Transcript garvey

Eileen Garvey
Article: Comparative Morphology of the Eye
in Primates
E. CHRISTOPHER KIRK*
The Anatomical Record Part A: Discoveries in
Molecular, Cellular, and Evolutionary Biology
Volume 281A, Issue 1, Pages 1095-1103
Published Online: November 2004
Background
Components of the eye:
– Rods: neurosensory cells which are insensitive to color,
absorb light over the entire range of the visual spectrum,
and are most effective in relatively low intesities of light,
such as shade, dusk or night time.
– Cones: neurosensory cells that are senstive to color,
absorb light in only one part of the visible spectrum (red,
green, blue), and function only in prescene of light that falls
into this wavelength.
Diurnal species are usually more active during the day when
the light levels are in the range of cone mediated vision.
Nocturnal species are usually active at night when light levels
are in the range of rod mediated vision.
However there are many mammalian species that are
considered, cathemeral, which means they are active in both
light and dark periods.
Background continued
In the article, the morphological adaptations for
different activity patterns are compared with the
gross anatomy of the eye of primates.
The size of the cornea places an upper limit on
the maximum amount of light that the eye can
absorb.
Nocturnal species increase the size of the
cornea compared to the transverse diameter of
the eye so that it is possible to absorb more
light.
Diurnal species have smaller corneas compared
to the transverse diameter of the eye.
Hypothesis
The goal of the analysis:
– Provide a quantitative description of the
relationship between eye morphology and activity
pattern in broad sample of primate species.
– The researchers asked many questions; for
example:
Do nocturnal, cathemeral, and diurnal primates
exhibit systematic differences in eye morphology
as has been predicted by other studies conducted
on mammalian eyes?
Methods and Materials
Data were collected on eye and cornea size for 147
specimens of 55 primate species
Samples were taken from preserved specimens that
were frozen directly after the animal died or were
preserved in formalin
Eyes were removed from the orbit and cleaned
Each eye was refilled to prevent it from collapsing
A needle was inserted into the optic nerve and then
the measurements were determined
Activity patterns and mean eye measurements were
determined for all included taxa
Methods and Materials
– Data/calculations included:
Activty Patterns D=Diurnal, N=Nocturnal,
C=Cathemeral
Mean transvers diameter in mm
Standard deviation
Mean transverse corneal diameter in mm
Ratio of corneal diameter and mean transverse
eye diameter (C:E ratio)
Example of calculations: Table 2
Calculations
Table 2: Summary of statistics comparing C:E ratios of primates grouped by
suborder and activity pattern
Diurnal
haplorhine
Number
Nocturnal
haplorhine
Dirunal
Strepsirrhine
Cathemeral
strepsirrhine
Nocturnal
strepsirrhine
30
2
6
5
12
Mean C:E
ratio
0.51
0.74
0.73
0.75
0.83
Standard
Deviation
0.03
0.06
0.02
0.03
0.04
Results and Discussion
C:E ratios varied between primates that were of different
suborders and had different activity patterns; however
within the same subgroup the functional morphology was
consistent with previous testing results.
– For example: diurnal species had smaller relative
cornea size than nocturnal or cathemeral species
As expected nocturnal species showed higher C:E ratios
compared to diurnal species
Haplorhines had diurnal species with significantly lower
C:E ratios than the nocturnal species.
Strepsirrhines had diurnal species with significantly lower
C:E ratios than the nocturnal species
Cathemeral strepsirrhines had C:E ratios that were larger
than the diurnal strepsirrhines and smaller than the
nocturnal strepsirrhines
Summary
Eye morphology changed consistently with
activity pattern in primate suborders
For most suborders tested, such as
strepsirrhines, and haplorhines, relative
cornea size was largest in nocturnal
species and smallest in diurnal species
Discussion
Data supports the hypothesis that cornea
size is largest for species that are most
active in dark periods compared to those
that are active in the light
Primates have evolved their eye
morphologies to maximize their visual
sensitivity, in order to adapt to the activity
patterns