Data for: High contrast markings can negate the benefits of transparent camouflage

Transparency is, in theory, the ultimate form of concealment allowing for
perfect background matching camouflage regardless of the environment. In
nature, despite some remarkable examples of highly transparent organisms,
physiological constraints mean that transparency is often partial or
imperfect. This raises the question of how deviation from true
transparency may affect detectability and how camouflage functions.
Indeed, it has recently been suggested that partial transparency may
function as disruptive camouflage as adjacent transparent and opaque
patches differentially blend into the background. Differential blending
may therefore offer a route by which obligate opaque structures may be
concealed. The glass frogs (Centrolenidae) are a classic example of
transparency with ventral skin that allows for a view of the internal
organs. However, although the ventral skin is transparent, and the frogs
appear translucent, the internal organs are still largely opaque. Here we
performed visual modelling and a field predation study with model frogs,
to ask how the degree of transparency, and the arrangement of opaque
structures, affects detectability and survival. We predicted that greater
transparency would improve concealment by facilitating more effective
differential blending and that opaque elements which highlighted the
recognisable shape of the frog would suffer increased predation risk. We
found that greater translucency did improve background matching, but the
presence of salient opaque patterns negated this camouflaging effect.
Instead, survival was best explained by the distance at which the opaque
patterning could be resolved, with thinner edge stripes receiving fewer
attacks than thicker central stripes. Our data suggest that although
transparency may facilitate effective differential blending, camouflage
may be undermined by the presence of obligate opaque structures. These
limitations to the efficacy of transparent camouflage may favour the
evolution of translucency and explain why, despite having transparent
ventral skin, glass frogs retain sparse green pigmentation in their dorsal
skin.