Urban abiotic stressors drive changes in the foraging activity and colony growth of the black garden ant Lasius niger.

Changes in habitat characteristics are known to have profound effects on biotic communities and their functional traits. In the context of an urban-rural gradient, urbanisation drastically alters abiotic characteristics, e.g., by increasing environmental temperatures and through light pollution. These abiotic changes significantly impact the functional traits of organisms, particularly insects. Furthermore, changes in habitat characteristics also drive changes in the behavioural traits of animals, allowing them to adapt and thrive in new environments. In our study, we focused on the synanthropic ant species Lasius niger as a model organism. We conducted nocturnal field observations and complemented them with laboratory experiments to investigate the influence of night warming (NW) associated with Urban Heat Islands (UHI), light pollution (ALAN), and habitat type on ant foraging behaviour. In addition, we investigated the influence of elevated temperatures on brood development and worker mortality. Our findings revealed that urban populations of L. niger were generally more active during the night compared to their rural counterparts, although the magnitude of this difference varied with specific city characteristics. In laboratory settings, higher temperatures and continuous illumination were associated with increased activity level in ants, again differing between urban and rural populations. Rural ants exhibited more locomotion compared to their urban counterparts when maintained under identical conditions, which might enable them to forage more effectively in a potentially more challenging environment. High temperatures decreased the developmental time of brood from both habitat types and increased worker mortality, although rural colonies were more strongly affected. Overall, our study provides novel insights into the influence of urban environmental stressors on the foraging activity pattern and colony development of ants. Such stressors can be important for the establishment and spread of synanthropic ant species, including invasive ones, and the biotic homogenization of anthropogenic ecosystems.

Role of vibrational properties and electron-phonon coupling on thermal transport across metal-dielectric interfaces with ultrathin metallic interlayers.

We systematically analyze the influence of 5 nm thick metal interlayers inserted at the interface of several sets of different metal-dielectric systems to determine the parameters that most influence interface transport. Our results show that despite the similar Debye temperatures of Al2O3and AlN substrates, the thermal boundary conductance measured for the Au/Al2O3system with Ni and Cr interlayers is ∼2× and >3× higher than the corresponding Au/AlN system, respectively. We also show that for crystalline SiO2(quartz) and Al2O3substrates having highly dissimilar Debye temperature, the measured thermal boundary conductance between Al/Al2O3and Al/SiO2are similar in the presence of Ni and Cr interlayers. We suggest that comparing the maximum phonon frequency of the acoustic branches is a better parameter than the Debye temperature to predict the change in the thermal boundary conductance. We show that the electron-phonon coupling of the metallic interlayers also alters the heat transport pathways in a metal-dielectric system in a nontrivial way. Typically, interlayers with large electron-phonon coupling strength can increase the thermal boundary conductance by dragging electrons and phonons into equilibrium quickly. However, our results show that a Ta interlayer, having a high electron-phonon coupling, shows a low thermal boundary conductance due to the poor phonon frequency overlap with the top Al layer. Our experimental work can be interpreted in the context of diffuse mismatch theory and can guide the selection of materials for thermal interface engineering.

Investigation of Feshbach resonances in ultracold 40K spin mixtures.

Magnetically tunable Feshbach resonances are an indispensable tool for experiments with atomic quantum gases. We report on 37 thus far unpublished Feshbach resonances and four further probable Feshbach resonances in spin mixtures of ultracold fermionic 40K with temperatures well below 100 nK. In particular, we locate a broad resonance at B = 389.7G with a magnetic width of 26.7 G. Here 1 G = 10-4 T. Furthermore, by exciting low-energy spin waves, we demonstrate a means to precisely determine the zero crossing of the scattering length for this broad Feshbach resonance. Our findings allow for further tunability in experiments with ultracold 40K quantum gases.

The role of mode match in fiber cavities.

We study and realize asymmetric fiber-based cavities with optimized mode match to achieve high reflectivity on resonance. This is especially important for mutually coupling two physical systems via light fields, e.g., in quantum hybrid systems. Our detailed theoretical and experimental analysis reveals that on resonance, the interference effect between the directly reflected non-modematched light and the light leaking back out of the cavity can lead to large unexpected losses due to the mode filtering of the incoupling fiber. Strong restrictions for the cavity design result out of this effect and we show that planar-concave cavities are clearly best suited. We validate our analytical model using numerical calculations and demonstrate an experimental realization of an asymmetric fiber Fabry-Pérot cavity with optimized parameters.

