Fossil calibrated molecular phylogenies of Southern cave weta

Aim: The biota of continents and islands are commonly considered to have a source-sink relationship, but small islands can harbour distinctive taxa. The distribution of four monotypic genera within the southern subfamily Macropathinae on young oceanic islands indicates a role for long-distance dispersal and extinction. We used molecular dating to estimate the timing of the southern radiation and infer potential processes involved.

Location: Subantarctic islands, South Africa, South America, Australia, Aotearoa/New Zealand.

Taxon: Southern hemisphere camel crickets subfamily Macropathinae within the Orthopteran family Rhaphidophoridae (Cave crickets/camel crickets/cave weta/tokoriro).

Methods: Phylogenetic relationships were inferred from whole mtDNA genomes and nuclear sequences (45S cassette; four histones). We used a fossil and one palaeogeographic event to calibrate a molecular clock analysis.

Results: We confirm that neither the Australian nor Aotearoa/New Zealand Rhaphidophoridae fauna are monophyletic. The Macropathinae radiation may have begun in the late Jurassic but trans-oceanic dispersal is required to explain the distribution of some lineages within the subfamily Macropathinae. Dating the most recent common ancestor of seven island endemic species with their nearest mainland relative suggests that each existed long before land surface on their island home was available.

Main conclusions: If our molecular clock analysis is a good time estimate, then our data from the island endemic species suggest a failure to sample mainland species (New Zealand, Australia, or elsewhere) due to either extinction or lack of investment into taxonomy and species discovery.

Methods
We used high-throughput sequencing of whole genomic DNA to assemble entire mitochondrial genomes and multi-copy nuclear markers for molecular phylogenetics.