Cryptic species are species which resemble one-another physically yet are reproductively isolated from each other. While such species clusters can come about due to convergent evolution, the vast majority are closely related species which have become reproductively isolated, but which have not diverged morphologically, usually as a result of a physical barrier splitting a population, followed by genetic drift. This is particularly common among morphologically conservative groups with low distribution rates, such as Mygalomorphs (Tarantulas, Trapdoor Spiders etc.), which are large Spiders occupying silk-lined burrows, typically remaining at a single site for their entire lives.
In a paper published in the journal Ecology and Evolution on 1 March 2024, James Starrett, Emma Jochim, Iris Quayle, Xavier Zahnle, and Jason Bond of the University of California, Davis, present the results of a genetic study of the Trapdoor Spider genus Promyrmekiaphila, which is known only from California, and describe a new species, the third within the genus.
The genus Promyrmekiaphila was first described in 1950 by the Swiss arachnologist and herpetologist Ehrenfried Schenkel to describe a morphotype of Trapdoor Spider found across California, which he named Promyrmekiaphila gertschi. This was later found to have previously been described by the French naturalist Eugène Simon as Aptostichus clathratus in 1891, though it was later recognised that the assignation of the species to the genus Aptostichus was wrong, and Schenkel's name Promyrmekiaphila was adopted, leading to the combination Promyrmekiaphila clathratus.
In 2007 and 2008 Amy Stockman and Jason Bond, then both at the Department of Biology at East Carolina University, carried out a study of the population of Promyrmekiaphila clathratus using mitochondrial DNA (mtDNA), coming to the conclusion that there were in fact two species within the genus, Promyrmekiaphila clathratus found throughout the coastal ranges in central and northern California, and a new species, which they named Promyrmekiaphila winnemem, which was found at the northern end of the Central Valley.
However, Stockman and Bond recognised that a study based upon mtDNA alone had its limitations, and that there still remained the possibility of other, cryptic, species of Promyrmekiaphila being found in California.
Starrett et al.'s new study is based upon a wider gene set. This identified a number of deeply separated lineages within the Promyrmekiaphila clathratus population, although Starrett et al. decline to name these as new species at this time, reasoning that they are not yet sufficiently genetically different to be reproductively isolated. However, a small group of Spiders found close to the San Andreas Fault line, from mid-San Francisco Peninsula to the Diablo Range, east of Paicines, were found to comprise a sister group to the Promyrmekiaphila clathratus and Promyrmekiaphila winnemem pair, therefore clearly representing a new species.
This new species is named Promyrmekiaphila korematsui, in honour of Fred Toyosaburo Korematsu, who was awarded the United States Presidential Medal of Freedom in 1998 in recognition of his lifelong dedication as a civil rights activist and his resistance to the incarceration of Japanese Americans in concentration camps during World War II.
Promyrmekiaphila korematsui is found d in shaded ravines and along roadcuts in Oak woodland habitat. Its distribution overlaps with that of Promyrmekiaphila clathratus, which may have implications for evolution of the genus, although the small sample size available for the genus so far prevents any detailed analysis at this time.
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