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Joining the ranks of vertebrates that glow is the Pacific Spiny Lumpsucker, Eumicrotremus orbis, a subtidal species widely distributed across the North Pacific Ocean. Aside from their charismatic appearance, the Pacific Spiny Lumpsucker is known for its ventral suction disc that is used to stick to substrates amid changing currents and tides. Here we show that red lumpsuckers, which are usually male and a deep red color under broad-spectrum light, fluoresce bright red under ultraviolet (UV) light and blue light (360–460 nm), while green color morphs (usually female) do not. In all color morphs, the suctorial disc glows green-yellow. The red glow of the males matches the red glow of encrusting algae in their nesting areas, while the suctorial disc may be a signaling system. The green and red fluorescence observed in red lumpsuckers is the rarest fluorescent pattern and is only seen in 17 families of marine fishes. Pacific Spiny Lumpsuckers are cryptically colored under broad-spectrum light; our observed fluorescence suggests a potential avenue of communication and camouflage in an environment where red light is absent or rare.
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Dimorphic Fluorescence in the Pacific Spiny Lumpsucker
Karly E. Cohen
1
and Adam P. Summers
1
Joining the ranks of vertebrates that glow is the Pacific Spiny Lumpsucker, Eumicrotremus orbis, a subtidal species widely
distributed across the North Pacific Ocean. Aside from their charismatic appearance, the Pacific Spiny Lumpsucker is
known for its ventral suction disc that is used to stick to substrates amid changing currents and tides. Here we show
that red lumpsuckers, which are usually male and a deep red color under broad-spectrum light, fluoresce bright red
under ultraviolet (UV) light and blue light (360–460 nm), while green color morphs (usually female) do not. In all color
morphs, the suctorial disc glows green-yellow. The red glow of the males matches the red glow of encrusting algae in
their nesting areas, while the suctorial disc may be a signaling system. The green and red fluorescence observed in red
lumpsuckers is the rarest fluorescent pattern and is only seen in 17 families of marine fishes. Pacific Spiny Lumpsuckers
are cryptically colored under broad-spectrum light; our observed fluorescence suggests a potential avenue of
communication and camouflage in an environment where red light is absent or rare.
SOME materials will absorb energy at one wavelength
and emit it at another, longer wavelength; when the
emission is in the visible light spectrum, we see this as
fluorescence. From tree frogs to turtles, and swell sharks to
serranids, there are many examples of animals that fluoresce
(Sparks et al., 2014; Gruber and Sparks, 2015; Taboada et al.,
2017; Lamb and Davis, 2020). The emitted light comes from
one of two types of sources, either metabolites or fluorescent
proteins (Gruber et al., 2015; Park et al., 2019). When excited
by ultraviolet (UV) or near-UV light, vertebrates from a
diversity of lineages fluoresce across a range of colors from
reds through blues (500–700 nm). In several cases, the exact
compound responsible for the phenomenon is known, but in
most biofluorescent animals this remains a mystery. There
are few examples of vertebrates with more than one
fluorescent compound, which allows emissions at more than
one wavelength of light. For example, the Variegated Snail-
fish (Liparus gibbous) glows both green (523–530 nm) and red
(674–678 nm) when illuminated with near-UV light (Gruber
and Sparks, 2021).
Many fishes fluoresce, and two principal functions have
been ascribed to the phenomenon: photoprotection and
visual contrast (Meadows et al., 2014). In some cases, the
fluorescent molecules located around delicate structures
absorb short wavelength light and protect them from UV
damage (Salih et al., 2000; Losey et al., 2003; Meadows et al.,
2014). Visual contrast includes fluorescence that serves to
highlight and communicate, as well as that which serves to
conceal and camouflage (Gerlach et al., 2014; Wucherer and
Michiels, 2014; Kalb et al., 2015). Fishes can certainly see
these colors, but because water absorbs long wavelengths
very efficiently, these are short range effects (Haddock et al.,
2005). Most fishes that are biofluorescent have yellow
intraocular pigments that act as long-pass filters which
increase the contrast of the fluorescent patterns (Heiner-
mann, 1984; Sparks et al., 2014). Since little long-wavelength
light penetrates the depths, fluorescence is a way for fishes to
convert shorter wavelengths into longer ones, effectively
giving them a broader spectrum for concealment and
communication.
