Adaptive phenotypic plasticity provides a mechanism of developmental rescue in novel and rapidly changing environments. Understanding the underlying mechanism of plasticity is important for predicting both the likelihood that a developmental response is adaptive and associated life-history trade-offs that could influence patterns of subsequent evolutionary rescue. Although evolved developmental switches may move organisms toward a new adaptive peak in a novel environment, such mechanisms often result in maladaptive responses. The induction of generalized physiological mechanisms in new environments is relatively more likely to result in adaptive responses to factors such as novel toxins, heat stress, or pathogens. Developmental selection forms of plasticity, which rely on within-individual selective processes, such as shaping of tissue architecture, trial-and-error learning, or acquired immunity, are particularly likely to result in adaptive plasticity in a novel environment. However, both the induction of plastic responses and the ability to be plastic through developmental selection come with significant costs, resulting in delays in reproduction, increased individual investment, and reduced fecundity. Thus, we might expect complex interactions between plastic responses that allow survival in novel environments and subsequent evolutionary responses at the population level.

Zinc is a widespread pollutant released from industrial combustion, automobile residue, and mining. Zinc accumulates in soils and mobilises into plant tissue where it may be consumed to potentially toxic levels by leaf feeding insects, including developing pollinators. While zinc tolerance thresholds have been previously assessed in insect pollinators, most observations are limited to model organisms and pest species. We lack understanding of zinc tolerance in insects of conservation concern. We assess dietary zinc tolerance of developing caterpillars from wild populations of the monarch butterfly (Danaus plexippus), a species of conservation concern, whose caterpillars are commonly exposed to elevated dietary zinc exposure in milkweed plants along roadsides. We contrast monarch zinc tolerance with that of cabbage white butterfly caterpillars (Pieris rapae), a non‐native pest species. Tolerance was assessed by rearing caterpillars on artificial diets containing varying levels of zinc. Zinc reduced monarch survival at levels as low as 344 mg kg−1 but positively impacted cabbage white survival at 227 and 738 mg kg−1. Cabbage whites also displayed prolonged development time, smaller adult body size, and slower growth rate, consistent with the possibility that zinc tolerance had fitness costs. Our results support previous observations that heavy metal tolerance varies between species and highlight the importance of broadening our understanding of tolerance to insect species of conservation concern before drawing general conclusions about insect susceptibility to heavy metal pollution. Nonetheless, our results suggest that zinc pollution alone is unlikely a risk in developing roadside habitat for monarch butterflies.

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Exposure to low-dose ionizing radiation can have positive impacts on biological performance—a concept known as hormesis. Although radiation hormesis is well-documented, the predominant focus has been medical. In comparison, little research has examined potential effects of early life radiation stress on organismal investment in life history traits that closely influence evolutionary fitness (eg, patterns of growth, survival, and reproduction). Evaluating the fitness consequences of radiation stress is important, given that low-level radiation pollution from anthropogenic sources is considered a major threat to natural ecosystems. Using the cricket (Acheta domesticus), we tested a wide range of doses to assess whether a single juvenile exposure to radiation could induce hormetic benefits on lifetime fitness measures. Consistent with hormesis, we found that low-dose juvenile radiation positively impacted female fecundity, offspring size, and offspring performance. Remarkably, even a single low dose of radiation in early juvenile development can elicit a range of positive fitness effects emerging over the life span and even into the next generation.