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.

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