D4- Colour and thermoregulation

Climate is a strong predictor of nearinfrared reflectance but a poor predictor of colour in butterflies Joshua T. Munro et al., 2019

• Colour variation across climatic gradients is a common ecogeographical pattern, the underlying causes of this are argued, particularly selection for thermal benefits.

• Aim-> test the evolutionary association between climate gradients and reflectance of near-infrared (NIR) wavelengths, which influence heat gain but are not visible to animals. measured ultraviolet (UVA), visible (Vis) and NIR reflectance from calibrated images of 372 butterfly specimens from 60 populations (49 species, five families) spanning the Australian continent. 

• Results-> the association between climate and reflectance was stronger for NIR than UVA–Vis wavelengths. climate predicted reflectance of the thorax and basal wing, which are critical to thermoregulation; but it did not predict reflectance of the entire wing, which has a variable role in thermoregulation depending on basking behaviour. 

• Conclusions-> evidence that selection for thermal benefits has shaped the reflectance properties of butterflies.

The global distribution of avian eggshell colours suggest a thermoregulatory benefit of darker pigmentation Phillip A. Wisocki et al., 2020 

• Context-> the survival of a bird’s developing embryo depends on the egg’s ability to stay within strict thermal limits, how eggshell colours help maintain thermal balance is debated.

• Methods-> used data spanning a wide phylogenetic diversity of birds on a global spatial scale

• Results-> birds living in cold habitats, particularly those with nests exposed to incident solar radiation, have darker eggs. evidence that darker eggs heat more rapidly than lighter ones when exposed to solar radiation. 

• Conclusions-> egg pigmentation could play an important role in thermoregulation in cold climates, while a range of competing selective pressures further influence eggshell colours in warmer climates.

• recap and why the study is important

• explanation of study 1

  • effects of the climate on butterflies

  • heat regulation linking to colour reflectance of wings, wing and basal sections have more of an impact on thermoregulation than the thorax which is more about visibility and survival

  • reflected more heat in hotter areas

  • body size also plays a role

  • climate shapes colour and heat reflectance

• explanation of study 2

  • background on colour of eggs

  • link between thermoregulation and colour and Bogart’s rule, there are darker eggs towards the poles, they heat up more there, are more blue/green near the tropics, supports Bogart’s rule but at higher solar intensities other factors influence too

  • typically found in ectotherms

• venn diagram comparison- strengths and weaknesses of each paper

• future research and other papers