The evolution of age-dependent plasticity

When organisms encounter environments that are heterogeneous in time, phenotypic plasticity is often favored by selection. The degree of such plasticity can vary during an organism's lifetime, but the factors promoting differential plastic responses at different ages or life stages remain poorly understood. Here we develop and analyze an evolutionary model to investigate how environmental information is optimally collected and translated into phenotypic adjustments at different ages. We demonstrate that plasticity must often be expected to vary with age in a nonmonotonic fashion. Early in life, it is generally optimal to delay phenotypic adjustments until sufficient information has been collected about the state of the environment to warrant a costly phenotypic adjustment. Toward the end of life, phenotypic adjustments are disfavored as well because their beneficial effects can no longer be fully reaped before death. Our analysis clarifies how patterns of age-dependent plasticity are shaped by the interplay of environmental uncertainty, the accuracy of perceived information, and the costs of phenotypic adjustments with life-history determinants such as the relative strengths of fecundity and viability selection experienced by the organism over its lifetime. We conclude by comparing our results with expectations for alternative mechanisms, including developmental constraints, that promote age-dependent plasticity

Bromoform emission over the Antarctic sea ice

Bromoform is one of the volatile organic compounds emitted from the ocean surface to the atmosphere, and it is believed to affect ozone depletion in the atmosphere through photochemical reactions. While estimates of air−sea flux of bromoform are well examined in open ocean areas, fluxes have rarely been estimated in ice-covered seas, and so far, no observations have been made to evaluate the bromoform flux between the sea ice surface and atmosphere. Here, we present the first direct measurements of the air−sea ice bromoform flux obtained from first-year sea ice off east Antarctica. Measurements were made in early austral spring (September to November 2012) as part of the Sea Ice Physics and Ecosystem Experiment II (SIPEX-2). Vertical profiles of bromoform concentrations in snow and sea ice indicated that high concentrations were mainly found in the bottom of the snow and the surface layers of the sea ice (Figure 1) (including slush and brine) ranging from 281−1360 pM. Sea ice–atmosphere bromoform fluxes measured by the chamber method ranged from +0.3 to +7.5 nmol CHBr3 m–2 day–1 (positive value indicates the emission of the bromoform from ice surface to the atmosphere), and flux values increased with increasing bromoform concentrations at the surface layers (Figure 2). The mean flux estimate (+2.4 nmol CHBr3 m–2 day–1) obtained in this study was consistent with the flux estimate for the ice-free part of the Southern Ocean (+2.6 nmol CHBr3 m–2 day–1; Quack and Wallace, 2003). Our results suggest that the bromoform emitted from the sea ice surface to the atmosphere may account for an important fraction of the global bromine budget.第4回極域科学シンポジウム個別セッション：[OM] 気水圏11月14日（木） 統計数理研究所 ３階セミナー室１（D305

Three-body problem in Fermi gases with short-range interparticle interaction

We discuss 3-body processes in ultracold two-component Fermi gases with short-range intercomponent interaction characterized by a large and positive scattering length $a$. It is found that in most cases the probability of 3-body recombination is a universal function of the mass ratio and $a$, and is independent of short-range physics. We also calculate the scattering length corresponding to the atom-dimer interaction.Comment: 4 pages, 2 figure

Sea ice contribution to the air–sea CO₂ exchange in the Arctic and Southern Oceans

Although salt rejection from sea ice is a key process in deep-water formation in ice-covered seas, the concurrent rejection of CO2 and the subsequent effect on air–sea CO2 exchange have received little attention. We review the mechanisms by which sea ice directly and indirectly controls the air–sea CO2 exchange and use recent measurements of inorganic carbon compounds in bulk sea ice to estimate that oceanic CO2 uptake during the seasonal cycle of sea-ice growth and decay in ice-covered oceanic regions equals almost half of the net atmospheric CO2 uptake in ice-free polar seas. This sea-ice driven CO2 uptake has not been considered so far in estimates of global oceanic CO2 uptake. Net CO2 uptake in sea-ice–covered oceans can be driven by; (1) rejection during sea–ice formation and sinking of CO2-rich brine into intermediate and abyssal oceanic water masses, (2) blocking of air–sea CO2 exchange during winter, and (3) release of CO2-depleted melt water with excess total alkalinity during sea-ice decay and (4) biological CO2 drawdown during primary production in sea ice and surface oceanic waters

