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Manipulation Used (manipulation + used)
Selected AbstractsNo Plastic Responses to Experimental Manipulation of Sperm Competition per se in a Free-Living FlatwormETHOLOGY, Issue 4 2010Peter Sandner In the absence of sperm competition evolutionary theory predicts low mating rates and low ejaculate expenditure per mating, and sex allocation theory for simultaneous hermaphrodites predicts a strongly female-biased sex allocation. In the presence of sperm competition a shift towards a more male-biased sex allocation and a higher ejaculate expenditure are predicted. The free-living flatworm Macrostomum lignano has been shown to respond plastically in mating rate, testis size, and sperm transfer to manipulation of the social group size, a proxy of the strength of sperm competition. However, manipulation of social group size may manipulate not only sperm competition, but also other factors, such as food supply and metabolite concentration. In this study we therefore manipulated sperm competition per se by repeatedly exposing individuals to partners that have either mated with rivals or not, while keeping the social group size constant. Our results suggest that M. lignano does not have the ability to detect sperm competition per se, as worms experimentally exposed to the presence or absence of sperm competition did not differ in sex allocation, sperm transfer or mating behavior. A response to our manipulation would have required individual recognition, the ability to detect self-referencing tags, or tags or traces left by rivals on or in the mating partners. We first discuss the possibility that highly efficient sperm displacement may have decreased the difference between the treatment groups and then propose three alternative cues that may allow M. lignano to respond plastically to the social group size manipulation used in earlier studies: assessment of the mating rate, chemical cues, or tactile cues. [source] How is sexual conflict over parental care resolved?JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 9 2009A meta-analysis Abstract Biparental care of offspring is both a form of cooperation and a source of conflict. Parents face a trade-off between current and future reproduction: caring less for the current brood allows individuals to maintain energy reserves and increase their chances of remating. How can selection maintain biparental care, given this temptation to defect? The answer lies in how parents respond to changes in each other's effort. Game-theoretical models predict that biparental care is evolutionarily stable when reduced care by one parent leads its partner to increase care, but not so much that it completely compensates for the lost input. Experiments designed to reveal responses to reduced partner effort have mainly focused on birds. We present a meta-analysis of 54 such studies, and conclude that the mean response was indeed partial compensation. Males and females responded differently and this was in part mediated by the type of manipulation used. [source] Threat, Authoritarianism, and Selective Exposure to InformationPOLITICAL PSYCHOLOGY, Issue 2 2005Howard Lavine We examined the hypothesis that threat alters the cognitive strategies used by high authoritarians in seeking out new political information from the environment. In a laboratory experiment, threat was manipulated through a "mortality salience" manipulation used in research on terror management theory (Pyszczynski, Solomon & Greenberg, 2003). Subjects (N = 92) were then invited to read one of three editorial articles on the topic of capital punishment. We found that in the absence of threat, both low and high authoritarians were responsive to salient norms of evenhandedness in information selection, preferring exposure to a two-sided article that presents the merits of both sides of an issue to an article that selectively touts the benefits of the pro or con side of the issue. However, in the presence of threat, high but not low authoritarians became significantly more interested in exposure to an article containing uniformly pro-attitudinal arguments, and significantly less interested in a balanced, two-sided article. Finally, a path analysis indicated that selective exposure to attitude-congruent information led to more internally consistent policy attitudes and inhibited attitude change. Discussion focuses on the role of threat in conditioning the cognitive and attitudinal effects of authoritarianism. [source] The fragile basic anchoring effectJOURNAL OF BEHAVIORAL DECISION MAKING, Issue 1 2002Noel T. Brewer Abstract The anchoring bias, the effect of uninformative anchor numbers on judgments, is a robust finding. In experiments yielding the anchoring bias, typically participants are explicitly asked to compare the anchor and target. A logical question is whether any manner of considering a number will bias peoples' judgment. Wilson et al. (1996) showed that merely presenting a number to people will bias their judgments, a result they termed basic anchoring. The absence of any published studies that followed up on Wilson et al.'s work prompted us to examine the basic anchoring effect in three experiments. The three experiments (N,=,881, 205, and 117) suggest that basic anchoring is a weak effect limited to the precise manipulations used by Wilson et al. Trivial changes such as altering the order of a series of anchor numbers, or using different anchor numbers, eliminated the bias. Our findings suggest that basic anchoring has a much narrower scope of impact than traditional anchoring effects. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||