Notes on BIOL 2200: Life on Land - Vertebrate Animals

Learning Objectives

• Understand ecological impacts of insects.

• Comprehend evolution of jaws and its influence on vertebrate diversification.

• Investigate the transition of vertebrates from aquatic to terrestrial environments.

• Explore adaptations that enabled vertebrates to thrive on land.

• Describe adaptive advantages of the amniotic egg.

• Identify examples of amphibians and reptiles.

Insect Ecology

Beneficial Insects

• Pollinators: Vital for fruit and vegetable production; annual economic value exceeds $200 billion in the US.

• Pest Controllers: Predatory and parasitic insects effectively manage herbivore populations in crops.

• Decomposers: Play a crucial role in nutrient cycling in ecosystems.

Pests and Disease

• Herbivore Pests: Some insects can cause extensive damage to crops; growing resistance to pesticides is a concern.

• Disease Vectors: Certain insects are responsible for transmitting diseases:

• Mosquitoes: Malaria, Zika, Yellow Fever, West Nile Virus, Chikungunya.

• Kissing Bugs: Chagas Disease.

• Tsetse Flies: African Sleeping Sickness.

Vertebrate Phylogeny

• Major groups include:

• Myxini: Hagfish.

• Petromyzontida: Lampreys.

• Chondrichthyes: Cartilaginous fishes (like sharks).

• Actinopterygii: Ray-finned fishes.

• Amphibia: Amphibians.

• Mammalia: Mammals.

• Reptilia: Turtles, lizards, snakes, crocodiles, etc.

• Aves: Birds.

Evolution of Jaws

• Jaws emerged as an evolutionary innovation, leading to a rapid diversification of jawed fish.

• Hypotheses suggest jaws originated from skeletal rods supporting gill slits, sharing morphological similarities with jaws.

• Jaws and gill supporting rods are derived from the same embryonic cells; however, fossil evidence supporting this is currently inconclusive.

Sharks vs. Ray-finned Fish

• Sharks:

• Made of cartilage (derived trait), with mineralized teeth (made of calcium) adapted for hunting.

• Ray-finned Fish:

• Most diverse vertebrate group; possesses a fully mineralized skeleton and swim bladder for buoyancy.

Transition from Water to Land

• Lobe-finned Fish

• Coelacanths and lungfish

  • Bone structures in their fins resembling wrists, indicating evolutionary adaptation to land (

  • Closest living relative to tetrapods

• Tiktaalik: a pivotal fossil that showcases features facilitating land locomotion (e.g., developed rib cage, neck).

  • Between Lobe-finned fish and earliest extinct tetrapods

• Tetrapods: First appeared in the fossil record approximately 365 MYA, marked by key adaptations:

1. New modes of movement.

   1. Something other than fins to move

2. Enhanced skeletal support.

   1. Increased gravity means more support

3. Novel methods for gas exchange.

4. Water retention strategies.

Adaptations in Tetrapods

• Derived traits:

• Limbs featuring digits.

  • Snakes lose digits

• A distinct neck separating head from body.

• Pelvic girdle bones fused to the backbone.

  • Aids with pressure for gravity

• Adults exhibit a complete lack of gills.

  • Change to thoracic breathing

Amphibians

• Amphibians undergo metamorphosis from aquatic larvae to a form legs and lungs.

  • Complete metamorphosis

• Moist skin in many amphibian species enables gas exchange; some may lack lungs entirely.

• External fertilization occurs in moist environments, with unprotected eggs.

  • Tadpoles

Groups of Amphibians

• Salamanders: Varied life stages, including aquatic adults.

• Frogs: Notable for distinct aquatic larvae and the ability to vocalize; toads are not a monophyletic group.

Amniotic Egg

• Characterized by extraembryonic membranes:

• Allantois: Waste management for the embryo.

• Amnion: Fluid-filled cavity that protects the embryo.

• Chorion: Facilitates gas exchange.

• Provides a yolk for nutrients and an albumen for additional nourishment.

Extended Advantages of Amniotes

• Amniotic eggs allow for shell development or internal gestation, dramatically reducing water loss.

• Amniotes possess less permeable skin, decreasing adult water loss, and utilize rib cages for effective ventilation and gas exchange.

Reptiles

• Features include scales and feathers rich in keratin that minimize desiccation.

• Reptiles exhibit internal fertilization leading to shelled egg-laying on land.

• Thermoregulatory traits vary:

• Many are ectothermic (e.g., snakes, lizards).

• Birds are endothermic.

Specific Groups

• Lizards: Diverse in size and dietary habits.

• Snakes: Evolved from lizards, showing adaptations for hunting and predation.

• Turtles: Characterized by shells fused to their skeletal framework, inhabiting terrestrial, freshwater, and marine environments.