Mónika Tóth

Validation of climate model-inferred regional temperature change for late-glacial Europe

Comparisons of climate model hindcasts with independent proxy data are essential for assessing model performance in non-analogue situations. However, standardized paleoclimate datasets for assessing the spatial pattern of past climatic change across continents are lacking for some of the most dynamic episodes of Earths recent past. Here we present a new chironomid-based paleotemperature dataset designed to assess climate model hindcasts of regional summer temperature change in Europe during the late-glacial and early Holocene. Latitudinal and longitudinal patterns of inferred temperature change are in excellent agreement with simulations by the ECHAM-4 model, implying that atmospheric general circulation models like ECHAM-4 can successfully predict regionally diverging temperature trends in Europe, even when conditions differ significantly from present. However, ECHAM-4 infers larger amplitudes of change and higher temperatures during warm phases than our paleotemperature estimates, suggesting that this and similar models may overestimate past and potentially also future summer temperature changes in Europe.

Chironomid-inferred Holocene temperature changes in the South Carpathians (Romania)

We present a Holocene summer air temperature reconstruction based on fossil chironomids from Lake Brazi (1740 m.a.s.l.), a shallow mountain lake in the South Carpathians. Summer air temperature reconstruction was performed using transfer functions based on the Swiss (Sw-TF) and the merged Norwegian–Swiss calibration data set (NS-TF). Our results suggest that summer air temperatures increased rapidly from the onset of the early Holocene onwards (ca. 11,500–10,200 cal. yr BP), reaching close to present July air temperatures (~11.2°C). Between ca. 10,200 and 8500 cal. yr BP mean reconstructed temperatures increased further by 1.5–2.0°C. Later on, from ca. 8500 cal. yr BP, chironomid-based summer temperatures started to decrease, although mean values were still above present-day temperatures. The next time period (ca. 6000–3000 cal. yr BP) was cooler and with less variable temperature conditions than earlier. Afterwards (ca. 3000–2000 cal. yr BP), a sharp decrease occurred in inferred temperatures with values under present-day conditions by 1.8°C. Finally, in the last 2000 years, reconstructed temperatures showed again an increasing trend at Lake Brazi. Short-term temperature declines of 0.6–1.2°C were observed between ca. 10,350–10,190, 9750–9500, 8700–8500, 7600–7300, 7100–6900 and 4400–4000 cal. yr BP. These temperature declines are, however, within the estimated error of prediction of the chironomid-based inferences. Generally, our reconstructed temperatures complied with the summer insolation curve at 45°N, with other proxy-records (i.e. pollen and diatoms) from the same sediment and with other records from the Carpathians and from Western Europe.

Chronic Activation of γ2 AMPK Induces Obesity and Reduces β Cell Function

Summary Despite significant advances in our understanding of the biology determining systemic energy homeostasis, the treatment of obesity remains a medical challenge. Activation of AMP-activated protein kinase (AMPK) has been proposed as an attractive strategy for the treatment of obesity and its complications. AMPK is a conserved, ubiquitously expressed, heterotrimeric serine/threonine kinase whose short-term activation has multiple beneficial metabolic effects. Whether these translate into long-term benefits for obesity and its complications is unknown. Here, we observe that mice with chronic AMPK activation, resulting from mutation of the AMPK γ2 subunit, exhibit ghrelin signaling-dependent hyperphagia, obesity, and impaired pancreatic islet insulin secretion. Humans bearing the homologous mutation manifest a congruent phenotype. Our studies highlight that long-term AMPK activation throughout all tissues can have adverse metabolic consequences, with implications for pharmacological strategies seeking to chronically activate AMPK systemically to treat metabolic disease.

The relative importance of spatial and environmental processes in distribution of benthic chironomid larvae within a large and shallow lake

Although chironomids are popular model organisms in ecological research and indicators of bioassessment, the relative role of dispersal and environmental filtering in their community assembly is still poorly known, especially at fine spatial scales. In this study, we applied a metacommunity framework and used various statistical tools to examine the relative role of spatial and local environmental factors in distribution of benthic chironomid taxa and their assemblages in large and shallow Lake Balaton, Hungary. Contrary to present predictions on the metacommunity organisation of aquatic insects with winged terrestrial adults, we found that dispersal limitation can considerably affect distribution of chironomids even at lake scale. However, we also revealed the predominant influence of environmental filtering, and strong taxa–environment relationships were observed especially along sediment type, sediment organic matter content and macrophyte coverage gradients. We account that identified reference conditions and assemblages along with specified optima and tolerances of the abundant taxa can contribute to our understanding of chironomid ecology and be utilised in shallow lake bioassessment. Further, we propose that predictive models of species–environment relationships should better take into account pure spatial structuring of local communities and species-specific variability of spatial processes and environmental control even at small spatial scales.

