🔬General Biology I Unit 29 – Vertebrates

Key Characteristics of Vertebrates

• Possess a vertebral column (backbone) composed of vertebrae that provides structural support and protects the spinal cord
• Have an endoskeleton made of bone or cartilage that provides a framework for the body and attachment points for muscles
  • The endoskeleton allows for greater body size and complexity compared to invertebrates
• Exhibit bilateral symmetry, meaning their body can be divided into two mirror-image halves along a central axis
• Develop a distinct head region with sensory organs (eyes, ears, nose) and a brain enclosed in a skull
• Have a closed circulatory system with a heart that pumps blood through blood vessels
  • The closed circulatory system is more efficient than the open circulatory system found in invertebrates
• Possess jaws that allow for more efficient feeding and a wider range of food sources
• Have a highly developed nervous system with a centralized brain and spinal cord
• Exhibit a high degree of cephalization, with concentration of sensory organs and nervous tissue in the head region

Evolution and Diversity of Vertebrates

• Vertebrates evolved from a common ancestor that diverged from invertebrate chordates around 525 million years ago
• The earliest vertebrates were jawless fish (agnathans) that lacked paired fins and had a cartilaginous skeleton
  • Examples of extant jawless fish include hagfish and lampreys
• Jawed fish (gnathostomes) evolved around 450 million years ago and diversified into two main lineages: cartilaginous fish (Chondrichthyes) and bony fish (Osteichthyes)
  • Cartilaginous fish include sharks, rays, and skates
  • Bony fish are the most diverse group of vertebrates and include ray-finned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii)
• Tetrapods (four-limbed vertebrates) evolved from lobe-finned fish around 370 million years ago and adapted to life on land
  • The first tetrapods were amphibians, followed by the evolution of amniotes (reptiles, birds, and mammals)
• Birds evolved from theropod dinosaurs around 150 million years ago and are characterized by feathers, hollow bones, and a keeled sternum
• Mammals evolved from synapsid reptiles around 200 million years ago and are characterized by hair, mammary glands, and specialized teeth

Vertebrate Body Systems

• The integumentary system consists of the skin, hair, feathers, scales, and glands that protect the body and regulate temperature
• The skeletal system provides support, protection, and attachment points for muscles, and is composed of bone or cartilage
  • The axial skeleton includes the skull, vertebral column, and rib cage
  • The appendicular skeleton includes the limbs and girdles (pectoral and pelvic)
• The muscular system allows for movement and is composed of skeletal, smooth, and cardiac muscle tissue
• The circulatory system transports oxygen, nutrients, and waste products throughout the body and consists of the heart, blood vessels, and blood
• The respiratory system exchanges gases between the body and the environment and includes lungs, gills, or skin
• The digestive system breaks down food into usable nutrients and includes the mouth, esophagus, stomach, intestines, and accessory organs (liver, pancreas, gallbladder)
• The excretory system removes metabolic waste products from the body and regulates water and ion balance, and includes kidneys, ureters, bladder, and urethra
• The nervous system coordinates and controls body functions and includes the brain, spinal cord, and peripheral nerves
• The endocrine system regulates growth, development, and homeostasis through the secretion of hormones by glands (pituitary, thyroid, adrenal, gonads)

Vertebrate Locomotion and Movement

• Aquatic vertebrates (fish) use fins for swimming and maneuvering in water
  • Types of fins include dorsal, caudal (tail), anal, pectoral, and pelvic fins
  • Some fish (e.g., lungfish) also have fleshy, lobed fins that can be used for crawling on land
• Tetrapods have four limbs adapted for locomotion on land, water, or air
  • Amphibians have short, muscular limbs for walking, jumping, and swimming
  • Reptiles have limbs positioned more directly beneath the body for more efficient locomotion on land
  • Birds have wings adapted for flight and legs adapted for perching, walking, or swimming
  • Mammals have limbs adapted for running, jumping, climbing, flying (bats), or swimming (whales, seals)
• Vertebrate locomotion is powered by skeletal muscles that attach to bones via tendons
  • Muscles work in antagonistic pairs (flexors and extensors) to produce movement
• Some vertebrates have specialized gaits for efficient locomotion
  • Examples include the gallop in horses, the bounding gait in rabbits, and the undulating flight of snakes
• Arboreal vertebrates have adaptations for climbing and moving in trees, such as prehensile tails, claws, and opposable digits
• Aquatic mammals (cetaceans) have streamlined bodies and modified limbs (flippers) for swimming
• Flying vertebrates (birds, bats, and some gliding mammals) have wings and lightweight bones to reduce body mass

Vertebrate Reproduction and Development

• Most vertebrates reproduce sexually, with fusion of male and female gametes (sperm and egg) to form a zygote
  • Some vertebrates (e.g., some lizards and fish) can reproduce asexually through parthenogenesis
• Vertebrate embryonic development begins with cleavage, a series of rapid cell divisions that produce a hollow ball of cells called a blastula
• Gastrulation follows, where the blastula folds inward to form three germ layers: ectoderm, mesoderm, and endoderm
  • The ectoderm gives rise to the nervous system and skin
  • The mesoderm gives rise to muscles, bones, and circulatory system
  • The endoderm gives rise to the digestive and respiratory systems
• Vertebrate development can be oviparous (egg-laying), ovoviviparous (eggs develop inside the mother), or viviparous (live birth)
  • Oviparous vertebrates include most fish, amphibians, reptiles, and monotreme mammals
  • Ovoviviparous vertebrates include some sharks and reptiles
  • Viviparous vertebrates include most mammals and some sharks and reptiles
• Vertebrate eggs can be amniotic (with extraembryonic membranes) or anamniotic (without extraembryonic membranes)
  • Amniotic eggs have four extraembryonic membranes: amnion, chorion, allantois, and yolk sac
  • Amniotic eggs are found in reptiles, birds, and mammals
• Vertebrate parental care varies from no care (most fish) to extensive care (most birds and mammals)
  • Parental care can include guarding eggs or young, providing food, and teaching behaviors

