Circadian clock determines the timing of rooster crowing

of a widespread species than to be faced with the challenge of conserving every population because all are distinctive. Undoubtedly, some reptile species have already gone extinct before we even knew they existed. But a lot remain to be discovered: for example, a single square kilometre of Australian desert can contain 14 co-existing species of the lizard genus Ctenotus (many of them so similar that only an expert can tell them apart). On Caribbean islands, tree-dwelling anoline lizards similarly occur at remarkably high densities and diversities. Reptile conservation thus has the problem that on the one hand these small secretive animals do not attract much sympathy from the public, and on the other there are vast numbers of genetically distinct reptile populations whose loss would significantly erode biodiversity. Many of the threats that affect all animals also affect reptiles, such as habitat degradation, new predators, and overexploitation. Some of the most worrying cases involve turtles, highly prized as traditional food and medicine in many Asian countries. Most turtles have very ‘slow’ lifehistories, requiring several years to reach maturity, and reproducing at low rates. In such animals, even a small increase in adult mortality can cause rapid population declines. It is difficult to see how wild turtles will survive into the next century over much of Asia. Crocodilians also are under substantial hunting pressure, reflecting the economic value of their skins, but so far have proved surprisingly resilient. Many field biologists believe that reptile populations have declined precipitously over the last few decades, and fears are growing that reptiles may follow amphibians into an extinction vortex. The central role of temperature in reptile biology suggests that climate change will have enormous impacts on many reptiles. It has already affected breeding phenology in some species. Thermal effects can ramify through all aspects of reptilian society and reproduction. For cold-climate reptiles, higher temperatures may bring benefits. For example, warmer springtime weather translates into longer mating seasons for Swedish sand lizards (Lacerta agilis), thereby increasing mating opportunities and thus, the average number of males with which a female mates. This multiple mating enhances offspring viability because females of this species selectively use sperm from distantly related males to fertilise their eggs, thereby avoiding inbreeding. In contrast, global warming poses severe thermal challenges to tropical reptiles. Already forced to remain inactive in shaded shelters for most of the day to avoid lethal ambient temperatures, such animals may have fewer and fewer opportunities for activity in a warming world. In species where sex is determined by incubation temperature, increasing nest temperatures may shift offspring sex ratios and affect population growth. Modern reptiles are the results of millions of years of evolution and comprise a diverse suite of lineages with intricate adaptations to a low-energy lifestyle. Freed from the energy-guzzling demands of endothermy, a myriad array of shapes, sizes and ecologies have evolved in reptiles. Even within a single lineage, the reptiles range from tiny pond turtles to giant Galapagos tortoises; from dwarf caimans to 6 m saltwater crocodiles; from 1 g geckos to 150 kg Komodo Dragons; and from tiny wormsnakes that feed on ant eggs to anacondas that eat capybaras. In many parts of the world, reptiles comprise a high proportion of all terrestrial vertebrate species. As we ponder the challenges of conservation in a changing world, we need to find solutions that work for these remarkable creatures.