Meeting Abstract
The unique adaptations of cave-dwelling organisms are one of the most fascinating examples of convergent evolution. The reduction or total loss of eyes is an example of the suite of adaptations exhibited by troglobitic animals. But in arachnids, the genetic mechanisms underpinning this iconic phenotype are virtually unexplored. The study system of this contribution consists of disjunct populations of two arachnid orders from Israel and Palestine. These display a wide phenotypic spectrum of eye size, ranging from the typical arrangement eyes to complete blindness. Here, we implemented RAD-Seq approach to characterize the evolutionary dynamics and species boundaries of the cave and surface populations. To identify retinal determination gene network (RDGN) members involved in the reduction/loss of eyes, we performed differential gene expression (DGE) analysis of embryos prior and subsequent to eye formation from blind and eye-bearing populations of a whip-spider (Amblypygi, Charinus). DGE analysis identified RDGN members that are highly expressed in the eye bearing and lowly expressed in the blind whip-spider (or vice versa); among those, we found eye patterning candidates whose expression has been well-characterized in spiders. As validation of the DGE, we interrogated the function of a high-ranking RDGN homolog in the spider Parasteatoda tepidariorum using RNAi. The resulting phenotypes from these assays show an array of phenotypes that mirror the reduction in eyes observed the cave adapted spiders of Israel. Together, the integration of these approaches is providing the first insights as to the developmental genetic basis of eye evolution in arachnids.
