Maximum Temperature Tolerance Research Articles

Respiratory acidosis and O2 supply capacity do not affect the acute temperature tolerance of rainbow trout (Oncorhynchus mykiss).

The mechanisms that determine the temperature tolerances of fish are poorly understood, creating barriers to disentangle how additional environmental challenges-such as CO2-induced aquatic acidification and fluctuating oxygen availability-may exacerbate vulnerability to a warming climate and extreme heat events. Here, we explored whether two acute exposures (~0.5hours or ~72hours) to increased CO2 impact acute temperature tolerance limits in a freshwater fish, rainbow trout (Oncorhynchus mykiss). We separated the potential effects of acute high CO2 exposure on critical thermal maximum (CTmax), caused via either respiratory acidosis (reduced internal pH) or O2 supply capacity (aerobic scope), by exposing rainbow trout to ~1kPa CO2 (~1% or 10 000 μatm) in combination with normoxia or hyperoxia (~21 or 42kPa O2, respectively). In normoxia, acute exposure to high CO2 caused a large acidosis in trout (blood pH decreased by 0.43units), while a combination of hyperoxia and ~1kPa CO2 increased the aerobic scope of trout by 28%. Despite large changes in blood pH and aerobic scope between treatments, we observed no impacts on the CTmax of trout. Our results suggest that the mechanisms that determine the maximum temperature tolerance of trout are independent of blood acid-base balance or the capacity to deliver O2 to tissues.

Thresholds for Reduction in Fish Growth and Consumption Due to Hypoxia: Implications for Water Quality Guidelines to Protect Aquatic Life.

Control of hypoxia is a key element of water quality management, and guidelines are usually based on qualitative reviews of hypoxia impacts. In this study we use segmented regression to identify both thresholds for growth reduction and rate of decline of fish growth and food consumption under hypoxia; and then evaluate whether current freshwater guidelines for dissolved oxygen based on qualitative reviews are consistent with the quantitative analysis of hypoxia thresholds. Segmented regressions were fit to data from published growth-hypoxia studies for freshwater (N = 17) and marine fishes (N = 13). To understand potential drivers of hypoxia tolerance, we also modelled thresholds as simple functions of environmental and ecological covariates for each species including trophic level, marine vs. freshwater environment, maximum fish length, fish weight, and maximum temperature tolerance. The average threshold for growth reduction (Gcrit; 5.1 mg·l-1 DO) and decreased food consumption (Ccrit = 5.6 mg·l-1 DO) were not significantly different, and did not differ between marine and freshwater taxa. However, salmonids showed a significantly steeper decline in growth with increasing hypoxia relative to other taxa. Growth declined by 22% for every mg·l-1 reduction in DO below average Gcrit, and significant regressions indicate that warmwater (R2 = 0.25) and smaller-bodied (R2 = 0.44) species are more likely to be hypoxia tolerant. Observed mean Gcrit and Ccrit in the range of 5-6 mg·l-1 broadly match minimum water quality guidelines for the protection of aquatic life in freshwater in representative industrialized countries. However, this is much higher than the definition of hypoxia typically used in marine systems (2-2.5 mg·l-1), indicating a need to reconcile definition of hypoxia in the marine environment with empirical data. The principal challenge in freshwater hypoxia management is now translating discretionary guidelines into effective regulatory frameworks to reduce the incidence and severity of hypoxia.

Optimizing seawater temperature conditions to increase the productivity of ex situ coral nurseries.

