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Bergstrom, C. T., & Lachmann, M. (1997). Signalling among relatives. I. Is costly signalling too costly? Proc. Natl. Acad. Sci. U.S.A., 352(1353), 609–617.
Abstract: ahavi's handicap principle,originally proposed as an explanation for sexual selection ofelaborate male traits, suggests that a sufficient cost to dishonest signals can outweigh the rewards of deception and allow individuals to communicate honestly. Maynard Smith (1991) and Johnstone and Grafen (1992) introduce the Sir Philip Sidney game in order to extend the handicap principle to interactions among related individuals, and to demonstrate that stable costly signalling systems can exist among relatives.
In this paper we demonstrate that despite the benefits associated with honest information transfer, the costs incurred in a stable costly signalling system may leave all participants worse off than they would be in a system with no signalling at all. In both the discrete and continuous forms of the Sir Philip Sidney game, there exist conditions under which costly signalling among relatives, while stable, is so costly that it is disadvantageous compared with no signalling at all. We determine the factors which dictate signal cost and signal benefit in a generalized version of this game, and explain how signal cost can exceed signal value. Such results raise concerns about theevolutionary pathways which could have led to the existence of signalling equilibria in nature. The paper stresses the importance of comparing signalling equilibria with other possible strategies, beforedrawing conclusions regarding the optimality of signalling.
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Finarelli, J. A., & Flynn, J. J. (2009). Brain-size evolution and sociality in Carnivora. Proc. Natl. Acad. Sci. U.S.A., 106(23), 9345–9349.
Abstract: Increased encephalization, or larger brain volume relative to body mass, is a repeated theme in vertebrate evolution. Here we present an extensive sampling of relative brain sizes in fossil and extant taxa in the mammalian order Carnivora (cats, dogs, bears, weasels, and their relatives). By using Akaike Information Criterion model selection and endocranial volume and body mass data for 289 species (including 125 fossil taxa), we document clade-specific evolutionary transformations in encephalization allometries. These evolutionary transformations include multiple independent encephalization increases and decreases in addition to a remarkably static basal Carnivora allometry that characterizes much of the suborder Feliformia and some taxa in the suborder Caniformia across much of their evolutionary history, emphasizing that complex processes shaped the modern distribution of encephalization across Carnivora. This analysis also permits critical evaluation of the social brain hypothesis (SBH), which predicts a close association between sociality and increased encephalization. Previous analyses based on living species alone appeared to support the SBH with respect to Carnivora, but those results are entirely dependent on data from modern Canidae (dogs). Incorporation of fossil data further reveals that no association exists between sociality and encephalization across Carnivora and that support for sociality as a causal agent of encephalization increase disappears for this clade.
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Weisbecker, V., & Goswami, A. (2010). Brain size, life history, and metabolism at the marsupial/placental dichotomy. Proc. Natl. Acad. Sci. U.S.A., 107(37), 16216–16221.
Abstract: The evolution of mammalian brain size is directly linked with the evolution of the brain's unique structure and performance. Both maternal life history investment traits and basal metabolic rate (BMR) correlate with relative brain size, but current hypotheses regarding the details of these relationships are based largely on placental mammals. Using encephalization quotients, partial correlation analyses, and bivariate regressions relating brain size to maternal investment times and BMR, we provide a direct quantitative comparison of brain size evolution in marsupials and placentals, whose reproduction and metabolism differ extensively. Our results show that the misconception that marsupials are systematically smaller-brained than placentals is driven by the inclusion of one large-brained placental clade, Primates. Marsupial and placental brain size partial correlations differ in that marsupials lack a partial correlation of BMR with brain size. This contradicts hypotheses stating that the maintenance of relatively larger brains requires higher BMRs. We suggest that a positive BMR–brain size correlation is a placental trait related to the intimate physiological contact between mother and offspring during gestation. Marsupials instead achieve brain sizes comparable to placentals through extended lactation. Comparison with avian brain evolution suggests that placental brain size should be constrained due to placentals’ relative precociality, as has been hypothesized for precocial bird hatchlings. We propose that placentals circumvent this constraint because of their focus on gestation, as opposed to the marsupial emphasis on lactation. Marsupials represent a less constrained condition, demonstrating that hypotheses regarding placental brain size evolution cannot be generalized to all mammals.
