Research, Technology

Cave spiders in Israel have lost their eyes, and there is a scientific explanation for this

In the 1800s, the English naturalist Charles Darwin visited the Galapagos Islands and discovered 14 new species of birds there, which were named Galapagos finches. After that, he visited the uninhabited island of Cocos.in the Pacific Ocean and found birds of the same species, but with different sizes, beak shapes, behavior and singing. The scientist came to the conclusion that all Galapagos finches have a common ancestor who lived in South America. About 2-3 million years ago, they moved to two islands and acquired such noticeable differences that they were divided into two species. Recently, scientists found spiders in Israeli caves that did not need to move to different islands to acquire unique features. Spiders living at the entrance to the cave have well-developed eyes, and individuals that have gone several hundred meters deep are practically blind. The differences between these creatures are so great that they were divided into different types.

Spiders living in the depths of Israeli caves have lost their sight in the course of evolution

New species of spiders, discovery in 2023

During the expedition, scientists visited 30 caves,located in Israel. In them they found funnel spiders from the genus Tegenaria (Tegenaria), and they all had their own preferences about where it is better to live. According to scientists, representatives of the 27 species found preferred to live near the entrance to the caves, because they needed sunlight - they turned out to be troglophiles. Also, 14 species of funnel spiders that lived in only the dark depths of caves came to the eyes of scientists - such organisms are called troglobionts.

One of the representatives of the spider of the genus Tegenaria

Worth remembering:

Troglophiles are organisms that can live not only inside caves, but also on the surface. Troglobionts are living beings that liveonly in the depths of the caves, where sunlight does not penetrate. Recently, our site has published a selection of photos of amazing animals that live in dark caves. This article is about troglobionts - they look amazing!

Representatives of seven species living in the depths of caveswere new to science. Scientists immediately noticed that they were very different from relatives that live near sunlight - in five species, the eyes did not perform the function of vision and were useless, and two species were completely deprived of them. Representatives of the species that were found in the light areas of the caves, the eyes were in place and perfectly performed their functions.

In 2022, scientists decided to find out if spiders can dream. We talked about how they found this out in the article “Do spiders dream?”.

What is convergent evolution

As part of the study, the researchers decided to studyfound spiders at the genetic level. According to ecologist Efrat Gavish-Regev, they were surprised that the new species of sightless spiders were evolutionarily closer to arthropods that live in the depths of caves in the Mediterranean regions of Europe. They are minimally similar to representatives of species that live a few tens or hundreds of meters away from them in the same cave.

Three of the recently discovered species with weakened (top and middle) or completely missing eyes (bottom)

The presence of the same traits in animals can be explained convergent evolution. This is the name given to the evolutionary process.in which similarities arise between different animals associated with similar habitats. When funnel-web spiders found themselves in the depths of caves where no light enters, they no longer need eyes. Subsequently, evolution decreed that females began to give birth to cubs devoid of organs of vision - in conditions of pitch darkness, the absence of eyes is a plus, because it allows you not to waste energy on unnecessary body systems.

One of the most feared spiders in the world are tarantulas. We talked about why they got such a strange name and why they need body hair in a separate article.

Cave animals are threatened with extinction

Environmentalists believe that living in the caves of Israelspiders are threatened with extinction because scientists have long observed the negative impacts of climate change on a wide variety of habitats. Therefore, it is high time for conservationists to take action to protect even such hard-to-reach places as deep caves.

We must protect the unique nature of Israel, preserve its underground systems for the future, and further study the processes that resulted in these caves, the ecologists concluded.

Some representatives of the genus tegenaria look extremely creepy

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Finally, it should be noted that currentlyscience knows about the existence of 1500 species of funnel spiders. Their body length is 2-3 centimeters and some of them can be dangerous to humans. For example, cases of bites of meadow spiders (Tegenaria agrestis) have been recorded - usually these cases led to skin necrosis.