Large scale ex situ propagation of coral colonies for reef restoration is a relatively new and developing field. One of the many advantages of utilizing ex situ coral nurseries is the ability to optimize water quality conditions for coral health and survival. Slight alterations in environmental parameters (light, pH, temperature etc.) can affect the health and grow-out time of cultured coral, ultimately influencing production rates. However, corals are also subjected to pests associated with culture facilities such as ciliates, cyanobacterial blooms, and infectious diseases. Therefore, adjusting environmental parameters to optimize coral growth for a shorter ex situ residency time will lead to greater survival and faster restoration. Studies indicate that some coral species demonstrate parabolic tissue growth in response to increasing sea-surface temperatures until the maximum temperature tolerance is reached, whereafter they bleach. To maximize coral growth in Mote Marine Laboratory’s ex situ system, we tested the effect of two water temperature treatments (high temperature: 29.5 ± 0.03 °C; control: 25.2 ± 0.08 °C) on two coral species commonly used in reef restoration. To quantify this, we used four replicates of three genotypes each of Montastraea cavernosa (n = 12) and Acropora palmata (n = 12). Two-dimensional tissue area was recorded monthly using ImageJ and survival rates within each treatment were documented for 7 months. Results found that M. cavernosa had greater growth rates and equal survivorship in the high temperature treatment compared to the control treatment. A. palmata grew faster and had equal survivorship in the control treatment compared with the high temperature treatment. These results suggest that temperature preferences exist among coral species within ex situ systems and restoration practitioners should consider species-specific temperature regimes to maximize ex situ coral growth rates. This information is critical for optimizing production when corals are in the grow-out stage and should also be considered when designing ex situ systems to ensure temperature regulation can be controlled on a species-specific basis.

Application and Exploration of Early In-Situ Combustion Huff-and-Puff Technology in a Deep Undisturbed Reservoir with Extra Heavy Oil

Summary Achieving effective results using conventional thermal recovery technology is challenging in the deep undisturbed reservoir with extra-heavy oil in the LKQ oil field. Therefore, in this study, a novel approach based on in-situ combustion huff-and-puff technology is proposed. Through physical and numerical simulations of the reservoir, the oil recovery mechanism and key injection and production parameters of early-stage ultraheavy oil were investigated, and a series of key engineering supporting technologies were developed that were confirmed to be feasible via a pilot test. The results revealed that the ultraheavy oil in the LKQ oil field could achieve oxidation combustion under a high ignition temperature of greater than 450°C, where in-situ cracking and upgrading could occur, leading to greatly decreased viscosity of ultraheavy oil and significantly improved mobility. Moreover, it could achieve higher extra-heavy-oil production combined with the energy supplement of flue gas injection. The reasonable cycles of in-situ combustion huff and puff were five cycles, with the first cycle of gas injection of 300 000 m3 and the gas injection volume per cycle increasing in turn. It was predicted that the incremental oil production of a single well would be 500 t in one cycle. In addition, the supporting technologies were developed, such as a coiled-tubing electric ignition system, an integrated temperature and pressure monitoring system in coiled tubing, anticorrosion cementing and completion technology with high-temperature and high-pressure thermal recovery, and anticorrosion injection-production integrated lifting technology. The proposed method was applied to a pilot test in the YS3 well in the LKQ oil field. The high-pressure ignition was achieved in the 2200-m-deep well using the coiled-tubing electric igniter. The maximum temperature tolerance of the integrated monitoring system in coiled tubing reached up to 1200°C, which provided the functions of distributed temperature and multipoint pressure measurement in the entire wellbore. The combination of 13Cr-P110 casing and titanium alloy tubing effectively reduced the high-temperature and high-pressure oxygen corrosion of the wellbore. The successful field test of the comprehensive supporting engineering technologies presents a new approach for effective production in deep extra-heavy-oil reservoirs.

