Thursday, December 15, 2011

Scientists don't just learn from experiments!

If I ask students what a scientist does, they often answer "Do experiments!".  That is true of many scientists, but many great scientists have learned a lot without doing any experiment at all.  In my research I use experiments and something we call an observational study.
What is the difference between an experiment and a study?

Scientists often use controlled experiments and observational studies. There are many types of controlled experiments, but in general, the scientist will select a group of study subjects, randomly assign them to different treatments (or conditions where a variable is altered). It is important that the scientist is changing something about the conditions the study subjects will experience.   In an observational study, the scientist does not alter anything about the study subjects, but just makes careful observations and draws inferences.

Lets use an example to demonstrate the difference.  Suppose you have the question, Does temperature determine whether a turtle egg will become a male or female?  

Observational Study: You go out into the wild, and locate lots of fresh turtle nests from the same population, and monitor these nests until they hatch.  It would be best to record temperatures throughout the season within the nests, as well as other variables you think might be important (hydric conditions, soil pH, etc).  When they have hatched, you correlate the environmental variables with the sex ratio of the baby turtles in each nest.  Depending on what you find, you may want to repeat the study another year, or you may want to then further investigate these relationships in an  controlled experiment.
In the photo above, we are measuring various aspects of a natural painted turtle nest, as a part of a long term study started by my advisor Fred Janzen.  Who knew studying could be so fun!!  Photo by Brian Tugana.

Controlled experiment:  After collecting lots of turtle eggs from many moms in the same population of turtles, you can randomly divide the eggs from each mom into two treatments, warm and cool.   You set up two incubators at a cool temperature, and two at a warm temperature.  In this case, temperature will be the independent variable, or the thing the experimenter varies.  Then we need controls: all the eggs will be incubated in boxes that have the same substrate, the same water potential, the same amount of eggs in each box, etc.   After eggs hatch, you can see if the treatment (temperature) had an effect on the sex of the baby turtles.

To thoroughly answer this question, it would be best to do both this experiment and the study, as both give you different and important information.

Here we are measuring baby turtles in a lab.  These turtles were a part of one of my experiments! Most of this experiment took place in the field, but some parts happened in the lab.  Just because its an experiment, doesn't mean it needs to be in a lab.

Thursday, December 8, 2011

Why I study turtles!

I gave a research talk to Aaron Reedy's class this week on sex ratio evolution,  why I study the sex ratio in turtles, and I provided a case study on the topic from my own work.  Here is a bit of the background information about the theory that guides my research, and some slides that I shared with the high school students at Kelly High School in Chicago.
In many animal mating systems, one male can successfully produce offspring with many females.  In red deer for example, a single male fights off other males to gain mating access to a harem of females, at the exclusion of other males.  Females can only get pregnant once a year, yet males can get many females pregnant during the rut.    It seems as if the population could grow much faster if many more females were produced than males.

Yet, if that was the case, males would have much higher fitness than females, as they would be producing many more offspring.  In a situation with a female biased sex ratio, any females that could overproduce sons would have a huge fitness advantage, because sons would be able to have many more offspring than daughters.   We would expect this ability to overproduce sons would be selected for, and would drive the sex ratio towards unity.

Our expectation from sex ratio theory is that the primary sex ratio should be 50:50.

 Since turtles have temperature-dependent sex determination, rapidly changing climates can skew the sex ratio.  And turtles have been around for a very long time (turtles were around when dinosaurs were around), and have survived through many climate changes in the past.  There are several mechanisms by which turtles could adapt to changing climates, but I study how mom's nesting decisions may have played a role in adaptation to local climate.

I am working on writing up an experiment that shows mothers are maintaining a balanced sex ratio in the population by choosing specific places to lay their eggs.

Thursday, December 1, 2011

Going to Aaron Reedy's Class on Friday!

I am excited to go give a research talk at Kelly High School in Chicago this week!  I have collaborated with Mr. Reedy on some cool turtle and snake projects at our research site, "Turtle Camp" in Illinois. Along with other collaborators, we have worked to understand habitat use in hognose snakes. I have also helped him and Dan Warner  on a cool lizard project they have been working on in Florida.  Aaron has worked with the Janzen lab through the NSF Research Experience for Teachers program, and through the Turtle Camp Research and Education in Ecology (TREE) Program.   Aaron has proved to be a great collaborator in the field, so now we are going to start a collaboration between classrooms!  We are designing a science project which both Mr. Morris' and Mr. Reedy's classroom will engage in together.  Look for an update on how the day in Mr. Reedy's class went!

Check out Mr. Reedy's inspirational talk here: