Sensitivity of Pagurus bernhardus (L.) to substrate-borne vibration and anthropogenic noise

© 2015 Elsevier B.V. Despite the prevalence of vibration produced by anthropogenic activities impacting the seabed there are few data and little information as to whether these are detected by crustaceans and whether they interfere with their behaviour. Here the sensitivity of unconditioned Pagurus bernhardus to substrate-borne vibration was quantified by exposure to sinusoidal vibrations of 5-410Hz of varied amplitudes using the staircase method of threshold determination, with threshold representing the detection of the response and two behavioural responses used as reception indicators: movement of the second antenna and onset or cessation of locomotion. Thresholds were compared to measured vibrations close to anthropogenic operations and to the time in captivity prior to tests. Behaviour varied according to the strength of the stimulus with a significant difference in average threshold values between the two behavioural indicators, although there was an overlap between the two, with overall sensitivity ranging from 0.09-0.44ms -2 (root mean squared, RMS). Crabs of shortest duration in captivity prior to tests had significantly greater sensitivity to vibration, down to 0.02ms -2 (RMS). The sensitivity of P. bernhardus fell well within the range of vibrations measured near anthropogenic operations. The data indicate that anthropogenic substrate-borne vibrations have a clear effect on the behaviour of a common marine crustacean. The study emphasises that these vibrations are an important component of noise pollution that requires further attention to understand the long term effects on marine crustaceans

Modelling elements of microstructure in olivine

To solve problems in the Earth and planetary sciences ranging from mantle convection and plate tectonics, magma dynamics, glacial-isostatic adjustment, post-seismic creep, seismic attenuation, and tidal dissipation, we require a deep understanding of the rheological, seismic, and chemical properties of silicate materials. Elements of microstructure, such as grain size and dislocation density, exert a strong control on these properties. In this thesis, I apply novel approaches to modelling the time evolution of these quantities. I begin by examining grain-size evolution in the regime of normal grain growth, which is driven by surface energy reduction. I extend the canonical model of normal grain growth by limiting the interactions of a grain to its neighbourhood. In this extended model, heterogeneity in the local environments of grains is accounted for using a stochastic process. The model predicts the existence of a normal grain growth regime that evolves according to accepted grain-growth kinetics. Moreover, this regime is characterised by a grain-size distribution that agrees with observed distributions, in direct contrast to the distribution predicted by the canonical model. I then examine dislocation-density evolution. I construct a new theory of the physical processes affecting dislocations: storage and recovery. The evolution of dislocation density is fundamentally connected to intracrystalline plastic deformation, and thus also makes predictions about viscosity. We calibrate our theoretical framework for olivine using data from steady-state deformation experiments. This model explains the empirical relationships among strain rate, applied stress, and dislocation density in disparate laboratory regimes. Indeed, it predicts the previously unexplained dependence of dislocation density on applied stress in olivine. The predictions of our model for geological conditions differ from direct extrapolations from experimental data. For example, the calibrated model predicts rapid, transient deformation in the upper mantle, consistent with recent measurements of post-glacial rebound. The calibrated model of dislocation-density evolution sets out the hypothesis that dislocation recovery in olivine is controlled by pipe diffusion. This assumption is in direct contrast with previous work, which has assumed that dislocation recovery in olivine is controlled by lattice diffusion instead. The recovery process can be inferred from annealing experiments that track the decrease in dislocation density with time. Through statistical analysis of data from new annealing experiments, combined with previously published data from the literature, I determine that the dominant dislocation recovery process in olivine is likely controlled by pipe diffusion

Daily activity rhythms, chronotypes, and risk-taking behavior in the signal crayfish

Consistent inter-individual differences in daily activity rhythms (i.e., chronotypes) can have ecological consequences in determining access to food resources and avoidance of predators. The most common measure to characterize chronotypes in animals as well as humans is the onset of activity (i.e., early or late chronotypes). However, daily activity rhythms may also differ in the relative amount of activity displayed at particular time periods. Moreover, chronotypes may also be linked to other consistent inter-individual differences in behavior (i.e., personality), such as the propensity to take risks. Here, we used the signal crayfish Pacifastacus leniusculus to test the presence of chronotypes and risk-taking personality traits and a potential behavioral syndrome between these traits. We first exposed crayfish to 5 days of light–darkness to measure daily activity rhythms and then we applied a visual predator-simulating stimulus in 2 different contexts (neutral and food). Our results showed consistent (i.e., across 5 days) inter-individual differences in the relative nocturnal activity displayed in the early and middle, but not in the late part of darkness hours. Moreover, while crayfish displayed inter-individual differences in risk-taking behavior, these were not found to be consistent across 2 contexts. Therefore, we were not able to formally test a behavioral syndrome between these 2 traits. In conclusion, our study provides the first evidence of chronotypes in the relative amount of activity displayed at particular time periods. This could be a valuable information for applied ecological aspects related to the signal crayfish, which is a major invasive species of freshwater ecosystems

