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unfold in a fast-action theater of
fanciful fins. The gaudy, oversized
regalia belong to impassioned
male flasher wrasses showcasing
their genetic superiority in a late-
afternoon spawning ritual. The
show is simply stunning.
Anna and I have fallen in love
with many fishes during our lives,
but none has seduced us quite like
flasher wrasses — the underwater
world’s answer to the peacock.
It took nearly a decade of further
thought and experimentation before
Darwin finally presented his theory
of sexual selection, including an
unpalatable presentation of female
choice, in The Descent of Man, and
Selection in Relation to Sex. Although
Darwin opened the world’s eyes to
the reasonableness of evolution, his
ideas on both natural and sexual
selection, always struggling for
popularity during his lifetime, lost
favor following his death in 1882.
However, with insight from genetics
and molecular biology, Darwin’s
theories were resurrected with
veneration during the 20th century
and today stand as guiding principles
of biological science.
Even though the 16 known
species of flasher wrasses in
genus Paracheilinus are rather
common in Indo-Pacific waters
and breathtakingly beautiful,
few divers are familiar with this
spectacular group of fishes. This
is understandable — flashers are
easily overlooked. Males, usually
measuring less than 3 inches
long, mute their colors and keep
low profiles for much of the day
to avoid predation. The even
smaller, far more numerous and
nondescript females blend into
the bottom like ghosts. Adding to
their inconspicuousness, the little
plankton eaters typically live 40 to
100 feet deep in single- or mixed-
species aggregations over rubble- or
algae-covered slopes where they
dive for cover when threatened.
However, all this changes during
a brief 20-minute period between
4 p.m. and 5 p.m. each day when
aggregations, numbering anywhere
from a dozen to hundreds, erupt
into high-energy orgies.
If our timing hadn’t been right
several years ago, we would have
missed our first flasher show
altogether. This time we arrive on the
scene just as the spawning frenzy of
a hundred nears a crescendo. Dozens
of males, designed for seduction,
zip between isolated clusters of
females at full throttle, flaunting their
exaggerated fins and chasing rivals
at every turn. Eventually, out of what
appears to be chaos, females, plump
with eggs, calmly lift off the bottom
and wait for a male to fly to their
sides. Once together, pairs rocket
up like fireworks at a holiday picnic,
leaving powdery puffs of gametes at
the peak.
Ever since that first encounter,
Anna and I search for flashers on
every Pacific dive trip. To date
we’ve documented 12 species,
including the roundfin flasher
(P. togeanensis), once believed, before
it was sighted in Indonesia’s Lembeh
Strait in 2005, to be endemic to the
Togean Islands, located 200 miles
to the west. An informal survey
of known flasher sites in the strait
reveals a scattering of roundfins
mixed in with filamented flashers
(P. filamentosus, the most common
and wide-ranging flasher species) at
three locations. On subsequent visits
over the following year, we observe
the roundfin population first increase,
then plummet and finally disappear.
The suddenness of it all provides us
with a rare glimpse of evolution
in action.
From the start, we had noticed
distinct differences in color patterns,
fin sizes and fin shapes between
populations of filamented flashers
in Lembeh and at distant locations
across the region. During later stays
in Lembeh, we detected similar
changes taking place over time
within aggregations. In the summer,
following an absence of three months,
we found a new fish jetting about
during afternoon spawns looking for
all the world like a cross between a
roundfin and filamented. That winter
not a trace of the roundfins or the
lone hybrid could be found.
Our brief time with the flashers
illustrates a little-appreciated fact.
Even though natural selection typically
works at a snail’s pace, under certain
conditions evolutionary change can
happen rapidly, especially when
spurred on by the creative powers of
sexual selection.
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Filamented flasher (P. filamentosus)
Hybrid flasher, a cross between the
filamented and roundfin
Roundfin flasher (P. togeanesis)