Chromatic Contrast Alone Does Not Predict Predation Risk in the Longhorn Beetle Rosalia alpina

Area of Science:

• Ecology
• Evolutionary Biology
• Animal Behaviour

Background:

• Colouration plays a crucial role in predator-prey dynamics, influencing camouflage and signalling.
• The Rosalia alpina beetle's blue and black pattern's function in predator avoidance is not well understood.

Purpose of the Study:

• To investigate if the Rosalia alpina's blue colouration provides camouflage against beech bark.
• To determine if the black spots offer additional anti-predation benefits beyond the blue colouration.

Main Methods:

• Spectrophotometry was used to measure the reflectance of beetle colouration and beech bark.
• Chromatic contrasts were modelled under avian vision.
• Plasticine models of the beetle in black, blue, and natural patterns were used in field predation experiments.

Main Results:

• Both blue and black colourations were distinguishable from beech bark, with black spots showing lower contrast.
• Blue and naturally patterned models experienced fewer attacks than black models in September.
• Colour-based differences in predation risk diminished by October.

Conclusions:

• The blue body colouration and natural pattern of Rosalia alpina likely reduce predation risk, particularly early in the season.
• Black spotting does not appear to provide significant anti-predation benefits beyond the blue colouration.
• Alternative functions for the black spots, such as thermoregulation or signalling, warrant further investigation.