Differential evolutionary and ecological patterns in eye loss between parallel visual systems in spiders

bioRxiv (Cold Spring Harbor Laboratory)

Abstract

Abstract Eye loss has long fascinated evolutionary biologists and occurs across the animal kingdom. Spiders have two parallel visual systems — two primary and six secondary eyes — but eye losses, leaving six, four, two, or no eyes, have occurred in multiple lineages. Despite their significance, reports of eye loss are scattered, limiting broader analysis. Here we present the first comprehensive analysis of eye loss across all known spider lineages. We show that eye loss occurs in ∼12% of extant species, mainly within the clade Synspermiata. Six-eyed spiders are most common (>5,300 species), while four-eyed, two-eyed, and eyeless forms are rarer and often linked to troglobitic lifestyles. Principal eye loss is widespread, occurring in 49 families across nearly all major lineages. Using a recent phylogeny of the order Araneae, we demonstrate a strong correlation between eye loss and occupancy of low-light environments, but this is complicated by differential effects across eye types and phylogenetic groups through geological time. These findings reveal striking lability in eye number and lay groundwork for future research into ecological, developmental, and neurological drivers of eye loss. [hidden Markov models, ancestral state reconstruction, Araneae, discrete character evolution, principal eyes, secondary eyes, low light environments].

Authors 3

1. M. Antonio Galán-Sanchez

   Humboldt-Universität zu Berlin · Museum für Naturkunde

   Affiliation as printed

   Faculty of Life Sciences, Humboldt-Universität zu Berlin, Invalidenstraße 42, 10115, Berlin, Germany

   Museum für Naturkunde, Leibniz Institut für Evolutions- und Biodiversitätsforschung, Invalidenstraße 43, 10115, Berlin, Germany

2. F. Andrés Rivera-Quiroz Aachen Naturalis Biodiversity Center

   Naturalis Biodiversity Center

   Affiliation as printed

   Naturalis Biodiversity Center, Darwinweg 2, 2333 CR Leiden, the Netherlands

3. Lauren H. Sumner‐Rooney

   Museum für Naturkunde

   Affiliation as printed

   Museum für Naturkunde, Leibniz Institut für Evolutions- und Biodiversitätsforschung, Invalidenstraße 43, 10115, Berlin, Germany