To signal or not to signal? Chemical communication by urine-borne signals mirrors sexual conflict in crayfish

Background: Sexual selection theory predicts that females, being the limiting sex, invest less in courtship signals than males. However, when chemical signals are involved it is often the female that initiates mating by producing stimuli that inform about sex and/or receptivity. This apparent contradiction has been discussed in the literature as 'the female pheromone fallacy'. Because the release of chemical stimuli may not have evolved to elicit the male's courtship response, whether these female stimuli represent signals remains an open question. Using techniques to visualise and block release of urine, we studied the role of urine signals during fighting and mating interactions of crayfish (Pacifastacus leniusculus). Test individuals were blindfolded to exclude visual disturbance from dye release and artificial urine introduction. Results: Staged female-male pairings during the reproductive season often resulted in male mating attempts. Blocking female urine release in such pairings prevented any male courtship behaviour. Artificial introduction of female urine re-established male mating attempts. Urine visualisation showed that female urine release coincides with aggressive behaviours but not with female submissive behaviour in reproductive interactions as well as in intersexual and intrasexual fights. In reproductive interactions, females predominately released urine during precopulatory aggression; males subsequently released significantly less urine during mating than in fights. Conclusions: Urine-blocking experiments demonstrate that female urine contains sex-specific components that elicit male mating behaviour. The coincidence of chemical signalling and aggressive behaviour in both females and males suggests that urine release has evolved as an aggressive signal in both sexes of crayfish. By limiting urine release to aggressive behaviours in reproductive interactions females challenge their potential mating partners at the same time as they trigger a sexual response. These double messages should favour stronger males that are able to overcome the resistance of the female. We conclude that the difference between the sexes in disclosing urine-borne information reflects their conflicting interests in reproduction. Males discontinue aggressive urine signalling in order to increase their chances of mating. Females resume urine signalling in connection with aggressive behaviour, potentially repelling low quality or sexually inactive males while favouring reproduction with high quality males

The role of grain-environment heterogeneity in normal grain growth: a stochastic approach

The size distribution of grains is a fundamental characteristic of polycrystalline solids. In the absence of deformation, the grain-size distribution is controlled by normal grain growth. The canonical model of normal grain growth, developed by Hillert, predicts a grain-size distribution that bears a systematic discrepancy with observed distributions. To address this, we propose a change to the Hillert model that accounts for the influence of heterogeneity in the local environment of grains. In our model, each grain evolves in response to its own local environment of neighbouring grains, rather than to the global population of grains. The local environment of each grain evolves according to an Ornstein-Uhlenbeck stochastic process. Our results are consistent with accepted grain-growth kinetics. Crucially, our model indicates that the size of relatively large grains evolves as a random walk due to the inherent variability in their local environments. This leads to a broader grain-size distribution than the Hillert model and indicates that heterogeneity has a critical influence on the evolution of microstructure.Comment: 24 pages, 8 figures, to be published in Acta Materiali

Hybrid sideways/longitudinal swimming in the monoflagellate Shewanella oneidensis: from aerotactic band to biofilm

Shewanella oneidensis MR-1 are facultative aerobic electroactive bacteria, with an appealing potential for sustainable energy production and bioremediation. They gather around air sources, forming aerotactic bands and biofilms. Though accumulation is crucial to technological exploitation, their collective behaviour remains poorly reported. Here we establish a comprehensive framework for the study of aerotaxis, unveiling a novel hybrid locomotion pattern. Despite having only one flagellum, MR-1 combine motility features of mono- and multiflagellate bacteria, alternating longitudinal fast and sideways slow swimming. The adaptive tuning of the resulting bimodal velocity distributions fulfils different biological functions, such as aerotaxis and confinement. Overall, we reveal the mechanisms underlying the aerotactic collective behaviour of MR-1, in the process leading from accumulation to biofilm formatio

Dislocation theory of steady and transient creep of crystalline solids: predictions for olivine