Coral reefs of the Red Sea — Challenges and potential solutions

The Red Sea is a unique body of water, hosting some of the most productive and diverse coral reefs. Human populations along coasts of the Red Sea were initially sparse due to the hot and arid climate surrounding it, but this is changing with improved desalination techniques, accessible energy, and increased economic interest in coastal areas. In addition to increasing pressure on reefs from coastal development, global drivers, primarily ocean acidification and seawater warming, are threatening coral reefs of the region. While reefs in southern sections of the Red Sea live near or above their maximum temperature tolerance and have experienced bleaching events in the recent past, coral reefs in northern sections are considered a coral reef refugia from global warming and acidification, at least for the coming decades. Such differential sensitivities along the latitudinal gradient of the Red Sea require differential solutions and management. In an effort to identify the appropriate solutions to conserve and maintain resilience of these reefs along a latitudinal gradient, we used a SWOT analysis (strengths/weaknesses/opportunities/threats) to frame the present situation and to propose policy solutions as useful planning procedures. We highlight the need for immediate action to secure the northern sections of the Red Sea as a coral reef climate change refuge by management and removal of local stressors. There is a need to strengthen the scientific knowledge base for proper management and to encourage regional collaboration on environmental issues. Based on scientific data, solutions such as marine protected areas, fishing regulation, and reef restoration approaches were ranked for five distinct latitudinal sections in the Red Sea and levels of interventions are recommended.

The rich get richer: Invasion risk across North America from the aquarium pathway under climate change

AbstractAimTo evaluate how the establishment risk of freshwater fish species from the aquarium trade will change under a climate change scenario forecast for the year 2050.LocationNorth America.MethodsIn order to estimate changes in the magnitude of risk across geography and across different species in the aquarium pathway, we considered an integrated approach to modelling the probability of establishment, which simultaneously included proxies of propagule pressure, environmental variables, species traits and interactions between environment and traits. We then used the parameters of our model to predict how the risk of establishment will change under a scenario of climate change forecast for the year 2050.ResultsOur joint model performed better than submodels, suggesting that combining all components is worthwhile. The most predictive factors were precipitation, maximum temperature tolerance, maximum fish length and minimum temperature. Our joint model forecasted a 40% increase in the average risk of establishment by 2050 in the United States. In contrast to our expectations, the absolute establishment risk associated with this pathway remained very low for the entire suite of species in the aquarium trade in northern regions, such as Quebec, Canada. Instead, Florida, which has one of the highest current risks of establishment, was also forecasted to have the greatest absolute risk increase.Main conclusionsOur methodology for risk assessment allows invasive species management strategies to consider entire suites of species at a time and to forecast establishment risk for each species and location. While the aquarium pathway is likely to become more important for the United States, the Quebec government should prioritize other pathways of introduction in its exotic invasive species strategy. Our approach can be extended to be applied to different sets of species pertaining to the same or different pathways.

Intensifying postfire weather and biological invasion drive species loss in a Mediterranean-type biodiversity hotspot

Prolonged periods of extreme heat or drought in the first year after fire affect the resilience and diversity of fire-dependent ecosystems by inhibiting seed germination or increasing mortality of seedlings and resprouting individuals. This interaction between weather and fire is of growing concern as climate changes, particularly in systems subject to stand-replacing crown fires, such as most Mediterranean-type ecosystems. We examined the longest running set of permanent vegetation plots in the Fynbos of South Africa (44 y), finding a significant decline in the diversity of plots driven by increasingly severe postfire summer weather events (number of consecutive days with high temperatures and no rain) and legacy effects of historical woody alien plant densities 30 y after clearing. Species that resprout after fire and/or have graminoid or herb growth forms were particularly affected by postfire weather, whereas all species were sensitive to invasive plants. Observed differences in the response of functional types to extreme postfire weather could drive major shifts in ecosystem structure and function such as altered fire behavior, hydrology, and carbon storage. An estimated 0.5 °C increase in maximum temperature tolerance of the species sets unique to each survey further suggests selection for species adapted to hotter conditions. Taken together, our results show climate change impacts on biodiversity in the hyperdiverse Cape Floristic Region and demonstrate an important interaction between extreme weather and disturbance by fire that may make flammable ecosystems particularly sensitive to climate change.

A Key Marine Diazotroph in a Changing Ocean: The Interacting Effects of Temperature, CO2 and Light on the Growth of Trichodesmium erythraeum IMS101.

