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The Three-Spined Stickleback is the only Stickleback that
occurs in Virginia and furthermore, it is also the most widespread Stickleback
in the world. It’s name Gasterosteus
is derived from the Greek words (gastro and osteo) that literally translate to
“belly” “made of bone,” while aculeatus
means “spiny.” I believe that each fish
has something to teach us, if we just observe closely and ask the right
questions. However, the Three-Spined
Stickleback has so much to teach us. In
fact, in today’s library search on
“Three-Spined Stickleback Gasterosteus
aculeatus” I learned that there are 5,267 journal articles, 1,042 books,
and 336 doctoral dissertations written on this species alone! In this short post, I will briefly describe
many of the lessons the species can teach us.
How to be a fantastic Dad? How to
teach kids self defense? How to be a
good househusband? How to court the
ladies? How to keep embryos well oxygenated?
How to wear red to attract a mate? How to cooperate with others to avoid
predators? How to see all four major wavelengths of light including
ultra-violet?
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| Three-Spined Stickleback Photo by by Lubomir Hlasek |
The Three-Spined Stickleback is easy to identify by its
laterally compressed body with a very slender caudal peduncle, large terminal
mouth, large eye, and three spines anterior to a soft-rayed dorsal fin. It has
no scales on the body; instead it has bony plates on its back,
flanks, and belly. The number of plates on its flanks varies
widely across its range and that is another story worth telling. The pelvic fin is unique as it is made up of
only a single spine. Dorsal colors are drab
olive or a silvery green, sometimes with brown or black mottling. Flanks and belly are silvery. During breeding, the eyes of males become
blue and the lower head, throat, and anterior belly turn bright red. Do the Sticklebacks reflect the origin of a human preference for a blue-eyed mates?
The Three-Spined Stickleback inhabits
fresh, brackish, or salt water along coasts of North America, Europe, and
northern Asia. There are both freshwater
and anadromous forms. Freshwater forms
exist in waters with connections (current or past) to the coasts. In Virginia, it occurs in the York and James
basins and tributaries of the eastern shore.
The anadromous form spends most of its life in the sea, and returns to
freshwater to breed. This form shows
less geographic variation in number of lateral bony plates (usually 30-40) and
has long dorsal and pelvic spines. Freshwater forms of the Three-Spined
Stickleback have larger variation in bony armor and shorter dorsal and pelvic
spines. Apparently, since the end of
the last ice age, Three-Spined Sticklebacks have repeatedly colonized new
streams and lakes forming unique populations.
Because it is a small fish, there are
many predators including fish, birds, and even dragonflies. Predation pressure is a strong selective
pressure on the species and is reflected in the variation in size and number of
bony armor plates and size of spines.
These anti-predator defense mechanisms have been widely studied.
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| Photo by Marcin Lenart |
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| Photo by David Moreton |
In fact the difference in the bony skeletal patterns of
closely-related populations of Three-Spined Sticklebacks reflects a difference
in a single gene. This gene is called a
“tool-kit” gene because it possesses all the tools to program all processes
involved in bone formation. Interestingly,
two forms of the Three-Spined Stickleback, which differ in the size of their
pelvic fins, have repeatedly evolved in freshwater lakes. Mike Shapiro and David Kingsley showed that long pelvic spines protect the open-water form from
attack by other fish. Yet in the bottom-dwelling form (lower image), whose
principal predator is dragonfly larvae rather than other fish, the tool-kit
gene controlling the formation of the pelvic fin has been selectively turned
off.
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Two forms of Three-Spined Sticklebacks. The bony plates in are shown in red.
from David Kingsley,
modified from Cuvier (1829)
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The love life of the Three-Spined
Stickleback is complicated to say the least. The male Three-Spined Stickleback first digs a pit and begins
to assemble nest materials from algae and vegetation. During the nest builder phase he has inconspicuous colors. The
nest materials are glued together with spider-web-like threads in a spherical
shape with a tunnel for he and his mate to enter. The “glue” is called spiggin (the Swedish
name for Stickleback), which is a proteinaceous substance secreted from the
kidney. In more than a few experiments
on nest-construction, the male Stickleback demonstrated a preference for
brightly colored nest materials to decorate the nest entrance. After the nest is constructed, the male develops a
bright red throat, which is a sign that he is ready to
breed. When the male
develops bright colors he becomes very aggressive and defends his
territory from other males.
