Chimpanzees and bonobos distinguish between risk and ambiguity

Although recent research has investigated animal decision-making under risk, little is known about how animals choose under conditions of ambiguity when they lack information about the available alternatives. Many models of choice behaviour assume that ambiguity does not impact decision-makers, but studies of humans suggest that people tend to be more averse to choosing ambiguous options than risky options with known probabilities. To illuminate the evolutionary roots of human economic behaviour, we examined whether our closest living relatives, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), share this bias against ambiguity. Apes chose between a certain option that reliably provided an intermediately preferred food type, and a variable option that could vary in the probability that it provided a highly preferred food type. To examine the impact of ambiguity on ape decision-making, we interspersed trials in which chimpanzees and bonobos had no knowledge about the probabilities. Both species avoided the ambiguous option compared with their choices for a risky option, indicating that ambiguity aversion is shared by humans, bonobos and chimpanzees.     

Shorter-lived workers start foraging earlier

In social insects it is often observed that young workers perform tasks inside the nest and later switch to tasks outside the nest. By doing this the workers maximize their expected longevity, because tasks inside the nest are safe and tasks outside the nest are risky. The optimal strategy of workers should be expected to depend not only on their age but also on their health status if it is associated with reduction of longevity. Here a mathematical model is used to calculate the optimal time of switching between safe and risky tasks in a colony consisting of both healthy and unhealthy workers. The model predicts that unhealthy workers, with shorter longevity, should perform more risky tasks at an earlier age than their healthy nest mates should. The optimal time to switch between safe and risky tasks depends on the proportion of healthy and unhealthy workers in the colony, but the workers need not perceive the health status of their nest mates in order to adopt the optimal strategy. The workers need only perceive their own life expectancy, because the life expectancy of healthy and unhealthy workers should be the same at the time of switching from safe to risky tasks. The model predictions agree with a wide range of empirical data presented in this paper. Workers that are infected, poisoned, injured or affected by other harmful factors start to forage and perform other risky tasks at an earlier age than their healthy nest mates.     

Predation risk determines breeding territory choice in a Mediterranean cavity-nesting bird community

Non-direct effects of predation can be an important component of the total effect of predation, modulating animal population and community dynamics. The isolated effects of predation risk on the spatial organisation of the breeding bird community, however, remains poorly studied. We investigated whether an experimentally increased predation risk prior to reproduction affected breeding territory selection and subsequent reproductive strategies in three Mediterranean cavity-nesting birds, i.e., the little owl Athene noctua, European roller Coracias garrulus and scops owl Otus scops. We found that territories used the previous year were more likely to be re-occupied when they belonged to the safe treatment rather than to the risky treatment. The first choice of breeders of all three species was for safe territories over risky ones. When all breeding attempts in the season (i.e., final occupation) were considered, breeders also preferred safe to risky sites. In addition, little owls laid larger eggs in risky territories than in safe territories. Our study provides experimental evidence of a rapid preventive response of the three most abundant species in a cavity-nesting bird community to a short-term manipulation of predation risk. This response highlights the key role of the non-direct effects of predation in modulating avian community organisation.     

Temporal discounting predicts risk sensitivity in rhesus macaques

Humans and animals tend both to avoid uncertainty and to prefer immediate over future rewards. The comorbidity of psychiatric disorders such as impulsivity, problem gambling, and addiction suggests that a common mechanism may underlie risk sensitivity and temporal discounting. Nonetheless, the precise relationship between these two traits remains largely unknown. To examine whether risk sensitivity and temporal discounting reflect a common process, we recorded choices made by two rhesus macaques in a visual gambling task while we varied the delay between trials. We found that preference for the risky option declined with increasing delay between sequential choices in the task, even when all other task parameters were held constant. These results were quantitatively predicted by a model that assumed that the subjective expected utility of the risky option is evaluated based on the expected time of the larger payoff. The importance of the larger payoff in this model suggests that the salience of larger payoffs played a critical role in determining the value of risky options. These data suggest that risk sensitivity may be a product of other cognitive processes, and specifically that myopia for the future and the salience of jackpots control the propensity to take a gamble.     

Attenuated Neural Processing of Risk in Young Adults at Risk for Stimulant Dependence

Objective

Approximately 10% of young adults report non-medical use of stimulants (cocaine, amphetamine, methylphenidate), which puts them at risk for the development of dependence. This fMRI study investigates whether subjects at early stages of stimulant use show altered decision making processing.

