Scientists at the University of California, Davis have identified a new species of trapdoor spider in California’s coastal sand dunes. The newly named Aptostichus ramirezae is closely related to Aptostichus simus, which is found along the coast from Monterey to Baja California, Mexico.
The discovery was published in Ecology and Evolution. According to senior author Jason Bond, a professor in the UC Davis Department of Entomology and Nematology, “While there are over 50,000 species of spiders worldwide, there are probably hundreds of thousands left to be discovered, even along the coast where new spider species may be hiding just underfoot of California beachgoers.”
Trapdoor spiders are small relatives of tarantulas. Females spend their lives underground in silk-lined burrows sealed with camouflaged doors. They emerge only when prey comes close enough for capture.
Emma Jochim, corresponding author and doctoral student at UC Davis, noted that “There are now four known species of trapdoor spiders in California that live exclusively in coastal dune habitats. The one we were looking at as part of this study was the most widespread, ranging from Moss Landing near Monterey down to Baja California — which is a pretty wide range for a trapdoor spider, given that they don’t easily leave their burrows to disperse.”
Jochim and her colleagues analyzed genomic DNA from Aptostichus simus collected across its range. Bond had long suspected that what appeared as one species might actually be multiple cryptic species—organisms that look similar but are genetically distinct.
Researchers examined both molecular data and distribution patterns. Cryptic species do not interbreed due to reproductive isolation. Jochim explained: “Based on what we know about their natural history and lifestyles, they’re not going to be able to disperse to different coastal dunes to reproduce and ‘mix’ with each other.”
Jason Bond named the new brown spider Aptostichus ramirezae after Martina Giselle Ramirez, dean at California State University Stanislaus and former biology professor at St. Norbert College. Ramirez has contributed significantly to research on trapdoor spiders and supported underrepresented students in STEM fields.
Both Aptostichus simus and Aptostichus ramirezae inhabit shrinking coastal dune habitats from central California through northern Baja California—including some Channel Islands—due mainly to development, erosion, wildfire risk and sea-level rise.
“They’re definitely at risk, especially the lineage Aptostichus simus,” said Jochim. “The new species has a much wider range, but Aptostichus simus is now really only found in San Diego, and projections for sea-level rise in that area are very grim. These spiders are not really able to adapt that quickly to new habitats.”
Understanding genetic differences among these populations helps scientists prioritize conservation efforts for those most vulnerable groups. Jochim added: “If we don’t know how many species are in an area or understand the patterns of genetic diversity between populations, we don’t really know what areas would be most important for conservation efforts.”
Other contributors include James Starrett and Hanna R. Briggs with UC Davis; funding came from the National Science Foundation.
