Thermoregulatory morphodynamics of honeybee swarm clusters

During reproductive swarming, honeybees clusters of more than 10,000 individuals that hang from structures in the environment (e.g., tree branches) are exposed to diurnal variations in ambient temperature for up to a week. Swarm clusters collectively modulate their morphology in response to these variations (i.e., expanding/contracting in response to heating/cooling) to maintain their internal temperature within a tolerable range and to avoid exhausting their honey stores prematurely. To understand the spatiotemporal aspects of thermoregulatory morphing, we measured the change in size, shape and internal temperature profiles of swarm clusters in response to dynamic temperature ramp perturbations. We see that swarm clusters show a two-fold variation in their volume/density when heated from 15°C to 30°C. However, they do not reach an equilibrium size or shape when held at 30°C for 5 hours, long after the core temperature of the cluster has stabilized. Furthermore, the changes in cluster shape and size are hysteretic, contracting in response to cooling faster than expanding in response to heating. Although the base contact diameter of the cluster increased continuously when the swarm is heated, the change in length of the swarm (base totip) over time is non-monotonic. Consequently, the aspect ratio of the swarm fluctuated continuously even when held at a constant temperature. Taken together, our results quantify the hysteretic and anisotropic morphological responses of swarm clusters to ambient temperature variations while suggesting that both mechanical constraints and heat transfer govern their thermoregulatory morphodynamics.

DNA self-organization controls valence in programmable colloid design

Just like atoms combine into molecules, colloids can self-organize into predetermined structures according to a set of design principles. Controlling valence—the number of interparticle bonds—is a prerequisite for the assembly of complex architectures. The assembly can be directed via solid “patchy” particles with prescribed geometries to make, for example, a colloidal diamond. We demonstrate here that the nanoscale ordering of individual molecular linkers can combine to program the structure of microscale assemblies. Specifically, we experimentally show that covering initially isotropic microdroplets with N mobile DNA linkers results in spontaneous and reversible self-organization of the DNA into Z(N) binding patches, selecting a predictable valence. We understand this valence thermodynamically, deriving a free energy functional for droplet–droplet adhesion that accurately predicts the equilibrium size of and molecular organization within patches, as well as the observed valence transitions with N. Thus, microscopic self-organization can be programmed by choosing the molecular properties and concentration of binders. These results are widely applicable to the assembly of any particle with mobile linkers, such as functionalized liposomes or protein interactions in cell–cell adhesion.

Thermoregulatory morphodynamics of honeybee clusters

During reproductive swarming, honeybees form clusters of more than 10,000 bees that hang from structures in the environment (e.g., tree branches) and are exposed to diurnal variations in ambient temperature for up to one week during the search for a new nesting site. Swarm clusters collectively modulate their morphology in response to these variations (i.e., expanding/contracting in response to heating/cooling) to maintain their internal temperature within a tolerable range and to avoid exhausting their honey stores prematurely. To understand the spatiotemporal aspects of thermoregulatory morphing, we measured the change in size and shape of swarm clusters over time and the internal temperature profiles in response to dynamic temperature ramp perturbations. We found that swarm clusters can achieve a twofold increase/decrease their volume/density when heated from 15°C to 30°C, but they do not reach an equilibrium size or shape when held at 30°C for 5 hours, long after the core temperature of the cluster has stabilized. Furthermore, the changes in cluster shape and size are hysteretic, contracting in response to cooling faster than expanding in response to heating. Although the contact diameter of the cluster increased continuously when the swarm is heated, the change in length of the swarm (base to tip) over time is non-monotonic. Consequently, the aspect ratio of the swarm fluctuated continuously even when held at a constant temperature. Taken together, our results quantify the hysteretic and anisotropic morphological responses of swarm clusters to ambient temperature variations while suggesting that both mechanical constraints and heat transfer govern the thermoregulatory morphing dynamics of swarm clusters.

Stage-specific overcompensation, the hydra effect, and the failure to eradicate an invasive predator

As biological invasions continue to increase globally, eradication programs have been undertaken at significant cost, often without consideration of relevant ecological theory. Theoretical fisheries models have shown that harvest can actually increase the equilibrium size of a population, and uncontrolled studies and anecdotal reports have documented population increases in response to invasive species removal (akin to fisheries harvest). Both findings may be driven by high levels of juvenile survival associated with low adult abundance, often referred to as overcompensation. Here we show that in a coastal marine ecosystem, an eradication program resulted in stage-specific overcompensation and a 30-fold, single-year increase in the population of an introduced predator. Data collected concurrently from four adjacent regional bays without eradication efforts showed no similar population increase, indicating a local and not a regional increase. Specifically, the eradication program had inadvertently reduced the control of recruitment by adults via cannibalism, thereby facilitating the population explosion. Mesocosm experiments confirmed that adult cannibalism of recruits was size-dependent and could control recruitment. Genomic data show substantial isolation of this population and implicate internal population dynamics for the increase, rather than recruitment from other locations. More broadly, this controlled experimental demonstration of stage-specific overcompensation in an aquatic system provides an important cautionary message for eradication efforts of species with limited connectivity and similar life histories.