Trichodesmium is a globally important marine diazotroph that accounts for approximately 60 − 80% of marine biological N2 fixation and as such plays a key role in marine N and C cycles. We undertook a comprehensive assessment of how the growth rate of Trichodesmium erythraeum IMS101 was directly affected by the combined interactions of temperature, pCO2 and light intensity. Our key findings were: low pCO2 affected the lower temperature tolerance limit (Tmin) but had no effect on the optimum temperature (Topt) at which growth was maximal or the maximum temperature tolerance limit (Tmax); low pCO2 had a greater effect on the thermal niche width than low-light; the effect of pCO2 on growth rate was more pronounced at suboptimal temperatures than at supraoptimal temperatures; temperature and light had a stronger effect on the photosynthetic efficiency (Fv/Fm) than did CO2; and at Topt, the maximum growth rate increased with increasing CO2, but the initial slope of the growth-irradiance curve was not affected by CO2. In the context of environmental change, our results suggest that the (i) nutrient replete growth rate of Trichodesmium IMS101 would have been severely limited by low pCO2 at the last glacial maximum (LGM), (ii) future increases in pCO2 will increase growth rates in areas where temperature ranges between Tmin to Topt, but will have negligible effect at temperatures between Topt and Tmax, (iii) areal increase of warm surface waters (> 18°C) has allowed the geographic range to increase significantly from the LGM to present and that the range will continue to expand to higher latitudes with continued warming, but (iv) continued global warming may exclude Trichodesmium spp. from some tropical regions by 2100 where temperature exceeds Topt.

Seasonal and diurnal patterns of activity in honeybees (Apis spp.) on the northern edge of the Asian tropics; their implications for the climate-change resilience of pollination

Apis honeybees are very important pollinators in tropical Asia but their diversity declines rapidly north of the tropics. This suggests that climate is a major control on their distributions and that climate change may influence the services they provide. Four Apis honeybees coexist in a flower-rich botanical garden in Yunnan, China, on the northern margin of the tropics (21o41′N): A. florea and A. andreniformis (small, open-nesting), A. cerana (medium, cavity-nesting), and A. dorsata (large, open-nesting). We made standardized observations of their diurnal and seasonal activity patterns and recorded temperature, humidity, and solar radiation at flowers being visited. A. dorsata comprised two-thirds of honeybee individuals observed, although this species was largely absent from July to November. A. cerana was active on each day that observations were made and tolerated temperatures of 7℃–41.5℃ (including observations from two other sites in Yunnan). The other species had higher minimum temperature thresholds for activity, but A. florea had a higher maximum temperature tolerance (46.5℃) and A. dorsata was sometimes active at night. Generalized linear models showed abundances of A. cerana and A. dorsata had positive relationships with numbers of flowers and negative ones with temperature. A. florea abundance had a positive relationship with temperature, while the presence of A. andreniformis was positively related to temperature and humidity. Apis bees visited 48.6% of the flower species observed. Impacts of projected warming over coming decades are expected to vary among species, but overall pollination services by honeybees at this site seem likely to be resilient.

Global streamflow and thermal habitats of freshwater fishes under climate change

Climate change will affect future flow and thermal regimes of rivers. This will directly affect freshwater habitats and ecosystem health. In particular fish species, which are strongly adapted to a certain level of flow variability will be sensitive to future changes in flow regime. In addition, all freshwater fish species are exotherms, and increasing water temperatures will therefore directly affect fishes’ biochemical reaction rates and physiology. To assess climate change impacts on large-scale freshwater fish habitats we used a physically-based hydrological and water temperature modelling framework forced with an ensemble of climate model output. Future projections on global river flow and water temperature were used in combination with current spatial distributions of several fish species and their maximum thermal tolerances to explore impacts on fish habitats in different regions around the world. Results indicate that climate change will affect seasonal flow amplitudes, magnitude and timing of high and low flow events for large fractions of the global land surface area. Also, significant increases in both the frequency and magnitude of exceeding maximum temperature tolerances for selected fish species are found. Although the adaptive capacity of fish species to changing hydrologic regimes and rising water temperatures could be variable, our global results show that fish habitats are likely to change in the near future, and this is expected to affect species distributions.

