Related Experiment Video
Updated: Jul 2, 2025
05:07
Using Looming Visual Stimuli to Evaluate Mouse Vision
Published on: June 13, 2019
11.3K
A morphological basis for path-dependent evolution of visual systems
Rebecca M Varney1, Daniel I Speiser2, Johanna T Cannon1
1University of California, Santa Barbara, Santa Barbara, CA, USA.
Science (New York, N.Y.)
|February 29, 2024
Summary
Path dependence, or evolutionary history, shapes complex traits like vision in chitons. This study reveals how shell structure constrains the evolution of their eyes, demonstrating predictable yet variable outcomes in natural systems.
Area of Science:
- Evolutionary biology
- Macroevolutionary patterns
- Developmental constraints
Background:
- Path dependence influences macroevolutionary predictability by constraining evolutionary trajectories.
- Demonstrating path dependence in natural systems is challenging due to a lack of independent replicates.
- Distributed visual systems in chitons offer a model to study the evolution of complex traits.
Purpose of the Study:
- To demonstrate path dependence in the evolution of complex traits within natural populations.
- To investigate the role of developmental constraints in shaping macroevolutionary outcomes.
- To analyze the evolution of visual systems in chitons.
Main Methods:
- Comparative analysis of chiton lineages with different shell plate structures.
- Examination of the number of openings for sensory nerves in shell plates.
- Morphological assessment of visual system complexity (number of eyespots).
Main Results:
- Two types of distributed visual systems evolved independently twice in chitons.
- The number of sensory nerve openings in shell plates constrains the type of visual system evolved.
- Lineages with more openings evolved thousands of eyespots, while those with fewer evolved hundreds.
Conclusions:
- The evolution of chiton visual systems is a rapid, path-dependent process.
- Developmental constraints, specifically shell morphology, dictate macroevolutionary outcomes.
- These outcomes are both deterministic (constrained) and stochastic (variable).
Related Concept Videos
01:26Visual System
581
Light enters the eye through the cornea, a transparent, dome-shaped surface covering the surface of the eyeball that helps to direct and focus incoming light. This light is then channeled toward the pupil, an adjustable opening whose size is controlled by the iris. The iris, a pigmented muscle, regulates the amount of light entering the eye by contracting or dilating the pupil, thereby ensuring optimal light levels for clear vision.
Once through the pupil, the light passes through the lens, a...
Once through the pupil, the light passes through the lens, a...
581
01:24Vision
53.3K
Vision is the result of light being detected and transduced into neural signals by the retina of the eye. This information is then further analyzed and interpreted by the brain. First, light enters the front of the eye and is focused by the cornea and lens onto the retina—a thin sheet of neural tissue lining the back of the eye. Because of refraction through the convex lens of the eye, images are projected onto the retina upside-down and reversed.
53.3K
01:20Anatomy of the Eyeball
7.1K
The eye is a spherical, hollow structure composed of three tissue layers. The outer layer — the fibrous tunic, comprises the sclera — a white structure — and the cornea, which is transparent. The sclera encompasses some of the ocular surface, most of which is not visible. However, the 'white of the eye' is distinctively visible in humans compared to other species. The cornea, a clear covering at the front of the eye, enables light penetration. The eye's middle...
7.1K
01:22Photoreceptors and Visual Pathways
6.0K
At the molecular level, visual signals trigger transformations in photopigment molecules, resulting in changes in the photoreceptor cell's membrane potential. The photon's energy level is denoted by its wavelength, with each specific wavelength of visible light associated with a distinct color. The spectral range of visible light, classified as electromagnetic radiation, spans from 380 to 720 nm. Electromagnetic radiation wavelengths exceeding 720 nm fall under the infrared category,...
6.0K
02:37Gene Duplication and Divergence
6.1K
The seminal work of Ohno in 1970 popularized the idea of gene duplication and divergence. DNA sequence comparison studies reveal that a large portion of the genes in bacteria, archaebacteria, and eukaryotes was generated by gene duplication and divergence, indicating its critical role in evolution.
The duplicated copies of the gene are called Paralogs. Paralogs with similar sequences and functions form a gene family. Across several species, a large number of gene families are...
The duplicated copies of the gene are called Paralogs. Paralogs with similar sequences and functions form a gene family. Across several species, a large number of gene families are...
6.1K
02:55The Evidence for Evolution
42.7K
Genetic variations accumulating within populations over generations give rise to biological evolution. Evolutionary changes can result in the formation of novel varieties and entire new species. These changes are responsible for the diverse forms of life inhabiting the planet. The evidence for evolution suggests that all living organisms descended from common ancestors.
42.7K