Reptiles are important models in a number of biomedical and basic biological studies. Snake venom studies help treat heart attack victims and studies of reptile metabolism assist in developing pain-management drugs.
Scientists now recognise that reptiles are sentient animals capable of feeling pain, anxiety, fear and stress. Unfortunately, this recognition does not always reach those who care for reptiles as pets, who often ignore indicative behaviours and fail to make changes in their animals’ husbandry.
Reptiles are a challenging group to study as they often work in a different “time zone” and require patience when working with them. However, they can be quite rewarding for those that have the dedication and patience to succeed. For example, we’ve long thought that chameleons change colors as a form of camouflage but now we know it has much more to do with communicating.
A variety of behavioral traits have been studied in reptiles including shyness-boldness, exploration-avoidance, activity, sociability and interspecific aggression. Specifically, lizards are a model species for studying antipredator behavior and have a number of behavioral traits that can be measured including scalation, antipredator displays and defensive behaviors.
The sensory abilities of reptiles have evolved to match the varied ecological niches they inhabit. These adaptations impact how reptiles perceive stimuli in their captive environments, including zoo visitors. Studies have shown that reptiles rely heavily on visual cues to assess their surroundings and to locate and capture prey. Olfaction is also an important sense in the reptile world. Tongue-flicking is an expression of olfaction and brings chemosensory stimuli to the vomeronasal organ for processing.
While reptiles have a reputation for being quiet, they actually exhibit a wide range of behavioral responses to visitors. For example, a recent study showed that red kangaroos increased their interaction with the public during a zoo closure and European glass lizards decreased the evenness of space use and time spent visible in response to visitors.
Studying Anatomy and Physiology
Reptiles have a unique skull morphology with only one bone attaching to the first vertebrae, as opposed to mammals which have two bones (the stapes and malleus). They also have a single ear bone that transmits vibrations from the outer ear to the inner ear. They are known to engage in several types of play behaviour, including tug of war with objects and various forms of water play in aquatic species.
Physiologically, reptiles have a slower metabolism and lower heart rate than mammals or birds. This is reflected in the fact that their ventricular stroke volume is much lower (under 1 mL x kg-1 body weight) than the 1.4 mL x kg-1 body weight for mammalian species.
The physiology of reptiles is complex and requires a great deal of expertise. They have a variety of interesting physiological traits such as salt glands (oral and nasal, for example iguanas and crocodiles) that excrete excess salt to regulate their internal mineral balance, specialized sweat glands that are used to control body temperature, and horny scales which aid in prey detection.
There is still an abundance of research that needs to be done on the physiology of reptiles, especially the Squamata order (snakes and lizards). Despite being more commonly used than mammalian species in laboratories, there is a great deal of ignorance about their basic animal welfare needs, including their capacity to experience fear, stress, anxiety, pain and suffering. This may be due to a perception that they do not respond to stressors in the same way as mammals or that they are too small, slow and docile to feel much at all.
Studying Developmental Biology
Reptile research is often interdisciplinary and spans many subfields including embryology, anatomy, morphology, ecology and genetics. Developmental biology studies the process of growth and differentiation that result in the formation of body parts from simple cells, and this is an important aspect of evolution, as well as physiology and pathology (Lopez and McCay 2011).
The study of developmental processes focuses on a wide range of phenomena that have puzzled natural philosophers and scientists for two millennia: embryogenesis, pattern formation, cellular differentiation, cell migration, morphogenesis and organogenesis (see Section 1.1). The field draws on different experimental approaches to investigate these questions, with model organisms providing the best opportunity for precise dissection of causal relationships.
Scientists have developed a variety of methods to describe and explain developmental processes, and different interpretations of what it means for a scientific explanation to be “mechanistic” have emerged. However, there are at least four common elements that can be discerned across accounts of mechanistic explanation: what the mechanism does, its constituents, the spatiotemporal context of its operation, and its impact on a particular outcome (Love 2012).
Research in developmental biology is a complex enterprise that requires multidisciplinary collaboration at the molecule, cell, tissue, organ, and organism levels. For example, the evolutionary evo-devo of scales and feathers involves interactions among a diverse set of biological pathways, and the development of skin depends on both morpho-regulation (changing the shape of tissues to adapt to the environment) and morphological selection (altering the phenotype of a structure to better fit its habitat). In addition, there are important questions about what is the nature of the relation between morphological variation and the underlying genetic basis of an organism’s traits.
Studying Ecology and Evolution
Reptiles have emerged as one of the most successful animal groups on Earth. For years, scientists have attributed their success to luck: the extinction of many of their competitors during two of the planet’s biggest mass-extinction events, 261 and 252 million years ago, created an ecological window for reptiles to expand into diverse body types.
A more recent finding suggests that another key factor is the impact of climate change on reptile populations. A Harvard-led study found that the morphological evolution seen in early reptiles was more closely linked to climate than expected, with the body adaptations favoured by warm temperatures being selected for long after the mass extinction events.
The life-history traits evolved by reptiles in response to environmental pressures are fascinating. For example, terrestrial ectothermy has resulted in low energy needs and facilitated careful selection for incubation temperature management of eggs (e.g., oviparity in tropical lizards). Terrestrial ectothermy has also favoured the evolution of reptiles as predators with low metabolic rates that can keep pace with their prey.
Research has found that reptiles are tightly involved in key ecological interactions across tropical ecosystems. They perform a range of essential functions such as gene dispersal, nutrient cycling, trophic action and ecosystem engineering. The study of these interactions is vital to understanding the ecology and conservation of reptiles in their natural habitats. There is a growing awareness that reptiles are intelligent animals, with studies showing that they have the ability to feel pleasure, emotion and anxiety. This is particularly important when it comes to their welfare in captivity. An understanding of their sentience can help to improve husbandry conditions for these animals, ensuring they enjoy the highest quality of life possible.