Predator selection on multicomponent warning signals in an aposematic moth

Aposematic prey advertise their unprofitability with conspicuous warning
signals that are often composed of multiple color patterns. Many species
show intraspecific variation in these patterns even though selection is
expected to favor invariable warning signals that enhance predator
learning. However, if predators acquire avoidance to specific signal
components, this might relax selection on other aposematic traits and
explain variability. Here we investigated this idea in the aposematic moth
Amata nigriceps that has conspicuous black and orange coloration. The size
of the orange spots in the wings is highly variable between individuals,
whereas the number and width of orange abdominal stripes remain
consistent. We produced artificial moths that varied in the proportion of
orange in the wings or the presence of abdominal stripes. We presented
these to a natural avian predator, the noisy miner (Manorina
melanocephala), and recorded how different warning signal components
influenced their attack decisions. When moth models had orange stripes on
the abdomen, birds did not discriminate between different wing signals.
However, when the stripes on the abdomen were removed, birds chose the
model with smaller wing spots. In addition, we found that birds were more
likely to attack moths with a smaller number of abdominal stripes.
Together, our results suggest that bird predators primarily pay attention
to the abdominal stripes of A. nigriceps, and this could relax selection
on wing coloration. Our study highlights the importance of considering
individual warning signal components if we are to understand how predation
shapes selection on prey warning coloration.