Presentation Information
[POS-48]Anxiety-causing alleles are favored in moderately stressful environments
*Kenta Motoyashiki1, Motohide Seki1 (1. Kyushu University (Japan))
Keywords:
Evolutionary medicine,Depression,Anxiety
Evolutionary biologists have hypothesized that humans have evolved to experience excessive emotional pain such as anxiety and depression because these responses have conferred survival advantages by promoting avoidance of harmful situations in ancestral environments. In fact, several stress-sensitive alleles are known to have evolved. They coexist with relatively stress-insensitive wild-type alleles at higher frequencies in Eurasia than in Africa. However, the selection pressures responsible for this geographic gradient remain debated. In addition, the complex relationship among stress sensitivity, anxiety, and depression is still unclear, especially concerning whether these psychological traits share common genetic origins. In this study, we developed three models—anxiety, depression, and combined models—to investigated how environmental diversity could lead to genetic divergence.
We applied a population genetics model to investigate the evolution of stress-sensitive alleles. Suppose that a diploid player engages in N rounds of trials at a site that represents a foraging ground or a workplace. Site condition is either Good or Bad, and players cannot distinguish between them. The failure rates of a trial at Good and Bad sites are wG and wB, respectively (0 < wG < wB < 1). In each round, players who have succeeded receive a payoff of 1. Those who have failed gain at most a (a < 1). Some of them withdraw from the failed trial with a genotype-dependent probability, in which case they receive (1 - s)a (0 < s < 1). The fitness of a player is defined as the sum of payoffs over N rounds. In the depression model, those withdrawing from a trial do nothing else and the site condition changes probabilistically. In the anxiety model, the withdrawers move to another site driven by anxiety, which may change the situation.
We found that stress-sensitive alleles are favored in moderately stressful environments, in which those alleles help avoid harmful situations, in the anxiety model. The anxiety model predicts that the equilibrium frequency of stress-sensitive alleles is influenced by environmental diversity rather than absolute environmental risk that harm fitness. The fact that several stress-sensitive alleles are more frequent in Eurasia than in Africa suggests that Eurasia has had a greater environmental variation. In contrast, lower environmental diversity in Africa could indicate either consistently favorable or consistent situations that harm fitness.
We applied a population genetics model to investigate the evolution of stress-sensitive alleles. Suppose that a diploid player engages in N rounds of trials at a site that represents a foraging ground or a workplace. Site condition is either Good or Bad, and players cannot distinguish between them. The failure rates of a trial at Good and Bad sites are wG and wB, respectively (0 < wG < wB < 1). In each round, players who have succeeded receive a payoff of 1. Those who have failed gain at most a (a < 1). Some of them withdraw from the failed trial with a genotype-dependent probability, in which case they receive (1 - s)a (0 < s < 1). The fitness of a player is defined as the sum of payoffs over N rounds. In the depression model, those withdrawing from a trial do nothing else and the site condition changes probabilistically. In the anxiety model, the withdrawers move to another site driven by anxiety, which may change the situation.
We found that stress-sensitive alleles are favored in moderately stressful environments, in which those alleles help avoid harmful situations, in the anxiety model. The anxiety model predicts that the equilibrium frequency of stress-sensitive alleles is influenced by environmental diversity rather than absolute environmental risk that harm fitness. The fact that several stress-sensitive alleles are more frequent in Eurasia than in Africa suggests that Eurasia has had a greater environmental variation. In contrast, lower environmental diversity in Africa could indicate either consistently favorable or consistent situations that harm fitness.