Heat stress

• Non-renewable fuel sources produce Carbon dioxide (CO2)
• CO2 is a heat-trapping gas
• The atmosphere warms up
• The safe margin was 1.5℃
• IPCC projection pathways have wide margins but hazard risks increase at any level
• Global average temperatures do not reflect seasonal and regional variation well

  
• 2023 has exceeded 1.5℃ the entire year (begin of 4-year El Niño cycle)
• Weather patterns change
• Extreme weather events are increasing in frequency and magnitude
• Heatwaves


  Periods of 5 or more days in which the average temperature is surpassed by 5℃ or more
• Impending collapse of the AMOC (atlantic meridional overturning circulation)
• Mass mortalities have started to occur
• Both on land and in the ocean
• Linked to extreme heat events such as the blob or terrestrial heat domes
• 2022: Alaska snow crab collapse, 11 billion disappeared
• Was most abundant species in Eastern Bering Sea
• Snow crab is one of the most
• Paleocene-Eocene Thermal Maximum


  56 million years ago
• Animal groups that evolved during Paleocene-Eocene Thermal Maximum


  • Hominoidea (apes)
  • Simiiformes (apes & monkeys)
  • Homo
  • H. sapiens s.s.
  • Primates
• Temperate lizards have diversified during the Cenozoic (cooling / stable climate)
• Moved from a tropical origin towards north and south higher latitudes
• Evolution rates across 7,000 genes declined with northward expansion of the group


  Many younger species cold-adapted, while older/tropical species retain heat adaptations
• This is a general pattern for extant vertebrate clades
• Ectothermy


  The body temperature cannot be actively modified with respect to the environmental temperature

  
• Endothermy


  The body temperature is maintained constant through increase in metabolism (warming) or sweating (cooling)
• Ectotherms


  • Reptiles
  • Amphibians
  • Fishes
  • Invertebrates
• Endotherms


  • Mammals
  • Birds
• Endotherms


  • More mitochondria per cell to provide more energy if needed
  • Need more food for keeping up metabolic rate
  • Can be nocturnal
  • Too hot? Evaporative cooling through sweating, panting and blood flow increase
• Ectotherms


  • Depend on enough sun energy to become active
  • Requires them to be more diurnal for foraging
  • Nocturnal ectotherms are sit-and-wait predators
  • Too hot? Behavioural thermoregulation (hide)
  • Lower metabolism (Aestivation)
• Heterothermy


  • Variable thermal strategy
  • Torpor and hibernation in endotherms to conserve energy in the cold
  • Aestivation in ectotherms to survive heat
  • Both result in metabolic depression
• These responses are "tried and true" by Evolution
• Short term stress response to restore homeostasis (phase 1)


  • ATP -> ADP+P
• Stress response phase 2


  • Behavioural
  • Migration
  • Genomic plasticity
  • Epigenetic changes
• Trait shifts


  • Favoring persistence
  • Favoring migration
• Existing variation, Mutation + Selection

  Climate adaptation
• Skin & fur modifications


  • Reduction of fur density in desert animals to enhance heat dissipation
  • Evolution of light-colored skin or fur in some species to reflect solar radiation
  • E.g. Hyperolius nitidulus accumulates Purines in iridophores that cause reflective coating of skin
• Behavioral adaptations


  • Nocturnal activity or burrowing to avoid daytime heat (e.g., desert rodents, some large predators)
  • Use of water and mud bathing to cool down (e.g., elephants, buffalo)
  • Concealment of areas that could cause water loss in H. nitidulus
• Anatomical adaptations


  • Increase surface area / volume ratio for better heat loss
  • Large mammals have specialized blood vessels (carotid rete) for efficient heat exchange
  • Primates and horses evolved specialized sweat glands for cooling
• Optimal temperature (Topt)


  The temperature at which performance, energy use and fitness are optimal
• Preferred temperature (Tpref)


  The temperature an organism selects through behavioral thermoregulation