Le début des expériences (The Start of the Experiments)

After two months of planning, acquiring equipment, conducting pilot studies, and logistical wrangling I’m very pleased to say that we have begun our first experiment with Project PODARCIS. For this initial study, we are collecting lizards from populations around Moulis (~400-500 meters above sea level) and subjecting them to two experimental treatments: half the lizards will be kept in the lab in Moulis (at the same elevation) and half will be brought to the high-elevation lab at Pic du Midi (at about 2900 meters above sea level). We will then test the lizards’ performance (sprint speed) and parameters related to their oxygen-carrying capacity (such as red-blood cell density and hemoglobin concentrations). We expect that lizards will be initially slower at high altitudes, as we found in our pilot study. We will measure both performance and blood parameters three times over the course of six weeks to quantify how the lizards are affected by the low oxygen levels and how they may physiologically adjust to compensate.

James and Anna help catch lizards in Astien.

Last week, Mahaut and I (with some assistance from James and Anna) collected the first experimental animals from several populations around Moulis. I think it’s fair to say that we’re both improving our lizard-noosing skills. Also, we’re improving in our ability to identify the sex of an individual from a distance, before we even try to catch it – since this experiment involves only males, we don’t want to inflict undue stress on the unsuspecting females. The last outing, I was on my own but managed to catch the target number, six males, in less than an hour! For others with more experience lizard-wrangling than me, this is probably an unimpressive statistic. But for me, this represents a marked improvement. We will continue our collection this week, sampling from a few more populations. The weather is cooperating magnificently so far and hopefully will hold up for the next week.

Female (left) and male (right) Podarcis muralis. Notice that the male has a more spotted/mottled color pattern and a proportionally larger heard. Photo courtesy of Jérémie Souchet.

Today, Fabien and I are at Pic du Midi to begin the measurements. We are currently running the performance trials and will collect our first blood samples tomorrow morning to bring back to the lab at the CNRS in Moulis. This study will provide some data to get us started in understanding how these animals can respond to changes in their environments and how their physiological flexibility might facilitate their ability to colonize higher elevations. Interestingly, however, this kind of plastic response may not always facilitate the colonization of new habitats in the long-term – in fact, studies in birds and mammals have shown that these response can actually be detrimental in the long-term. A great review from a few years ago (Storz et al., 2010 in the Journal of Experimental Biology) discusses important differences between acclimatization responses and genetic (evolutionary) responses to hypoxia. For example, when brought to high elevations individual responses may include increasing red-blood cell counts, which allows for greater oxygen transport in the blood. In the long-term, however, such a response can be detrimental because it makes the blood more viscous and therefore requires more energy to circulate.

We hope the data from this experiment will provide  a basis for future experiments to understand how ectothermic vertebrates respond, both within an individual’s lifetime and across generations.

After a day in the lab, Fabien and I enjoy some sunshine at Pic du Midi.