Huelva (EFE).- A study carried out by the Doñana Biological Station (EBD-CSIC) has revealed that most amphibian species do not reproduce by “the typical and ancestral method”, with a life cycle with aquatic larvae that metamorphose terrestrial adults, but through alternative modes.
This is the first study that compares how amphibians have evolved in life cycles and reproductive modes in their three large groups: frogs, salamanders and caecilians, and for it the largest database of reproductive modes to date has been prepared, a study of approximately 4,000 species, the EBD-CSIC has reported in a note.
Most animals have complex life cycles, with one or more larval stages separated from an adult stage by profound anatomical changes known as metamorphosis; however, several of the large groups of vertebrates, such as mammals or birds, do not have larval stages.
To understand how this simplification of life cycles evolves and its consequences for species formation and rate of evolution, researchers have studied the evolution of life cycles in amphibians, which have the greatest diversity of life cycles and modes. reproductive of all terrestrial vertebrates.
Applying comparative phylogenetic analysis techniques, it has been verified that, despite more than 300 million years of evolution, many amphibian species maintain their ancestral reproductive mode.
However, contrary to what it may seem, most amphibians present alternative cycles, which include terrestrial eggs deposited in nests such as burrows or foam nests, kept in folds of the skin of adults, or even viviparity.
“In many species, the larval phase has been lost independently, so that toads, salamanders or caecilians hatch from terrestrial eggs, dispensing with the aquatic tadpole phase”, explained Christoph Liedtke, researcher at the EBD-CSIC, adding that “in other cases, the adult phase has been eliminated. In some species, the larvae become sexually mature without metamorphosing into adults.
The evolutionary passage from aquatic egg to terrestrial egg has been common in all lineages, but the various reproductive modes that have arisen from it have done so non-sequentially.
The team has also observed that, despite the important ecological consequences for each lineage of adopting one type of life cycle or another, these changes have had little consequence for their evolutionary success in terms of the number of species that have emerged afterwards.
“Only in salamanders do we observe a pattern in which the loss of the larval phase seems to have encouraged the formation of new species, while the loss of the adult phase seems to have increased their probability of extinction”, has indicated Iván Gómez, from the EBD-CSIC .
This study demonstrates that large developmental and life-span changes can evolve repeatedly and more rapidly than previously thought, and in some cases may be reversible.