Physiological and Transcriptional Responses to Acute and Chronic Thermal Stress in the Ark Shell Scapharca subcrenata

Ark shells (Scapharca subcrenata) grown on the tidal flats are often exposed to high temperature stresses in summer. In order to better understand their adaption to extreme or natural high temperature, we first determined the 96-h upper lethal temperature of ark shell and then investigated their physiological and transcriptional responses to acute or chronic thermal stress at the 96-h upper median lethal temperature (32°C). A significantly higher cumulative mortality (52% in 96 h) was observed in the acute heating treatment (AHT) group than that (22% in 7 days) in the chronic heating treatment (CHT) group. The apoptosis and necrosis rates of hemocytes were increased significantly in a time-dependent manner under both thermal stress strategies. Activities of antioxidant enzymes [superoxide dismutase (SOD) and catalase (CAT)] increased dramatically in a short time followed by a quick decline and reached to a lower level within 12 h in the AHT group, but maintain relatively high levels over a long period in the CHT group. The contents of malondialdehyde (MDA) were increased significantly firstly and restored to the original later in both acute and chronic thermal stress. Moreover, expression of the genes related to heat shock proteins (HSPs; HSP90, HSP70, HSP20, and sHSP), apoptosis [TNF receptor-associated factor 6 (TRAF6), glucose regulated protein 78 kD (GRP78), and caspase-3 (Casp-3)] and antioxidant responses [glutathione S-transferase (GST) and multidrug resistance protein (MRP)] could be induced and up-regulated significantly by thermal stress, however, expression of regucalcin (RGN), metallothionein (MT), and peroxiredoxin (PRX) was down-regulated dramatically under the two heating treatments. These results suggested that anti-apoptotic system, antioxidant defense system and HSPs could play important roles in thermal tolerance of ark shells, and the heat-resistant ark shell strains could be selected continuously by properly chronic thermal stress.

Quantifying Freeze Tolerance of Hybrid Bermudagrasses Adapted for Golf Course Putting Greens

The susceptibility of warm-season turfgrasses such as bermudagrass (Cynodon spp.) to winter injury in the transition zone is a major concern. Therefore, the objective of the study was to evaluate five golf course putting green-type experimental genotypes (OKC6318, OKC0805, OKC1609, OKC0920, and OKC3920) and three commercially available bermudagrasses (‘Champion Dwarf’, ‘TifEagle’, and ‘Tahoma 31’) for freeze tolerance by subjecting them to 11 freezing temperatures (–4 to –14 °C) under controlled environment conditions. The experiment was conducted in batches, with four genotypes per batch, and each batch was replicated in time. The mean lethal temperature to kill 50% of the population (LT50) for each genotype was determined. There were significant differences in LT50 values among the bermudagrass genotypes. ‘Champion Dwarf’ had an LT50 value ranging from –5.2 to –5.9 °C across all three batches. The experimental genotypes tested in this study had LT50 values ranging from –7.0 to –8.1 °C and were each lower than that of ‘Champion Dwarf’. ‘Tahoma 31’, the top performing genotype, had an LT50 value ranging from –7.8 to –9.0 °C across all three batches. OKC 3920 was the only experimental genotype with an LT50 value in the same statistical group as ‘Tahoma 31’. The information gained from this research would be useful for breeders to gauge the genetic gain in freeze tolerance in breeding golf course putting green-type bermudagrass.