Intrinsic survival advantage of social insect queens depends on reproductive activation.

The central trade-off between reproduction and longevity dominates most species' life history. However, no mortality cost of reproduction is apparent in eusocial species, particularly social insects in the order Hymenoptera: one or a few individuals (typically referred to as queens) in a group specialize on reproduction and are generally longer lived than all other group members (typically referred to as workers), despite having the same genome. However, it is unclear whether this survival advantage is due to social facilitation by the group or an intrinsic, individual property. Furthermore, it is unknown whether the correlation between reproduction and longevity is due to a direct mechanistic link or an indirect consequence of the social role of the reproductives. To begin addressing these questions, we performed a comparison of queen and worker longevity in the ant Cardiocondyla obscurior under social isolation conditions. Survival of single queens and workers was compared under laboratory conditions, monitoring and controlling for brood production. Our results indicate that there is no intrinsic survival advantage of queens relative to workers unless individuals are becoming reproductively active. This interactive effect of caste and reproduction on life expectancy outside of the normal social context suggests that the positive correlation between reproduction and longevity in social insect queens is due to a direct link that can activate intrinsic survival mechanisms to ensure queen longevity.

Mating with an allopatric male triggers immune response and decreases longevity of ant queens.

In species with lifelong pair bonding, the reproductive interests of the mating partners are aligned, and males and females are expected to jointly maximize their reproductive success. Mating increases both longevity and fecundity of female reproductives (queens) of the ant Cardiocondyla obscurior, indicating a tight co-evolution of mating partners. Here, we show that mating with a male from their own population increases lifespan and reproductive success of queens more than mating with a male from a different population, with whom they could not co-evolve. A comparison of transcriptomes revealed an increased expression of genes involved in immunity processes in queens, which mated with males from a different population. Increased immune response might be proximately associated with decreased lifespan. Our study suggests a synergistic co-evolution between the sexes and sheds light on the proximate mechanisms underlying the decreased fitness of allopatrically mated queens.

Soil biota effects on local abundances of three grass species along a land-use gradient.

Biotic plant-soil interactions and land-use intensity are known to affect plant individual fitness as well as competitiveness and therefore plant-species abundances in communities. Therefore, a link between soil biota and land-use intensity on local abundance of plant species in grasslands can be expected. In two greenhouse experiments, we investigated the effects of soil biota from grassland sites differing in land-use intensity on three grass species that vary in local abundances along this land-use gradient. We were interested in those soil-biota effects that are associated with land-use intensity, and whether these effects act directly or indirectly. Therefore, we grew the three plant species in two separate experiments as single individuals and in mixtures and compared their performance. As single plants, all three grasses showed a similar performance with and without soil biota. In contrast, in mixtures growth of the species in response to the presence or absence of soil biota differed. This resulted in different soil-biota effects that tend to correspond with patterns of species-specific abundances in the field for two of the three species tested. Our results highlight the importance of indirect interactions between plants and soil microorganisms and suggest that combined effects of soil biota and plant-plant interactions are involved in structuring plant communities. In conclusion, our experiments suggest that soil biota may have the potential to alter effects of plant-plant interactions and therefore influence plant-species abundances and diversity in grasslands.

Giant spin oscillations in an ultracold Fermi sea.

Collective behavior in many-body systems is the origin of many fascinating phenomena in nature, ranging from the formation of clouds to magnetic properties of solids. We report on the observation of collective spin dynamics in an ultracold Fermi sea with large spin. As a key result, we observed long-lived and large-amplitude coherent spin oscillations driven by local spin interactions. At ultralow temperatures, Pauli blocking stabilizes the collective behavior, and the Fermi sea behaves as a single entity in spin space. With increasing temperature, we observed a stronger damping associated with particle-hole excitations. Unexpectedly, we found a high-density regime where excited spin configurations are collisionally stabilized. Our results reveal the intriguing interplay between microscopic processes either stimulating or suppressing collective effects in a fermionic many-body system.

Engineering spin waves in a high-spin ultracold Fermi gas.

We report on the detailed study of multicomponent spin waves in an s=3/2 Fermi gas where the high spin leads to novel tensorial degrees of freedom compared to s=1/2 systems. The excitations of a spin-nematic state are investigated from the linear to the nonlinear regime, where the tensorial character is particularly pronounced. By tuning the initial state we engineer the tensorial spin-wave character, such that the magnitude and the sign of the counterflow spin currents are effectively controlled. A comparison of our data with numerical and analytical results shows good agreement.

