SPECIATION BY POLYPLOIDY IN TREEFROGS: MULTIPLE ORIGINS OF THE TETRAPLOID, HYLA VERSICOLOR

Area of Science:

• Amphibian genetics
• Evolutionary biology
• Speciation research

Background:

• Polyploidy is a rare mode of speciation in animals, but is disproportionately frequent in anuran amphibians.
• Gray treefrogs (Hyla chrysoscelis and Hyla versicolor) represent a diploid-tetraploid species pair, making them a model for studying polyploid speciation.

Purpose of the Study:

• To investigate the phylogenetic relationships between the diploid gray treefrog (Hyla chrysoscelis) and the tetraploid gray treefrog (Hyla versicolor).
• To determine the number of independent origins for the tetraploid species, Hyla versicolor.
• To explore the evolutionary history and ancestral relationships within this anuran amphibian group.

Main Methods:

• Mitochondrial DNA (mtDNA) was utilized, specifically sequencing the cytochrome b gene.
• Phylogenetic analyses were conducted on 37 populations of Hyla chrysoscelis and Hyla versicolor.
• Sequence divergence was calculated to infer evolutionary relationships.

Main Results:

• The diploid species, H. chrysoscelis, comprises distinct eastern and western lineages with 2.3% sequence divergence.
• The tetraploid species, H. versicolor, originated independently at least three times.
• Two tetraploid lineages are more closely related to specific diploid lineages (0.18%-1.4% divergence) than to each other (1.9%-3.4% divergence).
• The maternal ancestor of a third tetraploid lineage remains unidentified.

Conclusions:

• Phylogenetic data strongly support the hypothesis of multiple, independent origins for the tetraploid gray treefrog lineages.
• The evolutionary history of Hyla versicolor is characterized by recurrent polyploidization events.
• Understanding these multiple origins provides critical insights into the mechanisms of animal speciation via polyploidy.