Temperature treatment assignment
All experimental plants were assigned to one of two greenhouse bays programmed to achieve different temperatures at the University of California, Riverside. Temperature treatments were designed to approximate (1) ambient July air temperatures near the site of C. sulphurea seed collection (Rocky Mountain Biological Lab, Gothic, Colorado, USA) and (2) these summer air temperatures elevated by 3°C on average. Supplemental lights (Pro 1000° 120/240 DE US, Gavita Holland bv) were programmed to turn on from 1630-2100 to extend the ambient photoperiod to 14 h of light to match the photoperiod of Gothic in July.
Quantities: 3°C temperature elevation, 14 hour photoperiod, lights on 1630-2100, 20 'parasite alone' pots, 36 and 24 'host alone' pots, 67 'host + parasite' potsDuration: Supplemental lighting 1630-2100 dailyConditions: Ambient July temperatures (12.7°C mean) vs warmed treatment, matched to Gothic Colorado photoperiod
Equipment: greenhouse bays, supplemental lights (Pro 1000° 120/240 DE US, Gavita Holland bv), data loggers (HOBO MX2302, Onset)
Temperature monitoring and plant care
Temperatures throughout the study were measured at 15 min intervals with data loggers (HOBO MX2302, Onset). Plants were watered as needed to maintain adequate soil moisture. The warmed greenhouse bay achieved significantly higher temperatures than the ambient bay overall during the course of the experiment (16.5 ± 0.1°C vs. 13.9 ± 0.1°C), with warming of about 3.8°C on average.
Quantities: 15 minute measurement intervals, 16.5 ± 0.1°C warmed vs 13.9 ± 0.1°C ambient average temperatures, 3.8°C actual warming achievedDuration: Throughout the 70-day experiment, continuous monitoring at 15-minute intervals