Transition to Land

• Overview of Transition
  • Examines the adaptations needed for life both in water and on land.

Obstacles in Water Locomotion

• Gravity and Drag
  • Gravity: The natural downward force exerted by water.
  • Adaptations: Swim bladders and pectoral fins help counteract gravity.
  • Drag: Refers to the friction encountered from water which affects the fish's movement.
  • Pitch and Yaw: Two forms of movement affected by drag.

Mechanisms of Locomotion in Water

• Contraction and Relaxation:
  • Fish achieve movement through a sequence of anterior-to-posterior contractions on one side of their body, followed by relaxation on the opposite side.
  • This contraction wave moves from anterior (front) to posterior (back).
• Thrust Production:
  • Water behind the bend is pushed, resulting in forward thrust.
  • Side-to-side motion is minimized to maintain forward movement.

Types of Fish Locomotion

• Most movements are concentrated in the posterior region (tail area) of fish.
• Types of Movement:
  • Anguilliform: Entire body undulates.
  • Carangiform: Movement is primarily in the caudal (tail) half of the body.
  • Ostraciiform: Rigid bodies with motion predominantly from the caudal fin.

Fin Movements and Other Adaptations

• Variations in Movement:
  • Not all fish use their bodies exclusively for flexing. Some movements of the fins or use them solely for locomotion.
  • Amiiform Motion: Oscillation of dorsal fins.
  • Gymnotiform Motion: Oscillation of the ventral or anal fins.
  • Labriform Motion: Rowing movement using pectoral fins.
  • Rajiform Motion: Anterior-posterior undulations of pectoral fins.

Drag vs. Thrust Considerations

• Types of Drag:
  • Viscous Drag: Results from friction between the fish's body and water; remains constant across different speeds.
  • Inertial Drag: Caused by pressure differences due to water being displaced; increases with speed.
• Thrust Optimization:
  • Body Thickness: Ideal fish body should have a thickness of about 25% of its body length to optimize thrust and minimize drag.

Morphological Adaptations for Thrust

• Teardrop Shape: Most effective for minimizing drag. The thickest part of the body should be around 1/3 of the distance from the anterior end.
• Examples of Fish Shapes:
  • Tuna: Shorter, less flexible body optimal for high-speed movement.
  • Dolphins: Adapted to reduce drag effectively for swimming.

Appendicular Skeleton Adaptations

• Structure of Paired Fins:
  • The girdles that attach fins to the trunk function mainly for anchoring muscles, not for direct support.
  • Elements:
  • Proximal regions: Pterygiophores for muscle attachment.
  • Distal regions: Ceratotrichia, which are keratinized rods supporting fin structure.

Evolutionary Theories of Limb Development

• Gill Arch Theory: Suggests that pectoral girdles evolved from posterior gill arches, where gill rays became more complex to form fins.
• Fin Fold Theory: Proposes that paired ventral fins originated as stabilizers, leading to the evolution of pectoral and pelvic regions simultaneously.
• Molecular Evidence: Engrailed-1 and T-box genes play a critical role in defining the structure and evolution of fish fins.

Transition from Water to Land

• Key Factors for Land Locomotion:
  • Greater influence of gravity and substrate complexity.
  • Skeletal adaptations necessary for supporting body weight outside of water.
  • Limbs must provide backward force when moving against various substrates in air.