Variability of currents and mixing processes during the onset of the equatorial cold tongue in the Atlantic

The heat content of the surface water masses is important for the circulation of the oceans and the atmosphere. The surface layer serves as a medium for the ocean-atmosphere exchange and thereby significantly affects the dynamics of our climate. Despite this, many of the mechanisms that allow exchange between the surface layer and the ocean interior are still elusive. Measurements of the turbulent dissipation rate of kinetic energy in May and June 2011 in the Atlantic Cold Tongue region depict mixing events that extend below the surface mixed layer. These mixing processes show a distinct diurnal cycle with a nighttime maximum, which is preserved until some hours after sunset. These deep mixing events occur when the stratification is weak and high vertical shear is present. The diurnal cycle is superimposed on a ow-frequent variation of the turbulent dissipation rate of kinetic energy. Due to this low frequent cycle with a period of 11 days, the increased mixing events below the mixed layer vanish completely during some days while they extend 30 meters below the mixed layer depth on other day

A review of suggested mechanisms of MHC odor signaling

Although an individual’s mix of MHC immune genes determines its resistance, findingMHC-dependent mate choice occurred by accident in inbred mice. Inbred mice prefer MHC dissimilarmates, even when the choice was restricted to urine. It took decades to find the info-chemicals, whichhave to be as polymorphic as the MHC. Microbiota were suggested repeatedly as the origin ofthe odor signal though germ-free mice maintained normal preference. Different versions of the‘carrier hypothesis’ suggested MHC molecules carry volatiles after the bound peptide is released.Theory predicted an optimal individual MHC diversity to maximize resistance. The optimallycomplementary mate should be and is preferred as several studies show. Thus, the odor signal needsto transmit the exact information of the sender’s MHC alleles, as do MHC ligand peptides but notmicrobiota. The ‘MHC peptide hypothesis’ assumes that olfactory perception of the peptide ligandprovides information about the MHC protein in a key-lock fashion. Olfactory neurons react onlyto the anchors of synthesized MHC peptides, which reflect the binding MHC molecule’s identity.Synthesized peptides supplemented to a male’s signal affect choice in the predicted way, however,not when anchors are mutated. Also, the human brain detects smelled synthesized self-peptidesas such. After mate choice, the lottery of meiosis of randomly paired oocyte and sperm haplotypeswould often produce MHC non-optimal offspring. In sticklebacks, eggs select MHC-compatiblesperm, thus prefer the best combination close to the population optimum

Extortion - a voracious prosocial strategy

Recently Press and Dyson have dramatically changed our view on the Prisoner's Dilemma by proposing a new class of strategies that enforce a linear relationship between the two players' scores. Players adopting ‘extortion’ respond with cooperation to cooperation in most cases, defect in other rounds, but respond to defection with defection. In this way, extortion enforces full cooperation of the partner who accedes to it because he profits from doing so. This unbeatable strategy is nevertheless prosocial because it is mostly cooperative and induces cooperation even though it gains most itself. Experiments show that about 40% of humans choose to use extortion in competitive situations or when they have the power to exchange coplayers. On being punished in egalitarian situations, they use a generous strategy

Neural signatures of tinnitus across the sleep-wake cycle

Subjective tinnitus is an internally generated auditory percept, most commonly taking the form of hissing or ringing. Especially long-lasting tinnitus is associated with anxiety, depression, and sleep impairments. There is no effective treatment for tinnitus, although research has made progress in uncovering its neural basis, including identifying hyperactivity in the central auditory pathway and several cortical regions, including those involved in brain state control. We have proposed that the occurrence of aberrant neural activity associated with tinnitus has important implications for natural brain state dynamics across sleep and wakefulness and vice versa (Milinski et al., 2022). Our first prediction was that the neural representation of tinnitus interferes with global sleep maintenance, while a strong sleep drive (such as high homeostatic pressure) overrides aberrant tinnitus-related activity. To test this empirically, a longitudinal assessment of behavioural and neural markers of tinnitus across the sleep-wake cycle was conducted in a ferret model of tinnitus after noise overexposure (NOE) over a period of ~6 months. The changes in behavioural performance and auditory evoked activity after NOE differed between individuals and suggest distinct degrees of tinnitus and hearing impairment with early or late onset. The emergence of tinnitus symptoms was associated with disrupted and reduced sleep, corroborating the possibility that noise-induced tinnitus is linked to sleep disturbance. In addition, neural markers of tinnitus were reduced during sleep, suggesting that sleep may transiently mitigate tinnitus. Our second prediction was that besides the interaction between sleep and tinnitus, sleep might facilitate tinnitus emergence. To test this, we assessed in mice the effect of acute sleep deprivation after NOE on tinnitus development. Sleep deprivation mitigated behavioural and hearing impairment after NOE, which indicates that sleep may play a role in mediating the consequences of noise-induced peripheral trauma. Overall, these results highlight the potential of further research on the interactions between natural brain states dynamics and tinnitus to uncover new avenues for future treatments

MHC mediates social odor via microbiota—it cannot work: a comment on Schubert et al.

