Cane Toads - Ecology, Behaviour and Life History

Ecology, Behaviour and Life History

The common name "marine toad" and the scientific name Bufo marinus suggest a link to marine life, but the adult cane toad is entirely terrestrial, only venturing to fresh water to breed. Tadpoles have been found to tolerate salt concentrations equivalent to at most 15% that of seawater. The cane toad inhabits open grassland and woodland, and has displayed a "distinct preference" for areas that have been modified by humans, such as gardens and drainage ditches. In their native habitats, the toads can be found in subtropical forests, although dense foliage tends to limit their dispersal.

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 metres (66 ft) in length. The black eggs are covered by a membrane and their diameter is approximately 1.7–2.0 mm (0.067–0.079 in). The rate at which an egg evolves into a tadpole is dependent on the temperature; the pace of development increases with temperature. Tadpoles typically hatch within 48 hours, but the period can vary from 14 hours up to almost a week. This process usually involves thousands of tadpoles—which are small, black and have short tails—forming into groups. It takes between 12 and 60 days for the tadpoles to develop into toadlets, 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, Zug and Zug found an average initial growth rate of 0.647 mm (0.0255 in) per day, 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. Because they lack this key defence, only 0.5% of cane toads are estimated to reach adulthood.

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. The cane toad has a high tolerance to water loss—one study showed some can withstand a 52.6% loss of body water, allowing them to survive outside tropical environments.