Methods

158 occasional stimulants users (OSU) and 50 comparison subjects (CS) performed a “risky gains” decision making task during which they could select safe options (cash in 20 cents) or gamble them for double or nothing in two consecutive gambles (win or lose 40 or 80 cents, “risky decisions”). The primary analysis focused on risky versus safe decisions. Three secondary analyses were conducted: First, a robust regression examined the effect of lifetime exposure to stimulants and marijuana; second, subgroups of OSU with >1000 (n = 42), or <50 lifetime marijuana uses (n = 32), were compared to CS with <50 lifetime uses (n = 46) to examine potential marijuana effects; third, brain activation associated with behavioral adjustment following monetary losses was probed.

Results

There were no behavioral differences between groups. OSU showed attenuated activation across risky and safe decisions in prefrontal cortex, insula, and dorsal striatum, exhibited lower anterior cingulate cortex (ACC) and dorsal striatum activation for risky decisions and greater inferior frontal gyrus activation for safe decisions. Those OSU with relatively more stimulant use showed greater dorsal ACC and posterior insula attenuation. In comparison, greater lifetime marijuana use was associated with less neural differentiation between risky and safe decisions. OSU who chose more safe responses after losses exhibited similarities with CS relative to those preferring risky options.

Discussion

Individuals at risk for the development of stimulant use disorders presented less differentiated neural processing of risky and safe options. Specifically, OSU show attenuated brain response in regions critical for performance monitoring, reward processing and interoceptive awareness. Marijuana had additive effects by diminishing neural risk differentiation.     

The evolution of risky behaviour in the presence of a sexually transmitted disease

Sexually transmitted diseases (STDs) are widespread in nature, often sterilizing their hosts or causing other pathogenic effects. Despite this, there is a widespread occurrence of behaviours that are likely to increase the risk to an individual of contracting an STD. Here, we examine the evolution of behaviours such as promiscuity or mate choice that increase the risk of contracting an STD, but also provide a fitness benefit. As might be expected, the balance between risk and fitness benefit defines the optimal strategy, but this relationship is not straightforward. In particular, we often predict the coexistence of highly risky and highly risk-averse individuals. Surprisingly, very safe strategists that only suffer a small cost will tend to coexist with highly risky strategists rather than outcompete them as might have been expected. Rather than selecting for monogamy or for reduced mate choice, therefore, the presence of an STD may often lead to variability in either promiscuity or mate choice.     

Out of the Frying Pan and into the Fire: a Novel Trade-Off for Batesian Mimics

A mimicry system was investigated in which the models were ants (Formicidae) and both the mimics and the predators were jumping spiders (Salticidae). By using motionless lures in simultaneous‐presentation prey‐choice tests, how the predators respond specifically to the static appearance of ants and ant mimics was determined. These findings suggest a rarely considered adaptive trade‐off for Batesian mimics of ants. Mimicry may be advantageous when it deceives ant‐averse potential predators, but disadvantageous in encounters with ant‐eating specialists. Nine myrmecophagic (ant‐eating) species (from Africa, Asia, Australia and North America) and one araneophagic (spider‐eating) species (Portia fimbriata from Queensland) were tested with ants (five species), with myrmecomorphic (ant‐like) salticids (six species of Myrmarachne) and with non‐ant‐like prey (dipterans and ordinary salticids). The araneophagic salticid chose an ordinary salticid and chose flies significantly more often than ants. Portia fimbriata also chose the ordinary salticid and chose flies significantly more often than myrmecomorphic salticids. However, there was no significant difference in how P. fimbriata responded to ants and to myrmecomorphic salticids. The myrmecophagic salticids chose ants and chose myrmecomorphic salticids significantly more often than ordinary salticids and significantly more often than flies, but myrmecophagic salticids did not respond significantly differently to myrmecomorphic salticids and ants.     

Effects of Cover on Loud Trill-Call and Soft Seet-Call Use in the Crested tit Parus Cristatus

Predation is one of the main factors responsible for winter mortality in small birds. Contact vocalizations of crested tits ( Parus cristatus ) can be divided into two categories: long- and short-range communication calls. The long-range calls are loud, frequency-modulated trills, which are well suited for acoustic communication over long distances. The short-range calls, in contrast, are soft, high-pitched tones, which are strongly attenuated as they radiate through the environment. As the predation cost in this species is mostly associated with the use of loud calls, we investigated whether crested tits adjust the use of loud trill-calls and of soft seet-calls to changes in habitat safety. We arranged two feeding sites that differed with respect to predicted safety, and observed the utterance of loud trill-calls and soft seet-calls. Calling rates of the loud trill-calls were highest when male crested tits foraged at the safe site. The loud trill-calls were given significantly less often while visiting risky feeders placed just a few metres away from the safe sites. The soft seet-calls were uttered both at risky and safe feeders at similar rates. This study suggests that the long-range part of contact communication in crested tits is strongly affected by the level of perceived predation risk. In accordance with the data on hearing ability of predators, dominant male crested tits decrease their exposure to predation in risky habitats by choosing a less risky type of communication with high-pitched sounds.     