Pacific Spiny Lumpsuckers (Eumicrotremus orbis, Cyclop-
teridae) have large, conical, dermal tubercles armoring their
body and a ventral suctorial disc derived from modified
pelvic fins (Budney and Hall, 2010). Their habitat stretches
across the North Pacific, and they are commonly spotted in
both intertidal and subtidal habitats (Arita, 1969). In the
wild and in captivity, lumpsuckers will stick to rocks,
barnacles, and even eelgrass, and, despite their round bodies
and rough suckers, they can stick to smooth surfaces better
than snailfishes or clingfishes (Nachtigall, 1974; Budney and
Hall, 2010; Tietbohl et al., 2015). Here we describe the
sexually dimorphic fluorescent patterns of the Pacific Spiny
Lumpsucker (Eumicrotremus orbis) and offer a potential
function.
MATERIALS AND METHODS
We dip netted Pacific Spiny Lumpsuckers at near-shore
locations at Friday Harbor Labs, Friday Harbor, WA, USA.
Sexually mature lumpsuckers have a variety of color morphs,
including yellow, orange, dark green, light green, and a deep
red. We caught and imaged individuals with green to red
color patterns. Lumpsuckers were housed in flow-through sea
tables and fed dried krill (IACUC 4238-03). All lumpsuckers
were first imaged under white light with a digital single-lens
reflex (DSLR; Canon 5DMk3, MP-E-65 mm macro lens) and a
phone camera (Apple iPhone 12). Fluorescent images of
lumpsuckers and habitat were taken with the same DSLR and
phone camera and illuminated with a NIGHTSEA Stereo
Microscope Fluorescence illuminator with the ultraviolet
(UV) head (360–380 nm) and Royal Blue (RB) head (440–460
nm). For fluorescent imaging, fish were placed in black photo
tanks to minimize reflected light. To capture biofluorescence,
a scientific grade yellow filter (long-pass, 500 nm) was
attached to the outside of the camera lens. The same
methods were used to image red algae encrusted rocks and
barnacles under white, ultraviolet, and blue light.
RESULTS
Male and female lumpsuckers were sexed based on their color
in accordance with previous reports that male Pacific Spiny
1
University of Washington, Biology Department, Friday Harbor Laboratories, Friday Harbor, Washington; Email: (KEC) kecohen@uw.edu. Send
reprint requests to KEC.
Submitted: 8 February 2021. Accepted: 15 November 2021. Associate Editor: W. L. Smith.
Ó2022 by the American Society of Ichthyologists and Herpetologists DOI: 10.1643/i2021019 Published online: 15 June 2022
Ichthyology & Herpetology 110, No. 2, 2022, 350–353
Lumpsuckers are red while females are brown or green. The
red lumpsucker (n¼1) fluoresced under the UV and RB
illuminator with a bright red color all over the body
including all tubercles and the eyes. None of the other green
or brown color morphs (n¼4) had any fluorescence on their
eyes, sides, or dorsum (Fig. 1). Additionally, papilla surround-
ing the ventral suctorial disc of all lumpsuckers fluoresced
with a bright green-yellow light (Fig. 1).
We also found that fluorescence revealed damaged papillae
(Fig. 2, arrow and inset) and papillae that had been ripped
away (Fig. 2, *). A thin surface layer emits green-yellow light
while the underlying tissue emits red light or no light. This
dichotomy meant that we could see places where papillae
evident under white light had been completely abraded and
other areas where parts of a papilla were lost. When fish are
free swimming, unattached to a substrate, they cover most of
the suctorial disc with their pectoral fins, shielding most of
the green-yellow light. Our examination of the natural
habitat of the Pacific Spiny Lumpsucker revealed that rocks
encrusted with sponges and coraline red algaes have bright
red fluorescence similar in character to that of the red color
morph (Fig. 3).
