Thermal Maximum Research Articles

Paleoenvironmental and sea level changes across the Paleocene-lower Eocene interval at the central and southwestern Sinai, Egypt

Detailed stratigraphic studies of the Paleocene-lower Eocene interval were conducted on four stratigraphic successions (Sudr-Alhitan, Thamad, Abu-Qada, and Nukhul) in central and southwestern Sinai. These sections are arranged along a North-South direction as: Sudr-Alhitan, Thamad, Abu-Qada, and Nukhul. The biostratigraphic framework was achieved by integrating data of calcareous nannofossils and planktonic foraminifera. The studied area experienced two major tectonic events, most likely related to the Syrian Arc System (SAS), which led to two distinct hiatuses of significant magnitude, evidenced from integrated biostratigraphic analysis and thorough field observations. Benthic foraminifera assemblages suggest a deposition in outer neritic to upper bathyal setting for investigated sites, except for the Tarawan and Thebes formations in Abu-Qada and Sudr-Alhitan sections, which were deposited in middle-outer neritic and outer neritic settings, respectively. Benthic foraminiferal indices indicate an oligo-mesotrophic environment associated with oxic/suboxic conditions at the bottom of the seawater for the studied interval. Low oxygen levels and mesotrophic conditions were seen to mark the Paleocene Eocene Thermal Maximum event, as evidenced by the organic-rich laminated sediment, low benthic foraminiferal indices, and the occurrence of agglutinated taxa Repmanina charoides and Ammobaculites spp., which reflects a major change in food supply. The obtained sequence stratigraphic framework shows that the depositional record of the studied area is significantly influenced by both the regional tectonics and eustatic sea level.

THE IMPORTANCE OF UPWELLING CONDITIONS AS DRIVERS OF FEEDING BEHAVIOR AND THERMAL TOLERANCE IN A PROMINENT INTERTIDAL FISH

Upwelling, as a large oceanographic phenomenon, increases coastal productivity and influences all levels of biological complexity. Despite decades of research on it, much remains to be understood about the impact of upwelling on the feeding behavior and thermal tolerance of important groups such as fish. Hence, our aim was to investigate how upwelling conditions modify the feeding behavior and thermal tolerance of a prominent intertidal fish, Girella laevifrons. We collected purple mussels (Perumytilus purpuratus) from upwelling (U) and downwelling sites (DU) in central Chile, and used them as prey in feeding trials and measuring the concentration of organic matter and proteins in their tissues. We assessed fish consumption rates and growth in fish collected from the same U and DU sites, feeding on either U or DU mussels. Lastly, we assessed the thermal tolerance of U and DU fish fed with the aforementioned U vs DU mussels. We found that U mussels held higher concentrations of organic matter and proteins compared to their DU counterparts. U mussels were also selected and consumed in larger amounts than DU mussels, although the origin of the fish also influenced consumption rates. Thermal tolerance assays revealed that U fish exhibited higher maximum performance (Max.pf) and critical thermal maxima (Ctmax) and lower sensitivity to temperature changes (as measured by Q10), compared to DU fish. Altogether, these results point to a strong influence of upwelling on the quality of organisms' tissues, indirectly altering key aspects of fish feeding behavior and thermal tolerance. These findings also contribute to understanding the physiological adjustments organisms make in productive upwelling systems, and how they may change in the future with ongoing climate events.

Disruption of boreal lake circulation in response to mid-Holocene warmth; evidence from the varved sediments of Lake Nautajärvi, southern Finland.