Intrinsic photoconductivity of ultracold fermions in optical lattices.

We report on the experimental observation of an analog to a persistent alternating photocurrent in an ultracold gas of fermionic atoms in an optical lattice. The dynamics is induced and sustained by an external harmonic confinement. While particles in the excited band exhibit long-lived oscillations with a momentum-dependent frequency, a strikingly different behavior is observed for holes in the lowest band. An initial fast collapse is followed by subsequent periodic revivals. Both observations are fully explained by mapping the system onto a nonlinear pendulum.

Sex at the margins: parthenogenesis vs. facultative and obligate sex in a Neotropical ant.

Geographic parthenogenesis is a distribution pattern, in which parthenogenetic populations tend to live in marginal habitats, at higher latitudes and altitudes and island-like habitats compared with the sexual forms. The facultatively parthenogenetic ant Platythyrea punctata is thought to exhibit this general pattern throughout its wide range in Central America and the Caribbean Islands. Workers of P. punctata from the Caribbean produce diploid female offspring from unfertilized eggs by thelytokous parthenogenesis, and mated females and males are rare. In contrast, workers in one colony from Costa Rica were incapable of thelytoky; instead mated workers produced all female offspring. Because sample sizes were very low in former studies, we here use microsatellite markers and explicit tests of thelytoky to examine the population genetic structure of ancestral and derived populations of P. punctata throughout the Caribbean and Central America. Populations from the Caribbean islands were fully capable of parthenogenesis, and population genetic signatures indicate that this is the predominant mode of reproduction, although males are occasionally produced. In contrast, the northernmost population on the mainland (Texas) showed signatures of sexual reproduction, and individuals were incapable of reproduction by thelytoky. Contrary to expectations from a geographic parthenogenesis distribution pattern, most parts of the mainland populations were found to be facultatively thelytokous, with population genetic signatures of both sexual and parthenogenetic reproduction.

Multiband spectroscopy of ultracold fermions: observation of reduced tunneling in attractive Bose-Fermi mixtures.

We perform a detailed experimental study of the band excitations and tunneling properties of ultracold fermions in optical lattices. Employing a novel multiband spectroscopy for fermionic atoms, we can measure the full band structure and tunneling energy with high accuracy. In an attractive Bose-Fermi mixture we observe a significant reduction of the fermionic tunneling energy, which depends on the relative atom numbers. We attribute this to an interaction-induced increase of the lattice depth due to the self-trapping of the atoms.

In vitro influence of D/L-lactic acid, sodium chloride and sodium nitrite on the infectivity of feline calicivirus and of ECHO virus as potential surrogates for foodborne viruses.

The importance of foodborne viruses is increasingly recognized. Thus, the effect of commonly used food preservation methods on the infectivity of viruses is questioned. In this context, we investigated the antiviral properties of D,L-lactic acid, sodium chloride and sodium nitrite by in vitro studies. Two model viruses, Feline Calicivirus (FCV) and Enteric Cytophatic Human Orphan (ECHO) virus, were chosen for this study simulating important foodborne viruses (human noroviruses (NoV) and human enteroviruses, resp.). The model viruses were exposed to different solutions of D,L-lactic acid (0.1-0.4% w/w, pH 6.0-3.2), of sodium chloride (2-20%, w/v) and of sodium nitrite (100, 150 and 200 ppm) at 4 and 20 °C for a maximum of 7 days. Different results were obtained for the two viruses. ECHO virus was highly stable against D,L-lactic acid and sodium chloride when tested under all conditions. On the contrary, FCV showed less stability but was not effectively inactivated when exposed to low acid and high salt conditions at refrigeration temperatures (4 °C). FCV titers decreased more markedly at 20 °C than 4 °C in all experiments. Sodium nitrite did not show any effect on the inactivation of both viruses. The results indicate that acidification, salting or curing maybe insufficient for effective inactivation of foodborne viruses such as NoV or human enteroviruses during food processing. Thus, application of higher temperature during fermentation and ripening processes maybe more effective toward the inactivation kinetics of less stable viruses. Nevertheless, more studies are needed to examine the antiviral properties of these preserving agents on virus survival and inactivation kinetics in the complex food matrix.

Social influence on age and reproduction: reduced lifespan and fecundity in multi-queen ant colonies.

