6. AdaptationsAquaticEnvironments.pdf

Adaptations to Aquatic Environments (Ch. 3) Learning Objectives Describe the main adaptations that organisms have evolved to cope with water density, friction, depth and salinity. Understand the alternative osmoregulatory strategies in fresh- and saltwater. Explain the limitations to gas...

Adaptations to Aquatic Environments (Ch. 3) Learning Objectives Describe the main adaptations that organisms have evolved to cope with water density, friction, depth and salinity. Understand the alternative osmoregulatory strategies in fresh- and saltwater. Explain the limitations to gas exchange in water and how countercurrent circulation maximizes gas exchange. Describe thermoregulation strategies, and adaptations to extreme temperatures in aquatic environments. Chemical and physical properties of water Thermal properties of water Water density and viscosity Water depth (pressure, light) O H Water as a solvent Salinity H Gas solubility and availability Credits: Wikipedia Thermal properties of water Pure water becomes solid at 0°C (32°F) and gas at 100°C (212°F). Dissolved salts decrease freezing temperature below 0°C, and increases the boiling point above 100°C. Water has a high specific heat: cools down and warms up relatively slowly. Water is very resistant to change state. Highest density at 4°C: ice floats. Problem: living tissues are denser that water and tend to sink Solution: flotation devices and increased friction fats and oils pockets of air buoyancy control complex appendages Swim bladder Credits: Wikipedia Problem: water has high viscosity and imposes high resistance Solution: hydrodynamic body shapes reduce friction Credits: S Dahal, M Lee, E Levy  Problem: Pressure increases with depth and cavities and organs could collapse Solution: no air cavities or collapsible ones In whales, the air cavities are adapted to collapse with pressure (they dive up to 6,000 feet for 20 min to an hour!). Credit: Piscitelli et al. 2013 Credits: Wikipedia Problem: light extinguishes with depth Solution: chemosynthesis and bioluminescence Production is not based on Some organisms are bioluminescent, photosynthesis, but on chemosynthesis producing light to communicate or to (e.g., bacteria in hydrothermal vents). lure prey. Credits: NOAA, NOAA/OER Video deep sea creatures: https://www.youtube.com/watch?v=UXl8F-eIoiM Water as a solvent Powerful solvent of polar compounds: ions available for organisms. Medium for chemical reactions. Water acidity and pH Water molecules can break apart into hydrogen ions (H+) and hydroxide ions (OH-). The concentration of hydrogen ions in a solution is its acidity: pH. Some ecosystems are naturally acidic (e.g., bogs), others close to neutral (e.g., lakes, wetlands) or sometimes basic (e.g., some lakes). Water salinity also imposes challenges to organisms Water contains dissolved solutes (and so does water in tissues). Water crosses between semipermeable membranes to equalize the concentration of solutes: osmosis. The force with which an aqueous solution attracts water by osmosis is the osmotic potential. Credits: Wikipedia Biological semi-permeable membranes limit the movement of solutes Passive transport: along a concentration gradient (e.g., diffusion, ion channels). Active transport: use of energy by the cell (against the concentration gradient). Credits: Penn State Problem: aquatic environments differ in salinity Solution: osmoregulation Aquatic organisms live in water that has (in most cases) a different solute concentration than their bodies. Osmoregulation involves the mechanisms used to maintain a proper solute balance between body and the environment: Freshwater organisms are hyperosmotic. Saltwater organisms are hypoosmotic. Credit: E Engbretson for U.S. Fish and Wildlife Service  MOVEMENT OF WATER MOVEMENT OF SOLUTES FRESHWATER (hyperosmotic organisms) SALTWATER (hypoosmotic organisms) Migratory salmons face both challenges Credits: The Seattle Times, Washington Forest Protection Association  Migratory salmons face both challenges In saltwater In freshwater Drinks several liters per day Does not drink at all Kidneys produce very ACCLIMATION Kidneys produce a lot of diluted concentrated urine urine Gill epithelial cells actively Gill epithelial cells actively transport salt ions (Na+ and Cl-) transport salt ions (Na+ and Cl-) out of the body into the body Adaptations in sharks and rays Sharks and rays that live in the ocean accumulate urea (excretion by-product) in their bloodstream to make them isosmotic with seawater. Urea harms proteins, so sharks and rays accumulate trimethylamine oxide to protect them. Osmoregulation in aquatic plants Mangroves retain high concentrations of solutes in their roots and leaves to make them hyperosmotic with the seawater, and passively diffuse water in. Mangroves use salt glands in their leaves to actively secrete salt. Gas solubility in water: CO2 Required for photosynthesis in plants and algae. CO2 solubility in water reaches similar concentrations as in air. The reaction in water is in equilibrium: more available CO2 when used by organisms. Problem: slow diffusion in water. The problem of slow diffusion and boundary layers The CO2 diffusion in unstirred water is 10,000 slower than in air. Aquatic plants, algae (and microbes) normally have a boundary layer: region of unstirred air or water surrounding the surface. Thus, photosynthesis can be limited by CO2 availability. O2 has even lower solubility in water Much lower solubility in water (1%) than in air (21%). Even worse given its low diffusion in water. Required for respiration. Countercurrent circulation in fish gills improves oxygen intake Equilibrium achieved Exchange stops Countercurrent circulation in fish gills improves oxygen intake Other adaptations to improve access to oxygen Increase the concentration of hemoglobin. Take gulps of air from the surface. Use air stored in the swim bladder. Mutualisms with algae. Thermoregulation e.g., swimming, flying, digesting, hunting, growth rate, molecular reactions, etc. Thermal optimum >Ability of an organism to control its body temperature. How will climate warming affect thermoregulation in organisms? Critical minimum Temp Critical maximum Temp  Is an organism’s temperature constant or variable? Homeothermic organisms maintain a constant temperature within its cells. Poikilothermic organisms do not have constant body temperatures. Heterothermic organisms maintain sometimes constant temperature, and sometimes changes with environmental temperature (e.g., tuna).  Is the control of temperature external or internal? >Ectothermic organisms: body temperature is largely determined by environmental temperature (reptiles, amphibians, insects, plants) >Endothermic organisms: generate sufficient metabolic heat to raise the body temperature higher than the external environment (mammals, birds). It costs energy (metabolic heat) but allows for broader niches. How do certain organisms survive in freezing waters? Ice crystals can damage cell structure causing death. Problem: saltwater freezes at -1.9°C, so organisms can freeze before water does (lower salt content in the body). Adaptations: Use of antifreezers: some Antarctic and Artic fish accumulate glycerol and glycoproteins in blood and tissues, decreasing the freezing temperature below the water freezing temperature. Supercooling: glycoproteins in the blood impede the formation of ice by coating crystals when they start to form (body temperature can decrease dramatically without freezing). How do certain organisms survive in hot springs up to 110°C? Proteins tend to denature above 45°C. Thermophilic bacteria and archaea can live in hot springs using proteins more resistant to denaturation. Credit: B Thaller