Future climate projections are expected to have a substantial impact on boreal lake circulation regimes. Understanding lake sensitivity to warmer climates is therefore critical for mitigating potential ecological and societal impacts. The Holocene Thermal Maximum (HTM; ca 7-5ka BP) provides a valuable analogue to investigate lake responses to warmer climates devoid of major anthropogenic influences. Here, we analyse the micro-X-ray core scanning profiles (μ-XRF) of the annually laminated (varved) sediments from Lake Nautajärvi (NAU-23) in southern Finland to elucidate changes in lake circulation and sedimentation patterns. Principal component analysis (PCA) identifies two key components in the geochemical data associated with the nature of the sediments, i.e. detrital vs organic sedimentation (PC1), and hypolimnetic oxidation (PC2). Our findings reveal that during the HTM, the lake became more sensitive to changes in oxygenation and mixing intensity. These changes were triggered by a warmer climate, which increased organic matter and redox sensitive metal solute concentrations in the water column, strengthening lake stratification and weakening dimictic circulation patterns. Superimposed on HTM weakened circulation are distinct phases of increased oxidation and iron-rich varve formation that do not happen when the background conditions are cooler (i.e. the early and late Holocene). This is driven by temporary strengthening of the mixing regime in response to climatic variability and storminess cycles across southern Scandinavia. These findings demonstrate that whilst warmer conditions weaken boreal lake circulation regimes, they can also make them increasingly vulnerable to short term oscillations in prevalent climatic conditions and weather patterns, which could have significant impacts on lake water quality and aquatic ecosystems. These findings underscore the non-stationary nature of lake sensitivity to short-term climatic variability and emphasize the potential for similar shifts to occur under future warming scenarios.

Two Sites in East Asia Add to Spatiotemporal Heterogeneity of Wildfire Activity Across the Paleocene–Eocene Thermal Maximum

Two Sites in East Asia Add to Spatiotemporal Heterogeneity of Wildfire Activity Across the Paleocene–Eocene Thermal Maximum

Supercritical Crossover Lines in the Cell Fluid Model

The cell fluid model with a modified Morse potential is studied. The supercritical states are considered with respect to the possibility of the construction of a separation boundary between liquid-like and gas-like behaviors. We will calculate three different lines that can be used for this purpose: the loci of the isothermal compressibility maxima, the loci of the thermal expansion coefficient maxima, and the line, where the effective chemical potential is zero, M = 0. By the symmetry of the functionals for the partition functions, the condition M = 0 in fluids is analogous to the absence of an external field in the Ising model.

Patterns of interpopulation variation and physiological trade-offs of the acute thermal tolerance of juvenile Chinook salmon (Oncorhynchus tshawytscha)

IntroductionThe capacity of species and populations to respond to rapid environmental change will be pivotal for their resilience in the coming decades. To explore thermal plasticity, physiological trade-offs, and associations with environmental characteristics, we assessed the heat hardening response and acclimation capacity of juvenile Chinook salmon (Oncorhynchus tshawytscha) from seven hatchery populations spanning diverse ecoregions along the West Coast of the United States.MethodsProgeny from each population were acclimated to one of three temperatures (11, 16, or 20°C) and subjected to two acute thermal maximum (CTMAX) trials 24 h apart. The heat hardening response (ΔCTM) was calculated as the difference between an individual's second and first CTMAX trials. Acclimation capacity was determined as the maximum difference in CTMAX between fish acclimated to 11°C and 20°C during their second trial, capturing the full acclimatory scope. Bayesian models were employed to test the thermal trade-off hypothesis, which posits that individuals or populations with higher thermal tolerance have reduced capacity for acclimation. Trade-offs were analyzed at both individual and population scales. Associations between ΔCTM, acclimation capacity, and source population environmental characteristics were also examined using data from a landscape-scale, regional, river temperature model.ResultsFish acclimated to 16°C or 20°C exhibited heat hardening (positive ΔCTM), while those acclimated to 11°C exhibited “heat weakening” (negative ΔCTM), a rare phenomenon in the literature. At the individual level, fish adhered to the thermal trade-off hypothesis, with higher thermal tolerance associated with reduced plasticity. However, no such trade-off was observed at the population level. Acclimation capacity was positively correlated with latitude and the temperature of the natural rearing environment. Additionally, ΔCTM performance improved when fish were acclimated to temperatures closer to those of their natural habitats.DiscussionIndividual fish exhibited a trade-off between thermal tolerance and plasticity, while populations did not. Thermal plasticity was associated with environmental conditions, with populations from warmer habitats demonstrating greater acclimation and heat hardening capacities. This study highlights the importance of understanding interpopulation variation to identify at-risk populations, such as those from colder habitats or with limited thermal plasticity, like the Trinity population. These findings emphasize the need to account for interpopulation differences when predicting species responses to climate change and developing conservation strategies.

