Cane toad

The cane toad begins life as an egg, which is laid as part of long strings of jelly in water. A female lays 8,000–25,000 eggs at once and the strings can stretch up to 20 m (66 ft) in length. The black eggs are covered by a membrane and their diameter is about 1.7–2.0 mm (0.067–0.079 in). The rate at which an egg grows into a tadpole increases with temperature. Tadpoles typically hatch within 48 hours, but the period can vary from 14 hours to almost a week. This process usually involves thousands of tadpoles—which are small, black, and have short tails—forming into groups. Between 12 and 60 days are needed for the tadpoles to develop into juveniles, with four weeks being typical. Similarly to their adult counterparts, eggs and tadpoles are toxic to many animals.

When they emerge, toadlets typically are about 10–11 mm (0.39–0.43 in) in length, and grow rapidly. While the rate of growth varies by region, time of year, and gender, an average initial growth rate of 0.647 mm (0.0255 in) per day is seen, followed by an average rate of 0.373 mm (0.0147 in) per day. Growth typically slows once the toads reach sexual maturity. This rapid growth is important for their survival; in the period between metamorphosis and subadulthood, the young toads lose the toxicity that protected them as eggs and tadpoles, but have yet to fully develop the parotoid glands that produce bufotoxin. Only an estimated 0.5% of cane toads reach adulthood, in part because they lack this key defense - but also due to tadpole cannibalism. Although cannibalism does occur in the native population in South America, the rapid evolution occurring in the unnaturally large population in Australia has produced tadpoles 30x more likely to be interested in cannibalising their siblings, and 2.6x more likely to actually do so. They have also evolved to shorten their tadpole phase in response to the presence of older tadpoles. These changes are likely genetic, although no genetic basis has been determined.

As with rates of growth, the point at which the toads become sexually mature varies across different regions. In New Guinea, sexual maturity is reached by female toads with a snout–vent length between 70 and 80 mm (2.8 and 3.1 in), while toads in Panama achieve maturity when they are between 90 and 100 mm (3.5 and 3.9 in) in length. In tropical regions, such as their native habitats, breeding occurs throughout the year, but in subtropical areas, breeding occurs only during warmer periods that coincide with the onset of the wet season.

The cane toad is estimated to have a critical thermal maximum of 40–42 °C (104–108 °F) and a minimum of around 10–15 °C (50–59 °F). The ranges can change due to adaptation to the local environment. Cane toads from some populations can adjust their thermal tolerance within a few hours of encountering low temperatures. The toad is able to rapidly acclimate to the cold using physiological plasticity, though there is also evidence that more northerly populations of cane toads in the United States are better cold-adapted than more southerly populations. These adaptations have allowed the cane toad to establish invasive populations across the world. The toad’s ability to rapidly acclimate to thermal changes suggests that current models may underestimate the potential range of habitats that the toad can populate. The cane toad has a high tolerance to water loss; some can withstand a 52.6% loss of body water, allowing them to survive outside tropical environments.