Some (worms) like it hot: fish parasites grow faster in warmer water, and alter host thermal preferences

Abstract

Elevated environmental temperatures associated with anthropogenic warming have the potential to impact host-parasite interactions, with consequences for population health and ecosystem functioning. One way that elevated temperatures might influence parasite prevalence and intensity is by increasing life cycle completion rates. Here, we investigate how elevated temperatures impact a critical phase of the life cycle of the bird tapeworm Schistocephalus solidus -the growth of plerocercoid larvae in host fish (three-spined sticklebacks Gasterosteus aculeatus). By 8 weeks post-infection, plerocercoids recovered from experimentally infected sticklebacks held at 20°C weighed on average 104.9 mg, with all exceeding 50 mg, the mass considered consistently infective to definitive hosts. In contrast, plerocercoids from sticklebacks held at 15°C weighed on average 26.5 mg, with none exceeding 50 mg. As small increases in plerocercoid mass affect adult fecundity disproportionately in this species, enhanced plerocercoid growth at higher temperatures predicts dramatically increased output of infective parasite stages. Subsequent screening of thermal preferences of sticklebacks from a population with endemic S. solidus infection demonstrated that fish harbouring infective plerocercoids show significant preferences for warmer temperatures. Our results therefore indicate that parasite transmission might be affected in at least two ways under anthropogenic warming; by enhancing rates of parasite growth and development, and by increasing the likelihood of hosts being able to seek out proliferating warmer microhabitats. Furthermore, our results suggest the potential for positive feedback between parasite growth and host thermal preferences, which could dramatically increase the effects of even small temperature increases. We discuss the possible mechanisms underpinning our results, their likely ecological consequences and highlight key areas for further research.

Local adaptation drives thermal tolerance among parasite populations: a common garden experiment

“…This result supports the idea that, although high temperatures should increase growth rate (e.g. [14]), a trade-off with survival rate might limit these benefits [47]. Interestingly, we failed to find differences between populations when considering the upper experimental temperature (approx.…”

“…Warming temperatures are expected to affect virulence [11] and dynamics of transmission [12,13], as well as physiological development and survival rate of pathogens. At the same time, hosts may undergo an increased susceptibility to infection due to thermal stresses [10,14]. Because both host and pathogen traits can be affected by temperature, predicting the outcome of future climate change on the spatial distribution of infectious diseases is still a great challenge [10,15].…”

Heat and immunity: an experimental heat wave alters immune functions in three‐spined sticklebacks (Gasterosteus aculeatus)

“…The experiments were (i) temperature shift experiment, where we investigated the effect of a temperature change from a supposed optimal temperature (18°C) to a suboptimal (13°C) and above optimum (24°C) temperature; (ii) heat wave experiment, where we investigated how a Hopkins et al, 2011Lefebure et al, 2011Barre et al, 2010Jordan & Garside, 1972 Experimental temperature range e g n a r e r u t a r e p m e t l a r u t a N Blahm & Snyder, 1975Macnab & Barber, 2012Guderley & Leroy, 2001 present study Fig. 2.…”

Climate impacts on landlocked sea lamprey: Implications for host‐parasite interactions and invasive species management

“…For at least a part of their life cycle, parasites rely on the temperatures provided through their host's behavioral thermoregulation or internal metabolism (Elliot et al 2002). Therefore, parasites using ectotherms as hosts may be more strongly affected by changing thermal regimes Blanford 2003, Macnab andBarber 2012). Determining how host-parasite interactions will change under altered climatic conditions, and predicting the ecological consequences, will be important for minimizing parasite and disease impacts on ecosystems.…”

“…Two major concerns for future climate change are how these changes will impact host-parasite interactions (Elliot et al 2002) and invasive species (Hellmann et al 2008). Host-parasite interactions may be influenced by elevated environmental temperatures through changes to life cycle completion rates, parasite growth and subsequent impacts on host survival (Macnab and Barber 2012). Parasite life cycles are complex and altered thermal regimes could have varying effects from potentially reduced larval and host survival, to increased larval development rates (Molnár et al 2013).…”