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

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.

Evolutionary Markovian Strategies in 2 x 2 Spatial Games

Evolutionary spatial 2 x 2 games between heterogeneous agents are analyzed using different variants of cellular automata (CA). Agents play repeatedly against their nearest neighbors 2 x 2 games specified by a rescaled payoff matrix with two parameteres. Each agent is governed by a binary Markovian strategy (BMS) specified by 4 conditional probabilities [p_R, p_S, p_T, p_P] that take values 0 or 1. The initial configuration consists in a random assignment of "strategists" among the 2^4= 16 possible BMS. The system then evolves within strategy space according to the simple standard rule: each agent copies the strategy of the neighbor who got the highest payoff. Besides on the payoff matrix, the dominant strategy -and the degree of cooperation- depend on i) the type of the neighborhood (von Neumann or Moore); ii) the way the cooperation state is actualized (deterministically or stochastichally); and iii) the amount of noise measured by a parameter epsilon. However a robust winner strategy is [1,0,1,1].Comment: 18 pages, 8 figures (7 of these figures contain 4 encapsulapted poscript files each

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

Experimental parasite infection reveals costs and benefits of paternal effects

Forces shaping an individual's phenotype are complex and include transgenerational effects. Despite low investment into reproduction, a father's environment and phenotype can shape its offspring's phenotype. Whether and when such paternal effects are adaptive, however, remains elusive. Using three-spined sticklebacks in controlled infection experiments, we show that sperm deficiencies in exposed males compared to their unexposed brothers functionally translated into reduced reproductive success in sperm competition trials. In non-competitive fertilisations, offspring of exposed males suffered significant costs of reduced hatching success and survival but they reached a higher body condition than their counterparts from unexposed fathers after experimental infection. Interestingly, those benefits of paternal infection did not result from increased resistance but from increased tolerance to the parasite. Altogether, these results demonstrate that parasite resistance and tolerance are shaped by processes involving both genetic and non-genetic inheritance and suggest a context-dependent adaptive value of paternal effects

Tit for Tat: sticklebacks (Gasterosteus aculeatus) ‘trusting' a cooperating partner

Individual three-spined sticklebacks (Gasterosteus aculeatus) moved closer to a predatory trout when a ‘cooperator' stickleback, which the test fish could see through a one-way mirror, swam up to the predator than when a ‘defector' stickleback appeared to swim only half as close to the predator. After four training runs with both types of partners, the former cooperator also defected. The test fish continued to move closer to the predator in the presence of the former cooperator even though both the former cooperator and the defector now appeared to stop in their approach to the predator at the same distance. This shows that probable partners build up trus

Consistent Strategy Updating in Spatial and Non-Spatial Behavioral Experiments Does Not Promote Cooperation in Social Networks

The presence of costly cooperation between otherwise selfish actors is not trivial. A prominent mechanism that promotes cooperation is spatial population structure. However, recent experiments with human subjects report substantially lower level of cooperation then predicted by theoretical models. We analyze the data of such an experiment in which a total of 400 players play a Prisoner's Dilemma on a 4 x 4 square lattice in two treatments, either interacting via a fixed square lattice (15 independent groups) or with a population structure changing after each interaction (10 independent groups). We analyze the statistics of individual decisions and infer in which way they can be matched with the typical models of evolutionary game theorists. We find no difference in the strategy updating between the two treatments. However, the strategy updates are distinct from the most popular models which lead to the promotion of cooperation as shown by computer simulations of the strategy updating. This suggests that the promotion of cooperation by population structure is not as straightforward in humans as often envisioned in theoretical models.This work has funding by the German Initiative of Excellence of the German Science Foundation (DFG). J.G.'s work was supported in part by The Ministerio de Ciencia e Innovacion (MICINN) (Spain) through grants PRODIEVO, MOSAICO, FPI, EEBB, and by Comunidad de Madrid (Spain) through grant MODELICO-CM). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Publicad

Olfactory sensitivity of the marine flatfish Solea senegalensis to conspecific body fluids

Chemical communication is better understood in freshwater fish than marine fish. The Senegalese sole (Solea senegalensis) is a marine flatfish wherein one of the problems in aquaculture is the poor reproductive performance of hatchery-bred males. Is chemical communication involved in the reproduction of this species? Urine, intestinal fluid and mucus samples were taken from adult fish (wild-caught and hatchery-bred) over the spawning season (March-May), and assessed for olfactory potency using the electro-olfactogram (EOG). The effect of stimulation of the olfactory system with adult female urine on circulating luteinizing hormone (LH) levels was also tested in males. Intestinal fluid and urine were potent olfactory stimuli for both juvenile and adult conspecifics, evoking large-amplitude, concentration-dependent EOG responses, with thresholds of detection at approximately 1:10(6). However, the amplitude of the response to urine depended on the sex and state of maturity of both the donor and the receiver. Most olfactory activity could be extracted by C18 solid-phase cartridges. Urine from mature females evoked a slight, but significant, increase in circulating LH levels in mature males 30 min after exposure. Furthermore, the olfactory potency of urine differed between wild-caught and hatchery-bred fish; however, contrary to expectations, urine from wild-caught females was less potent than that from hatchery-bred females. Taken together, these results strongly suggest that faeces-and urine-released odorants are involved in reproduction in the Senegalese sole, and establish a basis for further investigation into pheromonal communication in marine teleosts.Instituto Nacional de Investigacion y Tecnologia Agraria y Alimentaria; EU through FEDER [RTA2011-00050, RTA2014-00048]; Ministerio de Economia y Competitividad (MINECO) [AGL2013-41196-R, RTA2013-00023-C02-01]; FPI-INIA - MINECO, Spain; Fundacao para a Ciencia e a Tecnologia (Foundation for Science and Technology, Portugal) [UID/Multi/04326/2013]info:eu-repo/semantics/publishedVersio

The Joker effect: cooperation driven by destructive agents

Understanding the emergence of cooperation is a central issue in evolutionary game theory. The hardest setup for the attainment of cooperation in a population of individuals is the Public Goods game in which cooperative agents generate a common good at their own expenses, while defectors "free-ride" this good. Eventually this causes the exhaustion of the good, a situation which is bad for everybody. Previous results have shown that introducing reputation, allowing for volunteer participation, punishing defectors, rewarding cooperators or structuring agents, can enhance cooperation. Here we present a model which shows how the introduction of rare, malicious agents -that we term jokers- performing just destructive actions on the other agents induce bursts of cooperation. The appearance of jokers promotes a rock-paper-scissors dynamics, where jokers outbeat defectors and cooperators outperform jokers, which are subsequently invaded by defectors. Thus, paradoxically, the existence of destructive agents acting indiscriminately promotes cooperation.Comment: Accepted for publication in the Journal of Theoretical Biology (JTB

Stay by thy neighbor? Social organization determines the efficiency of biodiversity markets with spatial incentives

Market-based conservation instruments, such as payments, auctions or tradable permits, are environmental policies that create financial incentives for landowners to engage in voluntary conservation on their land. But what if ecological processes operate across property boundaries and land use decisions on one property influence ecosystem functions on neighboring sites? This paper examines how to account for such spatial externalities when designing market-based conservation instruments. We use an agent-based model to analyze different spatial metrics and their implications on land use decisions in a dynamic cost environment. The model contains a number of alternative submodels which differ in incentive design and social interactions of agents, the latter including coordinating as well as cooperating behavior of agents. We find that incentive design and social interactions have a strong influence on the spatial allocation and the costs of the conservation market.Comment: 11 pages, 6 figure