Stress and immunity: Field comparisons among populations of invasive cane toads in Florida

Abstract

Cane toads (Rhinella marina) were introduced worldwide and have become invasive in multiple locations, representing a major driver of biodiversity loss through competition (food, shelter, territory), predation, and the poisoning of native species. These toads have been used in Australia as a model for studies concerning invasion biology and ecoimmunology, as longer‐established (core) and invasion front (edge) populations show altered stress and immune response profiles. Although cane toads were also introduced into the United States in the 1950s, these patterns have yet to be evaluated for the populations spanning Florida. Toads introduced into Florida have dispersed primarily northward along a latitudinal gradient, where they encounter cooler temperatures that may further impact stress and immune differences between core and edge populations. In this study, we sampled cane toads from nine different locations spanning their invasion in Florida. Cane toads from southern populations showed higher plasma bacterial killing ability and natural antibody titers than the toads from the northern populations, indicating they have a better immune surveillance system. Also, southern toads were more responsive to a novel stressor (1 hr restraint), showing a higher increase in corticosterone levels. These results indicate that possible trade‐offs have occurred between immune and stress responses as these toads have become established in northern cooler areas in Florida.

Sex‐based trade‐offs in the innate and acquired immune systems of Sternotherus minor

“…Plasma collected from experimental populations was challenged to a hemagglutination assay described by Matson et al (2005) and followed the protocols of Graham et al (2017) and Assis et al (2020). This assay tested the acquired immune response of the turtles by visibly titrating the antibody response to SRBC.…”

Introduction to the special issue: Ecoimmunology in ectotherms

“…Also, southern cane toads were more responsive to a short‐term stressor (1 h restraint) with higher corticosterone plasma levels. Together, these data indicate that individuals in Florida's edge areas have lower immune surveillance and stress reactivity than those in the core range, which could limit their expansion into further up northern populations (Assis et al, 2020).…”

“…Considering the stress response is integrated and the complex interrelationships between the immune system and glucocorticoids (the main endocrine mediator of the stress response), recent ecoimmunological studies are investigating these relations in ectotherms (Assis et al, 2015; Assis et al, 2019; French et al, 2006; Romero & Wikelski, 2010; Titon et al, 2018, 2019; Tort, 2011). In this SI, stress‐induced immunoenhancing effects were described for female cane toads ( Rhinella marina ), with increased post‐restraint antibody titers values (Assis et al, 2020). In accordance, restraint increased bacterial killing ability in plateau side‐blotched lizards ( Uta stansburiana uniformis ; Hudson et al, 2020).…”

“…Adaptive changes have been described in the invasion front populations of the cane toads, a well‐studied invasive species in Australia (Brown & Shine, 2014; Llewellyn et al, 2012). Herein, Assis et al (2020) compared physiological parameters of populations of invasive cane toads in Florida. Southern (core) cane toads populations had higher immunity (plasma bacterial killing ability and natural antibody titers) than the northern (edge) ones (Assis et al, 2020).…”

“…Herein, Assis et al (2020) compared physiological parameters of populations of invasive cane toads in Florida. Southern (core) cane toads populations had higher immunity (plasma bacterial killing ability and natural antibody titers) than the northern (edge) ones (Assis et al, 2020). Also, southern cane toads were more responsive to a short‐term stressor (1 h restraint) with higher corticosterone plasma levels.…”