Increased Thermal Sensitivity of a Tropical Marine Gastropod Under Combined CO2 and Temperature Stress

The ability of an organism to alter its physiology in response to environmental conditions offers a short-term defense mechanism in the face of weather extremes resulting from climate change. These often manifest as multiple, interacting drivers, especially pH and temperature. In particular, decreased pH can impose constraints on the biological mechanisms which define thermal limits by throwing off energetic equilibrium and diminishing physiological functions (e.g., in many marine ectotherms). For many species, however, we do not have a detailed understanding of these interactive effects, especially on short-term acclimation responses. Here, we investigated the metabolic plasticity of a tropical subtidal gastropod (Trochus maculatus) to increased levels of CO2 (700 ppm) and heating (+3°C), measuring metabolic performance (Q10 coefficient) and thermal sensitivity [temperature of maximum metabolic rate (TMMR), and upper lethal temperature (ULT)]. Individuals demonstrated metabolic acclimation in response to the stressors, with TMMR increasing by +4.1°C under higher temperatures, +2.7°C under elevated CO2, and +4.4°C under the combined stressors. In contrast, the ULT only increased marginally in response to heating (+0.3°C), but decreased by −2.3°C under CO2, and −8.7°C under combined stressors. Therefore, although phenotypic plasticity is evident with metabolic acclimation, acute lethal temperature limits seem to be less flexible during short-term acclimation.

The Absence of Hydrodynamic Stress Promotes Acquisition of Freezing Tolerance and Freeze-Dependent Asexual Reproduction in the Red Alga ‘Bangia’ sp. ESS1

The ebb tide causes calm stress to intertidal seaweeds in tide pools; however, little is known about their physiological responses to loss of water movement. This study investigated the effects of static culture of ‘Bangia’ sp. ESS1 at 15 °C on tolerance to temperature fluctuation. The freezing of aerobically cultured thalli at −80 °C for 10 min resulted in the death of most cells. By contrast, statically cultured thalli acquired freezing tolerance that increased cell viability after freeze–thaw cycles, although they did not achieve thermotolerance that would enable survival at the lethal temperature of 32 °C. Consistently, the unsaturation of membrane fatty acids occurred in static culture. Notably, static culture of thalli enhanced the release of asexual spores after freeze-and-thaw treatment. We conclude that calm stress triggers both the acquisition of freezing tolerance and the promotion of freezing-dependent asexual reproduction. These findings provide novel insights into stress tolerance and the regulation of asexual reproduction in Bangiales.

Elevational and Latitudinal Changes in Cold Tolerance of Nymph and Adult Mormon Crickets Anabrus simplex (Orthoptera: Tettigoniidae)

Insects that hatch in winter and early spring in desert and montane regions are likely to encounter extreme weather events, including precipitous drops in temperature. The susceptibility of insects to exposure to subzero temperatures is predicted to decrease with increasing latitude or elevation. Mormon crickets occur over a broad latitudinal range from southwestern United States to Canada and a broad elevational range from near sea-level to 3,000 m. Population declines have been attributed to late freezing events, but winter hatching suggests they may also be cold tolerant. Lower lethal temperature of high elevation populations in low latitude Arizona (AZ) and high latitude Wyoming (WY) was measured by exposing nymphs and adults to 6 h or 24 h of subzero temperature. From similar latitude, WY was compared with mid-elevation Idaho (ID) and low elevation Oregon (OR) populations. Contrary to the prediction, lethal temperature of third instar nymphs was lower in AZ than in the more northerly populations. Consistently, AZ was more tolerant of cold in early nymphal instars relative to populations from higher latitude. Early hatching at lower latitudes might increase the risk of early instars experiencing a severe cold snap relative to nymphs at high latitudes. Also, contrary to prediction, the lethal temperature of adults increased with elevation, whereas third instar nymphs from mid-elevation ID were the most susceptible to cold exposure. Cold tolerance in immature and mature stages is more likely to be uncoupled when life stages do not coincide, as with Mormon crickets.

