Evolution of Retinal Structure in Percid Fishes:
A Test of the Sensory Bias Hypothesis
by
Karen A. Lawrence and Rex Meade Strange
A Follow-Up Report Submitted to the
Funding For Results Committee
in Fulfillment of the Requirements for
the FFR Grant
Department of Biology
Southeast Missouri State University
Cape Girardeau, MO
31 January, 2002
INTRODUCTION
The evolution of communication systems is a process whereby a relationship is
established and maintained between a signal and a receiver. The evolutionary
sequence of signal and reception may take one of two forms. For example, color
patterns used in communication may have evolved prior to the visual acuity necessary
for the detection of color. Alternatively, color vision may have evolved prior to color
patterns. The sensory bias hypothesis explains the coevolution of signal and reception
as the exploitation by the signaler (through color pattern) of a preexisting neural
structure (color vision) in the receiver (Ryan et al. 1990). Phylogenetic distributions of
retinal structures and the presence or absence of color signals is one possible test of
the sensory bias hypothesis (Ryan et al. 1990; see comment by Ahlbert 1970: 447).
Fishes of the family Percidae represent an ideal group to test the sensory bias
hypothesis. Percidae is the second largest family of North American freshwater fishes
and consists of 5 genera with 145 described species (Burr and Mayden 1992). Darters
(Crystallaria, Etheostoma, and Percina) represent the most speciose group of Percids
and includes many colorful and a few monochromatic species (Table 1). Males of
many darters use their bright color patterns to attract females during breeding season
and to warn other males against territorial invasion (Page 1985). This use of color in
communication in darters suggests that these fishes possess the ability to detect color.
Despite the bright colors of many darter species, only the visual systems of the
larger percids (Stizostedion canadense, S. vitreum, and Perca flavescens) are well
documented (Ahlbert 1970; Ali et al. 1977; Zyznar and Ali 1974). The retinal structure
in Stizostedion and Perca is marked by the presence of abundant rods, large twin
1
cones, and multiple layers of horizontal cells characteristic of a visual system optimized
for low levels of ambient light (as opposed to visual acuity or color sensitivity).
There are ample reasons to suppose that the visual system of darters differs
from that of the larger percids. First, the use of color in communication is not found in
either Stizostedion or Perca. Second, darters are most active during daylight hours
(Page 1983) whereas Stizostedion and Perca are most active at night and during
twilight hours (Ali et al. 1977). Further, most darters occupy creeks and small streams
with clear water. Such well-lit habitats are conducive to the use of color
communication. However, retinal structure of darters remains undocumented and it is
unknown whether darters possess the ability to detect color.
I examined the retinal structure of representative percids to determine whether a
difference in color patterns coincides with visual acuity. I am now in the process of
collecting sequences of the cytochrome b protein coding region for the species included
in this study in order to estimate their phylogenetic relationships. I will use the
phylogenetic distribution of retinal structure characters and body color characters
documented herein on the DNA-based phylogeny as evidence to infer the evolutionary
sequence of color vision and color communication in darters.
2
METHODS
Histology.–All specimens included in this project were collected in their
respective habitats and promptly preserved at the collection site in 10% formalin.
Retinal tissue was dissected from light-adapted fish to control for light-sensitive cell
migration within the retina. The formalin-fixed tissues were then dehydrated in an
ethanol series and cleared in xylenes prior to embedding in paraffin. The paraffin block
was sectioned (transverse sections) and the sections were mounted to slides. I stained
the mounted sections with hematoxylin and counter-stained with eosin. The structure
of photoreceptive cells and the relative abundance of rods and different types of cones
was documented with a Leitz Ortholux microscope and Leica camera.
Phylogenetic analysis.–Sequences of the mitochondrial cytochrome b proteincoding region for many of the species included in this study are available from
Genbank. I will submit PCR products from species not documented with Genbank for
sequencing to Cornell University’s Biotechnology Laboratory. Sequences will be
aligned with CLUSTALW (Thompson et al. 1994) and imported into the Maximum
Likelihood algorithm available in PHYLIP (Felsenstein 1995). Character traits (i.e.,
presence/absence of cones, specific retinal structures, presence/absence of color on
bodies) will be mapped onto the phylogeny under the criterion of maximum parsimony.
RESULTS AND DISCUSSION
I examined the histological structure of 18 species representing the three genera
of darters (Table 1). Perca flavescens and two species of Stizostedion were included to
replicate the findings of previous studies (Ahlbert 1970; Ali et al. 1977; Zyznar and Ali
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1974). Distinctive histological structures of Stizostedion and Perca retinae are giant
twin cones (Figure 1) and three rows of stellate horizontal cells which function to
increase light sensitivity by laterally linking photoreceptors (rods and cones; Ahlbert
1970; Ali et al. 1977; Zyznar and Ali 1974). Darters have smaller, more densely packed
single cones and a specialized horizontal cell layer composed of cuboidal cells which
form an epithelial-like sheet (Figure 2). Bipolar cells are intermediaries between
photoreceptors and the ganglion cells that lead to the optic nerve. Stizostedion and
Perca have a higher ratio of photoreceptors to bipolar cells than darters. The greater
degree of neural convergence in Stizostedion and Perca supports the contention that
these large percids are more light sensitive than the diurnal darters. We conclude that
darters have a greater degree of visual acuity than the larger percids, which may be
correlated with color vision.