Screening and Characterisation ofPseudomonas fluorescence: A Biological Control Agent against Wilt Fungus inCajanus cajan(L.) Millsp.

About 310 Pigeon pea (Cajanus cajan (L.) Millsp.) rhizobacteria were isolated from cultivated soils of North-East India (Alwar district, Rajasthan). Among the total isolates, 25 isolates were confirmed as Pseudomonas fluorescence based on the biochemical tests, such as arginine hydrolysis, catalase activity, production of fluorescing compounds, gelatin liquefaction and growth at 4°C and 42°C. Their antifungal activity against wilt fungus Fusarium udum (strain of pigeon pea) was examined in vitro and in vivo. Survivality of the isolates under stress conditions of temperature and pH was examined. Five strains (BISR-E, BISR-T, BISR-V, BISR-X and BISR-Y) gave maximum temperature tolerance and four strains (BISR-B, BISR-C, BISR-D and BISR-H) could survive under variable pH range 4–10. Twelve isolates of P. fluorescence were exhibited strong antifungal activity against F. udum. Zone of inhibition was measured. Twelve isolates were observed with more than 30% RI value with maximum RI value recorded in strain BISR-W and BISR-N (42.0%). Net house pot studies screening results revealed that 17 isolates (BISR-A, BISR-B, BISR-C, BISR-D, BISR-E, BISR-G, BISR-H, BISR-I, BISR-K, BISR-L, BISR-N, BISR-O, BISR-P, BISR-R, BISR-U, BISR-W and BISR-X) were observed as good plant growth-promoting rhizobacteria and biological control agents. Among these strains, isolate numbers BISR—B, BISR-F, BISR-K, BISR-N, BISR-O, BISR-P, BISR-W and BISR-X were proved themselves superior isolates having good biocontrol potential to manage F. udum in Pigeon pea plant and to enhance plant growth parameters to a significant level. Out of 25 isolates, 20 isolates (BISR-A, BISR-B, BISR-C, BISR-D, BISR-F, BISR-G, BISR-H, BISR-I, BISR-J, BISR-K, BISR-L, BISR-M, BISR-N, BISR-O, BISR-P, BISR-Q, BISR-R, BISR-S, BISR-T and BISR-V) could produce siderophore.

Sensitivity of native and non-native mollusc species to changing river water temperature and salinity

Climate change may strongly affect the abiotic conditions in riverine ecosystems, for example by changing water temperature regimes and salinisation due to sea water intrusion and evaporation. We analysed the effects of changes in water temperature and salinity on the species pool of freshwater molluscs in the river Rhine. Species sensitivity distributions (SSDs) for maximum temperature and salinity tolerance were constructed for native and non-native species that are currently present in the river Rhine. The maximum temperature tolerance was significantly higher for non-native mollusc species than native ones. For salinity tolerance, no significant difference was found between the two groups. The SSDs were used to determine the potentially not occurring fractions (PNOFs) of each species group corresponding with the yearly maximum water temperature and salinity levels recorded in (1) different river sections for the extreme warm and dry year 2003, and (2) the river Rhine at Lobith (The Netherlands) over the period 1960–2009. Changing temperature and salinity conditions in the river Rhine over the past 50 years corresponded with a net increase in PNOF for native species. This was mainly due to rising river water temperatures, which had a larger influence than decreasing salinity levels. For non-native species no change in PNOF was found, indicating that future temperature rise will disproportionally affect native mollusc species. Validation of the PNOF estimated for Lobith with the not occurring fraction (NOF) of mollusc species derived from monitoring data revealed similar trends for native as well as non-native mollusc species richness. The increase in the PNOF accounted for 14% of the increase in the NOF. The construction and application of SSDs appeared a promising approach to address the separate and combined effects of changing abiotic conditions on native and non-native species pools.

