A new study has identified seven spider species previously unknown to science in the depths of Israeli caves, with the surprise finding that they are evolutionarily closer to arachnids found in southern Europe than to their neighbors at cave entrances in Israel.
The peer-reviewed research, published in the Molecular Phylogenetics and Evolution journal, was conducted by scientists from the Hebrew University in Jerusalem and the University of Madison-Wisconsin.
The study “has extensive scientific implications for uncovering the evolution of speciation in caves and the historical, geographic and climatic processes that occurred in Israel,” the Hebrew University said in a statement.
Most spiders living deep in caves develop partial or complete blindness over time, alongside loss of pigments, with other sensory organs enlarged to adapt to the unique, isolated conditions.
Such unusual environments commonly trigger a phenomenon called convergent evolution, in which species with no common origin nevertheless develop analogous traits due to the need to deal with similar conditions.
“In many cases, these adaptations will lead to the creation of new species, whose distribution is geographically limited in areas with unique ecological conditions, such as a single cave or a system of connected caves,” said Hebrew University doctoral student Shlomi Aharon, who led the study under the guidance of Dr. Efrat Gavish-Regev and Prof. Dror Hawlena.
“In this study we sought to understand the evolutionary relationships between funnel web spiders with normal eyes that are found at the entrance to the caves in Israel, and those that are deep in the cave and are pigment-less, eye-reduced and even completely blind,” he explained.
The spiders were collected from caves in the Galilee and central Israel, after which they were taken to labs, where the scientists extracted their DNA and conducted more tests.
“Among the spiders we found, five were unique to different caves, and the two other species were found in several caves,” said Gavish-Regev, from Hebrew U’s National Natural History Collections.
“One of the surprising findings in the study shows that the new species are evolutionarily closer to species from caves in Mediterranean areas in southern Europe, than to species living in close proximity to them at cave entrances in Israel,” she said.
This finding, the study says, suggests “a complex biogeographic history.”
Two of the newly identified species are blind, and the other five are classified as eye-reduced. The researchers suggest they adapted to the underground habitat after or simultaneously with the extinction of the ancestor species from which they evolved, which lived outside of caves and became extinct due to historical climate changes in the region.
“We are currently witnessing the effects of climate change on many habitats, which obliges us to consider, maintain and promote programs that include the preservation of underground habitats — many of which are at immediate risk,” said Hawlena of Hebrew U’s Department of Ecology, Evolution and Behavior.
“We must protect Israel’s unique nature, preserve its underground systems for the future and further explore the processes that created these systems in the country.”