Ecophysiological responses to heat waves in the marine intertidal zone.

One notable consequence of climate change is an increase in the frequency, scale and severity of heat waves. Heat waves in terrestrial habitats (atmospheric heat waves, AHW) and marine habitats (marine heat waves, MHW) have received considerable attention as environmental forces that impact organisms, populations and whole ecosystems. Only one ecosystem, the intertidal zone, experiences both MHWs and AHWs. In this Review, we outline the range of responses that intertidal zone organisms exhibit in response to heat waves. We begin by examining the drivers of thermal maxima in intertidal zone ecosystems. We develop a simple model of intertidal zone daily maximum temperatures based on publicly available tide and solar radiation models, and compare it with logged, under-rock temperature data at an intertidal site. We then summarize experimental and ecological studies of how intertidal zone ecosystems and organisms respond to heat waves across dimensions of biotic response. Additional attention is paid to the impacts of extreme heat on cellular physiology, including oxidative stress responses to thermally induced mitochondrial overdrive and dysfunction. We examine the energetic consequences of these mechanisms and how they shift organismal traits, including growth, reproduction and immune function. We conclude by considering important future directions for improving studies of the impacts of heat waves on intertidal zone organisms.

Repeatability of critical thermal maximum (CTmax) in two freshwater ectotherms across contexts.

Critical thermal maximum (CTmax) is the most widely used method for quantifying acute upper thermal limits in ectotherms. CTmax protocol exposes animals to a consistent rate of environmental warming until they lose motor function. CTmax has been used to assess intraspecific variation among life stages, populations, or as a function of body size, often with the assumption that it is a durable and heritable trait at the individual level. The existence of within-individual repeatability of CTmax has been used to infer the potential for thermal adaptation via the positive correlation between the repeatability of a trait and its heritability. However, for how widely used CTmax has become, surprisingly few studies have quantified within-individual repeatability in aquatic ectotherms, and none have assessed repeatability across contexts. We examined the cross-context repeatability of CTmax in two freshwater ectotherms (one decapod crustacean and one teleost fish): rusty crayfish Faxonius rusticus (n=31) and pumpkinseed Lepomis gibbosus (n=38). Individual repeatability was measured on a weekly basis across multiple trials (n=5 pumpkinseed CTmax measurements, n=7 rusty crayfish) that varied in acclimation temperature, oxygen saturation, and salinity. CTmax was most strongly influenced by acclimation temperature. Repeatability varied based on the statistical approach and between the two species. Pumpkinseed repeatability across contexts was moderate (ca. 0.4), similar to previous reports on within-context CTmax repeatability studies in fishes. In rusty crayfish, repeatability was much lower (ca. 0.16). This suggests CTmax repeatability may be both taxon- and context-dependent, thus further investigation into repeatability is needed across species for this important and widely used trait.

Assessing Heat Resistance and Selecting Heat-Resistant Individuals of Largemouth Bass (Micropterus salmoides) with Tiered Thermal Exposure.

Largemouth bass (LMB, Micropterus salmoides), a commercially important farmed fish, is vulnerable to heat stress. Breeding heat-resistant LMB is highly desirable in the face of global warming. However, we still lack an efficient method to assess the heat resistance of LMB. In this study, the critical thermal maximum (CTmax) and static exposure methods were first performed to assess the heat resistance of LMB juveniles. The CTmax values of the experimental fish (average body weight 9.87 ± 3.14 g) ranged from 39 to 40 °C but were too close together to differentiate the individual heat resistance. Static exposure experiments with varying temperatures and fish groups also did not provide a clear method for determining the heat resistance. To address these limitations, we developed a tiered exposure method, where the temperature was increased step-wise, starting from 28 to 34 °C at 2 °C increments and then at 0.5 °C increments above 34 °C, with each step lasting one day. The heat resistance of the fish was quantified as the lethal cumulative temperature (LCT), allowing for the classification of fish as sensitive or resistant to heat stress based on their LCT values. To correlate the changes in tissue structure and gene expression with the heat resistance, a new batch of LMB juveniles (average body weight 23.66 ± 6.98 g) were subjected to tiered heat exposure. Brain and liver tissues were collected from the control (without heat exposure), resistant and sensitive (still alive but demonstrated abnormal symptoms) individuals when the temperature was maintained at 35.5 °C for 24 h. The liver tissues of the heat-sensitive individuals showed significant damage and increased cell apoptosis (p < 0.05) relative to those of the resistant ones. The ddit3/chop, bax and casp3 genes demonstrated differential expressions in the liver of the sensitive and resistant fish. Additionally, the LMB juveniles (average body weight 84.06 ± 20.95 g) were found to be more heat resistant than the adults from different sources (average body weight 364.29 ± 84.43 g and 545.71 ± 184.56 g). Through the tiered exposure method, extremely heat-resistant individuals were successfully selected from the population (average body weight 22.69 ± 6.89 g). These findings provide valuable insights into the thermal biology of LMB and the potential for breeding heat-resistant LMB varieties.

