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The Giant African Snail (Achatina fulica) is considered to be one the world’s 100 worst invasive alien species. The snail has an impact on native biodiversity, and on agricultural and horticultural crops. In India, it is known to feed on more than fifty species of native plants and agricultural crops and also outcompetes the native snails. It was introduced into India in 1847 and since then it has spread all across the country. In this paper, we use ecological niche modeling (ENM) to assess the distribution pattern of Giant African Snail (GAS) under different climate change scenarios. The niche modeling results indicate that under the current climate scenario, Eastern India, peninsular India and the Andaman and Nicobar Islands are at high risk of invasion. The three different future climate scenarios show that there is no significant change in the geographical distribution of invasion prone areas. However, certain currently invaded areas will be more prone to invasion in the future. These regions include parts of Bihar, Southern Karnataka, parts of Gujarat and Assam. The Andaman and Nicobar and Lakshadweep Islands are highly vulnerable to invasion under changed climate. The Central Indian region is at low risk due to high temperature and low rainfall. An understanding of the invasion pattern can help in better management of this invasive species and also in formulating policies for its control.

The developmental environment can exert powerful effects on animal phenotype. Recently epigenetic modifications have emerged as one mechanism that can modulate developmentally plastic responses to environmental variability. For example, the DNA methylation profile at promoters of hormone receptor genes can affect their expression and patterns of hormone release. Across taxonomic groups, epigenetic alterations have been linked to changes in glucocorticoid (GC) physiology. GCs are metabolic hormones that influence growth, development, transitions between life-history stages, and thus fitness. To date, relatively few studies have examined epigenetic effects on phenotypic traits in wild animals, especially in amphibians. Here, we examined the effects of exposure to predation threat and experimentally manipulated DNA methylation on corticosterone (CORT) levels in tadpoles and metamorphs of the invasive cane toad (Rhinella marina). We included offspring of toads sampled from populations across the species’ Australian range. In these animals, exposure to chemical cues from injured conspecifics induces shifts in developmental trajectories, putatively as an adaptive response that lessens vulnerability to predation. We exposed tadpoles to these alarm cues, and measured changes in DNA methylation and CORT levels, both of which are mechanisms that have been implicated in the control of phenotypically plastic responses in tadpoles. To test the idea that DNA methylation drives shifts in GC physiology, we also experimentally manipulated methylation levels with the drug zebularine. We found differentially methylated regions between control tadpoles and their full-siblings exposed to alarm cues, zebularine or both treatments. However, the effects of these manipulations on methylation patterns were weaker than clutch (e.g. genetic, maternal, etc.) effects. CORT levels were higher in larval cane toads exposed to alarm cues and zebularine. We found little evidence of changes in DNA methylation across the glucocorticoid receptor gene (NR3C1) promoter region in response to alarm cue or zebularine exposure. In both alarm cue and zebularine-exposed individuals, we found differentially methylated DNA in the suppressor of cytokine signaling 3 gene (SOCS3), which may be involved in predator avoidance behavior. In total, our data reveal that alarm cues have significant impacts on tadpole physiology, but show only weak links between DNA methylation and CORT levels. We also identify genes containing differentially methylated regions in tadpoles exposed to alarm cues and zebularine, particularly in range-edge populations, that warrant further investigation.

In response to novel environments, invasive populations often evolve rapidly. Standing genetic variation is an important predictor of evolutionary response but epigenetic variation may also play a role. Here, we use an iconic invader, the cane toad ( Rhinella marina ), to investigate how manipulating epigenetic status affects phenotypic traits. We collected wild toads from across Australia, bred them, and experimentally manipulated DNA methylation of the subsequent two generations (G1, G2) through exposure to the DNA methylation inhibitor zebularine and/or conspecific tadpole alarm cues. Direct exposure to alarm cues (an indicator of predation risk) increased the potency of G2 tadpole chemical cues, but this was accompanied by reductions in survival. Exposure to alarm cues during G1 also increased the potency of G2 tadpole cues, indicating intergenerational plasticity in this inducible defence. In addition, the negative effects of alarm cues on tadpole viability (i.e. the costs of producing the inducible defence) were minimized in the second generation. Exposure to zebularine during G1 induced similar intergenerational effects, suggesting a role for alteration in DNA methylation. Accordingly, we identified intergenerational shifts in DNA methylation at some loci in response to alarm cue exposure. Substantial demethylation occurred within the sodium channel epithelial 1 subunit gamma gene ( SCNN1G ) in alarm cue exposed individuals and their offspring. This gene is a key to the regulation of sodium in epithelial cells and may help to maintain the protective epidermal barrier. These data suggest that early life experiences of tadpoles induce intergenerational effects through epigenetic mechanisms, which enhance larval fitness. This article is part of the theme issue ‘How does epigenetics influence the course of evolution?’