Do you ever wonder how
scientists learn about evolution?
Follow us this week as Dan, Tim, Andrew and I
will head down to the Guana Tolomato Matanzas National Estuarine Research
Reserve and Tomoka State Park in Florida to continue an exciting experiment we
began last year. We are really glad to
have you follow along as we do science and we are looking forward to answering
your questions on line. Let me tell you a
bit about what we will be doing down there on our islands. You can also follow on twitter @mr_reedy (#lizardproject) or on youngzine.com
What questions are you trying to answer with your experiment?
All science starts with a
question and the big question we are asking, “Why is there a 50/50 sex ratio in
so many animal populations?” If you really think about it, this doesn’t
necessarily make the most sense for an animal population. Since a population can often grow faster with
many females and few males, why is it that we so often find males and females
in almost equal numbers?
When thinking about this we also
wondered, “If the sex ratio, became really biased towards one sex or the other,
how quickly would natural selection push things back to 50/50?
And,” In a world that is mostly
female, would males have a better chance of surviving and reproducing? What
about in a world that is mostly male?
What are your hypotheses?
The leading theory on the 50/50
sex ratio is that when the ratio gets out of balance, natural selection pushes
it back towards 50/50. For example when
there are many male lizards all fighting for territory in the trees, you have a
better chance of surviving if you are a female.
Therefore in a world with more males, a balance will quickly be restored
as many males die before reproducing and many females survive to
adulthood. This is our general
hypothesis.
We also think that in situations
with biased sex ratios, natural selection will favor traits differently. We
think that on an island with many males and few females, the biggest males will be more likely to
survive. However, we think that on an
island with few males and many females, the smallest males will have a better
chance of survival and reproduction, because it will be easy for nearly all males
to find a territory and mate. In this case, the large body size may be a waste
of energy and be more noticeable to predators.
How are you testing these ideas?
With an experiment of course! Many
people wrongly think that questions about evolution can’t be tested in the wild
because evolution is a slow process.
However, evolution can be seen in the wild and measured if we look
carefully.
Since our question is big, so is
our lab. Instead of testing animals in laboratory cages, we use entire islands
as our animal enclosures for the experiments!
To test our hypotheses, we set up
9 experimental islands that did not have brown anole lizards living on them. On
five of the islands we released a 66% male population and on the other four
islands we released a 66% female population.
Before we introduced these populations to the islands, we took DNA
samples and careful measurements from each of our founder lizards. Now we will be able to check each year to see
which individual lizards were most and least successful at producing baby
lizards. We will also continue to
measure the future generations to see how natural selection is working to shape
the evolution of these populations on the different islands. We may be able to see evolution in action…but
first we have to catch, measure, and take DNA samples from nearly every lizard
on our nine islands. We are going to be
busy!
