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New Zealand; Pacific
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Cave crickets are found all over the world including on tiny subantarctic islands. We studied how endemic island species are related to species from other Southern Hemisphere lands using DNA sequences and fossil-calibrated molecular clocks. The divergence dates of island species were all much older than the geological age of their island homes. Finding old lineages on young islands shows that these wingless insects are successful at crossing the ocean and colonising new habitat. However, the absence of closely related species elsewhere suggests that extinction is a biologically influential factor with potential to contradict traditional biogeographic assumptions.
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Mary Morgan-Richards is a Professor in Evolutionary Biology at Massey University.
Did you think that cave wētā (tokoriro) were only to be found inside New Zealand caves? Think again - they don't need caves and they are found all around the world! A new study discovered that five young subantarctic islands each have their own amazing and "ancient" endemic cave wētā. [The species are not "ancient" but each one is phylogenetically distinct].
The study of cave wētā (camel crickets/Rhaphidophoridae) sequenced DNA from whole mitochondrial genomes and used fossils from a sister group of orthoptera to calibrate a molecular clock. Species found only on subantarctic islands have sister taxa in New Zealand but the age of the divergence (stem) was found to be much older than the age of their island homes. In all seven cases the island species shared its most recent common ancestor with a sampled relative more than 10 million years ago (most were >25 MYA). This study provides an excellent example of how stem (branch) age can mislead biologists into thinking lineages are very old. The reason the stem dates are older than the islands is because close relatives were not sampled. All extant New Zealand genera (with one exception) were included in the study so the lack of close relatives suggests either lack of investment into species discovery or due to extinction. There is still time for us to go looking for close relatives of these island endemics in New Zealand but the islands will be getting smaller and smaller as sea level rises.
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