Significance Many important deformation processes take place at strain rates that are too slow to be investigated experimentally. For example, strain rates in Earth’s mantle are typically ten orders of magnitude slower than in the laboratory. To bridge this gap, empirical relationships are extrapolated with large epistemic uncertainties. We propose a model for deformation derived from the microphysics of deformation. In application to olivine, the main mineral of Earth’s upper mantle, this model explains the scaling relationships observed under a range of laboratory conditions. In extrapolation to Earth’s mantle, the model predicts a transition in the dominant microphysical processes, leading to predictions distinct from previous studies. For instance, following abrupt stress changes, it predicts rapid transient deformation. Abstract In applications critical to the geological, materials, and engineering sciences, deformation occurs at strain rates too small to be accessible experimentally. Instead, extrapolations of empirical relationships are used, leading to epistemic uncertainties in predictions. To address these problems, we construct a theory of the fundamental processes affecting dislocations: storage and recovery. We then validate our theory for olivine deformation. This model explains the empirical relationships among strain rate, applied stress, and dislocation density in disparate laboratory regimes. It predicts the previously unexplained dependence of dislocation density on applied stress in olivine. The predictions of our model for Earth conditions differ from extrapolated empirical relationships. For example, it predicts rapid, transient deformation in the upper mantle, consistent with recent measurements of postseismic creep

Fighting over burrows : the emergence of dominance hierarchies in the Norway lobster (Nephrops norvegicus)

Animals fight over resources such as mating partners, territory, food or shelter and repeated contests lead to stable social hierarchies in different phyla. The group dynamics of hierarchy formation are not characterized in the Norway lobsters (Nephrops norvegicus). Lobsters spend most of the day in burrows and forage outside of them according to a diel (i.e. 24-h based) activity rhythm. Here, we use a linear and generalized mixed model approach to analyse, in 7 groups of 4 male lobsters, the formation of dominance hierarchies and rank related changes in burrowing behaviour. We show that hierarchies emerge within 1 to 3 days and increase in steepness over a period of 5 days, while rank changes and number of fights gradually decrease over a 5 day period. The rank position determined by open area fights predicts the outcome of fights over burrows, the time spent in burrows, and the locomotor activity levels. Dominant lobsters are more likely to evict subordinate lobsters from their burrows and more successful in defending their own burrows. They spend more time in burrows and display lower levels of locomotor activity outside the burrow. Lobsters do not change their diel activity rhythms as a result of a change in rank, and all tested individuals showed higher activity at night and dusk compared to dawn and day. We discuss how behavioural changes in burrowing behaviour could lead to rank related benefits such a reduced exposure to predators and energy savings

Intangible capital indicators based on web scraping of social media

Knowledge-based capital is a key factor for productivity growth. Over the past 15 years, it has been increasingly recognised that knowledge-based capital comprises much more than technological knowledge and that these other components are essentia for understanding productivity developments and competitiveness of both firms and economies. We develop selected indicators for knowledge-based capital,often denoted as intangible capital, on the basis of publicly available data from online platforms.These indicators based on data from Facebook and the employer branding and review platform Kununu are compared by OLS regressions with firm-level survey data from the Mannheim Innovation Panel (MIP). All regressions show a positive and significant relationship between survey-based firm-level expenditures for marketing and on-the-job training and the respective information stemming from the online platforms. We therefore explore the possibility of predicting brand equity and firm-specific human capital with machine learning methods

Mate choise in homarid lobsters, will they recognise their own species?

As European and American lobsters are so similar that it is difficult to spot the difference, and as they have so many similarities in behaviour and life history, this study was initiated to test if they could make distinctions between the species when coexcisting. Female European lobsters, close to moulting/spawning, were released in a tank with one European and one American male in a tank with two shelters available. The American and European males were dominant in half of the trials. Registrations were made of which lobsters where fighting, visiting another lobster, cohabitating and mating. Dominance had no importance. The European lobsters chose to interact more and for longer duration of time with each other. Mating, mating attempts and peaceful cohabitation occurred only between these lobsters. The American lobsters showed less social activity. It seems like it is a barrier between the species, where species-specific chemical communication probably is of importance. NORSK SAMMENDRAG: Siden europeisk og amerikansk hummer er så like at det er vanskelig å se forskjell, og de samtidig har tilsynelatende lik atferd og livshistorie, så ble det undersøkt hvorvidt hummeren selv kunne skille på art. Hunnhummer som ble vurdert til å være nær skallskifte/gyting ble introdusert til en europeisk og en amerikansk hann i et felleskar med to skjul. Den dominerende hannen var like ofte en amerikaner som en europeer, for å se om art eller dominans var viktig. Det ble registrert hvilke hummere som slåss, besøkte hverandre, delte skjul og parret seg. Dominans viste seg å være uten betydning. De europeiske hummerne fant fram til hverandre og brukte mest tid uansett aktivitet på hverandre. Parring og parringsforsøk forekom kun mellom europeisk hummer, i likhet med fredelig deling av skjul. Amerikansk hummer var gjennomgående mindre sosialt aktiv. Det ser ut til å være en barriere mellom artene, der artsforskjeller i kjemisk kommunikasjon trolig er til stede