Correlates of Cooperation in a One-Shot High-Stakes Televised Prisoners' Dilemma

Explaining cooperation between non-relatives is a puzzle for both evolutionary biology and the social sciences. In humans, cooperation is often studied in a laboratory setting using economic games such as the prisoners' dilemma. However, such experiments are sometimes criticized for being played for low stakes and by misrepresentative student samples. Golden balls is a televised game show that uses the prisoners' dilemma, with a diverse range of participants, often playing for very large stakes. We use this non-experimental dataset to investigate the factors that influence cooperation when “playing” for considerably larger stakes than found in economic experiments. The game show has earlier stages that allow for an analysis of lying and voting decisions. We found that contestants were sensitive to the stakes involved, cooperating less when the stakes were larger in both absolute and relative terms. We also found that older contestants were more likely to cooperate, that liars received less cooperative behavior, but only if they told a certain type of lie, and that physical contact was associated with reduced cooperation, whereas laughter and promises were reliable signals or cues of cooperation, but were not necessarily detected

Genetic structure of natural Nasonia vitripennis populations: validating assumptions of sex-ratio theory

The parasitic wasp Nasonia vitripennis has been used extensively in sex allocation research. Although laboratory experiments have largely confirmed predictions of local mate competition (LMC) theory, the underlying assumptions of LMC models have hardly been explored in nature. We genotyped over 3500 individuals from two distant locations (in the Netherlands and Germany) at four polymorphic microsatellite loci to validate key assumptions of LMC theory, in terms of both the original models and more recent extensions to them. We estimated the number of females contributing eggs to patches of hosts and the clutch sizes as well as sex ratios produced by individual foundresses. In addition, we evaluated the level of inbreeding and population differentiation. Foundress numbers ranged from 1 to 7 (average 3.0 ± 0.46 SE). Foundresses were randomly distributed across the patches and across hosts within patches, with few parasitizing more than one patch. Of the hosts, 40% were parasitized by more than one foundress. Clutch sizes of individual foundresses (average 9.99 ± 0.51 SE) varied considerably between hosts. The time period during which offspring continued to emerge from a patch or host correlated strongly with foundress number, indicating that sequential rather than simultaneous parasitism is the more common. Genetic differentiation at the regional level between Germany and the Netherlands, as estimated by Slatkin’s private allele method (0.11) and Hedrick’s corrected G′LT (0.23), indicates significant substructuring between regions. The level of population inbreeding for the two localities (FIL = 0.168) fitted the expectation based on the average foundress number per patch.

Behavioural adaptation of Coquillettidia (Coquillettidia) richiardii larvae to underwater life: environmental cues governing plant-insect interaction

International audienceDensely overgrown pre-alpine permanent aquatic habitats are overrun by the mosquito Coquillettidia (Coquillettidia) richiardii (Ficalbi) (Diptera: Culicidae). The invasive potential of this insect depends on the ability of its larvae to survive on the roots of emergent aquatic macrophytes. In order to characterize this particular ecological niche, which is out of reach for a direct investigation, environmental factors likely to influence the interaction between larvae and host plant roots were investigated using a simplified laboratory microcosm. Environmental light and oxygen concentrations appeared to be the main factors influencing larval attachment, a dark anoxic environment being significantly more favourable. Carbon dioxide produced by the root system of the host plant appeared to be an attractive cue for larval attachment. Knowledge of the hierarchy of these environmental factors may enable us to better understand the ecological traits of larval C. richiardii in deep water. With regard to their management, new ecological data are required to develop a long-term control strategy against Coquillettidia mosquitoes

Moral Bargain Hunters Purchase Moral Righteousness When it is Cheap: Within-Individual Effect of Stake Size in Economic Games

Despite the repeatedly raised criticism that findings in economic games are specific to situations involving trivial incentives, most studies that have examined the stake-size effect have failed to find a strong effect. Using three prisoner’s dilemma experiments, involving 479 non-student residents of suburban Tokyo and 162 students, we show here that stake size strongly affects a player’s cooperation choices in prisoner’s dilemma games when stake size is manipulated within each individual such that each player faces different stake sizes. Participants cooperated at a higher rate when stakes were lower than when they were higher, regardless of the absolute stake size. These findings suggest that participants were ‘moral bargain hunters’ who purchased moral righteousness at a low price when they were provided with a ‘price list’ of prosocial behaviours. In addition, the moral bargain hunters who cooperated at a lower stake but not at a higher stake did not cooperate in a single-stake one-shot game