Evolutionary theories of ageing predict that life span increases with decreasing extrinsic mortality, and life span variation among queens in ant species seems to corroborate this prediction: queens, which are the only reproductive in a colony, live much longer than queens in multi-queen colonies. The latter often inhabit ephemeral nest sites and accordingly are assumed to experience a higher mortality risk. Yet, all prior studies compared queens from different single- and multi-queen species. Here, we demonstrate an effect of queen number on longevity and fecundity within a single, socially plastic species, where queens experience the similar level of extrinsic mortality. Queens from single- and two-queen colonies had significantly longer lifespan and higher fecundity than queens living in associations of eight queens. As queens also differ neither in morphology nor the mode of colony foundation, our study shows that the social environment itself strongly affects ageing rate.

Influence of the polymerization potential on the transport properties of polypyrrole films.

Polypyrrole films have been prepared by potentiostatic electrochemical polymerization at low temperatures. The cyclic voltammograms and the electronic transport properties of the films are investigated as a function of the polymerization potential. As the potential increases from 520 mV to 1.2 V, the oxidation peak moves to larger voltages, while above 1.2 V, the peak voltage drops again. The film conductivity drops monotonously as the polymerization potential is increased. However, the localization length of the current-carrying states, which characterizes the temperature dependence of the conductivity, correlates with the oxidation peak and shows a minimum for films polymerized at 1.2 V. Furthermore, we show that, with an independent doping step after polymerization, the conductivity of the films can be increased by up to 50%. A maximum conductivity of 1360 S/cm has been observed.

Honest and dishonest communication in social Hymenoptera.

Communication in social insects usually serves the good of the whole society and thus increases the inclusive fitness of all individuals. Hence, cheating and dishonesty are not expected when nestmates are to be alarmed or recruited to food sources. However, kin selection predicts a conflict of interest among individuals about the partitioning of reproduction. Dishonest communication may then be advantageous. Workers usually do not lay eggs in the presence of a fertile queen, but in many species they do so when the queen is removed. This effect has been explained by manipulative, i.e. dishonest, queen control or honest fertility signalling. Numerous studies have documented qualitative and quantitative differences in the pheromone blends of reproductives and non-reproductives. We examine these data for signs of honest signalling, conflict and manipulation.

Hierarchy length in orphaned colonies of the ant Temnothorax nylanderi.

Workers of the ant Temnothorax nylanderi form dominance orders in orphaned colonies in which only one or a few top-ranking workers begin to produce males from unfertilized eggs. Between one and 11 individuals initiated 80% of all aggression in 14 queenless colonies. As predicted from inclusive fitness models (Molet M, van Baalen M, Monnin T, Insectes Soc 52:247-256, 2005), hierarchy length was found to first increase with colony size and then to level off at larger worker numbers. The frequency and skew of aggression decreased with increasing size, indicating that rank orders are less pronounced in larger colonies.

SECM characterization of immobilised enzymes by self-assembled monolayers on titanium dioxide surfaces.

SECM in generator-collector mode was used to detect the presence of immobilised enzymes on titanium dioxide layers which were chemically or electrochemically generated with possible application as chemical sensors and biosensors. Glucose oxidase (GOx) and horseradish peroxidase (HRP) were immobilised by SAM generation using aminopropyltriethoxysilane (APTES) and ascorbic acid. The enzymes were successfully immobilised on two different TiO(2) surfaces. A simple test of durability of the system was made and a model of SAM organisation is presented.

Polygyny and polyandry in small ant societies.

Social insects, ants in particular, show considerable variation in queen number and mating frequency resulting in a wide range of social structures. The dynamics of reproductive conflicts in insect societies are directly connected to the colony kin structure, thus, the study of relatedness patterns is essential in order to understand the evolutionary resolution of these conflicts. We studied colony kin structure and mating frequencies in two closely related Neotropical ant species Pachycondyla inversa and Pachycondyla villosa. These represent interesting model systems because queens found new colonies cooperatively but, unlike many other ant species, they may still co-exist when the colony becomes mature (primary polygyny). By using five specific and highly variable microsatellite markers, we show that in both species queens usually mate with two or more males and that cofounding queens are always unrelated. Polygynous and polyandrous colonies are characterized by a high genetic diversity, with a mean relatedness coefficient among worker nestmates of 0.27 (+/- 0.03 SE) for P. inversa and 0.31 (+/- 0.05 SE) for P. villosa. However, relatedness among workers of the same matriline is high (0.60 +/- 0.03 in P. inversa, 0.62 +/- 0.08 in P. villosa) since males that mated with the same queen are on average closely related. Hence, we have found a new taxon in social Hymenoptera with high queen-mating frequencies and with intriguing mating and dispersal patterns of the sexuals.