Metabolic responses of Plectus murrayi across a temperature gradient, McMurdo Dry Valleys, Antarctica, 2016-2017

Populations of Plectus murrayi, a mesophilic nematode, have been increasing in the McMurdo Dry Valleys, Antarctica over the past three decades. In contrast, most other Antarctic nematode species, including Scottnema lindsayae, have experienced constant population declines over the same time period due to climate change related increases in summer temperatures and wetting occurrences. To determine why P. murrayi populations are outperforming other Antarctic nematode species, we performed a laboratory experiment to measure their metabolic responses to increasing temperatures. For this experiment, P. murrayi were cultured from soils collected in Taylor Valley during the austral summers of 2016 and 2017 as part of the McMurdo Dry Valleys Long Term Ecological Research (LTER) Project. Using a TAM IV Isothermal Microcalorimeter, we measured the metabolic heat rates of these cultured P. murrayi populations in six sealed 4 mL vials. Three of these vials also contained 200 µl ampoules of 0.4 M NaOH. NaOH reacts with CO2 produced from metabolic processes to release a known amount of heat (108.5 kJ/mol CO2). The difference in metabolic heat rate produced in vials containing NaOH and those without NaOH is proportional to CO2 produced from P. murrayi metabolism. Consequently, this method allowed us to track metabolic heat rates as well as CO2 production rates. O2 consumption was calculated from vials without NaOH using Thornton's rule (455 kJ of metabolic heat/mol O2). P. murrayi metabolic heat rates were compared to C. elegans for reference, and baseline measurements included heat rates of E. coli and blank agar.