Gnathostomes Flashcards

Gnathostomes Overview

• Gnathostomes are jawed fishes, characterized by the development of jaws aiding in a broader diet.
• Key derived characteristics include a jaw, four sets of Hox genes due to duplication, complete genome duplication, and the lateral line system.

Evolutionary Significance of Jaws

• Jaws evolved from anterior rods of gill slits, providing a clamping action for feeding.
• Allows grasping, shearing, and chewing, enhancing dietary options.

Genetic Adaptations and Duplications

• Hox gene duplication allows for greater morphological complexity in organisms.
• Genome duplication enables advanced functions and capabilities in species.
• Gene duplication occurs through random mutation during meiosis, increasing mutation rates. Beneficial mutations can be passed on, leading to new functions or losses of function (nonfunctionalization).

Types of Duplicated Genes

• Nonfunctionalization: one duplicated gene loses its function.
• Neofunctionalization: one gene acquires a new function distinct from the ancestral gene.
• Subfunctionalization: each gene takes on a different function, both originating from the ancestral gene.

Lateral Line System

• A sensory system with mechanoreceptive hair cells that detect water movement.
• Essential for detecting predators and prey.

Early Gnathostomes and Fossil Record

• Early gnathostomes outnumbered jawless vertebrates due to superior swimming ability and feeding mechanics.
• Initial marine species later adapted to freshwater environments.

Notable Groups of Gnathostomes

• Placoderms (e.g., Dunkleosteus): Existed 450-360 million years ago, large and armored, known as early super predators with evidence of internal fertilization.
• Acanthodians (Spiny Sharks): Lived 430-250 million years ago, characterized by stout spines supporting fins, resembling sharks.

Chondrichthyans (Sharks, Skates, Rays)

• Key features: cartilaginous skeletons, placoid scales, well-developed paired fins, internal fertilization.
• Respiration is achieved through ram ventilation; constant movement ensures water flows over gills.
• Possess claspers for reproduction, located beside the cloaca.

Chondrichthyans Diversity and Ecology

• Includes approximately 1000 species, thriving in marine environments globally.
• They exhibit both predatory behaviors and filter feeding strategies.

Subclasses of Chondrichthyans

• Elasmobranchii: This group includes sharks, rays, and skates. Features include oviparity and viviparity (exclusively in sharks), a sophisticated lateral line, strong chemoreception, and specialized vision with a reflective tapetum lucidum.
• Holocephali: Includes ratfish primarily found in deep waters. Characterized by oviparity and males having tentaculums for reproduction, along with a unique jaw structure and grinding teeth for consuming crustaceans.

Osteichthyans (Bony Fishes)

• Defined by bony skeletons, dermal fin rays, swim bladders for buoyancy, and color vision.
• Adaptive reproductive strategies include internal fertilization among various species.