Final completion of the phylogenetic analysis and mapping of character traits
(retinal structures, body color, and temporal activity) onto the phylogeny will allow me to
infer the evolutionary sequence of darter body coloration and the darters’ ability to
detect body coloration. I am using the phylogenetic hypothesis proposed by Wiley
(1992) until my sequence data are complete (Figure 3). Phylogenetic placement of
color vision and color communication on the topology suggests that color vision
predates color communication in percids. The evolution of color vision prior to color
bodies supports the sensory bias hypothesis.
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LITERATURE CITED
Ahlbert, Inga-Britt. 1970. The organization of the cone cells in the retinae of four
teleosts with different feeding habits (Perca fluviatilis L., Lucioperca lucioperca
L., Acerina cernua L. and Coregonus albula L.). Arkiv for Zoologi 22:445-481.
Ali, M.A., R.A. Ryder, and M. Anctil. 1977. Photoreceptors and visual pigments as
related to behavioral responses and preferred habitats of Perches (Perca spp.)
and Pikeperches (Stizostedion spp.). Journal of the Fisheries Research Board of
Canada 34:1475-1480.
Felsenstein, J. 1995. PHYLIP: Phylogeny Inference Package, version 3.57c.
University of Washington, Seattle, WA.
Page, L.M. 1983. Handbook of darters. T.F.H. Publications, Inc. Neptune City, NJ.
Page, L.M. 1985. Evolution of reproductive behaviors in percid fishes. Illinois Natural
History Survey Bulletin 33:275-293.
Mayden, R.L., B.M. Burr, and R.R. Miller. 1992. Phylogenetics and North American
freshwater fishes. Pp. 827-863 in R.L. Mayden (ed.) Systematics, historical
ecology, and North American freshwater fishes. Stanford University Press,
Stanford, CA.
Ryan, M.J. and R.C. Drews. 1990. Vocal morphology of the Physalaemus pustulosus
specis group (Family Leptodactylidae): Morphological response to sexual
selection for complex calls. Biological Journal of the Linnean Society 40:37-52.
Thompson, J.D., D.G. Higgins, and T.J. Gibson. 1994. CLUSTAL W: improving the
sensitivity of progressive multiple sequence alighnment through sequence
weighting, positions-specific gap penalties, and weight matrix choice. Nucleic
Acids Research 22:4673-4680.
Wiley, E.O. 1992. Phylogenetic relationships of the Percidae (Teleostei: Perciformes):
A preliminary hypothesis. Pp. 247-267 in R.L. Mayden (ed.) Systematics,
historical ecology, and North American freshwater fishes. Stanford University
Press, Stanford, CA.
Zyznar, E.S. and M.A. Ali. 1975. An interpretative study of the organization of the
visual cells and tapetum lucidum of Stizostedion. Canadian Journal of Zoology
53:180-196.
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Table 1. Presence (1) or absence (0) of specific body colors, retinal optimization as
determined by retinal structures (A=optimized for acuity, S=optimized for light sensitivity), and
periods of peak activity (D=diurnal, T=twilight, N=nocturnal, and ?=undocumented) in percids
included in this study.
___________________________________________________________________________
Retinal
Temporal
Species
Red
Green
Blue
Optimization
Activity
___________________________________________________________________________
P. flavescens
0
0
0
S
T
S. canadense
0
0
0
S
N
S. vitreum
0
0
0
S
N
P. caprodes
0
0
0
A
D
P. maculata
0
0
0
A
D
P. shumardi
0
0
0
A
?
C. asprella
0
0
0
A
?
E. asprigene
1
0
1
A
D
E. barrenense
1
0
1
A
D
E. blennioides
1
1
0
A
D
E. caeruleum
1
0
1
A
D
E. chlorosomum
0
0
0
A
D
E. clara
0
0
0
A
?
E. crossopterum
0
0
0
A
D
E. flabellare
0
0
0
A
D
E. gracile
1
1
0
A
D
E. kennicotti
0
0
0
A
D
E. oophylax
0
0
0
A
D
E. prolaire
0
0
0
A
D
E. smithi
1
0
0
A
D
E. spectabile
1
0
1
A
D
E. vivax
0
0
0
A
?
___________________________________________________________________________
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List of figures
Figure 1. Section of neural retinal from Stizostedion vitreum. Note large cones and
abundant rod nuclei.
Figure 2. Section through neural retina of Etheostoma blennioides. Note approximately
equal number of rod nuclei and cone ellipsoids.
Figure 3. Hypothesized phylogenetic relationships among percid genera (after Wiley
1992). Green bar indicates origin of color vision, blue bar indicates origin of
color communication.