The physiology of Venezillo arizonicus (Isopoda, Armadillidae): metabolism and thermal tolerance

Venezillo arizonicus (Mulaik & Mulaik, 1942) is the only oniscidean isopod native to the Southwest Desert Province of North America. In accordance with its desert habitat, we hypothesized that V. arizonicus would have a higher upper lethal temperature than mesic oniscideans. If oniscidean thermal tolerance is limited by an oxygen consumption-uptake mismatch (physiological hypoxia), as indicated by recent work with other land isopods, we further hypothesized that V. arizonicus would possess highly efficient pleopodal lungs, as defined by its capacity for metabolic regulation in reduced . Other adaptations to counter oxygen limitation at high temperatures could include reduced temperature sensitivity of metabolism (low ) and an overall reduction in metabolic rate. Thermal tolerance was measured using the progressive method of Cowles & Bogert and the catabolic rate of animals () was measured as a function of temperature and . The critical thermal maximum (CTmax) of winter-acclimatized animals was 43.0 ± 0.85°C, 1.6-2.6°C higher than published values for summer-acclimatized mesic oniscideans. The catabolic rate at 25°C was 1.50 ± 0.203 μl min−1 g−1, markedly lower than values determined for mesic Oniscidea (4-6 μl min−1 g−1) and was unaffected by hypoxia as low as 2% O2 (ca. 2 kPa). Catabolism was, however, quite sensitive to temperature, showing a mean of 2.58 over 25-42°C. The efficient pleopodal lungs and low metabolic rate of V. arizonicus will both tend to mitigate physiological hypoxia, consistent with the species’ high CTmax. A low catabolic rate may also be an adaptation to low habitat productivity and seasonally constrained activity patterns.

The Asian gypsy moth (Lymantria dispar L.) populations: resistance of eggs to extreme winter temperatures

ABSTRACTGypsy moth Lymantria dispar (GM) is a polyphagous insect and one of the most significant pests in the forests of Eurasia and North America. Accurate information on GM cold hardiness is needed to improve methods for the prediction of population outbreaks, as well as for forecasting possible GM range displacements due to climate change.As a result of laboratory and field studies, we found that the lower lethal temperature (at which all L. dispar asiatica eggs die) range from –29.0 °C to –29.9 °C for three studied populations, and no egg survived cooling to –29.9 °C. These limits agree to within one degree with the previously established cold hardiness limits of the European subspecies L. dispar dispar, which is also found in North America. This coincidence indicates that the lower lethal temperature of L. dispar is conservative.Thus, we found that the Siberian populations of GM inhabit an area where winter temperatures go beyond the limits of egg physiological tolerance, because temperature often fall below –30 °C. Apparently, it is due to the flexibility of ovipositional behavior that L. dispar asiatica survives in Siberia: the lack of physiological tolerance of eggs is compensated by choosing warm biotopes for oviposition. One of the most important factors contributing to the survival of GM eggs in Siberia is the stability of snow cover.SummaryWithin the geographical range of Siberian gypsy moth populations, extreme temperatures go beyond the limits of the physiological tolerance of wintering eggs (–29.9 °C), and their survival depends on the choice of warm biotopes for oviposition.

Cold-Hardy Grape Cultivar Winter Injury and Trunk Re-Establishment Following Severe Weather Events in North Dakota

Extreme winter temperatures during the 2018–2019 dormant season contributed to trunk collapse and complete trunk death of numerous genotypes throughout a diverse grapevine planting in eastern North Dakota, USA. Through the early portion of the dormant season, 12 genotypes were screened to identify lethal temperature exotherms of primary buds; from these results, none were anticipated to be fully prepared to survive the −37 °C minimum temperature recorded in the region. Trunk collapse, death, and survival were monitored for 35 replicated genotypes. New trunks were retrained from suckers and monitored for growth following trunk removal. Only five genotypes exceeded 50% trunk survival at the end of the 2019 growing season, ‘Valiant’, ‘King of the North’, ‘John Viola’, ‘Baltica’, and ‘Bluebell’. Following re-establishment, ‘La Crescent’ was the most vigorous genotype with the largest sucker circumference, sucker length, and internode length. Nearly all genotypes evaluated produced suckers with lengths approaching the high-wire trellis height (1.8 m), designating their potential for cordon retraining in 2020. Cumulatively, however, the lethal temperature exotherm results and the trunk survival examination indicate a harrowing need for investigation of new management practices (such as protected training systems) and the generation of new cold-hardy genotypes to enhance productivity under standard unprotected systems.