Treatment design of radio frequency heating based on insect control and product quality

Non-uniform heating caused by different size, geometry, and properties of agricultural commodities is a major challenge that needs to be addressed in developing industrial-scale radio frequency (RF) treatments for postharvest phytosanitary and quarantine applications to dry grains or nuts. A mathematical model based on normal distributions of product temperatures and taking into account insect thermal mortality and product quality was developed to predict treatment temperature–time ranges as a function of number of mixing. To demonstrate its applications, this model considered two boundary conditions: complete mortality of fifth-instar navel orangeworm with temperature–time relationships (46, 48, 50, 52, and 54 °C for 140, 50, 15, 6, and 1 min, respectively), and maximum temperature tolerance relationship for walnut quality (53, 69, and 75 °C for 240, 5, and 1 min, respectively). This model was validated by experimental data of the uniformity index and applied to walnut, soybean, lentil, and wheat, each with its own unique RF heating characteristics. The results showed that the operation ranges (temperature–time combinations) for effective control of pests without causing adverse quality changes expanded with increasing mixing number and the improved heating uniformity. This study suggested more flexibility in developing RF treatments of pest control for small-size crops with better heating uniformity, as compared to large-size crops.

Evidence for Geographic Isolation and Signs of Endemism within a Protistan Morphospecies

The possible existence of endemism among microorganisms resulting from and preserved by geographic isolation is one of the most controversial topics in microbial ecology. We isolated 31 strains of "Spumella-like" flagellates from remote sampling sites from all continents, including Antarctica. These and another 23 isolates from a former study were characterized morphologically and by small-subunit rRNA gene sequence analysis and tested for the maximum temperature tolerance. Only a minority of the Spumella morpho- and phylotypes from the geographically isolated Antarctic continent follow the worldwide trend of a linear correlation between ambient (air) temperature during strain isolation and heat tolerance of the isolates. A high percentage of the Antarctic isolates, but none of the isolates from locations on all other continents, were obligate psychrophilic, although some of the latter were isolated at low ambient temperatures. The drastic deviation of Antarctic representatives of Spumella from the global trend of temperature adaptation of this morphospecies provides strong evidence for geographic transport restriction of a microorganism; i.e., Antarctic protistan communities are less influenced by transport of protists to and from the Antarctic continent than by local adaptation, a subtle form of endemism.

Tigers eating tigers: evidence of intraguild predation operating in an assemblage of tiger beetles

Summary1. Co‐occurrence of closely related predators in a prey‐limited habitat appears to contradict the principle of competitive exclusion, however it may be explained through indirect effects, niche shifts, and intraguild predation.2. The interactions between sympatric tiger beetle Cicindela species were examined. Cicindela circumpicta is the largest of three species (C. circumpicta, C. togata, C. fulgida) found in saline habitats throughout central North America. The temporal occurrence of these species overlaps, as does their spatial occurrence on exposed salt flats of saline marshes. During field observations, exoskeletal remains of C. togata were found at the study site in Nebraska, U.S.A.3. In laboratory trials, male C. circumpicta ate C. togata in 38% of trials and female C. circumpicta ate C. togata in 50% of trials (n = 24).4. In the field, potential prey, consisting mainly of small flies, was found mostly in shaded conditions but tiger beetles differed significantly in shade use, with C. circumpicta spending 70% of the time in the shade compared with ≈ 20% for C. togata. Differential habitat use was not explained by maximum temperature tolerances, which did not differ between the species.5. Laboratory trials established that both tiger beetle species consumed small prey (apterous Drosophila) but C. togata was more efficient at capturing winged Drosophila.6. Foraging efficiency, as measured by the time taken for a C. togata to capture three prey items, decreased significantly in the presence of other tiger beetles, especially C. circumpicta.7. These results are an indication that intraguild predation and induced changes in foraging behaviour operate in the ecology of adult tiger beetles.

