RESEARCH ARTICLE Ciliary and rhabdomeric photoreceptor- cell circuits form a spectral depth gauge in marine zooplankton Csaba Veraszto´ 1,2†, Martin Gu¨ hmann1†, Huiyong Jia3, Vinoth Babu Veedin Rajan4, Luis A Bezares-Caldero´ n1,2, Cristina Pin˜ eiro-Lopez1‡, Nadine Randel1§, Re´ za Shahidi1,2, Nico K Michiels5, Shozo Yokoyama3, Kristin Tessmar-Raible4, Ga´ spa´ r Je´ kely1,2* 1Max Planck Institute for Developmental Biology, Tu¨ bingen, Germany; 2Living Systems Institute, University of Exeter, Exeter, United Kingdom; 3Department of Biology, Emory University, Atlanta, United States; 4Max F. Perutz Laboratories, University of Vienna, Vienna, Austria; 5Department of Biology, University of Tu¨ bingen, Tu¨ bingen, Germany Abstract Ciliary and rhabdomeric photoreceptor cells represent two main lines of photoreceptor-cell evolution in animals. The two cell types coexist in some animals, however how these cells functionally integrate is unknown. We used connectomics to map synaptic paths between ciliary and rhabdomeric photoreceptors in the planktonic larva of the annelid Platynereis and found that ciliary photoreceptors are presynaptic to the rhabdomeric circuit. The behaviors *For correspondence: mediated by the ciliary and rhabdomeric cells also interact hierarchically. The ciliary photoreceptors
[email protected] are UV-sensitive and mediate downward swimming in non-directional UV light, a behavior absent in †These authors contributed ciliary-opsin knockout larvae. UV avoidance overrides positive phototaxis mediated by the equally to this work rhabdomeric eyes such that vertical swimming direction is determined by the ratio of blue/UV light. Since this ratio increases with depth, Platynereis larvae may use it as a depth gauge during vertical Present address: ‡EMBL migration.