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Harvey, P. H., Clutton-Brock, T. H., & Mace, G. M. (1980). Brain size and ecology in small mammals and primates. PNAS, 77(7), 4387–4389.
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Warmuth, V., Eriksson, A., Bower, M. A., Barker, G., Barrett, E., Hanks, B. K., et al. (2012). Reconstructing the origin and spread of horse domestication in the Eurasian steppe. Proc Natl Acad Sci U S A, .
Abstract: Despite decades of research across multiple disciplines, the early history of horse domestication remains poorly understood. On the basis of current evidence from archaeology, mitochondrial DNA, and Y-chromosomal sequencing, a number of different domestication scenarios have been proposed, ranging from the spread of domestic horses out of a restricted primary area of domestication to the domestication of numerous distinct wild horse populations. In this paper, we reconstruct both the population genetic structure of the extinct wild progenitor of domestic horses, Equus ferus, and the origin and spread of horse domestication in the Eurasian steppes by fitting a spatially explicit stepping-stone model to genotype data from >300 horses sampled across northern Eurasia. We find strong evidence for an expansion of E. ferus out of eastern Eurasia about 160 kya, likely reflecting the colonization of Eurasia by this species. Our best-fitting scenario further suggests that horse domestication originated in the western part of the Eurasian steppe and that domestic herds were repeatedly restocked with local wild horses as they spread out of this area. By showing that horse domestication was initiated in the western Eurasian steppe and that the spread of domestic herds across Eurasia involved extensive introgression from the wild, the scenario of horse domestication proposed here unites evidence from archaeology, mitochondrial DNA, and Y-chromosomal DNA.
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Sebilo, M., Mayer, B., Nicolardot, B., Pinay, G., & Mariotti, A. (2013). Long-term fate of nitrate fertilizer in agricultural soils. PNAS, .
Abstract: Increasing diffuse nitrate loading of surface waters and groundwater has emerged as a major problem in many agricultural areas of the world, resulting in contamination of drinking water resources in aquifers as well as eutrophication of freshwaters and coastal marine ecosystems. Although empirical correlations between application rates of N fertilizers to agricultural soils and nitrate contamination of adjacent hydrological systems have been demonstrated, the transit times of fertilizer N in the pedosphere–hydrosphere system are poorly understood. We investigated the fate of isotopically labeled nitrogen fertilizers in a three–decade-long in situ tracer experiment that quantified not only fertilizer N uptake by plants and retention in soils, but also determined to which extent and over which time periods fertilizer N stored in soil organic matter is rereleased for either uptake in crops or export into the hydrosphere. We found that 61–65% of the applied fertilizers N were taken up by plants, whereas 12–15% of the labeled fertilizer N were still residing in the soil organic matter more than a quarter century after tracer application. Between 8–12% of the applied fertilizer had leaked toward the hydrosphere during the 30-y observation period. We predict that additional exports of 15N-labeled nitrate from the tracer application in 1982 toward the hydrosphere will continue for at least another five decades. Therefore, attempts to reduce agricultural nitrate contamination of aquatic systems must consider the long-term legacy of past applications of synthetic fertilizers in agricultural systems and the nitrogen retention capacity of agricultural soils.
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Lergetporer, P., Angerer, S., Glätzle-Rützler, D., & Sutter, M. (2014). Third-party punishment increases cooperation in children through (misaligned) expectations and conditional cooperation. Proc. Natl. Acad. Sci. U.S.A., 111(19), 6916–6921.
