Pan-Arctic soil moisture control on tundra carbon sequestration and plant productivity

Long-term atmospheric CO₂ concentration records have suggested a reduction in the positive effect of warming on high-latitude carbon uptake since the 1990s. A variety of mechanisms have been proposed to explain the reduced net carbon sink of northern ecosystems with increased air temperature, including water stress on vegetation and increased respiration over recent decades. However, the lack of consistent long-term carbon flux and in situ soil moisture data has severely limited our ability to identify the mechanisms responsible for the recent reduced carbon sink strength. In this study, we used a record of nearly 100 site-years of eddy covariance data from 11 continuous permafrost tundra sites distributed across the circumpolar Arctic to test the temperature (expressed as growing degree days, GDD) responses of gross primary production (GPP), net ecosystem exchange (NEE), and ecosystem respiration (ER) at different periods of the summer (early, peak, and late summer) including dominant tundra vegetation classes (graminoids and mosses, and shrubs). We further tested GPP, NEE, and ER relationships with soil moisture and vapor pressure deficit to identify potential moisture limitations on plant productivity and net carbon exchange. Our results show a decrease in GPP with rising GDD during the peak summer (July) for both vegetation classes, and a significant relationship between the peak summer GPP and soil moisture after statistically controlling for GDD in a partial correlation analysis. These results suggest that tundra ecosystems might not benefit from increased temperature as much as suggested by several terrestrial biosphere models, if decreased soil moisture limits the peak summer plant productivity, reducing the ability of these ecosystems to sequester carbon during the summer.     

Rate Equations and Product Yields of Serine Proteinase Catalysed Transfer Reactions

The steady state rate equations of transfer reactions catalysed by enzymes that follow the serine proteinase reaction mechanism in their hydrolysis reactions, have been solved and integrated. The integrated equations allow for calculations of maximal yields of product and of the time, t_max, at which that yield is present in a given reaction mixture. These important quantities have not been dealt with in previous theoretical studies of such systems.     

Recolonization following past persecution questions the importance of persistent snow cover as a range limiting factor for wolverines

Globally, climate is changing rapidly, which causes shifts in many species' distributions, stressing the need to understand their response to changing environmental conditions to inform conservation and management. Northern latitudes are expected to experience strongest changes in climate, with milder winters and decreasing snow cover. The wolverine (Gulo gulo) is a circumpolar, threatened carnivore distributed in northern tundra, boreal, and subboreal habitats. Previous studies have suggested that wolverine distribution and reproduction are constrained by a strong association with persistent spring snow cover. We assess this hypothesis by relating spatial distribution of 1589 reproductive events, a fitness-related proxy for female reproduction and survival, to snow cover over two decades. Wolverine distribution has increased and number of reproductive events increased 20 times in areas lacking spring snow cover during our study period, despite low monitoring effort where snow is sparse. Thus, the relationship between reproductive events and persistent spring snow cover weakened during this period. These findings show that wolverine reproductive success and hence distribution are less dependent on spring snow cover than expected. This has important implications for projections of future habitat availability, and thus distribution, of this threatened species. Our study also illustrates how past persecution, or other factors, that have restricted species distribution to remote areas can mask actual effects of environmental parameters, whose importance reveals when populations expand beyond previously restricted ranges. Overwhelming evidence shows that climate change is affecting many species and ecological processes, but forecasting potential consequences on a given species requires longitudinal data to revisit hypotheses and reassess the direction and magnitude of climate effects with new data. This is especially important for conservation-oriented management of species inhabiting dynamic systems where environmental factors and human activities interact, a common scenario for many species in different ecosystems around the globe.     

Local interneurons and information processing in the olfactory glomeruli of the moth Manduca sexta

Intracellular recordings were made from the major neurites of local interneurons in the moth antennal lobe. Antennal nerve stimulation evoked 3 patterns of postsynaptic activity: (i) a short-latency compound excitatory postsynaptic potential that, based on electrical stimulation of the antennal nerve and stimulation of the antenna with odors, represents a monosynaptic input from olfactory afferent axons (71 out of 86 neurons), (ii) a delayed activation of firing in response to both electrical- and odor-driven input (11 neurons), and (iii) a delayed membrane hyperpolarization in response to antennal nerve input (4 neurons).Simultaneous intracellular recordings from a local interneuron with short-latency responses and a projection (output) neuron revealed unidirectional synaptic interactions between these two cell types. In 20% of the 30 pairs studied, spontaneous and current-induced spiking activity in a local interneuron correlated with hyperpolarization and suppression of firing in a projection neuron. No evidence for recurrent or feedback inhibition of projection neurons was found. Furthermore, suppression of firing in an inhibitory local interneuron led to an increase in firing in the normally quiescent projection neuron, suggesting that a disinhibitory pathway may mediate excitation in projection neurons. This is the first direct evidence of an inhibitory role for local interneurons in olfactory information processing in insects. Through different types of multisynaptic interactions with projection neurons, local interneurons help to generate and shape the output from olfactory glomeruli in the antennal lobe.Abbreviations AL antennal lobe - EPSP excitatory postsynaptic potential - GABA -aminobutyric acid - IPSP inhibitory postsynaptic potential - LN local interneuron - MGC macroglomerular complex - OB olfactory bulb - PN projection neuron - TES N-tris[hydroxymethyl]methyl-2-aminoethane-sulfonic acid     

Environmental,geographical and time-related impacts on avian malaria infections in native and introduced populations of house sparrows (Passer domesticus), a globally invasive species

Aim

The increasing spread of vector-borne diseases has resulted in severe health concerns for humans, domestic animals and wildlife, with changes in land use and the introduction of invasive species being among the main possible causes for this increase. We explored several ecological drivers potentially affecting the local prevalence and richness of avian malaria parasite lineages in native and introduced house sparrows (Passer domesticus) populations.

