If you venture into caves in the Galilee or northern Samaria, watch your step. In a new study by researchers from the Hebrew University of Jerusalem (HU) and the University of Madison-Wisconsin, seven new species of funnel web spiders (Agelenidae, Tegenaria) that are unique to caves in Israel have been discovered.
These species join a large number of invertebrates recently found in Israeli caves that are new to science. The team said that the study, published in the journal Molecular Phylogenetics and Evolution under the title “In the land of the blind: exceptional subterranean speciation of cryptic troglobitic spiders of the genus Tegenaria in Israel,” has significant scientific implications for uncovering the evolution of speciation in caves and the historical, geographic and climatic processes that have occurred in this country.
Caves have long been recognized as a window into the mechanisms of diversification and convergent evolution due to the unique conditions of isolation and life in the dark. These locations constitute promising places for investigating how new species develop due to their isolation from surface habitats and unique collection of environmental conditions.
What are the unique spiders of Israel's caves?
Doctoral student Shlomi Aharon led the study under the guidance of Dr. Efrat Gavish-Regev from HU’s National Natural History and Prof. Dror Hawlena from the ecology, evolution and behavior department. “The unique conditions in cave habitats, as well as the isolation from other habitats, lead to a process of convergent evolution, in which we observe the development of exceptional adaptations to life in the dark, such as blindness, loss of pigments and enlargement of sensory organs,” they wrote.
“The unique conditions in cave habitats, as well as the isolation from other habitats, lead to a process of convergent evolution, in which we observe the development of exceptional adaptations to life in the dark, such as blindness, loss of pigments and enlargement of sensory organs.”
Study
“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,” Aharon explained. “In this study, we sought to understand the evolutionary relationships between funnel web spiders (Agelenidae, Tegenaria) with normal eyes that are found at the entrance to the caves in Israel and those that are deep in the cave and have no pigments, have small eyes and may even be completely blind.”
Among the spiders they found, five were unique to different caves, and the two other species were found in several caves in the Galilee and in caves situated at the Ofra karst field formed from the dissolving of rocks like gypsum, limestone and dolomite that is currently under threat from construction plans, said Gavish-Regev. “One of the surprising findings in the study show 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.”
They found troglobitic funnel-web spiders (that spend all or most of their lives in caves) of the genus Tegenaria in 26 caves, present mostly at the entrances. They also identified at least 14 caves inhabited by these spiders, which are present mostly in the twilight and dark ecological zones. Ten of the caves, which are located in the north and center of Israel, are inhabited by both troglophilic species that can survive outside the caves if they find an appropriate environment and troglobitic species.
After the spiders were collected by hand, the team of researchers conducted a series of microscopic examinations, recorded their morphology (structure), and extracted DNA from each to compare them to sequences of known species of the same genus that exist in GenBank.
A genetic sequence database belonging to the US National Institute of Health, GenBank has an annotated collection of all publicly available DNA sequences and part of the International Nucleotide Sequence Database Collaboration, which comprises the DNA databanks in the US National Library of Medicine, in Japan and in Europe. These three organizations exchange data on a daily basis.
Five of the new species described were “eye-reduced,” while the other two were completely blind. The researchers suggest that the new species developed adaptations to life in underground habitats and developed into new species in caves after or simultaneously after the extinction due to climate changes of the ancestor species from which they evolved that lived outside of caves.
“We are now witnessing the effects of climate change on many habitats, and it obliges us to consider, maintain and promote programs that include the preservation of underground habitats, many of which are at immediate risk,” concluded Hawlena. “We must protect Israel’s unique nature, preserve its underground systems for the future and further explore the processes.”