VISUALEYES COST · To See or Not to See: The Metabolic Cost of Having Eyes and its Role in the Evolution of Vision
FP7 — People (Marie Curie Actions)
- Duration
- 2010-10-01 → 2013-01-15
- EU contribution
- €179,169
- Participants
- 1
- Scheme
- MC-IEF
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Results in brief
To See or Not to See: The Metabolic Cost of Having Eyes and its Role in the Evolution of Vision
Project objectives A 24-month Marie Curie IEF project was undertaken to study the energy expenditure of eyes and the role of energy as a factor in the evolution of eyes. The Mexican cavefish was used as a study organism as this species has naturally occurring eyed and non-eyed forms. The non-eyed forms live in caves in north-eastern Mexico. One hypothesis for the reason they lost their eyes is that eyes are energetically expensive and natural selection favoured individuals living in food-limited caves with successively smaller eyes. Project tasks Methods were developed to measure the whole body energetic expenditure of both eyed and non-eyed forms, and also the expenditure of isolated brains and eyes. The eyed forms and non-eyed Mexican cavefish were found to differ in the way their metabolism varied throughout the day. Eyed forms showed a daily (circadian) rhythm in metabolism typical of animals. Non-eyed forms did not have a circadian rhythm in metabolism, which allowed this type of Mexican cavefish to substantially lower its daily energy expenditure. This loss of a circadian rhythm in metabolism is a new phenomenon not previously observed in animal physiology studies. This work has been submitted for peer review. Project results A side project that evolved from the fundamental science project was a collaboration with medical researchers on improved techniques for culturing retina outside of the host animal. We discovered that stretch is an important force in maintaining the intergrity of the retina. This finding has both fundamental and applied science implications and was published in the journal Investigative Ophthalmology and Visual Science. The energy expenditure of the eye and visual centres of the brain were found to be a significant portion (2-6 %) of the total body energy expenditure of eyed Mexican cavefish. Non-eyed Mexican cavefish therefore make significant energy savings in their food-limited caves by having lost their visual sense. The significant energy expenditure of the visual system in Mexican cavefish lends weight to the idea that organs made of nervous tissue are energetically expensive and under pressure are likely to become smaller where food is limited
Data: CORDIS, © European Union
Project objective
The evolution and regression of vision in animals has long interested scientists, and researchers have strived to identify the proximate (how did eyes evolve or regress?) and ultimate (why did eyes evolve or regress?) explanations for the appearance and disappearance of eyes. This Marie Curie proposal will use the Mexican blind cavefish to test whether the metabolic cost of the eye has been a significant selective force in the evolution and regression of vision. The Mexican blind cavefish is model species used in developmental biology, and is useful in the study of visual evolution as it has eyed, surface-dwelling ecomorphs, and non-eyed, cave-dwelling ecomorphs. I will measure the energy demand (oxygen consumption rate) of the eye in eyed ecomorphs using both in vivo and in vitro techniques. In vivo oxygen consumption measurements of the eye will be performed on anaesthetised individuals using oxygen microsensors. The energetic demand of the eye will be compared to the whole body metabolic rate of eyed and non-eyed individuals to infer a metabolic cost of vision. The in vitro oxygen consumption measurements of isolated retina will be performed on a specially constructed device where the incoming light intensity can be varied. The retinal oxygen consumption rate will be measured over a range of light intensities to quantify how the cost of the eye changed as Mexican blind cavefish diversified from surface habitats into caves. It is hypothesised that the energy requirements of the retina will be higher in the dark than that in the light. This project will offer an energetic explanation as to why eyes would be disadvantageous in the absence of light, and why selection would act to regress eyes in dark habitats. By understanding the metabolic cost of eyes, we can also learn about the energetic advantages that must have been gained by evolving vision.
Original text from CORDIS.
Participants
- MAX IV Laboratory, Lund University · LUNDCoordinatorSweden
Links
Data: CORDIS, © European Union