Risk-sensitivity and the mean-variance trade-off: decision making in sensorimotor control

Numerous psychophysical studies suggest that the sensorimotor system chooses actions that optimize the average cost associated with a movement. Recently, however, violations of this hypothesis have been reported in line with economic theories of decision-making that not only consider the mean payoff, but are also sensitive to risk, that is the variability of the payoff. Here, we examine the hypothesis that risk-sensitivity in sensorimotor control arises as a mean-variance trade-off in movement costs. We designed a motor task in which participants could choose between a sure motor action that resulted in a fixed amount of effort and a risky motor action that resulted in a variable amount of effort that could be either lower or higher than the fixed effort. By changing the mean effort of the risky action while experimentally fixing its variance, we determined indifference points at which participants chose equiprobably between the sure, fixed amount of effort option and the risky, variable effort option. Depending on whether participants accepted a variable effort with a mean that was higher, lower or equal to the fixed effort, they could be classified as risk-seeking, risk-averse or risk-neutral. Most subjects were risk-sensitive in our task consistent with a mean-variance trade-off in effort, thereby, underlining the importance of risk-sensitivity in computational models of sensorimotor control.     

Behaviour and resource use of two competing vole species under shared predation risk

Indirect interaction between two competing species via a shared predator may be an important determinant of population and community dynamics. We studied the effect of predation risk imposed by the least weasel Mustela nivalis nivalis on space use, foraging and activity of two competing vole species, the grey-sided vole Myodes rufocanus, and the bank vole Myodes glareolus. The experiment was conducted in a large indoor arena, consisting of microhabitat structures providing food, shelter, trees for refuge and separated areas with high and low predation risk. Voles were followed for 5 days: 2 days before, 1 day during and 2 days after the presence of weasel. Our results suggest an effect of weasel presence on the vole community. Voles of both species shifted their activity from risky to less risky areas, climbed trees more often and were less active. Seed consumption was not affected by weasel presence. The time spent in the risky and less risky area did not differ between species, but bank voles spent more time in trees than grey-sided voles. Males of both species were more exposed to predation risk than females, i.e. generally spent more time in the risky area. Proportion of time spent in the risky area, the use of area, trees and food stations were sex dependent. Activity and use of trees were species dependent. We found no evidence for despotic distribution between our two species, although bank voles seemed to be more affected by coexistence, since they lost weight during the experiment. Based on our results we conclude that predator response was largely similar between species, while the sex-specific responses dominated. Besides a stronger escape response in the bank vole, the strongest individual differences were sex specific, i.e. males were more prone to take risks in space use and activity.     

Influence of caste polyethism on longevity of workers in social insect colonies

Different patterns of division of labor can affect the expected longevity of social insects workers. It has been earlier suggested that when tasks performed inside and outside colony are equally risky then the expected longevity of workers in colonies with caste polyethism is greater than that in colonies without polyethism. To verify these predictions I used a model assuming two sets of tasks, associated with different mortality rates. In the colony without polyethism the workers preformed safe and risky tasks in turn, while in the colony with caste polyethism the workers specialized in only one set of tasks. The outcomes suggest that the expected longevity of workers in colonies with caste polyethism cannot be greater than that in colonies without polyethism. Only if there is no aging and under some special and rare conditions are there no differences in expected longevity between colonies with and without caste polyethism. If aging is independent of activity, caste polyethism does not shorten longevity when all tasks in the colony are equally risky. The results can explain why caste polyethism is not as widespread among social insects as age polyethism.     

Reward context determines risky choice in pigeons and humans

Whereas humans are risk averse for monetary gains, other animals can be risk seeking for food rewards, especially when faced with variable delays or under significant deprivation. A key difference between these findings is that humans are often explicitly told about the risky options, whereas non-human animals must learn about them from their own experience. We tested pigeons (Columba livia) and humans in formally identical choice tasks where all outcomes were learned from experience. Both species were more risk seeking for larger rewards than for smaller ones. The data suggest that the largest and smallest rewards experienced are overweighted in risky choice. This observed bias towards extreme outcomes represents a key step towards a consilience of these two disparate literatures, identifying common features that drive risky choice across phyla.     

