Data from: Why has transparency evolved in aposematic butterflies? insights from the largest radiation of aposematic butterflies, the Ithomiini

Defended species are often conspicuous and this is thought to be an honest
signal of defences, i.e. more toxic prey are more conspicuous. Neotropical
butterflies of the large Ithomiini tribe numerically dominate communities
of chemically-defended butterflies and may thus drive the evolution of
mimetic warning patterns. Although many species are brightly coloured,
most are transparent to some degree. The evolution of transparency from a
warningly coloured ancestor is puzzling as it is generally assumed to be
involved in concealment. Here we show that transparent Ithomiini species
are indeed less detectable by avian predators (i.e. concealment).
Surprisingly, transparent species are not any less unpalatable, and may in
fact be more unpalatable than opaque species, the latter spanning a larger
range of unpalatability. We put forth various hypotheses to explain the
evolution of weak aposematic signals in these butterflies and other
cryptic defended prey. Our study is an important step in determining the
selective pressures and constraints that regulate the interaction between
conspicuousness and unpalatability.

具有防御能力的物种通常外观醒目，这被认为是防御能力的诚实信号（honest signal）——即毒性越强的猎物，其外观越醒目。大型绡蝶族（Ithomiini）的新热带区蝴蝶在化学防御性蝴蝶群落中占据数量优势，因此可能推动了拟态警戒模式的演化。尽管该类群诸多物种色彩艳丽，但多数均具备一定程度的透明性。从具有警戒色（aposematic coloration）的祖先类群演化出透明性的过程令人困惑，因为学界普遍认为透明性与隐蔽性相关。本研究证实，透明的绡蝶族物种确实更难被鸟类捕食者察觉，即实现了隐蔽效果。令人意外的是，透明物种的不可食性并未降低，事实上甚至可能高于不透明物种——后者的不可食性跨度范围更广。我们提出了多种假说，以解释这类蝴蝶及其他具有隐蔽性的防御性猎物的弱警戒信号（aposematic signal）演化机制。本研究为明确调控醒目性与不可食性之间相互作用的选择压力与限制因素，迈出了重要的一步。