Research ArticleEYE EVOLUTION

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

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Science Advances  11 Sep 2015:
Vol. 1, no. 8, e1500363
DOI: 10.1126/sciadv.1500363
  • Fig. 1 A comparison of brain size and body morphology in the four Mexican tetra morphs used in this study.

    Scale bars are approximate.

  • Fig. 2 Brain and eye mass allometry in the four Mexican tetra morphs.

    (A) Eye mass (percentage of body weight) versus total body weight. (B) Brain mass (percentage of body weight) versus total body weight. (C) Dependence of brain mass on eye mass among eyed morphs.

  • Fig. 3 Summary graphs of respirometry data showing the oxygen consumption rates of eyes and brains in surface and Pachón ecotypes at different times of day.

    Each gray line represents a single organ measurement. A running mean ± 95% confidence interval is overlaid.

  • Fig. 4 Output from a model used to calculate the relative energetic costs of eyes, brain, and vision for three Mexican tetra ecotypes.

    (A) Whole body oxygen consumption (B) relative brain size (C) brain oxygen consumption (D) relative eye size (E) oxygen consumption of eyes (F) oxygen consumption of eyes plus brain (G) oxygen consumption of eyes plus optic tectum. Refer to the Supplementary Materials for the calculative approach.

  • Fig. 5 A schematic drawing of the respirometry apparatus used to measure the oxygen consumption rates of eyes and brains.
  • Fig. 6 Details of the method used to attach an enucleated eye to a pinhead.

    (A) Applying glue to pin (B and C) attaching pin to eye (D) using microscissors to puncture and cut through sclera and retina (E) making two more cuts to have eye in three segments (F) applying glue to pin (G and H) attaching sclera to pin (I) removing lens and irrigating (J) setting pin in septum (K) setting septum in respirometry vial.

  • Fig. 7 Details of the method used to dissect and attach the brain to a pinhead.

    (A) Series of cuts to remove dorsal skull (B) exposed brain (C) excised brain (D) attaching brain to pre-glued pinhead (E) brain set in respirometer.

  • Table 1 Sample calculations used for modeling eye and brain costs for a 4-g fish.
    PachónMicosSurfaceData origin
    aWhole-body minimal metabolic rate
    (mg O2 hour−1 per 5-g fish)
    0.8328*0.9291.026*Published data
    bWhole-body oxygen demand (mg O2 hour−1)0.6860.7660.846a(4 g ÷ 5 g)0.862
    cBrain mass (g)0.0270.0310.0344 g × organ mass scaling
    relationships in table S2
    dRelative brain mass (% body weight)0.680.780.85c ÷ 4 g
    eBrain metabolic rate (mg O2 hour−1 g wet mass−1)1.6031.6031.603Data from the current study
    fBrain oxygen demand (mg O2 hour−1)0.0430.0500.055e × c
    gRelative brain cost (% body O2 demand)6.276.526.50f ÷ b
    hEye mass (g)00.0380.0904 g × organ mass scaling
    relationships in table S2
    iRelative eye mass (% body weight)00.952.25h ÷ 4 g
    jEye metabolic rate (mg O2 hour−1 g wet mass−1)00.5250.525Data from the current study
    kEye oxygen demand (mg O2 hour−1)00.0200.047j × h
    lRelative eye cost (% body O2 demand)02.615.56k ÷ b
    mNeural tissue (eyes plus brain) oxygen demand
    (mg O2 hour−1)
    0.0430.0700.102f + k
    nNeural tissue cost (% body O2 demand)6.279.1412.06m ÷ b
    oCost of vision (% body O2 demand)03.526.97(mMicosmPachón) ÷ bMicos
    (msurfacemPachón) ÷ bsurface

    *Data taken from Moran et al. (19).

    †Estimated as a rate equidistant between Pachón and surface ecotypes based on data from Hüppop (11).

    ‡Mass metabolism scaling exponent (0.862) taken from Moran et al. (19).

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/1/8/e1500363/DC1

      Fig. S1. Sample respirometry data for a surface fish.

      Table S1. ANCOVA statistics for organ weight versus body weight regression for four morphs of A. mexicanus.

      Table S2. Linear regression statistics for organ weight versus body weight for four morphs of A. mexicanus.

      Additional data (separate file)

      Data file S1. Organ_weight_data.csv

      Data file S2. Eye_respiration_data.csv

      Data file S3. Brain_respiration_data.csv

    • Supplementary Materials

      This PDF file includes:

      • Fig. S1. Sample respirometry data for a surface fish.
      • Table S1. ANCOVA statistics for organ weight versus body weight regression for four morphs of A. mexicanus.
      • Table S2. Linear regression statistics for organ weight versus body weight for four morphs of A. mexicanus.

      Download PDF

      Other Supplementary Material for this manuscript includes the following:

      • Additional data (separate file)
      • Data file S1. Organ_weight_data.csv
      • Data file S2. Eye_respiration_data.csv
      • Data file S3. Brain_respiration_data.csv

      Download Data files

      Files in this Data Supplement: