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The energetic cost of vision and the evolution of eyeless Mexican cavefish.

Moran D, Softley R, Warrant EJ - Sci Adv (2015)

Bottom Line: One hypothesis for the reduction of vision in cave animals, such as the eyeless Mexican cavefish, is the high energetic cost of neural tissue and low food availability in subterranean habitats.The cost of vision was calculated to be 15% of resting metabolism for a 1-g fish, decreasing to 5% in an 8.5-g fish as relative eye and brain size declined during growth.Our results demonstrate that the loss of the visual system in the cave phenotype substantially lowered the amount of energy expended on expensive neural tissue during diversification into subterranean rivers, in particular for juvenile fish.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Lund University, Lund 22362, Sweden.

ABSTRACT
One hypothesis for the reduction of vision in cave animals, such as the eyeless Mexican cavefish, is the high energetic cost of neural tissue and low food availability in subterranean habitats. However, data on relative brain and eye mass in this species or on any measure of the energetic cost of neural tissue are not available, making it difficult to evaluate the "expensive tissue hypothesis." We show that the eyes and optic tectum represent significant metabolic costs in the eyed phenotype. The cost of vision was calculated to be 15% of resting metabolism for a 1-g fish, decreasing to 5% in an 8.5-g fish as relative eye and brain size declined during growth. Our results demonstrate that the loss of the visual system in the cave phenotype substantially lowered the amount of energy expended on expensive neural tissue during diversification into subterranean rivers, in particular for juvenile fish.

No MeSH data available.


Related in: MedlinePlus

A schematic drawing of the respirometry apparatus used to measure the oxygen consumption rates of eyes and brains.
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Figure 5: A schematic drawing of the respirometry apparatus used to measure the oxygen consumption rates of eyes and brains.

Mentions: The brain and eye metabolic measurement system was an automated intermittent-flow respirometer (Fig. 5) located in a temperature-controlled (20°C) dark room. Individual whole organs were placed inside respirometry vials, which were modified 3-ml clear-glass microreaction vessels with polytetrafluoroethylene-faced rubber septa and cap. Four respirometry vials were used in the system: one for the brain, two for the eyes, and one as a reference vial. The glass vials had two holes drilled into them to allow for ACSF inflow and an oxygen optode. The brain or eye was attached to a spherical pinhead using cyanoacrylate glue, and the organ was suspended at the center of respirometry vials by puncturing the pin through the septa. An effluent line was inserted into the septa to drain ACSF away during the flushing phase. A peristaltic pump pressurized the ACSF delivery system and replaced the volume of the respirometer in about 1 min. The peristaltic pump rollers noticeably increased the temperature (1° to 2°C) of the ACSF as it passed through the pump; therefore, it was necessary to have a 1-liter bottle between the peristaltic pump and the respirometry vials to act as a heat sink. The respirometry vials were semi-immersed in a water bath, which smoothed out the heat fluctuations associated with the temperature control of the room. The water bath was fixed atop a custom-built magnetic stirring unit in which the motors had a rotational velocity of about 60 rpm. The magnetic stirring bars inside the respirometers were custom-designed to give a high degree of mixing throughout the vial volume at low rotation. The triangular magnetic stirring bars sold as standard accessory for conical base microreaction vessels did not provide sufficient mixing at low revolution. At high revolution, the shear forces were too great for the organs that they rapidly disintegrated.


The energetic cost of vision and the evolution of eyeless Mexican cavefish.

Moran D, Softley R, Warrant EJ - Sci Adv (2015)

A schematic drawing of the respirometry apparatus used to measure the oxygen consumption rates of eyes and brains.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4643782&req=5

Figure 5: A schematic drawing of the respirometry apparatus used to measure the oxygen consumption rates of eyes and brains.
Mentions: The brain and eye metabolic measurement system was an automated intermittent-flow respirometer (Fig. 5) located in a temperature-controlled (20°C) dark room. Individual whole organs were placed inside respirometry vials, which were modified 3-ml clear-glass microreaction vessels with polytetrafluoroethylene-faced rubber septa and cap. Four respirometry vials were used in the system: one for the brain, two for the eyes, and one as a reference vial. The glass vials had two holes drilled into them to allow for ACSF inflow and an oxygen optode. The brain or eye was attached to a spherical pinhead using cyanoacrylate glue, and the organ was suspended at the center of respirometry vials by puncturing the pin through the septa. An effluent line was inserted into the septa to drain ACSF away during the flushing phase. A peristaltic pump pressurized the ACSF delivery system and replaced the volume of the respirometer in about 1 min. The peristaltic pump rollers noticeably increased the temperature (1° to 2°C) of the ACSF as it passed through the pump; therefore, it was necessary to have a 1-liter bottle between the peristaltic pump and the respirometry vials to act as a heat sink. The respirometry vials were semi-immersed in a water bath, which smoothed out the heat fluctuations associated with the temperature control of the room. The water bath was fixed atop a custom-built magnetic stirring unit in which the motors had a rotational velocity of about 60 rpm. The magnetic stirring bars inside the respirometers were custom-designed to give a high degree of mixing throughout the vial volume at low rotation. The triangular magnetic stirring bars sold as standard accessory for conical base microreaction vessels did not provide sufficient mixing at low revolution. At high revolution, the shear forces were too great for the organs that they rapidly disintegrated.

Bottom Line: One hypothesis for the reduction of vision in cave animals, such as the eyeless Mexican cavefish, is the high energetic cost of neural tissue and low food availability in subterranean habitats.The cost of vision was calculated to be 15% of resting metabolism for a 1-g fish, decreasing to 5% in an 8.5-g fish as relative eye and brain size declined during growth.Our results demonstrate that the loss of the visual system in the cave phenotype substantially lowered the amount of energy expended on expensive neural tissue during diversification into subterranean rivers, in particular for juvenile fish.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Lund University, Lund 22362, Sweden.

ABSTRACT
One hypothesis for the reduction of vision in cave animals, such as the eyeless Mexican cavefish, is the high energetic cost of neural tissue and low food availability in subterranean habitats. However, data on relative brain and eye mass in this species or on any measure of the energetic cost of neural tissue are not available, making it difficult to evaluate the "expensive tissue hypothesis." We show that the eyes and optic tectum represent significant metabolic costs in the eyed phenotype. The cost of vision was calculated to be 15% of resting metabolism for a 1-g fish, decreasing to 5% in an 8.5-g fish as relative eye and brain size declined during growth. Our results demonstrate that the loss of the visual system in the cave phenotype substantially lowered the amount of energy expended on expensive neural tissue during diversification into subterranean rivers, in particular for juvenile fish.

No MeSH data available.


Related in: MedlinePlus