Ammonotelism and Ammonia Excretion in Aquatic Organisms; nitrogen pages 89-101
Mosquito Larvae
Authors: Donini and O’Donnell, 2005
Key Topic: Uptake and secretion in mosquito larvae
Anal papillae are identified as the site of ammonia excretion in mosquito larvae.
Ion Selective Micro Electrode Technique is used for studying this excretion process.
Ammonotelism
Definition: The physiological process in which organisms primarily excrete ammonia as their nitrogenous waste product.
Examples of Ammonotelic Organisms:
Aeshna sp. (Dragon Fly Larva):
Lives in an aquatic environment and excretes ammonia as its primary waste product (ammonotelism).
Undergoes metamorphosis to become an adult, at which stage it shifts to excreting uric acid (uricotelism).
Examples of Ammonotelism in Different Species
American Bullfrog (Rana catesbeiana):
Tadpoles are ammonotelic.
Amphibians undergo metamorphosis, transitioning to adults which predominantly excrete urea (ureotelic).
Northern Leopard Frog (Rana pipiens):
A semi-aquatic amphibian.
During summer, exhibits ureotelism but during winter, when it stays at the bottom of ponds and lakes, it becomes ammonotelic.
Axolotl (Ambystoma mexicanum):
This amphibian never reaches full adult phenotype, remaining ammonotelic throughout its life cycle.
African Clawed Frog (Xenopus laevis):
Fully aquatic and remains ammonotelic throughout its life.
Ammonotelism and Skin Excretion
Mudpuppy (Necturus maculosus):
Fully aquatic and predominantly ammonotelic.
90% of plasma ammonia is excreted via the skin.
The “Rubber Eel (Typhonectes natans)” excretes similar amounts of both ammonia and urea.
Of the ammonia ejected, 90% is excreted via skin, and 70% of urea is also excreted via skin.
Adaptation during Environmental Changes
African Lungfish (Protopterus annectens):
Remains ammonotelic as long as sufficient water is present, excreting three times more ammonia than urea.
During dry periods, the fish retreats into a mud hole, switches to air-breathing, and undergoes a transition to ureotelism.
Accumulates urea within its body (0.5-2% of body mass).
In the wet season, the fish returns to normal aquatic life, first excreting excess urea before reverting back to ammonotelism.
Symbiotic Relationships Involving Ammonotelism
Clown Fish and Sea Anemones:
Species involved: Clownfish (Amphiprion bicinctus) and Sea Anemones (Entacmaea quadricolor).
Symbiotic relationship where clownfish excrete ammonia, which the sea anemones absorb.
Sea anemones also absorb ammonia from symbiotic phototrophic dinoflagellates, which in turn provide sugars and amino acids to the clownfish.
Ammonia Excretion in Marine Organisms
General belief: In marine invertebrates and teleosts, ammonia is excreted passively across gills or other forms of gas exchange epithelia.
The excretion process involves an equilibrium described by the equation:
along an outwardly directed Partial Pressure gradient ().
Ammonia Excretion in Marine Vertebrates
Research findings:
Ammonia transporter expression observed in marine Pufferfish (Takifugu rubripes).
Key transporters:
Rhbg: expressed basolaterally (near the blood side).
Rhcg: expressed apically (near the seawater side).
Ammonia Excretion in Freshwater Organisms
Factors Influencing Ammonia Excretion in Trout:
Gill boundary layer acidification contributes to ammonia trapping.
Major player: H+-ATPase, which modulates the pH.
Other components include Rh-like ammonia transporters, NH3 diffusion, and basal Na/K-ATPase function.
Ammonia Excretion in Aedes aegypti:
Research conducted by Weihrauch & O’Donnell in Current Opinion in Insect Science (2021).
Anal papillae of Aedes larvae are best studied models for freshwater animals regarding ammonia excretion.
Note: The exact role of AMTs (ammonia transporters) remains unclear.