Spatiotemporal evolution of wildfire activity during the Paleocene-Eocene Thermal Maximum in China

Spatiotemporal evolution of wildfire activity during the Paleocene-Eocene Thermal Maximum in China

Temperature tolerance of European fish species based on thermal maxima in southern Baltic Sea-basin streams

Temperature tolerance of European fish species based on thermal maxima in southern Baltic Sea-basin streams

Lack of thermal acclimation in multiple indices of climate vulnerability in bumblebees.

Indices of climate vulnerability are used to predict species' vulnerability to climate change based on intrinsic physiological traits, such as thermal tolerance, thermal sensitivity and thermal acclimation, but rarely is the consistency among indices evaluated simultaneously. We compared the thermal physiology of queen bumblebees between a species experiencing local declines (Bombus auricomus) and a species exhibiting continent-wide increases (B. impatiens). We conducted a multi-week acclimation experiment under simulated climate warming to measure critical thermal maximum (CTmax), critical thermal minimum (CTmin), the thermal sensitivity of metabolic rate and water loss rate and acclimation in each of these traits. We also measured survival throughout the experiment and after the thermal tolerance trials. Neither species acclimated to the temperature treatments by adjusting any physiological trait. We found conflicting patterns among indices of vulnerability within and between species. We also found that individuals with the highest CTmax exhibited the lowest survival following the thermal tolerance trial. Our study highlights inconsistent patterns across multiple indices of climate vulnerability within and between species, indicating that physiological studies measuring only one index of climate vulnerability may be limited in their ability to inform species' responses to environmental change.

Prior thermal acclimation gives White Sturgeon a fin up dealing with low oxygen.

Assessing how at-risk species respond to co-occurring stressors is critical for predicting climate change vulnerability. In this study, we characterized how young-of-the-year White Sturgeon (Acipenser transmontanus) cope with warming and low oxygen (hypoxia) and investigated whether prior exposure to one stressor may improve the tolerance to a subsequent stressor through "cross-tolerance". Fish were acclimated to five temperatures within their natural range (14-22°C) for one month prior to assessment of thermal tolerance (critical thermal maxima, CTmax) and hypoxia tolerance (incipient lethal oxygen saturation, ILOS; tested at 20°C). White Sturgeon showed a high capacity for thermal acclimation, linearly increasing thermal tolerance with increasing acclimation temperature (slope = 0.55, adjusted R2 = 0.79), and an overall acclimation response ratio (ARR) of 0.58, from 14°C (CTmax = 29.4 ± 0.2°C, mean ± S.E.M.) to 22°C (CTmax = 34.1 ± 0.2°C). Acute warming most negatively impacted hypoxia tolerance in 14°C-acclimated fish (ILOS = 15.79 ± 0.74% air saturation), but prior acclimation to 20°C conferred the greatest hypoxia tolerance at this temperature (ILOS = 2.60 ± 1.74% air saturation). Interestingly, individuals that had been previously tested for thermal tolerance had lower hypoxia tolerance than naïve fish that had no prior testing. This was particularly apparent for hypoxia-tolerant 20°C-acclimated fish, whereas naïve fish persisted the entire 15-h duration of the hypoxia trial and did not lose equilibrium at air saturation levels below 20%. Warm-acclimated fish demonstrated significantly smaller relative ventricular mass, indicating potential changes to tissue oxygen delivery, but no other changes to red blood cell characteristics and somatic indices. These data suggest young-of-the-year White Sturgeon are resilient to warming and hypoxia, but the order in which these stressors are experienced and whether exposures are acute or chronic may have important effects on phenotype.

