Impact of short and long-term warming on copepod temperature and salinity tolerance

Acartia tonsa is a cosmopolitan copepod, critical to the health and function of estuarine ecosystems. In order to better understand their resilience to global change, we examined the influence of elevated temperature on A. tonsa temperature and salinity tolerance. This is relevant for A. tonsa, as their environment is highly dynamic with respect to temperature and salinity. First, we compared the Upper Lethal Temperature and Lower Lethal Salinity of copepods from ambient (18°C) and elevated (22°C) temperature lines. These lines were at their respective temperatures for over 25 generations. We then examined the impact of short-term temperature conditions by looking at the effect of development and three generations of elevated temperature (22°C) on temperature and salinity tolerance. A two-way ANOVA showed no effect of temperature line (p=0.06), but an effect of short-term condition (p\u3c0.001) on Upper Lethal Temperature. This demonstrates that short-term condition plays a more important role than long-term temperature adaptation in determining resilience to acute temperature stress. These results may also indicate a cost to maintaining acute temperature tolerance across many generations. Interestingly, a two-way ANOVA does not show a cost of line or short-term condition on Lower Lethal Salinity (p= 0.8 and p= 0.3, respectively). However, when we examined the impact of environmental salinity on Upper Lethal Temperature, there was an effect (p \u3c 0.0001). This indicates that while temperature treatment doesn’t impact salinity tolerance, salinity and temperature tolerance are not completely independent traits