San francisco and the sea of cortez - A Fascination for Fish: Adventures of an Underwater Pioneer - page 56

and invertebrates that would later be flown back to Steinhart Aquar-
ium. By the end of the trip we had a fine collection of colorful but-
terflyfishes, angelfishes, squirrelfishes, wrasses, and assorted inverte-
brates. I had also managed to collect the ugly but very personable
finespotted jawfish ( Opistognathus punctatus ). While I concentrated on
the underwater life, the dry-land members of the expedition were
equally focused on everything from scorpions and snakes to desert plants
and birds. Discoveries of special interest were shared with all on board,
and we learned a lot from one another.
The Sea of Cortez is home to a species of fish-eating bat, Pizonyx
vivesi, several specimens of which Bob Orr and Ray Bandar collected
from a crevice in the rocks on Isla San Francisco. This remarkable an-
imal swoops low dragging its clawed feet in the glassy-calm water to
snag small fish. It's fascinating to ponder how such a behavior might
have originated among these flying mammals' insect-eating ancestors.
Did one bat with exceptionally long claws one day swoop especially
low over the water and “accidentally” snag a small fish? Did it then try
again, succeed, thrive, and pass its genes on to its o¤spring? Did other
bats see and copy this behavior? It's interesting and also fun to specu-
late on how such highly specialized behaviors as this begin.
The Gulf island of Santa Catalina in particular was a fascinating place
both above and below the water. This island was home to the world's
only rattleless rattlesnake. Did the absence of land predators eliminate
the survival advantage of having a warning rattle? Most likely. What
advantage, after all, is a complicated device like a rattle if there is noth-
ing to frighten away? It's generally true in the biological world that a
structure that no longer provides a survival advantage will tend to de-
generate over many generations. The remnant hind legs of some
snakes are an example of this degeneration.
As Charles Darwin so astutely observed on the Galápagos Islands,
evolution can go in radically di¤erent directions when animals are placed
in an environment quite di¤erent from that in which they originally
evolved. Animals and plants can change rapidly under the pressures of
natural selection in the new environment and also from what is called
genetic drift. Genetic drift occurs when a new population is founded
by a few colonizers, or in some cases even a single fertilized female.