Positive feedback promotes terrestrial emergence behaviour in an amphibious fish

Area of Science:

• Ecology
• Evolutionary Biology
• Physiology

Background:

• Ecological transitions, like vertebrates moving to land, may involve positive feedback loops.
• Phenotypic plasticity and habitat choice can drive evolutionary changes.

Purpose of the Study:

• To test if aquatic hypoxia, emergence behavior, and respiratory plasticity create a positive feedback loop in amphibious fish.
• To understand the mechanisms driving increased terrestrial activity in Kryptolebias marmoratus.

Main Methods:

• Comparing terrestrial-acclimated vs. water-acclimated Kryptolebias marmoratus.
• Exposing fish to aquatic hypoxia and measuring emergence behavior and hypoxia tolerance.
• Assessing gill morphology changes (inter-lamellar cell mass coverage) after hypoxia exposure.

Main Results:

• Terrestrially acclimated fish showed higher sensitivity to aquatic hypoxia and lower tolerance.
• Fish exposed to severe aquatic hypoxia spent nearly 50% of their time out of water.
• Gill lamellae coverage increased significantly, reducing aquatic respiratory function and hypoxia tolerance.

Conclusions:

• Emergence behavior in response to aquatic hypoxia leads to gill remodeling, which further promotes emergence.
• This positive feedback loop, driven by physiological plasticity, may explain the repeated evolution of amphibious behavior in fish.
• The findings offer insights into the ecological and evolutionary pressures facilitating major habitat transitions.