Turtle Ponds at the Hort Farm
It’s fairly straightforward to do research on many critters in the lab: insects, small fish, mice, and many lizards will readily reproduce in a small aquarium or cage in your laboratory. That’s not always the case though. The Janzen Lab studies painted turtles and we want to be able to manipulate some aspects of their environment that are impossible to manipulate in the wild, yet we can’t do it in the lab either. That is why we have created our turtle ponds at the Iowa State Horticulture Research Farm. We now have 4 turtle ponds, each with associated nesting habitats. These ponds are turtle proof (turtles can’t get in or out) and raccoon/skunk proof. They will be excellent for a variety of experiments that no one else has been able to do before because of the large logistical obstacles we have overcome.
Designing and constructing these ponds took a lot of creativity, trial and error and sweat! We have used other ponds before (For Jeanine’s research: http://www.public.iastate.edu/~fjanzen/pdf/12BiolConserv2.pdf), and I used earlier versions of these ponds for a recent experiment (manuscript being written, preliminary results here: (http://fpr.extension.iastate.edu/pdf/2012/EffectsOverwintering.pdf ). Learning from some of the issues we had with these earlier experiments, we have (hopefully) perfected our design. Fence durability was a concern before; the current ponds have a sturdy, hog-fence perimeter, which supports PVC paneling that turtles cannot get under nor climb over. And these fences are resilient to our lovely Iowa weather that includes high winds, heavy rains, and snow drifting during winter. Outside the hog fence is electric fencing, which keeps the mammalian predators at bay. The ponds are divided by removable PVC fence panels, which will allow us to easily change the pond set up for future experiments. The ponds themselves are ~1.5 meters deep and large enough to keep a lot of turtles happy, and there is ample terrestrial nesting habitat nearby. We can drain these ponds to easily retrieve turtles in the fall (we hibernate them in the lab).
These ponds were only possible through a tremendous amount of help from a lot of people. Nick Howell, Jeff Braland and others at the Hort Farm were extremely helpful in helping us plan and implement our design. Members of the Janzen lab and other volunteers provided plenty of elbow grease to get the job done. The facilities are funded by the NSF and ISU Research Farms, directed by Dr. Mark Honeyman.
What is the general focus of our research?
Painted turtles have temperature-dependent sex determination. The temperature an egg experiences during incubation will determine if the embryo will develop as a male or female. Nests experiencing warm temperatures will produce all females, where nests experiencing relatively cool temperatures will produce all males. Intermediate nest temperatures produce both sexes. We know from prior research that the mother (who abandons eggs after nesting) can partially influence her nest temperature by choosing where to nest. Generally, we are very interested in how turtles will respond to climate change. Will warming climates produce highly female biased populations? Will turtles be able to keep a healthy, balanced sex ratio as climates change? If so, how? Is it through long-term evolutionary changes in the populations, or through shorter term plasticity?
What is our current project at the ponds?
We are very interested in whether environmental factors experienced by female turtles will influence her reproductive decisions (i.e. where/when to nest, what resources will she allocate to eggs, etc.). We have already tested whether overwintering conditions influence the timing or placement of nests (see link above for preliminary findings). We are currently testing whether the adult sex ratio experienced by the female influences her nesting decisions. To do this, we have 10 female turtles in each of the 4 ponds, but we have different numbers of male turtles, such that the adult sex ratio varies. The most male biased pond is 3:1 (M:F) and the most female biased pond is 1:4. We will also see if these treatments influence female stress levels, and if it influences resource allocation to eggs (i.e. will mothers in a male biased population deposit different levels sex hormones in her eggs?). Next summer during nesting season, we expect that turtles in male biased ponds will select sunny nest sites, which will be more likely to produce females. We expect the opposite pattern in the female biased ponds (females will nest in shady areas to produce males). The turtles are in the ponds now, but we are excited for nesting season next year when this experiment will really be underway!