Evolution of gigantism in amphiumid salamanders

Area of Science:

• Herpetology
• Evolutionary Biology
• Molecular Systematics

Background:

• The family Amphiumidae comprises three species of large, aquatic salamanders.
• Two species, Amphiuma means and Amphiuma tridactylum, are among the world's largest salamanders, while Amphiuma pholeter is small.
• These species inhabit diverse aquatic environments in the southeastern United States.

Purpose of the Study:

• To analyze lineage diversity and phylogenetic relationships within Amphiumidae using mitochondrial and nuclear DNA.
• To investigate the evolutionary history of gigantism within the Amphiumidae clade.
• To understand the divergence timing and patterns of speciation in these salamanders.

Main Methods:

• Sequencing of mitochondrial and nuclear genetic loci across the distribution of the three Amphiumidae species.
• Phylogenetic analyses to reconstruct evolutionary relationships and divergence times.
• Comparative analysis of body size evolution in relation to phylogenetic history.

Main Results:

• Three distinct lineages corresponding to the three recognized species have diverged since the late Miocene.
• The two gigantic species, Amphiuma means and Amphiuma tridactylum, are not each other's closest relatives.
• Evidence suggests at least two independent origins of gigantism within the family, or a single origin followed by size reduction in one species.

Conclusions:

• The evolutionary history of Amphiumidae involves significant body size changes, with gigantism evolving multiple times or being secondarily lost.
• Phylogenetic patterns of body size are linked to differences in habitat and range size.
• These findings have implications for understanding reproductive isolation and diversification within Amphiumidae.