Zoology Ch 25

• Transition from water to land:

  • Adaptations for aquatic life co-opted for terrestrial breathing and locomotion
  • Instability of freshwater habitats led to evolution of multiple fish groups with some degree of terrestriality
  • Early Devonian period marked the transition of tetrapod vertebrae from aquatic to terrestrial habitats
  • Evolution of limbs in ancestral aquatic cavity prior to evolutionary movement on to land
• Characteristics of Tetrapods:

  • Double circulation directs deoxygenated blood into the lungs for oxygenation, and oxygenated blood from the lungs to other body tissues
  • Rich capillary network in the airfield cavity forms an efficient lung
  • Jointed limbs allow for movement on land
• Amphibians:

  • Transition from water to land in both their ontogeny and phylogeny
  • Ectothermic, relying on environmental context for body temperature regulation
  • Many depend on fresh water streams or pools for reproduction
  • Evolutionary origin traced back to the Devonian period
• AMPHIBIAN LIFE HISTORY - Metamorphosis:

  • Amphibians undergo metamorphosis, transforming from aquatic tadpoles to adult features such as limbs and lungs
  • Transition from water to land occurred over millions of years, with a series of alterations fitting the vertebrate body plan for life on land
• TETRAPOD EVOLUTION - Devonian Origin of Tetrapods:

  • Devonian period marked the diversification of Bonifishes, including many freshwater forms
  • Evolutionary adaptations like airfield cavity and paired internal nares allowed tetrapods to draw oxygen-rich air
  • Bony elements of paired fins evolved to support and move the body on land
• Exaptation:

  • Airfield cavity illustrates the evolutionary principle of exaptation, where a structure evolves for an initial utility and is later recruited for a new role
  • Internal airfield cavity and paired limbs of an aquatic tetrapod ancestor enabled the evolution of terrestrial breathing and support
  • Airfield cavity, lungs, and swimbladders are homologous, with specific terms distinguishing their roles in different species
• Co-Evolution of Tetrapods and Plants:

  • Vascular plants and trachea d'arthropods transitioned to land earlier than vertebrates, generating a food supply for terrestrial vertebrates
  • Evolution of terrestrial vertebrates and diversification of tetrapods closely tied to the evolution of vascular plants
  • Invasion of land by tetrapods and plants allowed for the development of a food supply and habitat for the evolution of terrestrial vertebrates
• CHISILIANS - Elongate, Limbless, Burrowing Creatures:

  • Chisilians possess a long, slender body, small dermal scales in skin, and many vertebrae
  • Most species are blind as adults with special sensory tentacles on the snout
  • Almost entirely burrowing or aquatic, inhabiting tropical forests of South America, Africa, India, and Southeast Asia
  • Fertilization of eggs occurs inside the female's body
• SALAMANDERS - Tailed Amphibians:

  • Typically small, with most North American salamanders less than 15 centimeters long
  • Limbs set at right angles to the trunk, with four limbs and hind limbs of approximately equal size
  • Carnivorous, preying on worms, small arthropods, and small mollusks
  • Ectotherms with a low metabolic rate
• SALAMANDERS - Respiration and Metamorphosis:

  • Aquatic larva with external gills and a fin-like tail
  • Parental care includes rotating eggs and protecting them from fungal infections and predation
  • Respiratory mechanisms include external gills, lungs, and both
  • Pedomorphosis, a persistent phylogenetic trend observed in salamander evolution, involves descendants retaining into adulthood features that occur only in pre-adult stages of their ancestors
• FROGS AND TOADS - Anura:

  • Frogs and toads occupy a variety of habitats
  • Absence of tails in adults, although all have a tail stage during embryonic or larval development
  • Specialized for jumping by simultaneous extensor thrusts of the hind limbs
  • Tadpoles have a long, ventail, both internal and external gills, no legs, specialized mouth parts for herbivorous feeding
• FROG ANATOMY AND PHYSIOLOGY - Frog Skin and Respiratory System:

  • Epidermis produces two types of integumentary glands that grow into the loose dermal connective tissue below
  • Small mucus glands secrete a protective mucus waterproofing onto the skin surface
  • Large granular glands produce a whitish, watery poison highly irritating to predators
  • Amphibians produce a skin poison, but its effectiveness varies among species and with different predators
• Decline of Amphibian Populations:

  • Epidemic infections by chytrid fungi
  • Loss of habitat
  • Climatic changes leading to reduced water depth, increased ultraviolet exposure
  • Increased incidence of malformed individuals, such as frogs with extra limbs
  • Introduction of invasive species, such as African clawed frog, Senapus Levis
• Conservation of Amphibians:

  • Importance of amphibians in controlling insect populations
  • Role of amphibians in maintaining ecosystem balance
  • Impact of amphibian declines on ecosystem health
  • Conservation efforts include habitat restoration and protection, disease management, control of invasive species, and research and monitoring of amphibian populations
• Future of Amphibians:

  • Uncertainty of the future of amphibians due to ongoing threats
  • Hope for the future due to conservation efforts and research
  • Potential for new discoveries and advancements in amphibian conservation
• Most amphibians have three types of chromatophores:

  • Xanthophores: containing yellow, orange, or red pigments
  • Lyridophores: containing a silvery, light-reflecting pigment
  • Melanophores: containing black or brown melanin
• Iridophores act like tiny mirrors, reflecting light back through xanthophores to produce the bright colors of many tropical frogs
• Green coloration in North American frogs is produced by an interaction of xanthophores containing a yellow pigment and lyridophores that produce a blue color by reflecting and scattering light
• Frogs can adjust their color to match their background for camouflage
• The musculoskeletal system of an adult frog is specialized for jumping and swimming by simultaneous extensor thrusts of the hind limbs
• The amphibian vertebral column supports the abdomen and limbs, with typical frogs having nine trunk vertebrae and a rod-like urostyle representing fused caudal vertebrae
• Frog limbs follow a typical tetrapod pattern with three main joints: hip, knee, and ankle, or shoulder, elbow, and wrist
• Limb muscles in frogs are homologous to radial muscles that move fish fins, but have become more complex for tetrapod movement
• In amphibians, limb and trunk musculature includes:

  • Anterior and ventral muscles for protraction and deduction
  • Posterior and dorsal muscles for retraction and deduction
  • Trunk musculature organized into powerful muscular bands
• The circulatory system in amphibians is a closed system of arteries and veins, serving a vast peripheral network of capillaries
• The respiratory system in amphibians includes vocal cords located in the larynx, lungs, and a respiratory tract
• The nervous system in amphibians includes a brain with three fundamental parts: midbrain, mesencephalon, and hindbrain, with emphasis on information processing and coordination of special senses
• Amphibian eyes have a structure for visual accommodation, essential for capturing prey, with lenses that move backward and forward to focus on distant and nearby objects
• Reproduction in amphibians involves breeding during warm seasons, with males calling to attract females, followed by amplexus where eggs are fertilized externally
• The life cycle of amphibians includes cleavage and embryonic stages within jelly-coated eggs, tadpoles with external gills that later become internal gills, and metamorphosis into adult frogs
• Some species of amphibians lay their eggs in foam masses on water surfaces, on leaves overhanging water, in damp burrows, or in water-filled chambers of plants
• Migration in frogs and toads involves males returning to ponds or streams before females, guided by olfactory cues and hormonal changes that increase sensitivity to temperature and humidity