Table 1 Characteristics summary (morphology, opsin, phototransduction cascade, and electrophysiology) of the transmuted photoreceptors of different species compared to true rods and true cones.

Lizard data are for the genus Anolis. Lamprey is the sea lamprey Petromyzon marinus. Salamander is the tiger salamander Ambystoma tigrinum. Pearlside is the Mueller’s pearlside M. muelleri. The snake with the cone-like rods is the diurnal garter snake Thamnophis proximus. The snake with the rod-like cones data are for the nocturnal genus Hypsiglena. The gecko is the nocturnal Tokay gecko Gekko gekko. The skate is the genus Raja. R, true rod; C, true cone; n.a., not available; poly, polysynaptic.

Photoreceptor
characteristics
True
rod (1, 19)
True
cone (1, 19)
Cone-like rodRod-like cone
Snake
(7, 78)
Skate
(10, 45, 79)
Lizard
(5, 80, 81)
Lamprey
(9, 82, 83)
Gecko
(6, 8486)
Snake
(4, 35)
Salamander
(8, 87)
Pearlside
(this study)
Outer segment
shape
Long, rod-
shaped
(cylindrical)
Short, cone-
shaped (distally
tapering)
CRCRRRRR
Outer segment
discs
Individual sealed
disc, separated
from the plasma
membrane
Discs continuous
with the plasma
membrane (open)
RRn.a.R CR Cn.a.n.a.R
IncisurePresentAbsentn.a.n.a.CCRn.a.RR
ParaboloidAbsentPresentCRRR
Oil dropletAbsentSometimes presentRn.a.Cn.a.RRRR
Synaptic endingSmall, spherical,
oligosynaptic
Large, conical,
flat-end base,
polysynaptic
n.a.Cn.a.R C
Small poly
Cn.a.R C
Small poly
R C
Small poly
Opsinrh1sws1, sws2, lws, rh2RRRRC
rh2
C
sws1
lws
C
sws2
C
rh2-1
rh2-2
Spectral
sensitivity
(nm)
480–510rh2, 450–530
sws1, 360–440
sws2, 400–450
m/lws, 510–560
R
482
R
500
R
491
n.a.C
521
C
358, 536
C
432
C
441 (both pigments)
Phototransduction
cascade
Rod-likeCone-likeRn.a.n.a.n.a.C(R)n.a.RC
Cell physiologyRod properties
(high sensitivity)
Cone properties
(fast, never
saturate)
n.a.R Cn.a.RRn.a.n.a.n.a.