When you tell people you are going to be studying lizards in Alabama for the summer, you get used to a raised eyebrow or two. The heat! The snakes! The bugs! When I told people I was going to be deliberately seeking out (ecological) public enemy number 1, fire ants, everyone made clear what I already knew – the theme of my summer was going to be STRESS.
In fact, stress (and in particular, maternal stress during gestation) is exactly what took me to Alabama. Stress during pregnancy can alter the characteristics of the resulting offspring, from morphology to behaviour. That’s assumed to be a bad thing. But could stress experienced by mothers during gestation actually program offspring for life in a stressful environment, giving them an advantage in the long run? This was the question I set out to test during my first, recently completed, field season.
For this study we focused on the eastern fence lizard, Sceloporus undulatus, a species well known to our lab. This lizard is particularly well suited to studying maternal stress because, as is the case for many reptile and amphibian species in the South East, it is subject to the considerable stress of coexisting with fire ants. We know a lot already about how fire ants change the behaviour and physiology of fence lizards – but what about the effects on the next generation through maternal stress effects?
A question this complex, with more than one generational level, required a number of steps. Step one was capturing gravid (carrying eggs) female fence lizards, which we did in May and early June. Having worked previously on mammals (meerkats) and birds (fairy wrens and hihi), this was a new and exciting experience for me! Safe to say, fence lizards (and herps in general!) quickly stole my heart.
Our next step was bringing the females into the lab, and subjecting them to a highly controlled “stress” treatment – a very low dose of a stress hormone every day, the equivalent of a single fire ant sting. It’s important to note that this is NOT a pain treatment – we use the hormone corticosterone, which is released as part of a lizard’s natural stress response, and which has a number of downstream effects including helping the body’s metabolic system turn amino acids into carbohydrates for use as fuel. In short, our treatment was tricking the lizards’ system (but not the lizard) into thinking they were in a stressful situation.
The next step was waiting for the females to lay their eggs, at which point our stress treatment ceased, and females were ready to be returned to the wild. We incubated their eggs (incubation takes around 50 days) and waited for the babies to hatch to begin the next step of our experiment…
We hypothesised that if maternal stress was adaptively programming offspring to be be better suited to a stressful environment (for example, by making them more responsive to predators, or better able to cope with frequent stressors), then we should see offspring from stressed mothers surviving better in stressful environments than offspring from mothers that did not experience stress during gestation.
To test this, we needed to create “stressful” and “non-stressful” environments in which to put the offspring. When we weren’t catching females or incubating eggs, we were building four 20x20m outdoor enclosures for this purpose! Thankfully, life in Alabama with fire ants everywhere is stressful enough, so we didn’t need to artificially create a stressful environment. To create a “non-stressful” environment, we removed fire ant mounds from two of the four enclosures. We hypothesised that in these enclosures, offspring from unstressed mothers should do best.
Once the offspring hatched, we put them into the enclosures and monitored their survival by checking them every day (not an easy task, they are small and wily!). I also recorded their habitat use, how far they were moving within the enclosures from their release spots, and how they responded to small, short-term stressors, like being picked up to be weighed. I’m now in the process of analysing this data, and am looking forward to seeing if our hypotheses hold true. Watch this space!
So, lizards aside, how did I cope with the stresses of a summer in Alabama? The heat – loved it! The snakes – try and keep me away from them! The bugs – who cares?! The people – a whole lot of new friends. There may be a million ways to die in the South, but there sure are a million and one things to love.