The debate over risk-related standards of competence

This discussion paper continues the debate over risk-related standards of mental competence which appears in Bioethics 5. Dan Brock there defends an approach to mental competence in patients which defines it as being relative to differing standards, more or less rigorous depending on the degree of risk involved in proposed treatments. But Mark Wicclair raises a problem for this approach: if significantly different levels of risk attach, respectively, to accepting and refusing the same treatment, then it is possible, on this account, for a patient to be considered competent to accept, but not refuse, the treatment, or vice versa. I argue that this puzzle does not constitute a genuine problem for a risk-related standard.
To this end I focus on the situation where, of two mutually exclusive options, one is riskier, but offering more pronounced benefit, while the other is safer, but offering less benefit. I argue for this proposition: it can take far less insight to know that the safe option is good than to know that the risky option is better. Now say one is actually informed enough to know that the safe option is good, but not enough to know whether the risky option is better; in such a case one is competent to say yes to that first option (the safe one), but not to say yes to the other. (I argue in passing that Pascal's Wager can be interpreted as having precisely this deliberative structure.)
I thus conclude that cases do indeed exist where one can be competent to say yes but not no, or vice versa; and that it is thus not an anomaly in the risk-related standard that it entails the existence of such cases.     

Assisted Colonization: A Question of Focal Units and Recipient Localities

Assisted colonization as an adaptation strategy to conserve or restore biodiversity in the face of climate change deservedly evokes controversy. Assisted colonization is perceived by some as a last option for conserving endangered species and by others as a risky and unwise management effort due to current gaps of knowledge. Based on the pros and cons of the recent debate, we show that the current discussion mainly focuses on the assisted colonization of rare and endangered species beyond their natural range of distribution. We suggest that a more useful approach for the conservation of endangered species could occur by focusing on the relevant foundation or keystone species, which ensure ecosystem integrity for a multitude of dependent species by governing the habitat structure and micro‐climate of the site. Examples of foundation species include dominant tree species in forests or dominant corals in coral reefs. For a given conservation or restoration need (e.g. conservation of rare species), we recommend the assisted colonization of pre‐adapted ecotypes of the relevant foundation species from climates similar to future expectations for the target site. This approach could lead to climate‐safe habitats for endangered species with minimal adverse effects on recipient ecosystems.     

Predation risk assessment by larval reef fishes during settlement-site selection

Predation rates of marine species are often highest during the transition from the pelagic to the benthic life stage. Consequently, the ability to assess predation risk when selecting a settlement site can be critical to survival. In this study, pairwise choice trials were used to determine whether larvae of three species of anemonefish (Amphiprion melanopus, A. percula and Premnas biaculeatus) are able to (1) assess the predation risk of potential anemone settlement sites through olfactory cues alone and (2) alter their settlement choices depending on the options available (host or non-host anemone). When predation risk was assessed with host and non-host anemone species independently, all species of anemonefish significantly chose the odor associated with the low-risk settlement option over the high-risk site. Most importantly, all species of anemonefish selected water with olfactory cues from their host anemone regardless of predation risk when paired against non-host anemone odor. These results demonstrate that larval reef fishes can use olfactory cues for complex risk assessment during settlement-site selection; however, locating the correct habitat is the most important factor when selecting a settlement site.     

Foraging choice and replacement reproductives facilitate invasiveness in drywood termites

All highly cryptic drywood termites derive their food and water from a single piece of wood. Despite the fact that most species share the same life cycles, only a few have become invasive tramp species. Variation in production of replacement reproductives and food size choice were determined for nine species of the important drywood genus Cryptotermes in a test with two different sized wooden blocks. Four native, non-pest species produced one or two reproductives, gnawed short tunnels and chose large blocks; four tramp pest species produced three or four reproductives, gnawed long tunnels and two species chose small blocks whereas the other two species chose both blocks; the ninth species, a native pest, was similar to tramp species. Longer tunnels and more replacement reproductives corresponded with pest status, acceptance of small blocks with tramp status. Although counter-intuitive, the foraging acceptance or preference for small blocks of wood corresponds with higher propagule pressure and an increased chance of (unwitting) human assisted transport, and therefore may be an important factor in determining tramp status of drywood termite species.     

