Development and evolution of eyes in Araneae

Most arthropods have two separate visual systems: the median and lateral eyes. Drosophila have a pair of lateral compound eyes, which are the main optical organs, and a group of three median ocelli. In contrast, spiders typically have four pairs of simple eyes; the median eye pair are usually the largest and thus, the main optical system. Spiders belong to the chelicerates, which branch at the base of the Arthropoda. Thus, spiders (namely Parasteatoda tepidariorum) are useful models to study whether aspects of development are ancestral or derived with respect to the arthropod common ancestor, and potentially other metazoans. Investigating the molecular and genetic underpinnings of spider eye development will deepen our understanding of the conservation and/or retooling of developmental pathways in the evolution of visual systems. Moreover, across spider families there is variation in the number, placement, size and function of spider eyes. This diversity presents an opportunity to study the genetic bases of visual specialisations. Furthermore, spiders have retained many duplicated genes from an ancestral whole genome duplication (WGD) event; this includes transcription factors belonging to the Drosophila retinal determination gene network (RDGN) and several Wnt ligands. The median and lateral eyes of P. tepidariorum develop separately and express a unique combination of RDGN paralogs. Therefore, ancestral gene duplicates could have played a role in the evolution, development and diversification of spider eyes. I aim to investigate the role of RDGN paralogs and key signalling pathways in the establishment and development of the eyes in the developing head of P. tepidariorum.