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From light to darkness: evolutionary history of the photosensory system in planarians (Platyhelminthes, Tricladida)

Grant number: 18/06418-0
Support type:Scholarships in Brazil - Doctorate
Effective date (Start): December 01, 2018
Effective date (End): October 31, 2021
Field of knowledge:Biological Sciences - Zoology - Morphology of Recent Groups
Principal researcher:Federico David Brown Almeida
Grantee:Luiza de Oliveira Saad
Home Institution: Instituto de Biociências (IB). Universidade de São Paulo (USP). São Paulo , SP, Brazil
Associated scholarship(s):19/18147-4 - The genetic basis of eye loss in an obligate cave-dwelling planarian of the Bodoquena Plateau in central Brazil (Mato Grosso do Sul), BE.EP.DR

Abstract

Due to their simplicity, planarian eyes depict the anatomy of the metazoan eye prototype. However, we postulate that eyes of planarians are more variable and complex than generally assumed. Sensory systems have diversified as a result of evolutionary pressures found in the distinct habitats that planarians occupy, including fresh water, terrestrial, caves, and oceanic systems. Among the Triclads, variation in eye morphology includes presence of one or numerous eyes, multicellular or unicellular eyes, few or several photoreceptors, or complete absence of eyes. In this study I will examine the diversity of photosensory systems and eye structures in triclads using a morphological comparative and evolutionary approach. The aims of this project are: 1) to characterize and compare the morphology of photosensory systems in triclads (Geoplanoidea) by histology and immunocytochemistry using the following microscopic techniques: brightfield, confocal, and scanning and transmission electron microscopy; 2) reconstruct the evolutionary history of photosensory systems in the Tricladida by mapping photosensory character onto a most current phylogeny; 3) to identify cellular and molecular changes involved in the loss of eyes in a cave planarian species by studying the gene expression of candidate genes of eye development using immunocytochemistry and in situ hybridization. I plan to study the development of two planarian species, one without eyes (Girardia multidiverticulata) and another with eyes (Girardia tigrina). By characterizing the morphology and development of eyes across triclad species, we expect to reveal the morphological, genetic and cellular changes involved in the evolution of eye forms, providing new insights into how organismal diversity, adaptations, and morphological novelties originate. (AU)

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