Vertebrate Adaptations and Habitats

• Vertebrates have adapted to a wide range of habitats, from the deep ocean to high mountains and from deserts to polar regions
• Aquatic vertebrates have adaptations for living in water, such as gills for respiration, streamlined bodies for swimming, and lateral line systems for detecting water movement
  • Examples of aquatic vertebrates include fish, amphibians (in larval stage), and some reptiles (sea turtles, marine iguanas) and mammals (whales, dolphins, seals)
• Terrestrial vertebrates have adaptations for living on land, such as lungs for respiration, limbs for locomotion, and skin that prevents water loss
  • Examples of terrestrial vertebrates include most amphibians, reptiles, birds, and mammals
• Desert-dwelling vertebrates have adaptations for conserving water and regulating body temperature, such as concentrated urine, nocturnal activity, and light-colored skin
  • Examples of desert vertebrates include some reptiles (e.g., horned lizards), birds (e.g., roadrunners), and mammals (e.g., camels, kangaroo rats)
• Arctic and Antarctic vertebrates have adaptations for surviving in cold environments, such as thick fur or feathers, insulating fat layers, and countercurrent heat exchangers
  • Examples of polar vertebrates include penguins, polar bears, and Arctic foxes
• Arboreal vertebrates have adaptations for living in trees, such as prehensile tails, claws, and grasping hands or feet
  • Examples of arboreal vertebrates include some reptiles (e.g., chameleons), birds (e.g., woodpeckers), and mammals (e.g., monkeys, sloths)
• Flying vertebrates have adaptations for aerial locomotion, such as wings, hollow bones, and efficient respiratory systems
  • Examples of flying vertebrates include birds, bats, and some gliding mammals (e.g., flying squirrels)

Ecological Roles of Vertebrates

• Vertebrates play important roles in ecosystems as consumers, predators, and prey
  • Herbivorous vertebrates (e.g., rabbits, deer) consume plants and can shape plant communities through grazing or browsing
  • Carnivorous vertebrates (e.g., wolves, hawks) consume other animals and can regulate prey populations
  • Omnivorous vertebrates (e.g., bears, crows) consume both plants and animals and can have a stabilizing effect on ecosystems
• Vertebrates can act as keystone species, whose presence or absence has a disproportionate effect on the ecosystem
  • Examples of keystone vertebrates include sea otters (which control sea urchin populations and maintain kelp forests) and wolves (which regulate deer populations and affect plant communities)
• Vertebrates can serve as ecosystem engineers, modifying their environment in ways that affect other species
  • Examples of vertebrate ecosystem engineers include beavers (which create wetlands by building dams) and elephants (which create clearings and maintain grasslands)
• Vertebrates can be important seed dispersers, helping to maintain plant diversity and distribution
  • Examples of vertebrate seed dispersers include birds (which carry seeds in their digestive tracts) and mammals (which cache seeds or carry them on their fur)
• Vertebrates can be indicators of ecosystem health, with changes in their populations or behavior signaling environmental problems
  • Examples of vertebrate indicators include amphibians (which are sensitive to water quality) and birds (which can reflect changes in insect populations or habitat availability)

Conservation and Human Impact on Vertebrates

• Many vertebrate species are threatened or endangered due to human activities such as habitat destruction, overhunting, pollution, and climate change
  • Examples of threatened vertebrates include tigers, rhinoceroses, and many species of amphibians and reptiles
• Habitat fragmentation and loss are major threats to vertebrate populations, as they reduce available resources and disrupt migration and dispersal
  • Deforestation, urbanization, and agricultural expansion are major causes of habitat loss
• Overexploitation of vertebrates for food, medicine, or other products has driven many species to the brink of extinction
  • Examples include the hunting of whales for oil, the trade in shark fins for soup, and the collection of bird feathers for fashion
• Pollution, including chemical contamination, plastic waste, and noise pollution, can have detrimental effects on vertebrate health and behavior
  • Examples include the impact of DDT on bird eggshells, the ingestion of plastic by marine vertebrates, and the disruption of whale communication by underwater noise
• Climate change is altering vertebrate habitats and phenology (timing of life events), leading to mismatches between species and their environment
  • Examples include the earlier arrival of migratory birds to breeding grounds and the loss of sea ice habitat for polar bears
• Conservation efforts aim to protect vertebrate species and their habitats through a variety of strategies
  • Protected areas, such as national parks and wildlife reserves, provide safe havens for vertebrates
  • Captive breeding programs help to maintain populations of critically endangered species
  • International agreements, such as the Convention on International Trade in Endangered Species (CITES), regulate the trade in threatened vertebrates and their products
  • Public education and outreach help to raise awareness about the importance of vertebrate conservation and the threats facing these species
• Successful conservation efforts have led to the recovery of some vertebrate species, such as the bald eagle and the humpback whale
  • However, many vertebrate species continue to decline, and much work remains to ensure their long-term survival in the face of ongoing human impacts