Chemical defenses are widespread among animals, and the compounds involved may be either synthesized from nontoxic precursors or sequestered from an environmental source. Defensive sequestration has been studied extensively among invertebrates, but relatively few examples have been documented among vertebrates. Nonetheless, the number of described cases of defensive sequestration in tetrapod vertebrates has increased recently and includes diverse lineages of amphibians and reptiles (including birds). The best-known examples involve poison frogs, but other examples include natricine snakes that sequester toxins from amphibians and two genera of insectivorous birds. Commonalities among these diverse taxa include the combination of consuming toxic prey and exhibiting some form of passive defense, such as aposematism, mimicry, or presumptive death-feigning. Some species exhibit passive sequestration, in which dietary toxins simply require an extended period of time to clear from the tissues, whereas other taxa exhibit morphological or physiological specializations that enhance the uptake, storage, and/or delivery of exogenous toxins. It remains uncertain whether any sequestered toxins of tetrapods bioaccumulate across multiple trophic levels, but multitrophic accumulation seems especially likely in cases involving consumption of phytophagous or mycophagous invertebrates and perhaps consumption of poison frogs by snakes. We predict that additional examples of defensive toxin sequestration in amphibians and reptiles will be revealed by collaborations between field biologists and natural product chemists. Candidates for future investigation include specialized predators on mites, social insects, slugs, and toxic amphibians. Comprehensive studies of the ecological, evolutionary, behavioral, and regulatory aspects of sequestration will require teams of ecologists, systematists, ethologists, physiologists, molecular biologists, and chemists. The widespread occurrence of sequestered defenses has important implications for the ecology, evolution, and conservation of amphibians and reptiles.

The sources of individual differences in human and non-human animals remain controversial. We demonstrate that diet and genetics interact in determining the ontogenetic trajectory of chemosensory and prey preferences in the common garter snake, Thamnophis sirtalis, a dietary generalist. In litters of neonate snakes from a single small field in an earthworm-ingesting population, initial responses to chemical cues from fish and worm were similar, with zero heritabilities. After 12 meals on fish, however, the heritability of both fish and worm chemosensory responses increased markedly, the change in response to fish but not worm chemicals was heritable, the relative preference for fish versus worm was heritable, and the change in relative preference was heritable. In addition, growth rates on each diet were related to changes in chemoreceptive responses. Such genetic-environment variation that emerges only after equivalent ontogenetic experience may be a factor in responses to environmental change in many species.