Do upper thermal tolerances differ in geographically separated populations of the beachflea Orchestia gammarellus (Crustacea: Amphipoda)?

Fundamental (as opposed to realised) between-population differences in maximum temperature tolerances were examined for the common beachflea of European shores, Orchestia gammarellus. Individuals were collected from two distinct populations, one in S.E. England and one in N. Scotland, and were acclimated to a number of different thermal regimes (5, 10, 15, 20 and 25°C). Temperature tolerances increased with body size for virtually all combinations of population and acclimation temperature tested. Such a relationship complicates comparison between populations, although when body size differences were controlled for at two acclimation temperatures, individuals of the southern population tended to have higher thermal tolerances. Controlling for body size tends, however, to underestimate the difference in temperature tolerances of the two populations. This is because the southern population consisted of larger individuals than the northern, giving rise to markedly different frequency distributions of tolerances. Clearly upper thermal tolerance limits do vary between these two geographically widely separated populations of O. gammarellus and this variance cannot be accounted for by acclimation. Such a finding, were it to have general application, would have important implications for ecologists seeking to explain large-scale distribution patterns in terms of a `fixed' species physiology.

A Field Information-based System for Estimating Fish Temperature Tolerances

In 1979, Biesinger et al. described a technique for spatial and temporal matching of records of stream temperatures and fish sampling events to obtain estimates of yearly temperature regimes for freshwater fishes of the United States. This article describes the state of this Fish and Temperature Database Matching System (FTDMS), its usage to estimate thermal requirements for fishes, some proposed maximum temperature tolerances for several freshwater fish species, and the way these FTDMS-derived values relate to various laboratory test results. Although applicable to all species for which collection records exist, initial development and refinement of FTDMS has focused on estimating the maximum weekly mean temperature tolerance for 30 common fishes of the United States. The method involves extensive use of automated data processing during data incorporation, quality assurance checks, data matching, and endpoint calculation. Maximum weekly mean temperatures derived from FTDMS were always less than laboratory-determined lethal temperatures and were similar to temperature criteria obtained from laboratory data through Environmental Protection Agency (EPA) interpolation procedures. The technique is a cost-effective means of generating temperature tolerance estimates for many U.S. fish species (i.e., more than 100).

Leaf-level responses to light and temperature in two co-occurring Quercus (Fagaceae) species: implications for tree distribution patterns

Leaf-level responses to light environment (sun vs. shade) and high temperature were compared in two gallery forest oaks, bur oak ( Quercus macrocarpa) and chinquapin oak ( Quercus muehlenbergii). Our goal was to determine if species-specific differences in response to light or temperature could explain the distribution of these oaks in tallgrass prairie gallery forests. On the Konza Prairie Research Natural Area in NE Kansas (USA), bur oak is more abundant than chinquapin oak along lower reaches of streams where the forests are most productive and canopy closure is greatest. We hypothesized that bur oak is better able to acclimate physiologically to reduced light availability than chinquapin oak. Leaf level acclimation to low light in both oaks occurred through reduced photosynthetic light compensation points (PLC) (bur oak, 60.77 ± 3.02 μmol photons m −2 s −1 in sun leaves vs. 29.25 ± 0.29 photons m −2 s −1 in shade leaves; chinquapin oak, 49.47 ± 2.82 photons m −2 s −1 in sun leaves vs. 26.48 ± 1.74 photons m −2s −1 in shade leaves), resulting from nearly 50% reductions in dark respiration and specific leaf mass in both species. Apparent quantum requirement ( Q req; mol photons mol −1 O 2) did not differ between sun and shade leaves in either species, and only bur oak showed differences in sun and shade leaf shape. We also hypothesized that chinquapin oak, which is more abundant in exposed, upper stream reaches, has greater photosynthetic tolerance to the high temperatures characteristics of this region. The maximum temperature tolerances ( T max) of these oaks were compared by measuring increases in chlorophyll fluorescence. For most of the growing season, T max in chinquapin oak was 2.0°C higher than in bur oak. Field measurements of leaf vs. air temperatures in seedlings and adult trees indicated that T max was more likely to be exceeded in bur than in chinquapin oak, particularly in seedlings exposed to high solar radiation loads. We concluded that differences in thermal tolerance, in addition to previously documented differences in water relations are important determinants of distributional patterns of these oaks within gallery forests.