Location

Global.

Time period

2002–2019.

Major taxa studied

Avian Plasmodium parasites in house sparrows.

Methods

We analysed data from 2,220 samples from 69 localities across all continents, except Antarctica. The influence of environment (urbanization index and human density), geography (altitude, latitude, hemisphere) and time (bird breeding season and years since introduction) were analysed using generalized additive mixed models (GAMMs) and random forests.

Results

Overall, 670 sparrows (30.2%) were infected with 22 Plasmodium lineages. In native populations, parasite prevalence was positively related to urbanization index, with the highest prevalence values in areas with intermediate urbanization levels. Likewise, in introduced populations, prevalence was positively associated with urbanization index; however, higher infection occurred in areas with either extreme high or low levels of urbanization. In introduced populations, the number of parasite lineages increased with altitude and with the years elapsed since the establishment of sparrows in a new locality. Here, after a decline in the number of parasite lineages in the first 30 years, an increase from 40 years onwards was detected.

Main conclusions

Urbanization was related to parasite prevalence in both native and introduced bird populations. In invaded areas, altitude and time since bird introduction were related to the number of Plasmodium lineages found to be infecting sparrows.     

Characterization of 24 porcine (dA-dC)n-(dT-dG)n microsatellites: genotyping of unrelated animals from four breeds and linkage studies

Twenty-four PCR primer pairs were designed for the detection of porcine microsatellites. Polymorphism was investigated in 76 unrelated animals from four different breeds: Duroc, Landrace, Hampshire, and Yorkshire. Compared with human microsatellites, a general lower heterozygosity was detected; however, for each microsatellite a significant variation between breeds in number of alleles and heterozygosity was seen. Mean heterozygosity was found to be significantly higher (P<0.01%) in the Yorkshire breed than in the other three breeds. Linkage analyses with the CEPH linkage packet were performed in a backcross family comprising 45 animals, of which 43 had informative meioses. Ten of the microsatellites could be assigned to six different linkage groups, demonstrating that linkage mapping with microsatellites can be carried out with great efficiency in a relatively small number of animals. Four of the linkage groups represent Chromosomes (Chrs) 4, 6, 7, and 8 respectively, while two linkage groups are unassigned.The nucleotide sequence data reported in this paper have been submitted to GenBank and have been assigned the accession numbers listed in Table 1.     

Effect of Dietary Magnesium on Post Mortem Phosphocreatine Utilization in Skeletal Muscle of Swine: A Non-Invasive Study Using 31P-NMR Spectroscopy

The effect of dietary magnesium on the post mortem PCr (phosphocreatine) decay in muscle of heterozygote malignant hyperthermia pigs was studied after in vivo exposure to a combination of halothane and succinylcholine. The pigs were anaesthetized with halothane and succinylcholine was injected in the ear vein. Immediately after initiation of the depolarizing neuromuscular blocking effect of succinylcholine the animals were captive-bolt stunned. The PCr decay, reflecting ATP turnover, was followed in situ by 31P-NMR spectroscopy in the biceps femoris muscle for the subsequent 40-70 min post mortem. In 3 of the 4 experiments, the Mg-fed pig had a significantly reduced rate of PCr hydrolysis compared to the control animal. The mechanism of this magnesium effect is unknown.     

An Epidemiologic and Economic Study of Respiratory Diseases in Two Conventional Danish Swine Herds. I: Prevalence of Respiratory Lesions at Slaughter and Their Effects on Growth

A total of 578 slaughter pigs from 2 Danish conventional farrow-to-finish operations (Herds A and B) were followed from an age of 14 days to slaughter. Pigs were weighed at 3 weeks intervals and at slaughter and an extended post mortem examination of the plucks was done. Comparison of growth rates in pigs with and without specific types of lesions by the t-test and those with multiple lesions with regression models demonstrated that Mycoplasma-like pneumonia, complicated pneumonia, anterio-ventral pleuritis, fissures and atrophic rhinitis significantly reduced mean daily gain and increased the time required to reach slaughter weight. The total impact of the lesions in Herd A was an estimated reduction in mean daily gain of 27 grams and a 2 day increase in the interval from 14 days of age until slaughter (MDG14). Decreases in MDG14 in Herd B were more substantial, 98 grams and 16.7 days. Reductions in mean daily gains during the interval from the fourth weighing until slaughter were 31 grams in Herd A and 137 grams in Herd B. Chronic dorso-caudal and parietal pleuritis, without other lesions present, had no significant adverse effects on growth rates in either herd. Interactions between lesions did not significantly alter the estimates. The R2 values obtained for the regression models showed that the presence, absence or extent of lesions at slaughter explained only 13-27% of the variations in growth rates in the 2 herds.