Cicada minimum age tree: Cryptic speciation and exponentially increasing base substitution rates in recent geologic...

Area of Science:

• Evolutionary biology
• Phylogenetics
• Molecular evolution

Background:

• Cicadas (Cicadoidea) exhibit complex evolutionary histories.
• Recent global studies have provided new insights into cicada phylogeny.
• Endemic species, particularly from the Ryukyu Islands, offer unique evolutionary perspectives.

Purpose of the Study:

• To construct a time-calibrated phylogenetic tree for cicadas, focusing on Ryukyu Islands endemics.
• To investigate the evolutionary divergence times and patterns of cicada lineages.
• To explore the factors contributing to cicada biodiversity and cryptic species formation.

Main Methods:

• Phylogenetic analysis of 352 cicada specimens using BEAST v1.10.4 software.
• Incorporation of fossil calibrations dating back to the Triassic and Quaternary geological events.
• Utilized a relaxed clock model and COI gene data for molecular dating.

Main Results:

• The crown age of Cicadoidea was estimated at 200.63 Ma, with Tettigarctidae as the oldest lineage.
• Derotettiginae diverged at 99.2 Ma, followed by Tibicininae at 66.15 Ma.
• Cicadidae subfamilies diverged around 40.57 Ma, with evidence of adaptive radiation and cryptic species in Cicadinae.

Conclusions:

• Cicada substitution rates show an exponential increase in recent geological time.
• The spread of C4 grasses and Quaternary climate changes likely drove increased cicada biodiversity and cryptic speciation.
• The Ryukyu Islands serve as a key region for understanding these evolutionary processes.