Simulating the contribution of the Antarctic ice sheet to Miocene benthic δ18O variability

<p>Large benthic δ<sup>18</sup>O fluctuations, which are caused by deep-ocean temperature and ice-volume changes, are shown on multiple time scales during the early to mid-Miocene (23-14 Myr ago). To understand how these signals are related to orbital changes, it is necessary to disentangle them. Here, we approach this problem by simulating how the Antarctic ice sheet (AIS) responds to typical CO<sub>2</sub> changes during this period. We use the 3D thermodynamical model PISM, forced by climate model output, to conduct both transient and steady-state experiments. Our results indicate that even if equilibrium differences are relatively large (~40 m.s.l.e.), transient AIS variability on orbital time scales (20-400 kyr) still has a much smaller amplitude due to the slow ice-volume response to climatic changes. We analyse our results further using a conceptual model, based on the notion that at any CO<sub>2</sub> level an ice sheet will grow (shrink) by a specific rate towards its smaller (larger) equilibrium size. We show that phases of concurrent ice volume increase and rising CO<sub>2</sub> levels are possible, even though the equilibrium ice volume decreases monotonically with CO<sub>2</sub>. When the AIS volume is out of equilibrium with the forcing climate, the ice sheet can still be adapting to a relatively large equilibrium size, although CO<sub>2</sub> is rising after a phase of decrease. A delayed response of Antarctic ice volume to in-sync solar insolation and CO<sub>2</sub> changes can cause discrepancies between Miocene solar insolation and benthic δ<sup>18</sup>O variability.</p>

An Evolving Understanding of Enigmatic Large Ripples on Mars

<p>Unlike terrestrial sandy deserts, Mars hosts two scales of ripples in fine sand. Larger, meter-scale ripples are morphologically distinct from small, decimeter-scale ripples, and their size, in particular, decreases with increasing atmospheric density. As a result, it was recently proposed that the equilibrium size of the larger ripples is set by an aerodynamic process, which makes them larger under thinner atmospheres. Under this hypothesis, large martian ripples would be distinct from smaller, decimeter-scale impact ripples in a mechanistic sense. Several workers have followed up on these initial observations to either corroborate, counter, or expand upon that hypothesis. Notably, a mechanistic model that not only corroborates the hypothesis that the size of large martian ripples is set by an aerodynamic process but also suggests that they arise from an aerodynamic instability, distinct from the grain-impact instability thought to be responsible for the formation of impact ripples, was developed. Conversely, other workers proposed that large ripples can develop from small impact ripples in a numerical model due to Mars’ low atmospheric pressure. In the latter model, the ripples’ growth-limiting mechanism is consistent with an aerodynamic process, but the large ripples would not be a separate class of ripples – they would simply be a larger version of the small impact ripples. Here, we explore this debate by synthesizing recent advances in large-ripple formation and offer potential avenues to address outstanding questions. Although significant knowledge gaps remain, it is clear that large martian ripples are larger where the atmosphere is less dense. The size of large martian ripples thus remain a powerful paleoclimate indicator.</p>

О распределении по размерам дисперсных частиц фрактальной формы

In this paper, a dispersed system formed by an ensemble of particles of different volume has been modeled in the framework of a thermodynamical approach. Particle shape has been determined by its fractal dimension which correlates its volume and surface area. Using the methods of number theory and Hardy-Ramanujan-Rademacher formula, we have calculated the equilibrium size distributions for nanoparticles of different shape in an ensemble. Estimates of the average volume and fractal dimension of dispersed particles have been obtained based on distribution functions. The correlation between average geometrical characteristics of particles in the ensemble, thermodynamical conditions of the dispersed system and properties of its substance have also been revealed.

Equilibrium size distribution and phase separation of multivalent, molecular assemblies in dilute solution

Equilibrium self-assembly, gelation, and phase separation of multivalent molecules in dilute solutions analyzed using statistics of lattice animals depicted here.

Is Government Growth Inevitable?

Despite massive worldwide growth of government in the twentieth century, there have been periods in the U.S. and other countries when growth has slowed or reversed. Government growth is not inevitable. Explanations of government growth fall into three major categories. Path-dependent theories emphasize factors that continually push the size of government up, so the current size is in part a function of its past size. Theories about the equilibrium size of government explain why government is big, but not why government grows. If equilibrium conditions change, that can produce government growth. Theories also describe ideological shifts that cause people to want, or at least accept, bigger governments. All these explanations could have an effect on government growth. However, none appears to be persuasive enough to explain all the growth that occurred.