One Frog, Two Frog, Green Frog, Blue Frog

This past weekend, I headed down to Rondeau Bay to have a relaxing few days at the cottage. Usually this consists of boating, fishing, campfires, and enjoying the backyard scenery. Unfortunately, Saturday brought windy, rainy weather, so I couldn’t enjoy many of these activities. Even though Mother Nature was not being cooperative with my weekend plans, I still decided to go out and see what kind of things I could find in the rain. This was a great decision, as I found a very cool green frog (Lithobates clamitans).

Cut of stream flowing from Rondeau Bay, where many frogs can be found
Cut of stream flowing from Rondeau Bay, where many frogs can be found

Green frogs are abundant in the Rondeau area, and you can hear them calling to each other almost every night, sounding like the ‘twang’ of a rubber band. Listen to the call of the green frog here.  If you find a frog that has big round discs (tympanum) behind its eye, this is a good clue that you’ve found a green frog. Green frogs and bullfrogs are easy to mix up, however, since they both have large tympanum, and similar colouration. To distinguish green frogs from bullfrogs, look to see if there are raised ridges of skin along the back of the frog. If there is, you probably have a green frog.

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Top: Green frog (Lithobates clamitans) with ridges of skin down its back Bottom: American bullfrog (Lithobates catesbeiana)
Top: Green frog (Lithobates clamitans) with ridges of skin down its back
Bottom: American bullfrog (Lithobates catesbeiana)

The reason that this particular green frog that I found was so cool was because of its colour. This green frog was blue! I had never seen a blue frog in Ontario before, so I was excited. I was even more excited when I found a different blue-coloured green frog later in the day! The blue morph of Lithobates clamitans is considered rare, so I was lucky to find two different frogs in the same area. When I looked into why some green frogs have this colouration, I found an explanation.

Blue-coloured Green frog (Lithobates clamitans) in Rondeau Bay, hiding in the weeds
Blue-coloured Green frog (Lithobates clamitans) in Rondeau Bay, hiding in the weeds

Green frogs are normally green because of something called iridophores and xanthophores. Iridophores and xanthophores are pigment cells that work together to form the green colour of the frog. Blue wavelengths of light reflect off iridophores that are covered in a screen of xanthophores filled with yellow pigment. The yellow xanthophores over the blue-reflecting  iridophores creates the green colour that we see. Amphibians with blue skin are lacking the yellow pigment, so when the blue light is reflected, it is not filtered with yellow, and the skin appears blue. The yellow xanthophore pigments are often not present, or are replaced by a differently structured pigment cell in blue coloured frogs than in green coloured frogs.

It doesn’t seem to be clear whether these frogs get their blue skin passed down to them from their parents, or whether it is an environmental trigger that causes the yellow pigment to change. Maybe the two blue frogs I saw were from the same parent or parents, or maybe they grew up in a certain area of Rondeau Bay that somehow halted the development of their xanthophores.  Either way, it was really cool!

My next blog post will have even more cool stuff about Rondeau Bay, since the BIObus is heading out to Rondeau Provincial Park next week!

Stay tuned,

Jesse Sills

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