Holocene treeline and timberline changes in the South Carpathians (Romania): Climatic and anthropogenic drivers on the southern slopes of the Retezat Mountains

Two high-altitude lake-sediment sequences (Lake Lia, 1910 m a.s.l. and Lake Bucura, 2040 m a.s.l.) from the Retezat Mountains (South Carpathians, Romania) were analysed using multi-proxy methods to study responses of treeline, timberline and alpine/subalpine vegetation to climate change and human impact during the past 16,000 years. Woody species (Pinus mugo, Pinus cembra, Picea abies and Juniperus communis) reached Lake Lia between 12,000 and 11,800 cal. yr BP, whereas P. mugo colonised the shores of Lake Bucura at 9600 cal. yr BP. Lake Lia was in the timberline ecotone between 8000 and 3200 cal. yr BP, in semi-open P. cembra and Picea abies woodland, probably mixed with P. mugo on the steeper slopes. Lake Bucura was surrounded by the upper part of the krummholz zone during the mid-Holocene. The increase in P. cembra after c. 6000 cal. yr BP around Lake Lia suggests that the composition of the timberline forest changed. The disappearance of P. cembra and Picea abies around Lake Lia at ~3000 cal. yr BP reflects descent of the timberline. A large mean July temperature decline between 3300 and 2800 cal. yr BP may have driven or at least contributed to the descent of the Picea abies–P. cembra forests. An increase in human indicator pollen types in Lake Bucura around 4200 cal. yr BP may reflect human impact in the naturally open alpine zone in the Late Bronze Age. In contrast, human impact likely appeared considerably later, around 2650 cal. yr BP (Early Iron Age) around Lake Lia in the upper subalpine zone. Human impact likely intensified after 2200 cal. yr BP at both sites that resulted in the lowering of the krummholz zone. We conclude that climate change and human impact both played an important role in the lowering of the treeline and timberline in the late-Holocene.

Species diversity and abundance of plant-dwelling chironomids across hierarchical habitat and seasonal scales in the oxbow lakes of River Tisza, Hungary

In temperate regions, plant-dwelling chironomids can be considered as cyclic colonizers that inhabit seasonally ephemeral submerged and floating-leaved macrophytes. In this study, patterns of abundance and species richness of plant-dwelling chironomids were investigated within and among stands of three macrophyte species in oxbow lakes along the River Tisza (Hungary). Chironomids colonized macrophytes rapidly and most species occupied the habitat before it had completely developed in June. Assemblage structure and abundance of particular species varied considerably between plant species, oxbow lakes and summer months in a characteristic succession from June to August indicating the presence of dynamic selection mechanisms. Abundance of most species, except Endochironomus tendens, total chironomid abundance, within-sample and total species diversity were highest on the submerged plant Ceratophyllum demersum, and most species occurred at the beginning of the colonization succession, in June. The contribution of oxbow lakes (20.3%) and the month sampled (20.3%) to total chironomid diversity was higher than would be expected by chance alone and the contribution of within (19.7%) and between samples (13.5%) to total chironomid diversity was lower than would be expected by chance alone. We conclude that regional biodiversity conservation action plans should include multiple habitats. Moreover, the significant seasonal species turnover proved the need for seasonal sampling to assess accurately the total diversity of chironomids in the system.

