How Did Cave Spiders Get Their Eyes? Study Provides First Detailed Insight Into Their Development

Across planet Earth, the animal world is full of species perfectly adapted for life in their specific niche. From polar bears with translucent fur to the worlds longest living leaves, the environment shapes an organisms’ adaptations. Now, a study has honed in on the development of a spider species found within caves, and looking closer at how the spider embryos develop has revealed some surprising results.

The team decided to look closer at the cave-dwelling spider Tegenaria pagana. The Tegenaria genus is interesting because different species within the genus cover a large spectrum of adaptations having either retained their eyes, having quite reduced eyes, or having lost them entirely as an adaptation to the light conditions in which they live. There are 135 species within the genus and 11 species inhabit the caves in Israel. 

The team used the funnel-web spider Tegenaria pagana and studied its entire embryonic development from fertilization to hatching to look at the gene expression involved in eye development. They were particularly interested in genes in the eyes, known as the Retinal Determination Network (RDN). 

It was discovered that the sine oculis gene plays a role in the development of eyes in spiders in the genus regardless of their overall eye expression. The research also helps when comparing species in the Tegenaria genus that have different levels of eye reduction. The team found that even spiders that seem to be closely related can have big differences in their gene expression. 

“This research provides an essential reference for understanding how developmental and genetic factors influence eye formation in spiders. With several Tegenaria species in Israel’s caves exhibiting different levels of eye reduction, our findings lay the groundwork for future studies on the evolution of vision loss in subterranean environments. By establishing a developmental framework for Tegenaria pagana, we can begin to explore how genetic regulatory networks contribute to morphological adaptations in response to environmental change,” said study author Dr Efrat Gavish-Regevin in a statement. 

The study may also help explain how the species that have lost eyes at a genetic level have developed other senses to compensate, such as more developed touch or better chemical receptors. 

The paper is published in EvoDevo.