Effects of thermal shock on the survival and reproduction of Stratiolaelaps scimitus (Mesostigmata: Laelapidae)

Assessing the potential for predator-prey interactions in mesofaunal arthropod communities through temperature dependence of locomotion

Thermal performance curves (TPCs) have become an important part of the thermal biologists' toolbox in understanding how organisms may respond to temperature variation. The aim of this study was to investigate how temperature affects the locomotion of soil arthropods (Collembola and Acari), and explore how these responses might influence the potential for predator-prey interactions under different environmental conditions. Locomotion-based thermal performance curves of four species of Acari and three species of Collembola were estimated across seven test temperatures through automated tracking of individuals. Acari (predators) generally exhibited broader thermal tolerances compared to Collembola (prey), with overlapping thermal optima observed for some species, such as Parasitus sp. and Ceratophysella cf. gibbosa. However, differences in maximum thermal limits could influence predator-prey dynamics under warmer conditions. There were no significant effects of temperature on distance traveled or maximum walking speed for most species (Folsomina sp. p = 0.21, Ceratophysella cf. gibbosa p = 0.55, Mucrosomia sp. p = 0.36), with subclass-level analyses also showing no significant effects for Acari (p = 0.6) or Collembola (p = 0.96). Among Acari, Linopodes sp. exhibited a clear TPC, peaking at 30 °C (175 mm/s), while Parasitus sp. and Ceratophysella cf. gibbosa displayed broad thermal tolerances, with the temperature at which performance is maximized (Rmax) near 20 °C and 30 °C, respectively. Among the Acari species tested, Linopodes sp. and Parasitus sp. did show typical TPCs. Among Collembola, Folsomina sp. and Ceratophysella cf. gibbosa showed typical TPCs. These sit-and-wait predators with jump escaping prey groups are likely to be poorly captured by a TPC approach, suggesting other functional traits such as feeding rates, handling times and/or digestion efficiency should be employed in the future to better characterize temperature-dependent interactions.

Mismatches in thermal performance between ectothermic predators and prey alter interaction strength and top-down control

Climate change can alter predator-prey interactions when predators and prey have different thermal preferences as temperature change can exacerbate thermal mismatches (also called thermal asymmetry) with population-level consequences. We tested this using micro-arthropod predators (Stratiolaelaps scimitus) and prey (Folsomia candida) that differ in their temperature optima to examine predator-prey interactions across two temperature ranges, a cool (12 and 20 °C) and warm (20 and 26 °C) range. We predict that the lower thermal preference and optimum in F. candida will alter top-down control (i.e., interaction strength) by predators with interaction strength being strongest at intermediate temperatures, coinciding with F. candida thermal optimum. Predators and prey were placed in mesocosms, whereafter we measured population (predator and prey abundance), trait-based (average predator and prey body mass, and prey body length distribution), and predator-prey indices (predator-prey mass ratio (PPMR), Dynamic Index, and Log Response Ratio) to determine how temperature affected their interactions. Prey populations were the highest at intermediate temperatures (average temperature exposure: 16-23 °C) but declined at warmer temperatures (average temperature exposure: 24.5-26 °C). Predators consistently lowered prey abundances and average prey mass increased when predators were added. Top-down control was the greatest at intermediate temperatures (indicated by Log Response Ratio) when temperatures were near or below the thermal optimum for both species. Temperature-related prey declines negated top-down control under the warmest conditions suggesting that mismatches in thermal performance between predators and their prey will alter the strength and dominance of top-down or bottom-up forces of predator-prey interactions in a warmer world.

Evaluation of life-history traits in Folsomia candida exposed to combined repeated mild heat shocks with phenanthrene

Climate change increases the frequency and intensity of extreme weather events. In nature, organisms are often exposed to climatic stressors and contaminants simultaneously, and the effects of contaminants may be modified by climate change and vice versa. Here, the effects of repeated mild heat shocks (0-5 times, 30 °C for 6 h), alone or combined with phenanthrene (PHE) (80 mg kg^-1 dry soil), on life-history traits of the springtail Folsomia candida were investigated. The survival, growth, maturation, and reproduction of single juvenile springtails were assessed over a period of 37 days. Increasing number of heat bouts or PHE exposure did not have significant negative effects on overall survival at the termination of the experiment, but the interaction between the two stressors led to complex interactions for the dynamics of survival during the test. Neither body growth nor time to first oviposition was influenced by heat or PHE, but a reduction of egg production with increasing number of heat bouts was observed, and there was an interaction between the two stressors. Further, a trade-off between the number of eggs produced and egg size was observed, indicating that females invested the same amount of energy in reproduction despite exposure to stressful temperature and PHE. These results indicate that egg production (in terms of the number of eggs) was a more sensitive indicator of the combined effects of mild heat shocks and PHE than growth, and there was a trade-off between survival and egg production.