Corvids avoid odd evaluation by following simple rules in a risky exchange task

In their natural environment, animals often make decisions crucial for survival, such as choosing the best patch or food, or the best partner to cooperate. The choice can be compared to a gamble with an outcome that is predictable but not certain, such as rolling a dice. In economics, such a situation is called a risky context. Several models show that although individuals can generally evaluate the odds of each potential outcome, they can be subject to errors of judgment or choose according to decision-making heuristics (simple decision rules). In non-human primates, similar errors of judgment have been reported and we have recently shown that they also use a decisional heuristics when confronted with a risky choice in an exchange task. This suggests a common evolutionary origin to the mechanisms underlying decision-making under risk in primates. However, whether the same mechanisms are also present in more distantly related taxa needs to be further investigated. Other social species, like corvids, are renowned for their advanced cognitive skills and may show similar responses. Here, we analyse data on corvids (carrion crows, hooded crows, common ravens and rooks) tested in a risky exchange task comparable to the one used in non-human primates. We investigated whether corvids could exchange according to the odds of success or, alternatively, whether they used a heuristic similar to the one used by non-human primates. Instead, most corvids chose a course of action (either a low or high exchange rate) that remained constant throughout the study. In general, corvids’ mean exchange rates were lower compared to non-human primates, indicating that they were either risk-adverse or that they do not possess the cognitive capabilities to evaluate odds. Further studies are required to evaluate the flexibility in exchange abilities of these birds in exchange abilities of these birds.     

Motivational state and reward content determine choice behavior under risk in mice

Risk is a ubiquitous feature of the environment for most organisms, who must often choose between a small and certain reward and a larger but less certain reward. To study choice behavior under risk in a genetically well characterized species, we trained mice (C57BL/6) on a discrete trial, concurrent-choice task in which they must choose between two levers. Pressing one lever (safe choice) is always followed by a small reward. Pressing the other lever (risky choice) is followed by a larger reward, but only on some of the trials. The overall payoff is the same on both levers. When mice were not food deprived, they were indifferent to risk, choosing both levers with equal probability regardless of the level of risk. In contrast, following food or water deprivation, mice earning 10% sucrose solution were risk-averse, though the addition of alcohol to the sucrose solution dose-dependently reduced risk aversion, even before the mice became intoxicated. Our results falsify the budget rule in optimal foraging theory often used to explain behavior under risk. Instead, they suggest that the overall demand or desired amount for a particular reward determines risk preference. Changes in motivational state or reward identity affect risk preference by changing demand. Any manipulation that increases the demand for a reward also increases risk aversion, by selectively increasing the frequency of safe choices without affecting frequency of risky choices.     

Sex pheromones in maleMelittobia parasitic wasps: Female response to conspecific and congeneric males of 3 species

Presented a choice between conspecific males and 2 congeneric males, virgin females ofMelittobia australica andM. digitata chose conspecific males disproportionately more often, whereasM. femorata females distributed themselves evenly among the choices. Empty tubes, provided as the fourth choice in the test apparatus, were entered much less often than tubes containing live males. Females of all species chose “wrong” males about equally frequently. These observations suggest that even non-conspecific males possess some degree of attractiveness to virgin females. Chemicals in the sex pheromone of the males are presumed to be the source of the males' attractancy. The incomplete species specificity is interpreted in light of the life history of this genus, and it is suggested that specific recognition cues operate primarily after the sexes come together. Supported by a grant from Kagoshima Prefecture in Japan under the exchange program of faculty members between Kagoshima University and the University of Georgia.     

SPECIATION AND FEATHER ORNAMENTATION IN BIRDS

The hypothesis that sexual selection promotes speciation has rarely been tested. We identified 70 evolutionarily independent events of feather ornaments in birds. For each focal species we noted the number of ornamented and nonornamented species belonging to its genus and its number of subspecies, as well as its mating system and the extent of its geographic range. For purposes of comparison, we randomly chose a second, nonornamented species for which we obtained information on the number of subspecies, and in cases in which the nonornamented species was in the same genus, we chose a third, nonornamented species in a related genus and obtained the same information. We then noted the number of species in each genus and the difference in numbers of species, or species richness, between paired genera. For the genera of the focal ornamented species, we regressed number of ornamented species on number of nonornamented species and found a positive relationship. As number of species per genus rose, number of ornamented species per genus rose more rapidly, indicating that more speciose genera have a higher proportion of ornamented species than less speciose genera. We then took the deviations from this regression, the residual number of species, and regressed them on the differences in species richness between the paired genera. This relationship was positive indicating that ornamented genera with more than the expected number of ornamented species were more speciose with respect to their paired genera than were genera with fewer than the expected number of ornamented species. Finally, we compared the deviations from this regression, the residual number of ornamented species, with species' mating system and found a greater residual number of ornamented species among species whose mating system is associated with greater skew in male mating success and thus more intense sexual selection. Ornamented species had more subspecies than nonornamented species, even when controlling for geographic range, suggesting an association between subspeciation and ornaments.