Data from: Evolutionary adaptations of TRPA1 thermosensitivity and skin thermoregulation in vertebrates

Altering skin color and reflectance is crucial for temperature regulation
in poikilothermic vertebrates, while less so in homeotherms like birds and
mammals, which evolved feathers, fur, and other insulation for endothermy.
Heat-sensing in vertebrates relies primarily on Transient Receptor
Potential (TRP) channels, with certain channels (TRPA1) shifting
thermosensitivity over evolution and others retaining heat sensitivity
(TRPV1). Exploration of a role for TRP channels in skin physiology has
largely focused on human pigmentation and overlooked the evolution of
different thermoregulatory structures in the integument of distinct
vertebrates. For instance, colour/reflector pigment cells in ectotherms,
fur and feathers in endotherms, hairless skin in hominids, and blubber in
marine mammals. Therefore, we investigated whether a TRP channel mediates
skin darkening induced by heat in the ectotherm Xenopus laevis and then
explored the evolution of TRPA1 thermal sensitivity and its link with skin
physiology. We find Trpa1 mediates heat-induced melanosome dispersion,
darkening skin under warmer conditions. In contrast, TRPA1 is known to
mediate cold sensation in rodents and UV-induced tanning in humans,
leading us to investigate the co-evolution of TRPA1 and skin
thermoregulation. Our findings reveal that TRPA1 is a heat sensor in
ectotherms with uncovered integuments. In mammals, we suggest that TRPA1
was thermally insensitive in Euarchontoglires but became cold-sensitive in
several rodent lineages. TRPA1 shows reduced selection pressure for
thermosensitivity in aquatic mammals (manatees, whales) that depend on
blubber for insulation as compared to their terrestrial relatives. These
findings emphasize adaptive evolution of TRPA1 in vertebrates, linking
thermal sensitivity to the evolution of skin physiology.