Scientists Record First Undersea Organism to Use
Light to Communicate
This story entered on 12th Jan, 2004 07:00:00
AM PST
Research funded by the NURP
Center for the Southeastern U.S. and Gulf of Mexico Center at the
University of North Carolina at Wilmington was published in
this weeks Science Magazine (2 January 2004, vol. 303, Issue
5654, pg 51). Using NOAA's Aquarius, scientists documented
the first usage of fluorescent light as a behavioral signal to communicate
to other organisms in the marine environment. The mantis shrimp
was shown to use the fluorescent light to ward off other males during
mating season and potential predators.
For more information, please read the article below.
Fluorescent Enhancement of Signaling in a Mantis Shrimp
C. H. Mazel,1 T. W. Cronin,2 R. L. Caldwell,3 N. J. Marshall4
1 Physical Sciences Incorporated, 20 New England Business Center,
Andover, MA 01810, USA.
2 Department of Biological Sciences, University of Maryland Baltimore
County, Baltimore, MD 21250, USA.
3 Department of Integrative Biology, University of California, Berkeley,
CA 94720, USA.
4 Vision, Touch, and Hearing Research Centre, University of Queensland,
Brisbane 4072, Australia.
Visual signals based on colored pigments can be unreliable in aquatic
environments, because the optical properties of water spectrally
filter both the incident and the reflected light. Fluorescence has
more potential to contribute to color underwater than in terrestrial
situations, because the spectrum of the emitted light can contrast
effectively with that of the predominantly blue illumination (1).
Many corals have striking fluorescent coloration (2), and some vision-centered
marine organisms such as squids have fluorescent patches (3). Though
a behavioral function has been shown for fluorescence in budgerigar
plumage (4), the use of fluorescent colors as signals has not been
shown in the sea. Here, we show that fluorescent coloration used
in postural signaling by the mantis shrimp Lysiosquillina glabriuscula
contributes to signal brightness and visibility, particularly at
greater depths.
Several species of mantis shrimp (stomatopod crustaceans) have strongly
fluorescent yellow markings. In L. glabriuscula, these appear as
patches on the antennal scales and carapace (Fig. 1A). This species
is large (up to 22 cm long) and is found throughout the western
Atlantic from South Carolina to Brazil. Burrowing in sandy substrates
at depths from the low intertidal to 60 m, monogamous adults rarely
leave their burrows except to search for new mates. A common threat
display involves raising the head and thorax, spreading the striking
appendages and other maxillipeds, and extending the prominent, oval
antennal scales laterally (Fig. 1A). We have observed such displays
directed toward males of the same species as they approached a burrow
entrance and toward potential predators when encountered in the
open. The display increases the apparent size of the animal and
accentuates both its weapons and the yellow markings.
To human eyes, the patches appear yellow due to combined reflectance
and fluorescence when illuminated by white light, and they have
a strong yellow fluorescence when illuminated by ultra-violet or
blue light (Fig. 1B) (5). The excitation spectrum (Fig. 1C) peaks
in the blue (440 nm, 365 to 495 nm at half-maximum) and is well
matched to the wavelength range of maximum illumination (5). The
wavelengths of the fluorescence emission (524 nm at peak, 500 to
575 nm at half-maximum) transmit well through seawater, so the emitted
light would be visible at distances at which animal-to-animal interactions
occur.
The spectrum produced by the yellow patches under ambient illumination
at any depth is a combination of the reflectance and fluorescence
components (2, 5). At moderate depths, the interaction of reflectance
and ambient light produces a broad peak in the 475- to 575-nm (cyan
to yellow) range. The fluorescence overlays and intensifies this
peak (fig. S1). We estimate that, throughout the depth range from
2 to 40 m, the fluorescence accounts for 7 to 10% of the total (reflected
plus fluoresced) photons leaving the yellow patches.
The fluorescence contribution gains significance when we consider
the photoreceptors used by stomatopods. Mantis shrimp have a complex
system of color vision, based on at least eight primary spectral
receptor classes operating at wavelengths from 400 to 700 nm. Colored
markings play a critical role in visual communication (6). The fluorescence
spectrum is well placed to stimulate receptor classes that are tuned
to middle wavelengths (5) (Fig. 1D), so it should be highly recognizable
in a species-specific signaling system. For the pair of receptors
with the closest spectral match, the modeling indicates that, at
depths of 20, 30, and 40 m, the fluorescence contributes approximately
9, 11, and 12%, respectively, of the photons stimulating the shorter-wavelength
receptor, and 15, 22, and 30%, respectively, of those stimulating
the longer-wavelength receptor. Thus, the fluorescence enhances
and spectrally identifies a color signal in the variable lighting
over the depth range inhabited by this species.
References and Notes
1. J. N. Lythgoe, The Ecology of Vision (Clarendon Press, Oxford,
1979).
2. C. H. Mazel, E. Fuchs, Limnol. Oceanogr. 48, 390 (2003).[ISI]
3. L. Mathger, E. J. Denton, J. Exp. Biol. 204, 2103 (2001).[ISI][Medline]
4. K. E. Arnold, I. P. F. Owens, N. J. Marshall, Science 295, 92
(2002).[Free Full Text]
5. Materials and methods are available as supporting material on
Science Online.
6. T. W. Cronin, N. J. Marshall, R. L. Caldwell, Philos. Trans.
R. Soc. B 355, 1263 (2000).[CrossRef][ISI][Medline]
7. Supported by the Environmental Optics Program, Office of Naval
Research (C.H.M.), the National Undersea Research Center/UNC Wilmington
(T.W.C., R.L.C., N.J.M.), the National Science Foundation (T.W.C.),
and the Australian Research Council and Lizard Island Research Station
(N.J.M.). All co-authors contributed equally to this manuscript.
Paper title: Fluorescent Enhancement of Signaling
in a Mantis Shrimp
Publication name: Science
Date of publication: Fri, January 2 2004
Contact information
Name: Steven Miller
Tel: (305) 451-233
smiller@gate.net
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