Résumé
1. Predation is an important selective pressure and some prey have evolved
conspicuous warning signals that advertise unpalatability (i.e.
aposematism) as an antipredator defence. Conspicuous colour patterns have
been shown effective as warning signals, by promoting predator learning
and memory. Unexpectedly, some butterfly species from the unpalatable
tribe Ithomiini possess transparent wings, a feature rare on land but
common in water, known to reduce predator detection. 2. We tested if
transparency of butterfly wings was associated with decreased
detectability by predators, by comparing four butterfly species exhibiting
different degrees of transparency, ranging from fully opaque to largely
transparent. We tested our prediction using both wild birds and humans in
behavioural experiments. Vision modelling predicted butterfly
detectability to be similar for these two predator types. 3. In
concordance with predictions, the most transparent species were almost
never found first and were detected less often than the opaque species by
both birds and humans, suggesting that transparency enhances crypsis.
However, humans were able to learn to better detect the more transparent
species over time. 4. Our study demonstrates for the first time that
transparency on land likely decreases detectability by visual predators.