Fig. 1. Red color morph vs. green color morph under (A–B) white light conditions, (C–D) royal blue (RB) illuminator light (440–460 nm). (E–F) View
of the ventral suctorial disc under RB illuminator light (440–460 nm) showing the fluoresced papillae. Panel D shows fish illuminated by RB light but
the fish is not fluorescing (re-emitting) the light. All photos taken with Canon Mark 3 camera with a 100 mm macro lens.
Fig. 2. Fluorescing suctorial disc, papillae fluorescing bright green-
yellow on the red lumpsucker, arrow points to damaged papilla, *
shows a missing papilla. Where papillae are seen in broad-spectrum
light but not green-yellow fluorescence has been outlined. Arrow and
inset show damaged papilla where part of the fluorescing layer is
absent.
Cohen and Summers—Dimorphic fluorescence in the Pacific Spiny Lumpsucker 351
DISCUSSION
Male lumpsuckers are typically red with a strikingly purple
mouth, while females tend to be green or light brown (Arita,
1969). Males are smaller than females, covered with fewer
and smaller tubercles, and they are the primary caregivers
(Arita, 1969; Hart, 1973). Males guard nests, often in empty
barnacles, in subtidal waters. Short wavelength light reaches
the depths where lumpsuckers breed and tend eggs (,10 m),
so the red fluorescence could aid males in attracting mates.
Red fluorescence would stand out against the blue-skewed
environment as red wavelengths are rare or absent in the
ambient light that reaches their habitat (Meadows et al.,
2014; Sparks et al., 2014; Anthes et al., 2016). Additionally,
the brightly fluorescing sucker disc could act as a signaling
device, which would be completely hidden when the fish is
attached to a substrate. Similar signaling is strongly suggested
in flatfishes where the blind side of the fish, that with no eye,
has fluorescent green markings that are hidden when the
animal is lying on the seafloor (Sparks et al., 2014). They
flash their blind sides during mating, suggesting the
fluorescence, usually hidden, plays a role in finding or
attracting mates at close range (Sparks et al., 2014).
Additionally, the red color could camouflage males while
they are on their nests among the red algae covered rocks.
Fluorescence in the Pacific Spiny Lumpsucker extends this
complicated visual communication/camouflage system in
the Cottoidei. Male lumpsuckers represent one of the rarest
fluorescing patterns; in Scorpaeniformes only five families
have both red and green fluorescent patterns. The recent
interest in fluorescence, driven by its discovery in charismat-
ic species such as the Platypus, epaulet sharks, puffins, and
the Web-footed Geckos, is driven in part by its potential
importance as a cryptic line of communication (Gerlach et
al., 2014; Dunning et al., 2019; Park et al., 2019; Anich et al.,
2020; Pr¨
otzel et al., 2021). Since Pacific Spiny Lumpsuckers
are easily bred and maintained in captivity, they have
potential as a model species for understanding how fluores-
cent color patterns are used in communication and camou-
flage.
DATA ACCESSIBILITY
Unless an alternative copyright or statement noting that a
figure is reprinted from a previous source is noted in a figure
caption, the published images and illustrations in this article
are licensed by the American Society of Ichthyologists and
Herpetologists for use if the use includes a citation to the
original source (American Society of Ichthyologists and
Herpetologists, the DOI of the Ichthyology & Herpetology
article, and any individual image credits listed in the figure
caption) in accordance with the Creative Commons Attribu-
tion CC BY License.
ACKNOWLEDGMENTS
Thank you to the facilities at the Karel F. Liem Bioimaging
Facility and funding provided by the Stephen and Ruth
Wainwright Endowment to KEC and the Seaver Institute to
APS.
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Cohen and Summers—Dimorphic fluorescence in the Pacific Spiny Lumpsucker 353
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