The role of colour in thermoregulation and protection against ultraviolet radiation


Schematic of the major components of energy flux in grasshopper thermoregulation (from Umbers et al 2013)

Schematic of the major components of energy flux in grasshopper thermoregulation (from Umbers et al 2013)

Temperature-dependent colour change in Kosciuscola grasshoppers and its role in thermoregulation

Male Kosciuscola tristis grasshoppers change colour from black to turquoise when their body temperature reaches 25°C a change that is is not related to time of day or light intensity (Umbers 2011). Although we can measure and model the differences in body temperature between the two colour phases, it is unclear as to whether those temperature differences affect fitness. In trying to understand the evolution of temperature-dependent colour change and its relationship with temperature in this group, we are looking at whether all the Kosciuscola species change colour via TEM, and measuring their spectral reflectance across the ultraviolet, visible and near-infrared. The ultimate goal is to understand whether colour change can effect thermoregulation such that it provides a selective advantage.


Colour as protection against ultraviolet light in the blue layer

Creatures of the so called blue layer or blue armada are surprisingly common visitors to Sydney beaches in summer. The blue-bottles (Physalia physalia G) are very famous members of the Blue Layer because of their ability to cause a painful sting but there are many more organisms from diverse Phyla that inhabit this azure food chain. These include the sea lizards, (Glaucus atlanticus A, Glaucus marginatus B, C) the blue suns (Porpita porpita D), by-the-wind-sailors (Vellela vellela) and purple bubble snails (Janthina janthina E, F). We are working on a project to describe the spectral reflectance of this group and generate hypotheses about their convergent coloration and its role in protection against ultraviolet radiation.

Some members of the Blue Layer – A: sea lizard's blue venter (Glaucus atlanticus); B: sea lizard's white dorsum (Glaucus marginatus);  C: sea lizard's blue venter (Glaucus marginatus); D: blue sun (Porpita porpita); E: violet side of bubble snail (Janthina janthina); F white side of bubble snail (Janthina janthia); G: blue-bottle (Physalia physalia) © Kate Umbers & Nikolai Tatarnic

Some members of the Blue Layer – A: sea lizard's blue venter (Glaucus atlanticus); B: sea lizard's white dorsum (Glaucus marginatus);  C: sea lizard's blue venter (Glaucus marginatus); D: blue sun (Porpita porpita); E: violet side of bubble snail (Janthina janthina); F white side of bubble snail (Janthina janthia); G: blue-bottle (Physalia physalia) © Kate Umbers & Nikolai Tatarnic