Frog Species in Canada

Frog Species in Canada

Description

Adult frogs typically have longer hind limbs than forelimbs, well-developed eyes, and permeable skin with mucus and poison glands. They also lack ribs and a tail. Some of the more aquatic species have well-developed webbing between their toes to assist with swimming. Adult frogs have lungs and breathe air, whereas larvae, known as tadpoles, live in the water and breathe through gills. Tadpoles have a tail with large fins and do not have legs in their early stages of development.

Frogs belonging to the family Bufonidae, known as toads, generally have relatively drier skin and reduced webbing between their toes. In Canada, other frogs that are commonly referred to as toads are the Plains and Great Basin spadefoots (family Scaphiopodidae).

Amphibians are ectotherms, meaning that they do not generate their own body heat. Instead, their body temperature is governed by external conditions. For example, amphibians can regulate their body temperature through behaviour and habitat use (e.g., by moving in and out of shade). This is known as “behavioural thermoregulation.” Winter temperatures in northern temperate regions are too cold for continued activity or survival, so most frogs hibernate underwater or buried underground below the frost line. However, some species, such as the wood frog, are able to survive freezing for extended periods of time.

Evolution

Frogs appear very early in the fossil record. Triadobatrachus, found in deposits from the Triassic period (251.9–201.3 million years old) in Madagascar, is the earliest known frog. Jurassic period deposits (201.3–145 million years old) in South America contain frogs that have a general body plan similar to some present-day species. Various adaptations permit frogs to exploit habitats ranging from rain forests to deserts and from the tropics to the Arctic Circle.

Distribution

Twenty-four species of frogs live in Canada; climatic limitations restrict most species to the extreme southern portion of the country. However, some Canadian species are more cold-tolerant and extend into the northern reaches of the country. The wood frog, for example, ranges above the Arctic Circle. This species has an extensive Canadian range and is found in every province and territory. The mink frog also has an extensive Canadian distribution. Like the wood frog, the majority of the mink frog’s North American range is in Canada.

The American bullfrog and the green frog, although originally Eastern species, have been introduced to British Columbia. The island of Newfoundland has no native frogs, but green, mink and wood frogs, as well as American toads, have been introduced and have become established there.

Reproduction and Development

Frog eggs lack a protective shell and are deposited in water or moist environments to prevent them from drying out. The eggs are usually fertilized externally before developing into tadpoles, a frog’s free-swimming larval stage. The tadpole transforms into its adult state through metamorphosis. This process involves numerous morphological and physiological changes. These include the loss of its tail and gills, limb and lung development, and alteration of sensory receptors to suit a terrestrial lifestyle.

Biological Importance

Frogs are ecologically important. Tadpoles are primary consumers in aquatic food chains and are an important source of food for various invertebrates and vertebrates. Adult frogs are also important predators of invertebrates, as well as some smaller vertebrate species. They are, in turn, consumed by a wide range of other species, such as fish, birds, reptiles and mammals. With both terrestrial and aquatic life stages, frogs play an important role in the movement of nutrients between these different environments. Frogs are also used in many fields of research and for anatomical studies in educational institutions.

Did you know?
On 15 April 2024, Canada Post issued two new stamps featuring endangered Canadian frogs. The Fowler's toad (Anaxyrus fowleri) and the Oregon spotted frog (Rana pretiosa) have experienced a significant loss of healthy habitat due to human development, invasive species, and pollution.