Temperature does not influence functional response of amphipods consuming different trematode prey

Abstract

Direct consumption on free-living cercariae stages of trematodes by non-host organisms interferes with trematode transmission and leads to reduced infections in the next suitable hosts. Consumer functional responses provide a useful tool to examine relationships between consumption rates and ecologically relevant prey densities, whilst also accounting for abiotic factors that likely influence consumption rates. We investigated how temperature influences the consumer functional response of the amphipod Gammarus lacustris towards the cercariae of three freshwater trematodes (Diplostomum, Apatemon and Trichobilharzia). Amphipods displayed different functional responses towards the parasites, with Type II responses for Diplostomum and Type I responses for Apatemon prey. Temperature did not alter the consumption rate of the amphipod predator. Trichobilharzia was likely consumed at similar proportions as Diplostomum; however, this could not be fully evaluated due to low replication. Whilst Type II responses of invertebrate predators are common to various invertebrate prey types, this is the first time a non-filter feeding predator has been shown to exhibit Type I response towards cercarial prey. The prey-specific consumption patterns of amphipods were related to cercarial distribution in the water column rather than to the size of cercariae or temperature influence. The substantial energy flow into food webs by non-host consumer organisms highlights the importance of understanding the mechanisms that modulate functional responses and direct predation in the context of parasitic organisms.

Cercarial behaviour alters the consumer functional response of three‐spined sticklebacks

“…Until recently, the only study using a FR approach to understand the potential impact of aquatic predators on cercariae populations was confounded by the predator species also being a host of the focal parasite (Anderson et al., 1978). However new studies now demonstrate that non‐host invertebrate predators may display contrasting FR types on cercariae populations (Born‐Torrijos et al., 2020; Mironova et al., 2020).…”

“…While temperature may alter stickleback prey consumption (Wootton et al., 1980), the characteristic behavioural and physiological changes (reduced fright response, visible bulge and restricted stomach capacity) caused by severe S. solidus infections may also alter the foraging activity of this fish (Milinski, 1985; Tierney et al., 1993). Furthermore, parasite‐specific morphological and behavioural traits inherent to dispersal and transmission also alter its predation risk (Born‐Torrijos et al., 2020; Catania et al., 2016; Kaplan et al., 2009; Orlofske et al., 2015; Selbach et al., 2019).…”

Invaders as Diluents of the Cercarial Dermatitis Etiological Agent

“…In addition, although all gammarids were starved for the same length of time prior to the experiment, we can not rule out the possibility that individual predators may have experienced different levels of hunger at the beginning and during the experiment. As suggested by Born-Torrijos et al, [47] the continuous movement of prey may likely facilitate a constant consumption by visual predators such as amphipods. Therefore, if the predators did not feed from the beginning of the experiment, with the duration of the experiment more and more cercariae may have become less attractive prey, because due to the length of our experiment and the short life span of the cercariae, the cercariae may have slowed down their movement and sunk later in the experiment.…”

“…Moreover, Welsh et al [53] carried out an experiment on the dilution of cercariae using a very broad spectrum of non-host organisms and showed that amphipods may play a very important role in the dilution of the larvae. Additionally, Born-Torrijos et al [47] showed that another species of widespread freshwater gammarids also efficiently consumes digenean furcocercariae, including genus Trichobilharzia. However, we have observed wide between-replicate variability in the dilution of the parasitic cercariae by D. villosus.…”

“…The replicates for a given alien species were set at the same time-each diluent species was used only once for testing. The experimental animals were not fed for two days before the experiment (according to the protocol presented by Selbach et al [38] and Born-Torrijos et al [47]). The experiment was carried out in the beakers described above, with the cercariae released into the water by the host snails.…”