, cercarial emergence, freshwater, temperature, bioassay.RESUMEN. Efecto de cambios en la temperatura sobre la emergencia de cercarías de dos trematodes. Considerando que la temperatura es un factor clave en la emergencia de cercarias, el objetivo de este trabajo fue evaluar el efecto de ésta variable sobre la emergencia de dos tipos morfológicos de cercarias. Los bioensayos se realizaron con caracoles naturalmente infectados con cercarias de los tipos monostoma o pleurolofocerca, debido a que estos dos tipos fueron los más prevalentes en el ambiente en estudio. Los caracoles fueron ubicados en cápsulas plásticas de 6 ml conteniendo 3 ml de agua reconstituida, y entonces fueron secuencialmente expuestos por 24 h con un ciclo 14:10 h luz:oscuridad a 20, 25 y 30 °C. Los datos fueron analizados a un nivel de signifi cación de p<0.05 con el programa InfoStat. Los resultados mostraron que la temperatura óptima de la emergencia de cercarias estuvo en el rango de 25 °C, y disminuyó signifi cativamente a 30 °C. Se observó también que no existía diferencia signifi cativa en el número de cercarias emergentes entre los dos tipos morfológicos.PALABRAS-CLAVE. Parásitos, emergencia de cercarias, agua dulce, temperatura, bioensayo.

Parasitic fauna of Eurasian beavers (Castor fiber) in Sweden (1997–1998)

“…We assume that this climate difference is reflected in water temperatures. Our result is in accordance with other studies [61][62][63][64][65], demonstrating the influence of water temperature on release of cercariae from the intermediate hosts. Parasitic eye flukes in fish (Diplostomum sp.)…”

“…An increase in temperature leads to a reduction in the cercarial developmental time and also triggers cercarial release. In a study that tested the effect of temperature changes on the cercarial-shedding rate of two trematodes, the optimum temperature for cercarial emergence was ca 25 °C [65]. In accordance with this, water temperatures being higher in the southern part of Sweden than in the northern, the number of trematodes in beavers was expected to be higher in the South.…”

“…Larval development of trematodes is reported to be dependent on water temperature [61][62][63][64][65]. An increase in temperature leads to a reduction in the cercarial developmental time and also triggers cercarial release.…”

Taxonomic scale and community organization impact observed latitudinal gradients of parasite diversity

“…Extreme temperatures can slow development or kill parasites, while warmer temperatures within the tolerable range can speed up development (Morgan & van Dijk, 2012; Watertor, 1968; Wood et al, 2012). Temperature can also alter parasite transmission, for example by influencing the release of infective larvae (Achiorno & Martorelli, 2016; Paull et al, 2015), through the increase in predation of free‐living larval stages (Goedknegt et al, 2015), or by affecting a host's susceptibility and exposure to parasitic infection (Barber et al, 2016). These factors can all impact what species can survive in which environments.…”