Approaching the genomics of risk-taking behavior

Environmental correlates of adaptive diversification in postglacial freshwater fishes

Determining how environmental conditions contribute to divergence among populations and drive speciation is fundamental to resolving mechanisms and understanding outcomes in evolutionary biology. Postglacial freshwater fish species in the Northern Hemisphere are ideal biological systems to explore the effects of environment on diversification in morphology, ecology, and genetics (ecomorph divergences) within lakes. To date, various environmental factors have been implicated in the presence of multiple ecomorphs within particular lakes or regions. However, concerted evidence for generalizable patterns in environmental variables associated with speciation across geographical regions and across species and genera has been lacking. Here, we aimed to identify key biotic and abiotic factors associated with ecological divergence of postglacial freshwater fish species into multiple sympatric ecomorphs, focusing on species in the well-studied, widespread, and co-distributed genera Gasterosteus, Salvelinus, and Coregonus (stickleback, charr, and whitefish, respectively). We found that the presence of multiple sympatric ecomorphs tended to be associated with increasing lake surface area, maximum depth, and nutrient availability. In addition, predation, competition, and prey availability were suggested to play a role in divergence into multiple ecomorphs, but the effects of biotic factors require further study. Although we identified several environmental factors correlated with the presence of multiple ecomorphs, there were substantial data gaps across species and regions. An improved understanding of these systems may provide insight into both generalizable environmental factors involved in speciation in other systems, and potential ecological and evolutionary responses of species complexes when these variables are altered by environmental change.

Genetic polymorphisms in genes related to risk-taking behaviours predicting body mass index trajectory among Mexican American adolescents

OBJECTIVES

Obesity is associated with multiple health problems and often originates in childhood. The purpose is to investigate the associations of genetic polymorphisms in genes related to risk-taking behaviours with body mass index (BMI) trajectory over adolescence among Mexican Americans.

METHODS

This study included 1229 Mexican American adolescents who participated in a large population-based cohort study in Houston, Texas. BMI data were obtained at baseline and two follow-ups. The median follow-up time was 59 months. Participants were genotyped for 672 functional and tagging variants in genes involved in the dopamine, serotonin and cannabinoid pathways.

RESULTS

After adjusting for multiple comparisons, three genetic variants, namely, rs933271 and rs4646310 in COMT gene, and rs9567733 in HTR2A gene were significantly associated with BMI growth over adolescence. Using those three variants, we created an allelic score, and the allelic score was associated with BMI growth over adolescence (P < 0.001). With the increase number of variant allele, the rate of BMI growth over adolescence was slower. Finally, we identified another two genetic variants, namely, rs17069005 in HTR2A gene and rs3776511 in SLC6A3A gene were associated with obesity at last follow-up.

CONCLUSIONS

The results suggest that genetic variants in selected genes involved in dopamine and serotonin pathways have noticeable effects on BMI over adolescence.

Mechanisms underlying the control of responses to predator odours in aquatic prey

In aquatic systems, chemical cues are a major source of information through which animals are able to assess the current state of their environment to gain information about local predation risk. Prey use chemicals released by predators (including cues from a predator's diet) and other prey (such as alarm cues and disturbance cues) to mediate a range of behavioural, morphological and life-history antipredator defences. Despite the wealth of knowledge on the ecology of antipredator defences, we know surprisingly little about the physiological mechanisms that control the expression of these defensive traits. Here, we summarise the current literature on the mechanisms known to specifically mediate responses to predator odours, including dietary cues. Interestingly, these studies suggest that independent pathways may control predator-specific responses, highlighting the need for greater focus on predator-derived cues when looking at the mechanistic control of responses. Thus, we urge researchers to tease apart the effects of predator-specific cues (i.e. chemicals representing a predator's identity) from those of diet-mediated cues (i.e. chemicals released from a predator's diet), which are known to mediate different ecological endpoints. Finally, we suggest some key areas of research that would greatly benefit from a more mechanistic approach.