Differences in gene expression between high and low tolerance rainbow trout (Oncorhynchus mykiss) to acute thermal stress.

Understanding the mechanisms that underlie the adaptive response of ectotherms to rising temperatures is key to mitigate the effects of climate change. We assessed the molecular and physiological processes that differentiate between rainbow trout (Oncorhynchus mykiss) with high and low tolerance to acute thermal stress. To achieve our goal, we used a critical thermal maximum trial in two strains of rainbow trout to elicit loss of equilibrium responses to identify high and low tolerance fish. We then compared the hepatic transcriptome profiles of high and low tolerance fish relative to untreated controls common to both strains to uncover patterns of differential gene expression and to gain a broad perspective on the interacting gene pathways and functional processes involved. We observed some of the classic responses to increased temperature (e.g., induction of heat shock proteins) but these responses were not the defining factors that differentiated high and low tolerance fish. Instead, high tolerance fish appeared to suppress growth-related functions, enhance certain autophagy components, better regulate neurodegenerative processes, and enhance stress-related protein synthesis, specifically spliceosomal complex activities, mRNA regulation, and protein processing through post-translational processes, relative to low tolerance fish. In contrast, low tolerance fish had higher transcript diversity and demonstrated elevated developmental, cytoskeletal, and morphogenic, as well as lipid and carbohydrate metabolic processes, relative to high tolerance fish. Our results suggest that high tolerance fish engaged in processes that supported the prevention of further damage by enhancing repair pathways, whereas low tolerance fish were more focused on replacing damaged cells and their structures.

New quantified climate reconstruction in southern China suggests a potential influence of winter cloud cover across East Asia during the Holocene.

Previous studies have advanced our understanding of paleoclimate features and dynamics in East Asia, particularly within the East Asian monsoon domain (EAMD) since the last glacial period. However, a lack of quantitative reconstructions in the boundary area between tropical and subtropical zones has largely hindered our spatial comprehension of the relationship between precipitation and temperature throughout the EAMD. In this study, we present a continuous pollen record from the Pearl River delta over the past 13.2ka and a quantitative climate reconstruction using an updated modern pollen dataset. The findings indicate that from 13.2ka to 9.9ka, the study area was encompassed by mid-montane moist evergreen broadleaved forest (EBLF), transitioning to semi-humid EBLF or lowland monsoon EBLF during the late Holocene. Anthropochory plants have emerged as dominant taxa by about 1.9ka, indicating a large-scale impact of human activities. The results of quantitative climate reconstruction indicate that the range of annual precipitation varies by ca. 80-120mm, and the changing pattern is consistent with the traditional 'Holocene thermal maximum' mode, with summer solar radiation potentially being the primary controlling factor. The range of annual temperature variability fall between 19.5°C and 22.5°C, exhibiting a warming trend likely influenced by changes in Northern Hemisphere ice volume. There is a phase difference of about 2-4ka between the peak values of precipitation and temperature. The variation patterns of change across eastern Asia exhibit distinct differences when compared to the proxy records in the EAMD. It appears that such asynchrony between precipitation and temperature is more pronounced in southern China. In comparison with model simulations, it is believed that spatiotemporal variation in winter cloud cover may play a crucial role in explaining this phenomenon of regional heterogeneity.

