with Ken Kaneshiro, Biologist at the University of Hawaii:
NOVA: What are some of the unique features of the Hawaiian Islands that have
given rise to the tremendous number of species in even one family of flies?
KANESHIRO: Well, the first thing is that the Hawaiian Islands are probably the
most isolated island system in the world. It's sitting just about smack dab in
the middle of the Pacific Basin, nearly two thousand miles from the West Coast
of California and two thousand miles from Japan. So that not many organisms
made it to the Hawaiian Islands. Those that did make it however fell on a very
open niche, habitats that were available for it to occupy. So when the first
(insects) arrived in the Hawaiian Islands and laid (their) first batch of eggs
and produced some progeny, they found tremendous numbers of opportunities to
radiate into these different habitats.
So that's the other thing about the
Hawaiian Islands, the climatic situation is such that it's within very short
distances, you have tremendous diversity of environmental conditions; you have
on the windward side of the islands very wet rain forest. And on the leeward
side of the islands, almost desert-like conditions.
NOVA: You have pointed to a particular family of flies that has many species
on this island. Did they all come from the same original parents?
KANESHIRO: Based on data from many lines of study, for example using
chromosomal data, behavioral data, electrophoresis and so on, seem to indicate
that these one thousand species are all descedents from one ancestor, perhaps
two at the most. Now this one thousand species represent approximately 25
percent of the total number of species that are known from the rest of the
world. If you are to consider the small land mass of the Hawaiian Islands, if
you're to take all the Hawaiian Islands and put them all together, you can
probably stick them into the state of Connecticut. Geologically, it's a very
young land mass and yet we have 25 percent of the total number of species that
are found in the world in this family of flies.
NOVA: Is a kapuka in a way sort of a microcosm of the island itself, an
KANESHIRO: The volcanic activity of the Hawaiian Islands have created a
situation whereby for example a, a large piece of forest with recent volcanic
activity now can be cut into two or three or more patches of forest which are
sort of islands of vegetation that are surrounded by a sea of larva and this is
what we're in right here a kapuka and these kepukas create situations where
populations of (most species) are subjected to small population sizes. And
it's the small population that is most important for understanding speciation
NOVA: Is there a substantial difference between what you find among flies in
this kapuka and number 14 a mile or so away?
KANESHIRO: We've been
studying (one fly) species in this kapuka which we've been arbitrarily calling
Kapuka 9 and another adjacent kapuka which is about a quarter of a mile away,
Kapuka 14. Some of the studies that have been done on one of the species by
using molecular tools, electrophoresis for example, indicate that within the
140 years or so that these two kapukas, Kapuka 9 and 14 have been separated,
that there are significant genetic differences between these two populations.
There are very significant genetic differences that have already evolved within
the last 140 years.
NOVA: Now what does that tell you about the nature of evolution that is news
to scientists, the speed with which these things are changing, is this a new
KANESHIRO: Well, one of our ideas is that even though there
has been tremendous adaptive radiation, in other words, many of these species
have been able to adapt to different habitats and niches and so on, our idea is
that changes within the sexual environment, within the mating behavior of these
flies, have been more important in the speciation process than most of us ever
believed before. And so we've been focusing most of our efforts now in
understanding the mating system of these species. It turns out that under
small population size, there's a very strong selection for less discriminate
females. In other words, females that are very choosy as to who they mate
with, may never encounter a male that is able to satisfy her mating
requirements. So, while the population is under small population size for a
few generations, there's a very strong selection for females that are less
choosy and there is an increase in frequency of these types of females. So
along with that shift in frequency of mating types then there is a shift in the
genetic system as well. And it's the natural selection, the forces of the
environment, predator pressure, changes in the temperatures and, and changes
within the ambient environment that act on the shift in the genetic system that
is pulled along by the shift in the mating system.
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