Evolution of the vertebrate retina by repurposing of a composite ancestral median eye
(2026) In Current Biology 36(4). p.153-170- Abstract
The vertebrate retina is a uniquely complex and evolutionarily conserved structure, combining ciliary (rod and cone) and rhabdomeric (ganglion, amacrine and horizontal cells) photoreceptor lineages within a multilayered circuit. This arrangement contrasts with the ancestral bilaterian cephalic pattern, where rhabdomeric photoreceptors dominate lateral eyes and ciliary photoreceptors are largely limited to unpigmented, non-visual median positions. Here, we make a case that the vertebrate retina evolved through the lateralization of a complex median photoreceptive organ already containing both photoreceptor types. This shift likely followed the loss of lateral rhabdomeric eyes in a burrowing, suspension-feeding deuterostome ancestor that... (More)
The vertebrate retina is a uniquely complex and evolutionarily conserved structure, combining ciliary (rod and cone) and rhabdomeric (ganglion, amacrine and horizontal cells) photoreceptor lineages within a multilayered circuit. This arrangement contrasts with the ancestral bilaterian cephalic pattern, where rhabdomeric photoreceptors dominate lateral eyes and ciliary photoreceptors are largely limited to unpigmented, non-visual median positions. Here, we make a case that the vertebrate retina evolved through the lateralization of a complex median photoreceptive organ already containing both photoreceptor types. This shift likely followed the loss of lateral rhabdomeric eyes in a burrowing, suspension-feeding deuterostome ancestor that retained a pool of median photoreceptors. In the early chordates leading to vertebrates, this structure diversified into the pineal/parapineal complex and lateral retinas. Central to this transformation was the emergence of a bipolar cellular identity, linking ciliary and rhabdomeric circuits — an unusual feature in animal nervous systems. We suggest that bipolar cells predate the retina and have dual evolutionary origins: Off bipolar cells deriving from a ciliary ‘effector’ lineage and rod-On bipolar cells deriving from a chimeric sensory cell. This model explains key similarities between the retina and the pineal gland and supports a scenario in which vertebrate vision emerged by integrating and repurposing preexisting circuits. It reframes the retina not as a de novo innovation, but as a modified and lateralized solution to sensory challenges faced by early chordates.
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- author
- Kafetzis, George ; Bok, Michael J. LU ; Baden, Tom and Nilsson, Dan Eric LU
- organization
- publishing date
- 2026-02-23
- type
- Contribution to journal
- publication status
- published
- subject
- in
- Current Biology
- volume
- 36
- issue
- 4
- pages
- 153 - 170
- publisher
- Elsevier
- external identifiers
-
- pmid:41734753
- scopus:105030590563
- ISSN
- 0960-9822
- DOI
- 10.1016/j.cub.2025.12.028
- language
- English
- LU publication?
- yes
- additional info
- Publisher Copyright: © 2025 The Author(s).
- id
- 57fe74b9-55b5-486b-ad09-10462c85b597
- date added to LUP
- 2026-07-29 19:35:21
- date last changed
- 2026-10-08 22:38:29
@article{57fe74b9-55b5-486b-ad09-10462c85b597,
abstract = {{<p>The vertebrate retina is a uniquely complex and evolutionarily conserved structure, combining ciliary (rod and cone) and rhabdomeric (ganglion, amacrine and horizontal cells) photoreceptor lineages within a multilayered circuit. This arrangement contrasts with the ancestral bilaterian cephalic pattern, where rhabdomeric photoreceptors dominate lateral eyes and ciliary photoreceptors are largely limited to unpigmented, non-visual median positions. Here, we make a case that the vertebrate retina evolved through the lateralization of a complex median photoreceptive organ already containing both photoreceptor types. This shift likely followed the loss of lateral rhabdomeric eyes in a burrowing, suspension-feeding deuterostome ancestor that retained a pool of median photoreceptors. In the early chordates leading to vertebrates, this structure diversified into the pineal/parapineal complex and lateral retinas. Central to this transformation was the emergence of a bipolar cellular identity, linking ciliary and rhabdomeric circuits — an unusual feature in animal nervous systems. We suggest that bipolar cells predate the retina and have dual evolutionary origins: Off bipolar cells deriving from a ciliary ‘effector’ lineage and rod-On bipolar cells deriving from a chimeric sensory cell. This model explains key similarities between the retina and the pineal gland and supports a scenario in which vertebrate vision emerged by integrating and repurposing preexisting circuits. It reframes the retina not as a de novo innovation, but as a modified and lateralized solution to sensory challenges faced by early chordates.</p>}},
author = {{Kafetzis, George and Bok, Michael J. and Baden, Tom and Nilsson, Dan Eric}},
issn = {{0960-9822}},
language = {{eng}},
month = {{02}},
number = {{4}},
pages = {{153--170}},
publisher = {{Elsevier}},
series = {{Current Biology}},
title = {{Evolution of the vertebrate retina by repurposing of a composite ancestral median eye}},
url = {{http://dx.doi.org/10.1016/j.cub.2025.12.028}},
doi = {{10.1016/j.cub.2025.12.028}},
volume = {{36}},
year = {{2026}},
}