Wood Frog - Reproduction

Reproduction

Rana sylvatica primarily breeds in ephemeral pools rather than permanent water bodies such as ponds or lakes. This is believed to provide some protection of the adult frogs and their offspring (eggs and tadpoles) from predation by fish and other predators of permanent water bodies. Adult wood frogs emerge from hibernation in early spring and migrate to nearby pools. There, males chorus, emitting duck-like quacking sounds. The males approach the females and clasp her behind her forearms before hooking his thumbs together around her in a hold called “amplexus” which is continued until the female deposits the eggs. Females deposit eggs attached to submerged substrate, typically vegetation or downed branches. Most commonly, females will deposit eggs adjacent to other egg masses, creating large aggregations of masses. Some advantage is conferred to pairs first to breed, as clutches closer to the center of the raft absorb heat and develop faster than those on the periphery, and have more protection from predators. If pools dry before tadpoles metamorphose into froglets, they die. This constitutes the risk counterbalancing the anti-predator protection of ephemeral pools. By breeding in early spring, however, wood frogs increase their offspring's chances of metamorphosing before pools dry. The larvae undergo two stages of development: fertilization to free-living tadpoles, and free-living tadpoles to juvenile frogs. During the first stage, the larvae are adapted for rapid development, and the growth depends on the temperature of the water and has a higher mortality rate. The second stage of development features rapid development and growth, and depends on environmental factors including food availability, temperature, and population density. Following metamorphosis, a small percentage (less than 20%) of juveniles will disperse, permanently leaving the vicinity of their natal pool. The majority of offspring are philopatric, returning to their natal pool to breed. Most frogs will breed only once in their life, although some will breed 2 or 3 times, generally with differences according to age. The success of the larvae and tadpoles is very important in populations of wood frogs because they will affect the gene flow and genetic variation of the following generations.