Immune Response Varies with Rate of Dispersal in Invasive Cane Toads (Rhinella marina)

Abstract

What level of immunocompetence should an animal maintain while undertaking long-distance dispersal? Immune function (surveillance and response) might be down-regulated during prolonged physical exertion due to energy depletion, and/or to avoid autoimmune reactions arising from damaged tissue. On the other hand, heightened immune vigilance might be favored if the organism encounters novel pathogens as it enters novel environments. We assessed the links between immune defense and long-distance movement in a population of invasive cane toads (Rhinella marina) in Australia. Toads were radio-tracked for seven days to measure their activity levels and were then captured and subjected to a suite of immune assays. Toads that moved further showed decreased bacteria-killing ability in their plasma and decreased phagocytic activity in their whole blood, but a heightened skin-swelling response to phytohemagglutinin. Baseline and post-stress corticosterone levels were unrelated to distance moved. Thus, long-distance movement in cane toads is associated with a dampened response in some systems and enhanced response in another. This pattern suggests that sustained activity is accompanied by trade-offs among immune components rather than an overall down or up-regulation. The finding that high mobility is accompanied by modification of the immune system has important implications for animal invasions.

Costs of immunity and their role in the range expansion of the house sparrow in Kenya

“…Nevertheless, our work hints that intermediate levels of resource expenditure might be most favorable for animals (Long and Graham, 2011;Adelman, 2014): enough of an investment to limit infection but not so much as to require trade-offs with other traits. Damage costs, which appear to mitigate movement distance of individual Australian cane toads at the range edge (Brown and Shine, 2014), were not predicted by TLR-4 expression, but an influence of site of capture suggests that damage costs warrant additional attention in future work.…”

“…Surprisingly, we still know little about what traits comprise successful invaders, especially for vertebrates. Perhaps the best-studied introduced vertebrate species is the cane toad (Rhinella marina), which spread across Australia in ∼80 years (Phillips et al, 2006;Kolbe et al, 2009;Brown and Shine, 2014;Brown et al, 2015a,b;Rollins et al, 2015). Other non-native vertebrates, particularly rodents and songbirds (Losos et al, 1997;Kolbe et al, 2004;Lee et al, , 2005Fassbinder-Orth et al, 2013;Vilcinskas et al, 2013;White et al, 2013;Morand et al, 2015;Tian et al, 2015), have gained some recent attention, but the diversity of research approaches makes generalizations about facilitators of range expansions premature.…”

Immune and environment‐driven gene expression during invasion: An eco‐immunological application of RNA‐Seq

“…Furthermore, Rhimavirus A has only been detected in transcriptomes of toads from areas relatively close to the invasion front (Russo et al, 2018). Invasion history has complex effects on toad immunity (Brown, Phillips, Dubey, & Shine, 2015c;Brown & Shine, 2014;Selechnik, West, et al, 2017b).…”

The impact of lungworm parasites on rates of dispersal of their anuran host, the invasive cane toad

“…We used the blood samples to (1) measure differentials of white blood cell types, (2) measure concentrations of white and red blood cells, (3) assay phagocytic activity of whole blood, and (4) assay bacteria killing ability of plasma. A brief description of methods appears below, but more complete methodologies can be found elsewhere (Brown et al 2015;Brown and Shine 2014).…”