Global Warming and Equatorial Atlantic Paleoceanographic Changes During Early Eocene Carbon Cycle Perturbation V

AbstractA series of transient global warming events (“hyperthermals”) in the early Eocene is marked by massive environmental and carbon cycle change. Among these events, the impacts of the Paleocene Eocene Thermal Maximum (∼56 Ma), Eocene Thermal Maximum 2 (∼54 Ma) and Eocene Thermal Maximum 3 (∼53 Ma) are relatively well documented. However, much less is known about the many subsequent hyperthermals that apparently occurred on orbital eccentricity maxima until at least the end of the Early Eocene Climatic Optimum (EECO; ∼53–49 Ma). Ocean Drilling Program (ODP) Site 959 (Equatorial Atlantic Ocean), we report a large negative carbon isotope excursion (CIE) in both organic and carbonate substrates that we correlate to the “V” event sensu Lauretano et al. (2016), https://doi.org/10.1127/nos/2016/0077 (or C22nH1 sensu Sexton et al. (2011), https://doi.org/10.1038/nature09826) at ∼49.7 Ma, following combined bio‐ and chemostratigraphic constraints. Through TEX86 paleothermometry, we reconstruct a sea surface temperature rise of 1.3–2.0°C associated with this CIE, which, combined with evidence for warming from the deep sea, implies that this event indeed represents a transient global‐scale warming episode like the earlier hyperthermals. Organic walled dinoflagellate cyst assemblages indicate a productive paleoceanographic background setting, likely through regional upwelling, which alternated with episodes of stratification. Warming reconstructed across V at Site 959 is relatively similar to the higher‐latitude‐derived deep ocean reconstructions. However, the presence of upwelling and its variable intensity across the event compromises the use of the reconstructed warming as an estimate for the complete tropical band.

Probable Record of Paleocene - Eocene Thermal Maximum in Southwestern Nigeria: Indications from Nannofossils of FA-1 Borehole, Eastern Benin Basin.

The Paleocene – Eocene Thermal Maximum (PETM) interval has been reported in several calcareous nannofossil studies from Paleogene basins around world including the Southern Tethys basins of North Africa. The Southern Tethys basins are believed to be connected to the Eastern Benin Basin through the Trans – Saharan Seaway during the Paleogene. Based on these reports, we carried out a biostratigraphic and paleoclimatic analyses of the calcareous nannofossils recovered from 25 ditch cutting samples in the FA-1 borehole to investigate possible record of the PETM in the Eastern Benin Basin, Southwestern Nigeria. The samples yielded characteristic Paleocene – Eocene calcareous nannofossils species (Coccolithus pelagicus, Coccolithus formosus, Chiasmolithus solitus, Sphenolithus moriformis, Pontosphaera plana, Pontosphaera multipora, Lophodolithus mochioporus, Lophodolithus nanscens, Neochiastozygus perfectus and Zeugrhabdotus sigmoides) and the Maastrichtian species, Arkhangeskiella cymbiformis. The assemblages allow the recognition of CC 22 (Maastrichtian) and NP 4 – NP 6 (early – late Paleocene) nannofossil zones. The relatively abundant occurrences of the genus Coccolithus and Sphenolithus in the carbonate interval of borehole suggest prevailing oligotrophic, warm water condition. The barren interval succeeding the peak nannofossil abundance at sample 159 m coincides with the onset of continuous clastic sedimentation in the FA-1 borehole. This is believed to have resulted from the shoaling of the Calcite Compensation Depth (CCD) and increased clastic input occasioned by the climatic and ocean water perturbations of the PETM interval. The emergence of the genus Pontosphaera (Pontosphaera plana and Pontosphaera multipora) at depth 87 m above the barren interval suggest a return to cooler, mesotrophic to eutrophic water condition after the drastic temperature rise and oligotrophic waters of the PETM. Key-words - Calcareous nannofossils, Paleocene - Eocene, Benin Basin, Thermal Maximum.

Warming and Carbon Injection at the Paleocene‐Eocene Boundary: Bayesian Modeling Supports Synchroneity

