Plasticity of cold tolerance and body composition in response to varying winter conditions in a temperate wolf spider

The ability to adjust thermal tolerance in varying environmental conditions is a critical adaptation for species living in seasonal environments. While flexibility in cold tolerance is well documented in insects, few studies have investigated the capacity of spiders to alter cold tolerance through phenotypic plasticity. Here, we assessed plasticity in cold tolerance and body composition in the wolf spider Schizocosa stridulans exposed to three distinct simulated winter temperature regimes: one that reflects current conditions, one that reflects a warmer winter and one that reflects a warmer winter with increased diurnal variation. We found that the critical thermal minimum (CT_min; the lowest temperature a spider can remain active) was plastic. Specifically, CT_min was lowest at the coldest time of the simulated winter, and it was lowest in spiders exposed to current winter conditions compared to spiders exposed to warmer simulated winters. In contrast, the supercooling point, or the temperature at which spiders spontaneously freeze, was invariant across time and winter conditions. Growth rates were also dependent on winters, with spiders from the warmer and more variable winters having significantly higher growth rates. Protein and lipid contents, however, were not affected by winter environment, indicating that spiders are able to maintain these macronutrients at the same proportional level regardless of growth rate. In contrast, carbohydrate content was slightly but significantly lower in spiders maintained in a warmer and more variable winter. Our results indicate that while spiders exposed to warmer winters that have higher daily maximum temperatures may be able to grow faster, they do so at the expense of maintaining cold tolerance and thus may be more susceptible to sudden cold snaps.