The long-term evolution of multilocus traits under frequency-dependent disruptive selection

Frequency-dependent disruptive selection is widely recognized as an important source of genetic variation. Its evolutionary consequences have been extensively studied using phenotypic evolutionary models, based on quantitative genetics, game theory, or adaptive dynamics. However, the genetic assumptions underlying these approaches are highly idealized and, even worse, predict different consequences of frequency-dependent disruptive selection. Population genetic models, by contrast, enable genotypic evolutionary models, but traditionally assume constant fitness values. Only a minority of these models thus addresses frequency-dependent selection, and only a few of these do so in a multilocus context. An inherent limitation of these remaining studies is that they only investigate the short-term maintenance of genetic variation. Consequently, the long-term evolution of multilocus characters under frequency-dependent disruptive selection remains poorly understood. We aim to bridge this gap between phenotypic and genotypic models by studying a multilocus version of Levene's soft-selection model. Individual-based simulations and deterministic approximations based on adaptive dynamics theory provide insights into the underlying evolutionary dynamics. Our analysis uncovers a general pattern of polymorphism formation and collapse, likely to apply to a wide variety of genetic systems: after convergence to a fitness minimum and the subsequent establishment of genetic polymorphism at multiple loci, genetic variation becomes increasingly concentrated on a few loci, until eventually only a single polymorphic locus remains. This evolutionary process combines features observed in quantitative genetics and adaptive dynamics models, and it can be explained as a consequence of changes in the selection regime that are inherent to frequency-dependent disruptive selection. Our findings demonstrate that the potential of frequency-dependent disruptive selection to maintain polygenic variation is considerably smaller than previously expected

Sympatric speciation by sexual selection: A critical reevaluation

Several empirical studies put forward sexual selection as an important driving force of sympatric speciation. This idea agrees with recent models suggesting that speciation may proceed by means of divergent Fisherian runaway processes within a single population. Notwithstanding this, the models so far have not been able to demonstrate that sympatric speciation can unfold as a fully adaptive process driven by sexual selection alone. Implicitly or explicitly, most models rely on nonselective factors to initiate speciation. In fact, they do not provide a selective explanation for the considerable variation in female preferences required to trigger divergent runaway processes. We argue that such variation can arise by disruptive selection but only when selection on female preferences is frequency dependent. Adaptive speciation is therefore unattainable in traditional female choice models, which assume selection on female preferences to be frequency independent. However, when frequency-dependent sexual selection processes act alongside mate choice, truly adaptive sympatric speciation becomes feasible. Speciation is then initiated independently of nonadaptive processes and does not suffer from the theoretical weaknesses associated with the current Fisherian runaway model of speciation. However, adaptive speciation requires the simultaneous action of multiple mechanisms, and therefore it occurs under conditions far more restrictive than earlier models of sympatric speciation by sexual selection appear to suggest

Inter-comparison between chambers for CO2 flux measurements over sea ice

In order to validate the difference of air-sea ice CO2 flux measurements by different types of CO2 chamber, inter-comparison experiments were carried out on winter Antarctic pack ice in the Weddell Sea (R.V. Polarstern AWECS cruise, July-August 2013). Our ultimate goal is to understand the methodological gaps for the CO2 flux measurements betweem chamber and eddy covariance methods over sea ice as an activity for SCOR Working Group 152 (ECV-Ice). Two kinds of CO2 chamber systems were used: semi-automated CO2 chambers developed at Hokkaido University and automated long-term CO2 chambers (Li-8100A, LI-COR Biosciences, USA). These chambers were installed at the same ice/snow surface conditions within a 2-m × 2-m area. Based on the quantitative comparisons using least squares linear regression analyses, slope was 1.08, suggesting that the airsea ice CO2 flux from two chambers were good agreement. Therefore, our inter-comparison experiments confirmed that there was no instrumental bias between two chambers, thereby the past data for air-sea ice CO2 flux obtained by each chamber's group in the world polar oceans could be shared