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| Photo of Three-Spined Stickleback gluing materials in nest. |
The breeding male will attack anything
with red color that gets near its territory. This is called a fixed action pattern in ethology to denote an
“instinctive behavioral sequence that is relatively invariant within the
species and almost inevitably runs to completion.” Ethologist Nikolass Tinbergen first
described this automatic behavior in sticklebacks and also witnessed sticklebacks attacking red mail trucks they observed through the glass aquarium walls and
windows. The fixed action pattern has a proximate explanation -- the red color causes the male to respond aggressively. The ultimate explanation is that the male behavior decreases the chance that eggs laid in his nesting territory will be fertilized by another male.
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| Close up of male Three-Spined Stickleback with nuptial coloration. Photo (c) Ecomare. |
Females are courted and encouraged to
deposit eggs in that nest, but that courtship too is complicated. In order to successfully court a female,
the male must demonstrate traits of the superb, hypervigilant
house-husband. The male performs a courtship ritual to entice females to lay their
eggs. This includes a dance (or swim)
that has been named the “zigzag” dance. The male approaches with a zigzag dance, bites
the female, and then swims to the nest site with the same zigzag dance. The male hopes the female follows him to the nest.
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| Nuptial male Three-Spined Stickleback biting potential mate. |
The female selects a mate based on red
throat color and other visual signals, such as the nest decorations. The red nuptial coloration is clearly a cue
to females as experiments have shown that ripe females were more likely to
follow a “dummy” stickleback to a fake nest if the dummy had a red belly. Further, dominant males express redder colors
than subordinates. Maybe she is also attracted
to his intense blue eyes – though this hypothesis has not been tested. But there is more to the reproductive
behavior than color variations. Remember,
the love life of the Three-Spined Stickleback is complicated. The male may receive eggs from more than one
female but all parental care is provided by the male.
After the female lays her eggs and
leaves the nest, the male changes from sexual phase to a parental phase and his
color again becomes dull and cryptic. These
changes are associated with a dramatic drop in plasma testosterone levels. The parental (low testosterone, dull
color) phase includes parental duties, guarding the fertilized eggs, fanning
them with his pectoral fin and/or tail to provide them with oxygen, and
protecting eggs from predators. The parental phase may last 5-10 days until
the eggs hatch and the phase is energetically very costly.
Because of these costs associated with
being the perfect house-husband, the Three-Spined Stickleback male may engage in
other “bad” behaviors to more easily pass on genes. These bad behaviors include nest raiding to
steal fertilizations in other nests, stealing eggs from other nests, and eating
eggs from other nests.
Another lesson learned from numerous studies of the
Three-Spined Stickleback is the potential for rapid speciation. This is often apparent in the existence of
closely associated species pairs. In
Paxton Lake, Texada Island, southwestern British Columbia, two
distinct sympatric forms were derived after glacial retreat. Anadromous Three-Spined Stickleback
repopulated lakes after poisoning and rapidly adapted to the new environment
through natural selection. For more information, view this video.
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| Limnetic male (top left) and female (top right) and benthic male (bottom left) and female mature (bottom right) sticklebacks. The limnetics are about 65 mm total length and the Benthics about 75 mm. Photo by G. Velema, UBC |
Recently biologists discovered ultraviolet (UV) receptors in
the eyes of some fishes, including the Three-Spined Stickleback. The nuptially colored male reflects UV
radiation from parts of his body and this may permit short-range communication
between male and potential mates.
One of the anti-predation strategies used by Three-Spined
Sticklebacks is cooperation (tit for tat) in keeping a watch on potential
predators. In this behavior pairs of
sticklebacks reciprocate as each takes turns watching for predators.
The Three Spined Sticklebacks teach us
that evolution is occurring on a timescale much faster than we might
imagine. For example, marine and
freshwater forms are maintained in downstream and upstream locations with
extensive hybridization at intermediate sites.
We can expect future
studies that take advantage of recent sequencing of the entire genome (Jones et
al. 2012) allowing further study of the molecular basis for evolution of this
species.
References
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