AbstractWe evaluate lead‐lag relationships between warming associated with the Paleocene‐Eocene thermal maximum (PETM) and the attendant carbon isotope excursion (CIE) recorded in sedimentary archives from the mid‐Atlantic continental margin. Cores from the New Jersey coastal plain (NJCP) provide thick (up to 15 m), rapidly deposited shelf PETM sections recording a 6–8°C warming based on the TEX86 paleothermometer. Updip cores from Medford, NJ provide the most expanded CIE onset, associated with a gradual lithologic change from uppermost Paleocene glauconitic sands to the lowermost Eocene kaolinitic Marlboro Clay. The relative thickness of these transitional sediments and the CIE onset allow for high‐resolution stable isotopic (bulk sediment, foraminifera, and organic carbon) and lipid biomarker analyses. The TEXH86‐derived temperature records from Medford cores show no warming prior to the CIE onset, with the carbon isotopic decrease in phase with temperature. Previous studies of more downdip PETM sections on the NJCP suggested that warming preceded the CIE, consistent with a thermal trigger for carbon release. Re‐evaluation of published records and Bayesian analysis of TEXH86‐derived temperature and δ13C from five NJCP sites do not indicate a statistically discernible lead or lag of carbon injection and warming. Though we can not preclude that a lead or lag exists, our analysis suggests that a synchronous CIE onset and warming is the most likely scenario on the NJ paleoshelf.

A multi‐proxy reconstruction of Lateglacial and Holocene mountain vegetation dynamics in Uri, Central Switzerland

In the context of climate change, a long‐term perspective is essential to understand future trajectories of mountain vegetation. We analysed the sediment record of Golzerensee (1411 m a.s.l.), a mountain lake in the transitional zone between the montane and subalpine vegetation belt in Uri, Central Switzerland. We reconstructed past vegetation responses to anthropogenic impact, fire activity and climatic changes dating back to c. 14 550 cal. a BP using pollen, stomata, macrofossil and microcharcoal analyses. The tree line, composed of Betula and Pinus sylvestris, reached Golzerensee during the Allerød c. 13 200 years ago, but tundra vegetation re‐expanded during the Younger Dryas cooling (12 800–11 700 cal. a BP). With the rapid temperature increase at the onset of the Holocene, a closed forest established within a few decades around the study site. Concurrently, temperate taxa (Ulmus, Tilia, Acer, Corylus avellana) increased in the lowlands, likely reaching the elevation of the lake. Abies alba established locally during the Holocene Thermal Maximum (HTM) at 9600 cal. a BP and dominated closed, montane forests, delaying the westward expansion of Picea abies that established only from c. 7700 cal. a BP onwards. The concomitant occurrence of cultural indicator taxa, as well as an increase in charcoal influx and fungal dung spore concentrations suggest that human impact has facilitated the expansion of Picea abies by negatively affecting important competitors such as Abies alba through fire and browsing disturbance. With rising temperatures due to current climate change, Abies alba and other temperate species may regain their former relevance, leading to diverse mixed forests that were abundant during the HTM c. 10 000–5000 cal. a BP. However, future forest composition and landscape diversity will also be influenced by browsing disturbance and land use management.

Estimating optimal temperature conditions for growth, development, and reproduction of Tenebrio molitor (Coleoptera: Tenebrionidae)

Abstract The yellow mealworm, Tenebrio molitor L., is one of the most important industrialized insects worldwide. As a poikilotherm, T. molitor requires a temperature-regulated environment for its farming. Currently, the farming of T. molitor uses temperatures between 29 and 31°C determined to be optimal for maximizing growth. This study was aimed to test and determine optimal temperature for T. molitor impacting all stages including their development, reproduction, and fitness. Pupae of T. molitor were exposed to 8 different temperatures (18, 21, 24, 27, 30, 33, 36, and 39°C). Developmental rates (=1/d to develop) were calculated at 8 temperatures and fitted in a poikilotherm model to determine the temperature with the highest developmental rate (developmental maximum, To). The developmental maximum was 33°C and the thermal maximum (tm) (lethal temperature) was 39°C. The biological and demographic parameters of T. molitor were compared at 3 favorable temperatures below the To (31, 29, and 27°C) to determine the fitness of T. molitor populations. Fecundity and egg viability were the highest at 27°C (5.25 eggs/female/d and 73.99%, respectively) and the lowest at 31°C (1.55 eggs/female/d and 27.14%, respectively). The shortest larval development time was observed at 27°C and the longest at 31°C (142.81 and 161.97 d, respectively). The highest fitness was observed at 27°C with a population doubling time of 32.78 d compared to 40.58 and 239.4 d at 29 and 31°C, respectively. In conclusion, 27°C is closer to the optimal temperature for T. molitor productivity than 29°C, thus reducing its farming energy needs.