the fish face one another, make contact
with their open mouths, and push. This, in
turn, often escalates to mouth locking and
finally release and fleeing.
Fascinating Data
Their findings: the sexes did not differ
significantly in time taken to initiate
fights, but females were significantly more
inclined to escalate than were males. In
that sense they were the more aggressive
sex. Females consistently won fights when
they were the same size or bigger than
males. Given a female 90 percent the
mass (size to weight ratio) of a male, the
two have an equal chance of winning.
Since paired males average only about
56 percent of the mass of their mates in
nature, females should easily dominate
their mates, since they are, on average,
almost twice as heavy. One might expect
the optimum compatibility match would
be between a male and female who is about
90 percent of his size; this pair would have
equally dominant mates. But that’s not
what either sex selects in nature where
seemingly endless choices exist. The fact
that this doesn’t happen, Barlow and Lee
argue, suggests that in the case of J. marlieri
there is selective advantage in having
one individual—in this case the female—
constantly in charge, whose dominance in
the “relationship” is never in question (the
“heavy” of the pair, so to speak!). And if the
female is the dominant sex in pairs, this
would allow mating with multiple males
to occur (polyandry), which translates into
a higher potential rate of reproduction for
the female, just the reverse of the situation
for most monogamous biparental cichlids
whose males will opportunistically mate
with additional females. How and why did
this arise? Clearly, female Julidochromis
must be competing for access to a limited
number of males in Lake Tanganyika,
suggests Barlow.
As with most of Barlow’s experimental
behavioral work, this small study is an
exemplar of important questions framed
simply, and whose answers are eminently
testable in an equally simple experimental
paradigm. It also represents an intriguing
initial contribution to understanding the
increasingly exceptional biology of a group
of unique, polyandrous cichlids.
Though George Barlow is no longer here
to finish the work he started just a few
short years ago with Julidochromis, others
are and have been doing so, standing
on the shoulders of this early pioneer of
cichlid behavior. In a future column I will
continue our discussion of this unique
suite of cichlids based on more recently
published work, both in the field and in
the laboratory, that I discovered while
writing this piece. Meanwhile, as Ron
Coleman, a dear friend of and former postdoctoral fellow in Barlow’s lab, suggested
to us at ACA 2007 in tribute to George:
take the time to sit and really watch your
fish. That’s what George Barlow really was
about, understanding what cichlids do and
why. And he counted on and encouraged
us aquarists to generate those interesting
new observations that would provide leads
for future cichlid research. So let’s do
it—in his memory.
