Chapter 28 Outline
Animals in Freshwater
- Passive water and ion exchanges: Freshwater animals tend to gain water by osmosis and lose major ions by diffusion
- Most types of freshwater animals share similar regulatory mechanisms
- BOX 28.1 Fish Mitochondria-Rich Cells and Their Diversity
- A few types of freshwater animals exhibit exceptional patterns of regulation
- Why do most freshwater animals make dilute urine?
Animals in the Ocean
- Most marine invertebrates are isosmotic to seawater
- Hagfish are the only vertebrates with blood inorganic ion concentrations that make them isosmotic to seawater
- The marine teleost fish are markedly hyposmotic to seawater
- BOX 28.2 Where Were Vertebrates at Their Start?
- BOX 28.3 Epithelial NaCl Secretion in Gills, Salt Glands, and Rectal Glands
- Some arthropods of saline waters are hyposmotic regulators
- Marine reptiles (including birds) and mammals are also hyposmotic regulators
- Marine elasmobranch fish are hyperosmotic but hypoionic to seawater
- BOX 28.4 The Evolution of Urea Synthesis in Vertebrates
Animals That Face Changes in Salinity
- Migratory fish and other euryhaline fish are dramatic and scientifically important examples of hyper-hyposmotic regulators
- Genomic studies point to greater gene-expression changes in crustaceans than fish
- Animals undergo change in all time frames in their relations to ambient salinity
Responses to Drying of the Habitat in Aquatic Animals
- BOX 28.5 Anhydrobiosis: Life as Nothing More than a Morphological State
Animals on Land: Fundamental Physiological Principles
- A low integumentary permeability to water is a key to reducing evaporative water loss on land
- Respiratory evaporative water loss depends on the function of the breathing organs and the rate of metabolism
- An animal’s total rate of evaporative water loss depends on its body size and phylogenetic group
- Excretory water loss depends on the concentrating ability of the excretory organs and the amount of solute that needs to be excreted
- Terrestrial animals sometimes enter dormancy or tolerate wide departures from homeostasis to cope with water stress
- The total rates of water turnover of free-living terrestrial animals follow allometric patterns
Animals on Land: Case Studies
- Amphibians occupy diverse habitats despite their meager physiological abilities to limit water losses
- Xeric invertebrates: Because of exquisite water conservation, some insects and arachnids have only small water needs
- BOX 28.6 The Study of Physiological Evolution by Artificial Selection
- Xeric vertebrates: Studies of lizards and small mammals help clarify the complexities of desert existence
- Xeric vertebrates: Some desert birds have specialized physiological properties