Effects of metal and predator stressors in larval southern toads (Anaxyrus terrestris)

Abstract

Natural and anthropogenic stressors typically do not occur in isolation; therefore, understanding ecological risk of contaminant exposure should account for potential interactions of multiple stressors. Realistically, common contaminants can also occur chronically in the environment. Because parental exposure to stressors may cause transgenerational effects on offspring, affecting their ability to cope with the same or novel environmental stressors, the exposure histories of generations preceding that being tested should be considered. To examine multiple stressor and parental exposure effects we employed a 2 × 2 × 2 factorial design in outdoor 1000-L mesocosms (n = 24). Larval southern toads (Anaxyrus terrestris), bred from parents collected from reference and metal-contaminated sites, were exposed to two levels of both an anthropogenic (copper-0, 30 µg/L Cu) and natural (predator cue - present/absent) stressor and reared to metamorphosis. Toads from the metal-contaminated parental source population were smaller at metamorphosis and had delayed development; i.e., a prolonged larval period. Similarly, larval Cu exposure also reduced size at metamorphosis and prolonged the larval period. We, additionally, observed a significant interaction between larval Cu and predator-cue exposure on larval period, wherein delayed emergence was only present in the 30-µg/L Cu treatments in the absence of predator cues. The presence of parental effects as well as an interaction between aquatic stressors on commonly measured endpoints highlight the importance of conducting multistressor studies across generations to obtain data that are more relevant to field conditions in order to determine population-level effects of contaminant exposure.

Delayed effects and complex life cycles: How the larval aquatic environment influences terrestrial performance and survival

“…Similar to our data, the latter study also found a precipitous decrease in juvenile survival, with only 17% surviving after the first month (Earl and Semlitsch 2013). Our study indicates carryover and latent effects of parental source and larval metal exposure on juvenile survivorship, because there were no treatment effects on survival to metamorphosis (Rumrill et al 2016), but such effects did manifest in terrestrial-stage juveniles, with survival reduced to 19.9 AE 4.5% in the toads that were exposed to elevated Cu and were from D-Area parents. Our time-to-death analysis also suggests that either parental or larval metal contaminant exposure can result in deleterious effects, which are increased with the combination of the 2.…”

“…We exposed larval toads whose parents were sourced from either a metal-contaminated or a reference wetland to the presence or absence of Cu and/or predator cues from caged dragonflies in outdoor mesocosms; we then transferred metamorphs to terraria for 5 mo to measure performance, growth, and survival of juveniles. The results of the larval exposure on effects to metamorphosis are presented in a separate publication (Rumrill et al 2016), but, importantly, we found that both parental wetland source and larval exposure to Cu resulted in reduced size at metamorphosis. For our purposes in the present study, we expected to distinguish between carryover and latent effects seen post metamorphosis by assuming that carryover effects would be mediated through body size at metamorphosis and latent effects would occur via a direct relationship to a stressor experienced prior to metamorphosis.…”

“…Our time‐to‐death analysis also suggests that either parental or larval metal contaminant exposure can result in deleterious effects, which are increased with the combination of the 2. Neither of those treatments affected larval survival (Rumrill et al ), but did affect postmetamorphic survival. This finding highlights the importance of examining stressors beyond the larval period to assess critical carryover and latent effects.…”

“…Metamorphs were kept in these receptacles until tail resorption (typically 2 d) but were monitored daily to remoisten the paper towels. We discuss the effects at metamorphosis for the emerging toads, as well as additional details concerning breeding and the aquatic exposure portion of the present study in a separate publication (Rumrill et al ). To summarize the responses at metamorphosis, we found (Rumrill et al ) that both the metal‐contaminated parental source population and elevated larval Cu treatments produced toad metamorphs that were smaller at metamorphosis and had delayed development, but larval survival was not affected and thus larval densities were not different among mesocosms.…”

Effects of High Copper Exposure on Development and Survival During Early Ontogenesis in the Common Toad

“…As copper levels in the environment reach some critical level, it triggers the detoxication system of the organism (Herkovits, Helguero, 1998). Elevated Cu levels can increase embryonic and larvae mortality (Lance et al, 2012(Lance et al, , 2013Xia et al, 2012;Flynn et al, 2015), also cause sublethal effects including embryonic deformities (Chen et al, 2007), impaired predator avoidance (Garcı´a-Munoz et al, 2009;Rumrill, et al, 2016) and other. The boundary at which copper transforms from an activator of biological processes into a toxicant is blurred not only because of the adaptation capacities of the organism, but also because of the process of development as such.…”