Species that sequester toxins from prey for their own defense against predators may exhibit population-level variation in their chemical arsenal that reflects the availability of chemically defended prey in their habitat. Rhabdophis tigrinus is an Asian snake that possesses defensive glands in the skin of its neck (‘nuchal glands’), which typically contain toxic bufadienolide steroids that the snakes sequester from consumed toads. In this study, we compared the chemistry of the nuchal gland fluid of R. tigrinus from toad-rich and toad-free islands in Japan and determined the effect of diet on the nuchal gland constituents. Our findings demonstrate that captive-hatched juveniles from toad-rich Ishima Island that had not been fed toads possess defensive bufadienolides in their nuchal glands, presumably due to maternal provisioning of these sequestered compounds. Wild-caught juveniles from Ishima possess large quantities of bufadienolides, which could result from a combination of maternal provisioning and sequestration of these defensive compounds from consumed toads. Interestingly, juvenile females from Ishima possess larger quantities of bufadienolides than do juvenile males, whereas a small sample of field-collected snakes suggests that adult males contain larger quantities of bufadienolides than do adult females. Captive-born hatchlings from Kinkasan Island lack bufadienolides in their nuchal glands, reflecting the absence of toads on that island, but they can sequester bufadienolides by feeding on toads (Bufo japonicus) in captivity. The presence of large quantities of bufadienolides in the nuchal glands of R. tigrinus from Ishima may reduce the risk of predation by providing an effective chemical defense, whereas snakes on Kinkasan may experience increased predation due to the lack of defensive compounds in their nuchal glands.

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1. Host plant specialisation by herbivorous insects is ubiquitous, especially among the Lepidoptera. Many taxa have the ability to accumulate toxic compounds from their host plants that serve as chemical defences against natural enemies. Despite common knowledge of this pattern among insect ecologists, we still have much to learn about how dietary variation affects an insect's ability to acquire toxic plant chemicals.2. Longwing butterfly larvae (Heliconius) accumulate toxic cyanogenic glucosides from their host plants, passion vines (Passiflora), that make them toxic to most predators.3. Here, we present on zebra longwing (H. charithonia) caterpillar cohorts that were reared on native P. affinis, P. biflora, P. lutea, or P. suberosa to determine how host usage affected cyanide accumulation over larval developmental stages, and ultimately the toxicity of adult butterflies. Samples were collected at third, fourth and fifth instars, and teneral adults. Cyanogenic glucosides were extracted, the cyanide molecules were captured as sodium cyanide (CN), and CN content was quantified colorimetrically.4. The quantity of CN acquired increased linearly over larval ontogeny and was variable among host plants. CN concentration increased over larval development for

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