Robin M. Andrews’s research while affiliated with Virginia Tech and other places

This chapter considers the diversity of locomotor modes among amphibians and reptiles from a functional perspective, emphasizing the mechanics of locomotion and examining the underlying similarities observed among diverse taxa that have converged on similar locomotor patterns. The 17,000-plus extant species of amphibians and reptiles occupy habitats ranging from the open oceans to the crowns of rainforest trees and the depths of desert soils. Such diverse habitats require different modes of locomotion. Feet that gain purchase on a tree limb are very different from those required to propel their owner through a pond. Furthermore, several alternative solutions to the same locomotor challenge may exist, depending on the evolutionary starting points of the lineages involved. The chapter considers lever systems, terrestrial locomotion with limbs, jumping, terrestrial limbless locomotion, aquatic locomotion, burrowing, climbing, and aerial locomotion.

This chapter assesses the conservation and the future of amphibians and reptiles. Amphibian declines are occurring at a rate estimated to be 200 times that of historical extinction levels; the extent of decline varies from region to region and within and among species. Reptiles may be in even greater danger of extinction than amphibians are, but we do not know much about the population status of many species. Although extinction is a natural phenomenon, most current extinctions result from human activities. The single most important impact of humans on amphibians and reptiles is habitat modification and destruction. The most successful conservation programs programmes identify and address the reason a species is endangered and at the same time provide benefits to local people. As such, the most important conservation action humans can take for amphibians and reptiles is to protect habitat.

This chapter addresses energetics and performance of amphibians and reptiles. Metabolic characteristics have equally profound effects on the day-to-day activities of amphibians and reptiles. Because the physiological characteristics of amphibians and reptiles are so clearly reflected in their behaviour and ecology, these animals have played an important role in studies of ecological and evolutionary physiology. The chapter traces some of those relationships, emphasizing the close connections between physiology and the behaviour and ecology of amphibians and reptiles. It starts with the structures used for gas exchange before considering the cardiovascular system, which transports oxygen and other substances throughout the body. The chapter then looks at how the production of ATP meets the needs of different ways of life and the energy costs of natural activities. It also studies metabolic depression, discussing aestivation, hibernation, and freezing.

This chapter explores the reproduction and life histories of reptiles, including the behaviours associated with mating, sex determination, and embryonic development. Regardless of the nature of day-to-day social interaction, the annual cycles of nearly all reptiles include at least one social event, mating. Physiological, morphological, and behavioural events that lead up to mating include the maturation of gonads, the development of secondary sexual structures, and courtship. Mating by some species is associated with high levels of gonadal activity, whereas in others it occurs when levels of sex steroids are low and the gonads are undeveloped. In this latter situation, mating is not followed immediately by fertilization, and sperm are stored for later use.

This chapter demonstrates that amphibians and reptiles exhibit an extraordinary diversity of feeding modes, mirroring their range of habitats and the wide variety of foods consumed in water or on land. Most species are carnivorous and prey capture is enhanced in several groups by the use of a projectile tongue, which is fired from the mouth to ensnare the prey. Other species engulf prey with mobile cranial bones organized into complex linkages and controlled by a remarkable array of muscles. Venom-delivering systems have evolved independently in several lineages of snakes and lizards, apparently based on a shared genomic heritage, and the specializations associated with venom delivery can be spectacular. The chapter takes a functional perspective and groups organisms that exhibit similar feeding modes together. This organization requires the simultaneous consideration of independently evolved lineages, which emphasizes the pattern in which different evolutionary lines converge on similar solutions to shared functional problems.

This chapter describes the reproduction and life histories of amphibians, including the behaviours associated with mating, how eggs are fertilized, sex determination, development and metamorphosis of larvae, and parental care. Reproduction is by far the most conspicuous feature of amphibian biology, and most casual observers seldom encounter amphibians outside of the breeding season. Many amphibians have external fertilization, whereas others fertilize their eggs inside the body of the female. Some of the most successful amphibians, including most plethodontid salamanders and Neotropical frogs in the families Eleutherodactylidae and Craugastoridae, have abandoned aquatic reproduction altogether and lay terrestrial eggs that undergo direct development into miniature adults. Some amphibians retain their eggs inside the reproductive tract of the female and give birth to live young; others provide elaborate forms of parental care, including transporting and feeding their offspring.

This chapter discusses the phylogenetic systematics and the origins of amphibians and reptiles. It begins by looking at the principles of phylogenetics and taxonomy. The chapter then traces the origins of terrestriality from aquatic ancestors and the subsequent diversification of amphibian and reptile groups, many of which are extinct and have left no descendants living today. There are three hypotheses for the origin of extant amphibians: the temnospondyl hypothesis, the lepospondyl hypothesis, and the diphyly hypothesis. The chapter also considers the relationships among extant lissamphibian lineages, the characteristics and origin of the amniotes, lepidosauria, and archosauria, and the debated origins of turtles.

This chapter provides an overview of herpetology. Studies of amphibians and reptiles have played key roles in biological specializations as diverse as developmental biology, behaviour, ecology, and medicine. Many of these contributions are the result of unique characteristics that make a certain species of amphibian or reptile suitable for a particular technique. Herpetological studies have also contributed to advances in molecular biology and medicine. Many people are familiar with the major groups of amphibians and reptiles—salamanders, frogs and toads, turtles, crocodylians, and lizards and snakes—from visits to zoos or from televised nature programmes. The chapter then looks at the diversity of amphibians and reptiles, as well as their shared characteristics, focusing on ectothermy and endothermy. It also considers amphibians and reptiles in the context of terrestrial ecosystems.

This chapter begins by describing broad patterns of diet and the foraging behavior behaviour of amphibians and reptiles. These patterns are associated with morphological, physiological, and behavioral behavioural characters that facilitate location, identification, capture, ingestion, and digestion of food items. The chapter then considers amphibians and reptiles as food resources for other animals, including parasites. Because parasites are so small compared with their hosts, they are usually difficult or impossible to avoid. The response to parasitism is thus largely physiological, and defensive mechanisms involve the host's immune system. In contrast, predators can often be avoided or deterred, and amphibians and reptiles have evolved a range of overt defensive mechanisms. Finally, the chapter discusses an example of coevolution between a snake and its prey.

This chapter assesses biophysical ecology, which is the study of how animals exchange heat and water with their environments. Reptiles and amphibians have been especially important in the development of this field because interaction with the physical environment is such a conspicuous part of their lives. Regulating the amount of water in the body requires balancing gain and loss. In a steady state (i.e. no change in body water content), the total intake of water must equal the total water loss, and each side of the water-balance equation has several components. This is a general equation that fits terrestrial or aquatic amphibians or reptiles, but some of the details of water movement apply only to particular situations or certain kinds of animals. The chapter then looks at the mechanisms of thermoregulation, considering heliothermy, thigmothermy, and kleptothermy.