Saturday, July 23, 2011

Wood Froglets

Less than three months after the eggs were laid, young wood frogs are emerging from ponds and wetlands around Duluth.  Wood frog metamorphosis occurs fairly quickly and can be easily observed in pond edges.  

Over the last two weeks wood frogs in Hartley Park transformed from 2 inch long tadpoles into froglets about 3/4" long. 

The rainstorms that have rolled through Duluth this week likely encouraged wood frogs to emerge from the wetlands. There are many froglets hopping along the wet forest floor - watch for them on the trails and your lawn. 
Wood frog at Gosner stage 40/41. Hindlimbs are fully developed, forelimbs are about to emerge from under skin.

Wood frog at Gosner stage 42. Forelimb just emerged, full tail remains.
Wood frog at Gosner stage 43. Tail somewhat reduced.

Wood frog at Gosner stage 44. Tail greatly reduced.

Wood frog at Gosner stage 45. Only small tail stub remains.
Another wood frog at Gosner stage 45.

Amphibian growth and development is dependent on many factors, including temperature, availability of food, water depth, and photoperiod (the amount of daylight).  Many amphibian species can accelerate or delay larval (tadpole) development and metamorphosis based on quality of their aquatic habitat. Although most wood frogs in a pond transform into froglets at approximately the same time (calling synchronous metamorphosis), multiple stages can usually be found during a visit.
Wood frogs resting on a floating board.  Top at Gosner stage 44 or 45, bottom at Gosner stage 42.

*The Gosner staging system was developed for Northern Leopard Frog (Rana pipiens) to identify key points in developmental progress from embryo through metamorphosis, also used for other Ranid species such as the wood frog (Rana sylvatica). citation: Gosner KL. 1960. A simplified table for staging anuran embryos and larvae with notes on identification. Herpetologica 16:183-90.