Our next undergraduate guest post is from Courtney Norjen, a senior majoring in Veterinary and Biomedical Sciences. Courtney is in the Schreyer Honors College and is also the president of the Pre Vet Club. Courtney spent the summer running multiple projects in the Langkilde Lab, and she discusses her independent research below:
This summer, I had the opportunity to begin working on my honors project in the Langkilde Lab. In eastern fence lizards (Sceloporus undulatus), males have bright blue badges on their throats and bellies, while some females have paler forms of these badges and others are generally white underneath. The hormone testosterone regulates the development of these blue badges; lizards with more testosterone have larger, brighter badges. These color patterns are especially important for social interactions, particularly during mating season. Males will behave aggressively towards lizards with male-typical coloration (they’ll display their own bright colors by doing push-ups to show that they’re better than the other males), while they court lizards with female-typical coloration. Recently, however, we’ve started noticing “bearded ladies,” females that display light blue badges, a male-typical trait. Lindsey wanted to determine if males liked these bearded ladies as much as normal females. She set up arenas where males had a choice between a bearded lady and a normal one, and her results showed that males prefer to mate with normal, white females rather than bearded ladies. These blue females also tend to lay their eggs later in the season, which doesn’t give their offspring as much time to forage for prey and build up energy reserves before the coming winter.
If having blue badges is bad for the females and potentially for their offspring, then why are there still bearded ladies in the population? This is the question I hope to answer through my project! In order for that male-typical trait to be retained in the females, there theoretically must be some positive outcome. We hypothesized that females with higher testosterone levels (the ones that are blue) would produce bluer offspring, regardless of sex, and would produce more sons than daughters. This is also known as the “sexy son hypothesis:” perhaps masculinized females will produce more magnificent sons!
To test this, we used two different experimental designs. First, I took normal female lizards that were in the early stages of pregnancy and gave half of them testosterone five days per week while they were developing their eggs. The testosterone comes in a powder form; I took the powder and dissolved it in sesame oil, and then applied the oil to their backs. The oil, along with the testosterone, gets absorbed through their skin! The other half of the lizards was treated with plain sesame oil as a control. The second design involved using eggs that had already been laid by normal lizards. Half of the normal eggs were dosed once with testosterone prior to incubation, and the other half were given plain oil instead. In about 45 days, the eggs started hatching!
I am now in the midst of raising 70 hatchlings! I will be comparing the male to female sex ratios, the growth rates, and the coloration of these offspring between the two hormone treatment groups and between the two experimental designs. If my hypothesis is correct, the lizards that were dosed with testosterone will have more sons than daughters, and their offspring will generally be bluer than the lizards that were not given testosterone. I don’t have any results to present to you yet, but I’m really excited to see what happens!