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

We developed a new time-calibrated phylogenetic tree incorporating primarily endemic Ryukyu Islands cicada data, along with some cryptic species, following the recent global cicada studies by Marshall et al. (2018), Łukasik et al. (2018), Simon et al. (2019), Price et al. (2019), and Hill et al. (2021). A total of 352 specimens were analyzed using BEAST v1.10.4 software with a relaxed clock model. Fossil calibrations dating as far back as the Triassic were adopted, largely following Johnson et al. (2018) and Moulds (2018), with a Quaternary geological event calibration based on Osozawa et al. (2012, 2021b), which was input into BEAST v1.10.4. In the COI tree, the crown age of Cicadoidea was estimated at 200.63 Ma. Tettigarctidae was found to be the oldest lineage, sister to all remaining cicadas. Derotettiginae, at 99.2 Ma, is the next oldest lineage, sister to all other monophyletic cicadas. The Tibicininae clade branched at 66.15 Ma, with the subfamilies Tettigomyiinae, Cicadettinae, and Cicadidae diverging at a crown age of 40.57 Ma. The Cicadinae clade consists of many tribe and genus-specific clades, with numerous cryptic species emerging due to vicariance and adaptive radiation. We estimated the base substitution rate as a function of age, and the results strongly indicate an exponential increase in substitution rates during recent geological time. This increase in cicada biodiversity, including the generation of cryptic species in the Ryukyu Islands and surrounding regions, may have been driven by the spread of C4 grasses and concurrent Quaternary climate changes.