Three unrelated species, 3 sites, same host – monogenean parasites of the southern fiddler ray, Trygonorrhina fasciata, in South Australia: egg hatching strategies and larval behaviour

Abstract

The southern fiddler ray, Trygonorrhina fasciata (Rhinobatidae), is parasitized by 3 monogenean (platyhelminth) species from 3 families on 3 different sites of the host : Calicotyle australis (Monocotylidae) from the cloaca, Pseudoleptobothrium aptychotremae (Microbothriidae) from the skin and Branchotenthes octohamatus (Hexabothriidae) from the gills. Cues that promote egg hatching were investigated for each species and the behaviour of their larvae was also documented. Eggs were laid by parasites in vivo and maintained at 22 xC. Three different egg hatching and host finding strategies were discovered. Calicotyle australis eggs hatched spontaneously with a strong diurnal rhythm that is likely to be under circadian control. The larva is ciliated, photo-responsive and can survive for up to 24 h at 22 xC after hatching. Pseudoleptobothrium aptychotremae may have a ' bet-hedging ' strategy. Some eggs hatched spontaneously and rhythmically. However, since the hatching success was low, it is possible that other eggs require a different cue provided by the host. The larva is also ciliated but shows no photo-response and was observed to remain active for <4 h at 22 xC after hatching. Branchotenthes octohamatus has a ' sit-and-wait ' strategy that depends on mechanical disturbance to stimulate hatching. The larva is unciliated, shows no photo-response but may survive for more than 2 days at 22 xC after hatching. The implications of hatching strategy, larval behaviour and morphology in the goal to find a host are discussed for each species.

Bet Hedging in a Guild of Desert Annuals

“…Phenotypes with presumed fitness costs inter-pretable as bet hedging adaptations are widely taken as prima facie evidence of bet hedging (such as low or fractional germination or hatching, e.g., Glennon et al 2006, Matsuo 2006). Phenotypes with presumed fitness costs inter-pretable as bet hedging adaptations are widely taken as prima facie evidence of bet hedging (such as low or fractional germination or hatching, e.g., Glennon et al 2006, Matsuo 2006).…”

“…Previous evidence of bet hedging has come in several forms. Phenotypes with presumed fitness costs inter-pretable as bet hedging adaptations are widely taken as prima facie evidence of bet hedging (such as low or fractional germination or hatching, e.g., Glennon et al 2006, Matsuo 2006. There are many such observations When species are bootstrapped, 99% of 10 000 resampled correlations are negative.…”

Reproductive Strategies of the Insidious Fish Ectoparasite, Neobenedenia sp. (Capsalidae: Monogenea)

“…4 ). Monogeneans can maximise their chances of finding a host by extending the hatching period [11] , while some species respond to hatching cues such as shadows [12] , chemicals [11] , [13] , mechanical disturbance [14] – [16] and osmotic changes [17] , most of which are generated by the host. Hatching rhythms have been documented in other marine monogeneans in the first few hours of light ( Entobdella solea [60] ; Diclidophora spp.…”

“…Monogeneans also exhibit egg laying and egg hatching rhythms, which can reduce the risk of predation and coincide with host behaviours to ensure infection success. Monogeneans maximise their chances of finding a host by releasing eggs into the environment during certain times of the day or night [7] , extending the hatching period [11] , responding to hatching cues such as shadows [12] , chemicals [11] , [13] , mechanical disturbance [14] – [16] and osmotic changes [17] , most of which are generated by the host.…”

Experimental infections, using a fluorescent marker, of two elasmobranch species by unciliated larvae of Branchotenthes octohamatus (Monogenea: Hexabothriidae): invasion route, host specificity and post-larval development

“…light on at 06·00 h, light off at 18·00 h) achieved by a programmed timer connected to an 18W Grow-lux tube fitted to the cabinet ceiling. Eggs of B. octohamatus are fully embryonated after 8–10 days at 22°C and hatching is easily promoted when eggs are mechanically agitated (Glennon et al 2006). The FSW in each dish was replaced daily for the first 5 days of incubation, after which, eggs were left undisturbed so that hatching would not be induced until larvae were required for experiments.…”