Risk sensitivity as an evolutionary adaptation

Risk aversion is a common behavior universal to humans and animals alike. Economists have traditionally defined risk preferences by the curvature of the utility function. Psychologists and behavioral economists also make use of concepts such as loss aversion and probability weighting to model risk aversion. Neurophysiological evidence suggests that loss aversion has its origins in relatively ancient neural circuitries (e.g., ventral striatum). Could there thus be an evolutionary origin to risk aversion? We study this question by evolving strategies that adapt to play the equivalent mean payoff gamble. We hypothesize that risk aversion in this gamble is beneficial as an adaptation to living in small groups, and find that a preference for risk averse strategies only evolves in small populations of less than 1,000 individuals, or in populations segmented into groups of 150 individuals or fewer – numbers thought to be comparable to what humans encountered in the past. We observe that risk aversion only evolves when the gamble is a rare event that has a large impact on the individual's fitness. As such, we suggest that rare, high-risk, high-payoff events such as mating and mate competition could have driven the evolution of risk averse behavior in humans living in small groups.

High individual consistency in fear of humans throughout the adult lifespan of rural and urban burrowing owls

Human-induced rapid environmental changes challenge individuals by creating evolutionarily novel scenarios, where species encounter novel enemies, the new species sometimes being humans themselves. However, little is known about how individuals react to human presence, specifically whether they are able to habituate to human presence, as frequently assumed, or are selected based on their fear of humans. We tested whether fear of humans (measured as flight initiation distance in a diurnal owl) is reduced through habituation to human presence (plasticity) or whether it remains unchanged throughout the individuals' life. Results show an unusually high level of individual consistency in fear of humans throughout the adult lifespan of both rural (r = 0.96) and urban (r = 0.90) birds, lending no support to habituation. Further research should assess the role of inter-individual variability in fear of humans in shaping the distribution of individuals and species in an increasingly humanized world.

Mathematical description and analysis of adaptive risk choice behavior

Which risk should one choose when facing alternatives with different levels of risk? We discuss here adaptive processes in such risk choice behavior by generalizing the study of Roos et al. [2010]. We deal with an n -choice game in which every player sequentially chooses n times of lotteries of which there are two types: a safe lottery and a risky lottery. We analyze this model in more detail by elaborating the game. Based on the results of mathematical analysis, replicator dynamics analysis, and numerical simulations, we derived some salient features of risk choice behavior. We show that all the risk strategies can be divided into two groups: persistence and nonpersistence. We also proved that the dynamics with perturbation in which a mutation is installed is globally asymptotically stable to a unique equilibrium point for any initial population. The numerical simulations clarify that the number of persistent strategies seldom increases regardless of the increase in n , and suggest that a rarity of dominant choice strategies is widely observed in many social contexts. These facts not only go hand-in-hand with some well-known insights from prospect theory, but may also provide some theoretical hypotheses for various fields such as behavioral economics, ecology, sociology, and consumer behavioral theory.

Patrimony and the evolution of risk-taking

The propensity to make risky choices has a genetic component, and recent studies have identified several specific genes that contribute to this trait. Since risk-taking often appears irrational or maladaptive, the question arises how (or if) natural selection favors risk-taking. Here we show, using a stochastic simulation of selection between two hypothetical species, “R” (risk-seeking) and “A” (risk-averse) that, when expected reproductive fitness of the individual is unaffected by the making of the risky choice (winnings balanced by losses) natural selection (taken to the point of extinction) favors the risk-averse species. However, the situation is entirely reversed if offspring are permitted to inherit a small fraction of the parent's increased or decreased fitness acquired through risk-taking. This seemingly Lamarckian form of inheritance actually corresponds to the human situation when property or culture are transmitted in families. In the presence of this “cultural inheritance”, the long-shot risk-taking species was overwhelmingly favored, even when 90% of individuals were rendered sterile by a losing choice. Given this strong effect in a minimal model, it is important to consider the co-evolution of genes and culture when interpreting the genetics of risk-taking. This conclusion applies, in principle, to any species where parental resources can directly affect the fecundity of offspring. It might also be relevant to the effects of epigenetic inheritance, if the epigenetic state of zygotes can be affected by parental experiences.