Schubert et al. (2021) review the evidence from 577 publications about how the Major Histocompatibility Complex (MHC), might mediate social odor via the microbiota community to “stimulate advances in our knowledge of this key pathway for social communication.” The idea is that, as part of the immune system of all vertebrates, polymorphic MHC molecules control microorganisms present in the microbiome, which produce odor that may serve as a social signal. MHC, microbe, odor signal is the sequence of steps leading eventually from MHC to social signal, for example, for MHC-dependent mate choice. However, none of the 577 studies showed the odor to be a social signal

Smiling is a Costly Signal of Cooperation Opportunities: Experimental Evidence from a Trust Game

We test the hypothesis that "genuine" or "convincing" smiling is a costly signal that has evolved to induce cooperation in situations requiring mutual trust. Potential trustees in a trust game made video clips for viewing by potential trusters before the latter decided whether to send them money. Ratings of the genuineness of smiles vary across clips; it is difficult to make convincing smiles to order. We argue that smiling convincingly is costly, because smiles from trustees playing for higher stakes are rated as significantly more convincing, so that rewards appear to induce effort. We show that it induces cooperation: smiles rated as more convincing strongly predict judgments about the trustworthiness of trustees, and willingness to send them money. Finally, we show that it is a honest signal: those smiling convincingly return more money on average to senders. Convincing smiles are to some extent a signal of the intrinsic character of trustees: less honest individuals find smiling convincingly more difficult. They are also informative about the greater amounts that trustees playing for higher stakes have available to share: it is harder to smile convincingly if you have less to offer.

Do three-spined sticklebacks avoid consuming copepods, the first intermediate host of Schistocephalus solidus ? — an experimental analysis of behavioural resistance

Many parasites that use intermediate hosts are transmitted to the next host through predation. If the next host's fitness is strongly reduced by the parasite, it is under selection either to recognize and avoid infected intermediate hosts or to exclude that prey species from its diet when alternative prey are available. We investigated the predator-prey interaction between laboratory bred three-spined sticklebacks (Gasterosteus aculeatus), the second intermediate host of the cestode Schistocephalus solidus, from 2 parasitized and 1 unparasitized population, and different prey types: infected and uninfected copepods and size-matched Daphnia as alternative prey. Copepods with infective procercoids were more active, had a lower swimming ability and were easier to catch than uninfected controls. The sticklebacks preferred moving copepods. Therefore parasitized copepods were preferentially attacked and consumed. There was no effect of the sticklebacks' parent population being parasitized or not. The sticklebacks switched from Daphnia to (uninfected) copepods in the course of a hunting sequence; this switch occurred earlier in smaller fish. With this strategy the fish maximized their feeding rate: Daphnia were easier to catch than copepods but increasingly difficult to swallow when the stomach was filling up especially for smaller fish. However, there was no indication that sticklebacks from infected populations either consumed Daphnia rather than copepods or switched later in the hunting sequence to consuming copepods than fish from an uninfected population. Thus, sticklebacks did not avoid parasitized prey although S. solidus usually has a high prevalence and causes a strong fitness reduction in its stickleback hos

An experimental conflict of interest between parasites reveals the mechanism of host manipulation

Parasites can increase their host’s predation susceptibility. It is a long-standing puzzle, whether this is caused by host manipulation, an evolved strategy of the parasite, or by side effects due to, for example, the parasite consuming energy from its host thereby changing the host’s trade-off between avoiding predation and foraging toward foraging. Here, we use sequential infection of three-spined sticklebacks with the cestode Schistocephalus solidus so that parasites have a conflict of interest over the direction of host manipulation. With true manipulation, the not yet infective parasite should reduce rather than enhance risk taking because predation would be fatal for its fitness; if host behavior is changed by a side effect, the 2 parasites would add their increase of predation risk because both drain energy. Our results support the latter hypothesis. In an additional experiment, we tested both infected and uninfected fish either starved or satiated. True host manipulation should act independently of the fish’s hunger status and continue when energy drain is balanced through satiation. Starvation and satiation affect the risk averseness of infected sticklebacks similarly to that of uninfected starved and satiated ones. Increased energy drain rather than active host manipulation dominates behavioral changes of S. solidus-infected sticklebacks

Combining machine learning and SMILEs to classify, better understand, and project changes in ENSO events

The El Niño Southern Oscillation (ENSO) occurs in three phases: neutral, warm (El Niño) and cool (La Niña). While classifying El Niño and La Niña is relatively straightforward, El Niño events can be broadly classified into two types: Central Pacific (CP) and Eastern Pacific (EP). Differentiating between CP and EP events is currently dependent on both the method and observational dataset used. In this study, we create a new classification scheme using supervised machine learning trained on 18 observational and reanalysis products. This builds on previous work by identifying classes of events using the temporal evolution of sea surface temperature in multiple regions across the tropical Pacific. By applying this new classifier to seven single model initial-condition large ensembles (SMILEs) we investigate both the internal variability and forced changes in each type of ENSO event, where events identified behave similar to those observed. It is currently debated whether the observed increase in the frequency of CP events after the late 1970s is due to climate change. We found it to be within the range of internal variability in the SMILEs. When considering future changes, we do not project a change in CP frequency or amplitude under a strong warming scenario (RCP8.5/SSP370) and we find model differences in EP El Niño and La Niña frequency and amplitude projections. Finally, we find that models show differences in projected precipitation and SST pattern changes for each event type that do not seem to be linked to the Pacific mean state SST change, although the SST and precipitation changes in individual SMILEs are linked. Our work demonstrates the value of combining machine learning with climate models, and highlights the need to use SMILEs when evaluating ENSO in climate models due to the large spread of results found within a single model due to internal variability alone