Trematode Parasite Infection Affects Temperature Selection in Aquatic Host Snails

Abstract

Animals infected by parasites or pathogens can exhibit altered behaviors that may reduce the costs of infection to the host or represent manipulations that benefit the parasite. Given that temperature affects many critical physiological processes, changes in thermoregulatory behaviors are an important consideration for infected hosts, especially ectotherms. Here we examined the temperature choices of freshwater snails (Helisoma trivolvis) that were or were not infected by a trematode (flatworm) parasite (Echinostoma trivolvis). Active snails that explored the experimental temperature gradient differed in their thermal preference based on their infection status, as parasitized snails chose to position themselves at a significantly higher temperature (mean: 25.47C) compared to those that were uninfected (mean: 23.37C). Given that snails rarely eliminate established trematode infections, we suggest that this altered thermal preference shown by infected hosts likely benefits the parasite by increasing the odds of successful transmission, either through enhanced production and emergence of infectious stages or by increasing spatial overlap with the next hosts of the complex life cycle. Further studies that employ experimental infections to examine temperature selection at different time points will be needed to understand the extent of altered host thermal preferences, as well as the possible benefits to both host and parasite.

Staying warm is not always the norm: behavioural differences in thermoregulation of two snake species

“…The open habitat-preferring T. s. sirtalis showed higher thermal preferences, was more active, and exhibited clear evidence of thermotaxis within the thermal gradient in relation to the semi-fossorial S. o. occipitomaculata, which showed cool thermal preferences and relatively low evidence for orientation-based thermotaxis. Both snakes were studied within a circular thermal gradient, which avoided the cold trap thigmotactic behaviour often seen in linear thermal gradient studies (Anderson et al 2007;Wang et al 2019). Given that several factors are known to affect measurements of temperature selection (Cadena and Tattersall 2009), researchers should pay attention to experimental design and their study systems, and recognize that if appropriate null models of behaviour are not examined simultaneously, then all possible thermoregulatory behaviours and behavioural choices made over time should be examined to obtain relevant results.…”

“…Moreover, comparing behavioural and physiological data from reportedly active thermoregulating species (i.e., open-habitat, basking reptiles) with that of species not predicted to actively thermoregulate (i.e., forest-dwelling, shade and cover specialists) could elucidate whether animals are making truly thermally motivated decisions during trials (Cadena and Tattersall 2009;Black and Tattersall 2017). Thus, the use of null models that simulate random movement patterns and temperature selection within a gradient (Anderson et al 2007;Wang et al 2019) could be bypassed, as species with contrasting movement patterns would be expected to exhibit different thermoregulatory drives.…”

Infection burdens and virulence under heat stress: ecological and evolutionary considerations

“…Interestingly, some species manipulate parasite reproduction through febrile behaviour by plastically regulating their temperature to below the parasite's optimum [ 122 ]. In longer-lived parasites that can manipulate host behaviour—for example, trematode worm infections in snail hosts—heat tolerance of infected hosts can be parasite species-dependent [ 123 ] and can lead hosts to select for thermal niches that may benefit the parasite [ 124 ].…”

Biogeography of the freshwater gastropod, Planorbella trivolvis, in the western United States

“…The snails were identified by the collectors as H. trivolvis , based on diagnostic shell attributes originally described in Hubendick & Rees [ 54 ]. Both Helisoma and Planorbella are genus names used today to refer to P. trivovlis specimens [ 42 , 55 ]. In this paper, we use the accepted name listed by the Integrated Taxonomic Information System ( https://www.itis.gov/ ), Planorbella trivolvis , as described in Burch [ 51 ].…”

“…Planorbella are genus names used today to refer to P. trivovlis specimens [42,55]. In this paper, we use the accepted name listed by the Integrated Taxonomic Information System (https://www.itis.gov/), Planorbella trivolvis, as described in Burch [51].…”