Data condition dependence in biosynthesized chemical defenses of an aposematic and mimetic Heliconius butterfly

Aposematic animals advertise their toxicity or unpalatability with bright
warning coloration. However, acquiring and maintaining chemical defenses
can be energetically costly, and consequent associations with other
important traits could shape chemical defense evolution. Here, we have
tested whether chemical defenses are involved in energetic trade-offs with
other traits, or whether the levels of chemical defenses are condition
dependent, by studying associations between biosynthesized cyanogenic
toxicity and a suite of key life-history and fitness traits in a
Heliconius butterfly under a controlled laboratory setting. Heliconius
butterflies are well known for the diversity of their warning color
patterns and widespread mimicry, and can both sequester the cyanogenic
glucosides of their Passiflora host plants and biosynthesize these toxins
de novo. We find energetically costly life-history traits to be either
unassociated or to show a general positive association with biosynthesized
cyanogenic toxicity. More toxic individuals developed faster, had higher
mass as adults, and a tendency for increased lifespan and fecundity. These
results thus indicate that toxicity level of adult butterflies may be
dependent on individual condition, influenced by genetic background or
earlier conditions, with maternal effects as one strong candidate
mechanism. Additionally, toxicity was higher in older individuals,
consistent with previous studies indicating accumulation of toxins with
age. As toxicity level at death was independent of lifespan, cyanogenic
glucoside compounds may have been recycled to release resources relevant
for longevity in these long-living butterflies. Understanding the origins
and maintenance of variation in defenses is necessary in building a more
complete picture of factors shaping the evolution of aposematic and
mimetic systems.