Experimental investigations on the behaviour of the cercariae of an ectoparasitic digenean transversotrema patialense: general activity patterns

Abstract

The activity patterns of the cercariae of Transversotrema patialense have been examined by monitoring the behaviour of individual larvae. Records of three different behavioural modes, namely active, tail–first swimming, passive dropping and resting periods were made separately. The age- and temperature–dependence of the activity patterns during the spontaneously active life of the cercariae were examined and estimates made of the absolute speeds of swimming and dropping. Through the temperature range 25–32° C, the spontaneously active life of cercariae declined from about 18 h to about 6 h. Within this interval, after an initial period of high activity rates, a gradual decline in activity followed. The decline was a result of a decreasing frequency of swimming events rather than any change in the durations of such events. The neural control and energetic significance of the cercarial activity patterns are discussed.

The effects of age, temperature and shadow stimuli on activity patterns of the cercariae of Cryptocotyle lingua (Digenea: Heterophyidae)

“…This study confirms Chapman's (1974) observation that with age, the length of active periods declined while inactive periods increased. These findings are in contrast to those of Whitfield et al (1977) who reported that the mean duration of swimming and dropping events of T. patialense did not alter significantly during ageing. The discrepancy in the behaviour of the cercariae can now be firmly attributed to inter-species differences.…”

“…He found that the behaviour of the cercariae consists of short upwardly directed swimming bursts alternating with longer periods of sinking or resting. Whitfield, Anderson & Bundy (1977), however, pointed out that because of the design of the apparatus, in some experiments it was not possible to differentiate between sinking and resting events. In these experiments the cercariae were confined to a 2 mm high horizontal cell and were photographed from above.…”

“…The design of the cell also prevented cercariae from engaging in prolonged sinking behaviour. Whitfield et al (1977) noted that by illuminating the parasites from below and by constraining them to swim predominantly in a horizontal plane, Chapman probably observed activity patterns in a set of environmental conditions quite different from those in which the cercariae would normally swim. They also suggested that the monitoring of the behaviour of individual parasites over a long period was not part of Chapman's experimental design.…”

“…Such studies mainly described the different behavioural modes observed or quantified behavioural parameters at the population level with measures such as 'percentage active'. According to Whitfield et al (1977) any comprehensive understanding of cercarial behaviour must include long-term studies at the individual cercaria level and take into account that cercarial behaviour is probably age dependent. Rea & Irwin (1992 a) used the cercariae's phototactic response to investigate the effect of age, temperature, light quantity and wavelength on their lateral swimming behaviour.…”

Current strength, temperature, and bodyscape modulate cleaning services for giant manta rays

“…Larvae live freely in the water column before they attach to their terminal host, which they locate from host-derived chemical or mechanical cues, or shadows (Whittington et al 2000). Attachment typically occurs during seasonal epizootic events, which are characterised by cool (~ 25 °C) or warm (~ 32 °C) water conditions (Whitfield et al 1977) and may coincide with a time when hosts are particularly vulnerable to infection (Möller 1978;Silan et al 1983;Tubbs et al 2005;Rückert et al 2008). We conjecture for further study that the seasonality with which giant manta rays visit Monad Shoal might coincide with ectoparasite attachment events in the area, leading to heightened parasitism and a greater need for interacting with cleaners.…”