New wild Tetrahymena from Southeast Asia, China, and North America, including T. malaccensis, T. asiatica, T. nanneyi, T. caudata, and T. silvana n. spp.

Tetrahymena of the T. pyriformis complex collected from varied habitats in Malaysia, Thailand, and The People's Republic of China include strains of the micronucleate species T. americanis and T. canadensis and the amicronucleate T. pyriformis and T. elliotti. Two new breeding species are described-T. malaccensis from Malaysia and T. asiatica from China and Thailand. Two wild selfers from China and some of the amicronucleate strains from all three countries fall into isozymic groups similar to named micronucleate and amicronucleate species. The T. patula complex is represented by two groups of clones from Malaysia that fit the morphological description of T. vorax. They, however, have radically different isozymic electrophoretic patterns and both groups differ from those of previously described T. vorax. As their molecules indicate relationships to other "T. vorax" strains as distant as that between T. vorax and T. leucophrys, they are considered to be new species, T. caudata and T. silvana. A third new breeding species, T. nanneyi, was identified among strains previously collected in North America. Viable immature progeny were obtained from the new strains of the five breeding species. Maximum temperature tolerances were determined for the new strains of four of the breeding species.

Thermal ecology of the tree agama (Agama atricollis) in Zaire with a review of heat tolerance in reptiles

Territorial behaviour and thermal ecology in relation to heat resistance in the tree agama (or black‐necked agama), Agama atricollis, were studied during two expeditions 1951–2 and 1958–9 in eastern Zaire (the former Belgian Congo) in an area just south of the equator. The maximum temperature tolerance of A. atricollis lies within the range of 43–43·9°C, but the maximum voluntary tolerance is somewhat lower, 42·5°C. Territorial males, retreating from their guard posts after having exposed themselves to direct sunlight during the hottest hours of the day for 10–16 minutes, reach body temperatures of 42·2–42·5°C before they retreat into the shade. In shady places it takes the males from 14 to 21 minutes to cool down to 38·1–39·9°C, at which body temperatures they return to the lookout within the territory. The territoriality in A. atricollis and several other species of the same genus, as well as other diurnal lizards with similar behaviour, may have contributed, through selection, to the evolution of their extraordinary resistance to substratum heat and direct sunlight. In an attempt to review and compare maximum voluntary body temperatures (MVT), critical thermal maxima (CTM) and lethal body temperatures (LT) in reptiles with pronounced heat resistance, data have been compiled for 96 species representing 11 families and six continents. The family Agamidae appears to be the most adapted to high body temperatures with 13 species (of 18 species tested) having body temperatures above 43°C in comparison with six species in Iguanidae (of 33 species tested), four in Gekkonidae (of nine species tested) and so forth. Agamids, iguanids, teeids and geckos, in hot environments of five continents, have evolved along the same lines behaviourally and physiologically as responses to territoriality in combination with high temperatures. This feature may be of adaptive significance.This paper also reports on body temperatures, obtained in Africa from free‐living individuals of seven other species of the genera Agama and Mabuya, namely A. atra, A. colonorum, A. hispida, A. planiceps, Mabuya quinquetaeniata, M. maculilabris and M. striata.