September 10,
2012, Phys.org
All tadpoles grow into frogs,
but not all frogs start out as tadpoles, reveals a new study on 720 species of
frogs to be published in the journal Evolution.
The study, "Phylogenetic
analyses reveal unexpected patterns in the evolution of reproductive modes in
frogs," led by John J. Wiens, an Associate Professor in the Department of
Ecology and Evolution at Stony Brook University, and colleagues Ivan Gomez-Mestra
from the Doñana Biological Station in Seville, Spain, and R. Alexander Pyron
from George Washington University, uncovers the surprising evolution of life
cycles in frogs.
Roughly half of all frog
species have a life cycle that starts with eggs laid in water, which hatch into
aquatic tadpoles, and then go through metamorphosis and become adult frogs. The
other half, according to the authors, "includes an incredible diversity of
life cycles, including species in which eggs are placed on leaves, in nests
made of foam, and even in the throat, stomach, or back of the female
frog.
There are also hundreds of
species with no tadpole stage at all, a reproductive mode called direct
development." For decades, it has been assumed that the typical mode (with
eggs and tadpoles placed in water) gave rise to direct development through a
series of gradual intermediate steps involving eggs laid in various places
outside water. "However, the results show that in many cases, species with
eggs and tadpoles placed in water seem to give rise directly to species with
direct development, without going through the many seemingly intermediate steps
that were previously thought to be necessary," Dr. Wiens said.
"The results also
suggests that there many potential benefits for species that have retained
aquatic eggs and tadpoles, such as allowing females to have more offspring and
to colonize regions with cooler and drier climates. These advantages may
explain why the typical frog life cycle has been maintained for more than 220
million years among thousands of species," said Professor Wiens.
Read more
at: http://phys.org/news/2012-09-unexpected-patterns-evolution-frog-life.html#jCp
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