# Cretaceous Connections Among Camel Cricket Lineages in the Himalaya Revealed Through Fossil-Calibrated Mitogenomic Phylogenetics

## TL;DR

This study uses DNA and fossils to show that camel crickets in the Himalaya evolved long before continents drifted apart, challenging old theories about their spread.

## Contribution

The paper provides new mitogenomic data and fossil-calibrated phylogenetics to challenge continental drift as the driver of camel cricket distribution.

## Key findings

- The common ancestor of camel crickets lived in the Early Jurassic, before Pangea broke apart.
- The most recent common ancestor of two subfamilies lived 137 million years ago, before the Bering Land Bridge existed.
- Continental drift is not a major factor in the current distribution of camel crickets.

## Abstract

The flightless camel crickets are one of the oldest living lineages of Orthoptera, believed to have originated around 250 million years ago. In this paper we infer the timing of their radiation using DNA sequences from whole mitochondrial genomes of 20 camel crickets, with a focus on the neglected Rhaphidophorinae and Aemodogryllinae groups. To determine whether the taxonomic groups share a single common ancestor, we combined new DNA sequences from camel crickets from Bhutan with published genetic data. Our phylogenetic tree supports the monophyly of most of the genera sampled but supports the reinstatement of Gymnaeta Adelung, which forms a lineage sister to the group comprising Diestrammena, Tachycines, Gymnaetoides, Homotachycines, and Pseudotachycines. Based on our fossil-calibrated molecular clock phylogeny, the common ancestor of camel crickets was estimated to have lived in the Early Jurassic when the supercontinents were still connected. We estimate that the most recent common ancestor of Aemodogryllinae and Rhaphidophorinae lived about 137 million years ago, well before America and Asia were connected by the Bering Land Bridge. Thus, we find little evidence to suggest that continental drift explains the current distribution of this wingless orthopteran family.

The nocturnal, flightless camel crickets (Rhaphidophoridae) have a global distribution and are believed to have originated prior to the breakup of Pangea. We investigated the phylogeny and the timing of the radiation of East Asian species with mitogenomic data. Initially we analyzed a large taxon dataset (n = 117) using available partial mitochondrial and nuclear DNA sequences to confirm the monophyly of subfamilies and current taxonomy. Our findings support the monophyly of each genus within the subfamily Aemodogryllinae, with a minor inconsistency between taxonomy and phylogeny resolved by resurrection of the genus Gymnaeta Adelung. Fossil-calibrated molecular clock analysis used 11,124 bp alignment of 13 complete mitochondrial protein-coding genes for 20 species of Rhaphidophoridae, with a focus on the neglected Rhaphidophorinae and Aemodogryllinae lineages. Divergence time estimates suggest that the most recent common ancestor of the family lived during the Early Jurassic (189 Mya ± 23 Mya) before Pangea broke into the supercontinents or possibly during the early stage of breakup when Gondwana and Laurasia were still connected by land. The two subfamilies, Rhaphidophorinae and Aemodogryllinae, that overlap in Asia are estimated to have diverged 138 Mya ± 17 Mya, well before the Late Cretaceous northern connection between America and Asia (the Bering Land Bridge). Thus, our extended sampling of species from East Asia and Oceania refutes the importance of continental drift in the evolution of this wingless orthopteran family.