Possible mechanism of host manipulation resulting from a diel behaviour pattern of eye-dwelling parasites?

Abstract

S U M M A R YParasitic infection often results in alterations to the host's phenotype, and may modify selection pressures for host populations. Elucidating the mechanisms underlying these changes is essential to understand the evolution of host-parasite interactions. A variety of mechanisms may result in changes in the host's behavioural phenotype, ranging from simple by-products of infection to chemicals directly released by the parasite to alter behaviour. Another possibility may involve parasites freely moving to certain sites within tissues, at specific times of the day to induce behavioural changes in the host. We tested the hypothesis that parasites shift to certain sites within the host by quantifying the location and activity of the trematode Tylodelphys sp., whose mobile metacercarial stages remain unencysted in the eyes of the second intermediate fish host, the common bully (Gobiomorphus cotidianus). This parasite's definitive host is a piscivorous bird feeding exclusively during daytime. Ocular obstruction and metacercarial activity were assessed within the sedated host's eye at three time points 24 h −1 period, using video captured via an ophthalmoscope. Although observed metacercarial activity did not change between time periods, ocular obstruction was significantly reduced at night. Increased visual obstruction specifically during the foraging time of the parasite's definitive host strongly suggests that the parasite's activity pattern is adaptive.

No impact of a presumed manipulative parasite on the responses and susceptibility of fish to simulated predation

“…Trematodes in the family Diplostomidae infect a variety of fish species as metacercariae and can be found, among other areas, in the eyes (Karvonen, Paukku, & Seppälä, ; Seppälä, Karvonen, & Valtonen, , , ; Stumbo & Poulin, ). Some diplostomids, such as Diplostomum spp., are found in the lens of the fish eye, wherein metacercariae release waste products that result in cataracts (Karvonen, Seppälä, & Valtonen, ; Shariff, Richards, & Sommerville, ).…”

“…Recently, a new species of Tylodelphys was described in New Zealand from lakes on the South Island (Blasco‐Costa et al, ). As with many diplostomid trematodes, Tylodelphys darbyi has a three‐host life cycle, first utilizing an unknown snail, likely a lymnaeid, then the common bully Gobiomorphus cotidianus and finally the Australasian great crested grebe Podiceps cristatus australis as the definitive host (Blasco‐Costa et al, ; Presswell & Blasco‐Costa, ; Stumbo & Poulin, ). Within the fish, G. cotidianus, T. darbyi metacercariae inhabit the vitreous and aqueous humours of the eye, moving freely between the two; they can reach lengths greater than 1mm and may occur in high intensities, for example often >10 metacercariae per eye (Blasco‐Costa et al, ; Presswell & Blasco‐Costa, ).…”

“…Within the fish, G. cotidianus, T. darbyi metacercariae inhabit the vitreous and aqueous humours of the eye, moving freely between the two; they can reach lengths greater than 1mm and may occur in high intensities, for example often >10 metacercariae per eye (Blasco‐Costa et al, ; Presswell & Blasco‐Costa, ). Recently, Stumbo and Poulin () demonstrated that T. darbyi shows a diel behaviour pattern in which individuals moved farther up in the eye during the day, potentially increasing obstruction, and retreated to the bottom of the eye at night. The authors hypothesized that this diel movement could increase the likelihood of transmission during the day when grebes are active by impairing the vision, and consequently the evasiveness, of the bullies (Stumbo & Poulin, ).…”

“…Gobiomorphus cotidianus is the most widespread bully species in New Zealand, occurring across freshwater streams, lakes and estuaries (McDowall, ; Michel et al, ; Vanderpham, Nakagawa, & Closs, ). At present, only G. cotidianus from a single lake, Lake Hayes, in the Otago region of the South Island have been identified as infected with T. darbyi (Blasco‐Costa et al, ; Presswell & Blasco‐Costa, ; Stumbo & Poulin, ). As for the only identified definitive host, in New Zealand, P. cristatus australis is only found on lakes of the South Island and, like many native birds, is considered nationally vulnerable (Presswell & Blasco‐Costa, ; New Zealand's Department of Conservation).…”

A new R package and web application for detecting bilateral asymmetry in parasitic infections

“…The latter, less obvious form of asymmetry is sometimes overlooked when lateralisation of infection is investigated (e.g. Buchmann 1988, Rodrigues and Saraiva 1996, Dzika 1999, Stumbo and Poulin 2016.…”