Evolution
We've
now explained to you the reason frogs can be seen with extra legs, but
what about when legs are completely missing? While it was previously
believed to be caused by chemical pollution, the cause seems to be good
old-fashioned predation.
Missing legs are the most common
defect seen in frogs and toads. In an effort to find the cause, Stanley
Sessions (Hartwick College, New York) and Brandon B
allengee
(University of Plymouth, UK) tested how a variety of predators preyed
on tadpoles. The only predator whose behaviour explained limbless frogs
was the dragonfly nymph. They rarely ate tadpoles whole, grabbing it and
chewing at a hind limb or limb bud. They were even noted to grab the
tadpole and turn it with their forelegs to find the tender spots.
The tadpole is then released and swims away, becoming either a frog
with missing or deformed limbs (depending on how advanced
developmentally it is, as younger tadpoles are more capable of
regenerating limbs). But why only eat legs? Dragonfly nymphs also eat
toad tadpoles, and immature toad tadpoles develop poison glands - but
these glands develop in the body before the legs. So by only eating the
tasty hind legs of frogs and toads, the nymph is actually protecting
itself from ingesting poison.
Photo credit: Judy Helgen.
http://news.bbc.co.uk/earth/
http://www.examiner.com/
We've
now explained to you the reason frogs can be seen with extra legs, but
what about when legs are completely missing? While it was previously
believed to be caused by chemical pollution, the cause seems to be good
old-fashioned predation.
Missing legs are the most common defect seen in frogs and toads. In an effort to find the cause, Stanley Sessions (Hartwick College, New York) and Brandon B
Missing legs are the most common defect seen in frogs and toads. In an effort to find the cause, Stanley Sessions (Hartwick College, New York) and Brandon B
allengee
(University of Plymouth, UK) tested how a variety of predators preyed
on tadpoles. The only predator whose behaviour explained limbless frogs
was the dragonfly nymph. They rarely ate tadpoles whole, grabbing it and
chewing at a hind limb or limb bud. They were even noted to grab the
tadpole and turn it with their forelegs to find the tender spots.
The tadpole is then released and swims away, becoming either a frog with missing or deformed limbs (depending on how advanced developmentally it is, as younger tadpoles are more capable of regenerating limbs). But why only eat legs? Dragonfly nymphs also eat toad tadpoles, and immature toad tadpoles develop poison glands - but these glands develop in the body before the legs. So by only eating the tasty hind legs of frogs and toads, the nymph is actually protecting itself from ingesting poison.
Photo credit: Judy Helgen.
http://news.bbc.co.uk/earth/
http://www.examiner.com/
The tadpole is then released and swims away, becoming either a frog with missing or deformed limbs (depending on how advanced developmentally it is, as younger tadpoles are more capable of regenerating limbs). But why only eat legs? Dragonfly nymphs also eat toad tadpoles, and immature toad tadpoles develop poison glands - but these glands develop in the body before the legs. So by only eating the tasty hind legs of frogs and toads, the nymph is actually protecting itself from ingesting poison.
Photo credit: Judy Helgen.
http://news.bbc.co.uk/earth/
http://www.examiner.com/
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