A Transgenic Mouse Model for Detection of Tissue-Specific Thyroid Hormone Action

Thyroid hormone (TH) is present in the systemic circulation and thus should affect all cells similarly in the body. However, tissues have a complex machinery that allows tissue-specific optimization of local TH action that calls for the assessment of TH action in a tissue-specific manner. Here, we report the creation of a TH action indicator (THAI) mouse model to study tissue-specific TH action. The model uses a firefly luciferase reporter readout in the context of an intact transcriptional apparatus and all elements of TH metabolism and transport and signaling. The THAI mouse allows the assessment of the changes of TH signaling in tissue samples or in live animals using bioluminescence, both in hypothyroidism and hyperthyroidism. Beyond pharmacologically manipulated TH levels, the THAI mouse is sufficiently sensitive to detect deiodinase-mediated changes of TH action in the interscapular brown adipose tissue (BAT) that preserves thermal homeostasis during cold stress. The model revealed that in contrast to the cold-induced changes of TH action in the BAT, the TH action in this tissue, at room temperature, is independent of noradrenergic signaling. Our data demonstrate that the THAI mouse can also be used to test TH receptor isoform-specific TH action. Thus, THAI mouse constitutes a unique model to study tissue-specific TH action within a physiological/pathophysiological context and test the performance of thyromimetics. In conclusion, THAI mouse provides an in vivo model to assess a high degree of tissue specificity of TH signaling, allowing alteration of tissue function in health and disease, independently of changes in circulating levels of TH.

Neuronal connections of the central amygdalar nucleus with refeeding-activated brain areas in rats

Following fasting, satiety is accompanied by neuronal activation in brain areas including the central amygdalar nucleus (CEA). Since CEA is known to inhibit food intake, we hypothesized that CEA contributes to the termination of meal during refeeding. To better understand the organization of this satiety-related circuit, the interconnections of the CEA with refeeding-activated neuronal groups were elucidated using retrograde (cholera toxin-β subunit, CTB) and anterograde (phaseolus vulgaris leucoagglutinin, PHA-L) tracers in male rats. C-Fos-immunoreactivity was used as marker of neuronal activation. The refeeding-activated input of the CEA primarily originated from the paraventricular thalamic, parasubthalamic and parabrachial nuclei. Few CTB-c-Fos double-labeled neurons were detected in the prefrontal cortex, lateral hypothalamic area, nucleus of the solitary tract (NTS) and the bed nuclei of the stria terminalis (BNST). Only few refeeding-activated proopiomelanocortin-producing neurons of the arcuate nucleus projected to the CEA. Anterograde tract tracing revealed a high density of PHAL-labeled axons contacted with refeeding-activated neurons in the BNST, lateral hypothalamic area, parasubthalamic, paraventricular thalamic and parabrachial nuclei and NTS; a low density of labeled axons was found in the paraventricular hypothalamic nucleus. Chemogenetic activation of the medial CEA (CEAm) inhibited food intake during the first hour of refeeding, while activation of lateral CEA had no effect. These data demonstrate the existence of reciprocal connections between the CEA and distinct refeeding-activated hypothalamic, thalamic and brainstem nuclei, suggesting the importance of short feedback loops in the regulation of satiety and importance of the CEAm in the regulation of food intake during refeeding.

The roles of environment, site position, and seasonality in taxonomic and functional organization of chironomid assemblages in a heterogeneous wetland, Kis-Balaton (Hungary)

Environmental heterogeneity plays a determinant role in structuring taxonomic and functional composition of local assemblages via various interacting processes as synthesized in the metacommunity theory. In this study, we evaluate the relative roles of local environmental and landscape filters, spatial constraints and seasonality in organization of assemblages of Chironomidae (Diptera), a diverse aquatic insect group with winged adults, in an extremely heterogeneous wetland system, Kis-Balaton, Hungary. As expected, local environmental variables explained a substantial proportion of assemblage variance mainly along sediment structure, macrophyte coverage, and decomposing plant matter gradients. Considering the narrow spatial range of the study area, pure spatial influence was unexpectedly strong, likely because of the dispersal limitation related to tall terrestrial vegetation patches and mass effect related to the uneven distribution and area of certain microhabitats and their species pools. However, landscape- and season-related variability proved to be low or negligible. Taxonomic and functional feeding guild (FFG)-based approaches revealed the same main trends in assemblage data; however, FFGs seemed to track environmental changes more tightly. We argue for the common use of taxonomic and functional-based approaches and advise the improvement of species optima and tolerance spectra databases to expand bioassessment power.

An improved female-targeted semiochemical lure for the European Corn Borer Ostrinia nubilalis Hbn.

The addition of synthetic 4-methoxy-2-phenethyl alcohol to the known attractant phenylacetaldehyde synergized attraction of the European corn borer Ostrinia nubilalis, the blend invariably catching 3 to 5 times more than phenylacetaldehyde on its own. Highest catches were recorded by the 1:1 blend. Both females and males were attracted, supposedly in the natural sex ratio of the local population. This improved bisex O. nubilalis attractant could be more efficient and more suitable for detection and monitoring purposes than previously know lures, making possible to draw more reliable plant protection decisions.