Abstract: The human ability to establish cooperation, even in large groups of genetically unrelated strangers, depends upon the enforcement of cooperation norms. Third-party punishment is one important factor to explain high levels of cooperation among humans, although it is still somewhat disputed whether other animal species also use this mechanism for promoting cooperation. We study the effectiveness of third-party punishment to increase children’s cooperative behavior in a large-scale cooperation game. Based on an experiment with 1,120 children, aged 7 to 11 y, we find that the threat of third-party punishment more than doubles cooperation rates, despite the fact that children are rarely willing to execute costly punishment. We can show that the higher cooperation levels with third-party punishment are driven by two components. First, cooperation is a rational (expected payoff-maximizing) response to incorrect beliefs about the punishment behavior of third parties. Second, cooperation is a conditionally cooperative reaction to correct beliefs that third party punishment will increase a partner’s level of cooperation.
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Liker, A., & Bókony, V. (2009). Larger groups are more successful in innovative problem solving in house sparrows. Proc Natl Acad Sci USA, 106(19), 7893–7898.
Abstract: Group living offers well-known benefits to animals, such as better predator avoidance and increased foraging success. An important additional, but so far neglected, advantage is that groups may cope more effectively with unfamiliar situations through faster innovations of new solutions by some group members. We tested this hypothesis experimentally by presenting a new foraging task of opening a familiar feeder in an unfamiliar way to house sparrows in small and large groups (2 versus 6 birds). Group size had strong effects on problem solving: sparrows performed 4 times more and 11 times faster openings in large than in small groups, and all members of large groups profited by getting food sooner (7 times on average). Independently from group size, urban groups were more successful than rural groups. The disproportionately higher success in large groups was not a mere consequence of higher number of attempts, but was also related to a higher effectiveness of problem solving (3 times higher proportion of successful birds). The analyses of the birds' behavior suggest that the latter was not explained by either reduced investment in antipredator vigilance or reduced neophobia in large groups. Instead, larger groups may contain more diverse individuals with different skills and experiences, which may increase the chance of solving the task by some group members. Increased success in problem solving may promote group living in animals and may help them to adapt quickly to new situations in rapidly-changing environments.
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Morand-Ferron, J., & Quinn, J. L. (2011). Larger groups of passerines are more efficient problem solvers in the wild. Proc Natl Acad Sci USA, 108(38), 15898–15903.
Abstract: Group living commonly helps organisms face challenging environmental conditions. Although a known phenomenon in humans, recent findings suggest that a benefit of group living in animals generally might be increased innovative problem-solving efficiency. This benefit has never been demonstrated in a natural context, however, and the mechanisms underlying improved efficiency are largely unknown. We examined the problem-solving performance of great and blue tits at automated devices and found that efficiency increased with flock size. This relationship held when restricting the analysis to naive individuals, demonstrating that larger groups increased innovation efficiency. In addition to this effect of naive flock size, the presence of at least one experienced bird increased the frequency of solving, and larger flocks were more likely to contain experienced birds. These findings provide empirical evidence for the “pool of competence” hypothesis in nonhuman animals. The probability of success also differed consistently between individuals, a necessary condition for the pool of competence hypothesis. Solvers had a higher probability of success when foraging with a larger number of companions and when using devices located near rather than further from protective tree cover, suggesting a role for reduced predation risk on problem-solving efficiency. In contrast to traditional group living theory, individuals joining larger flocks benefited from a higher seed intake, suggesting that group living facilitated exploitation of a novel food source through improved problem-solving efficiency. Together our results suggest that both ecological and social factors, through reduced predation risk and increased pool of competence, mediate innovation in natural populations.
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Sol, D., Duncan, R. P., Blackburn, T. M., Cassey, P., & Lefebvre, L. (2005). Big brains, enhanced cognition, and response of birds to novel environments. Proc. Natl. Acad. Sci. U.S.A., 102(15), 5460–5465.
Abstract: The widely held hypothesis that enlarged brains have evolved as an adaptation to cope with novel or altered environmental conditions lacks firm empirical support. Here, we test this hypothesis for a major animal group (birds) by examining whether large-brained species show higher survival than small-brained species when introduced to nonnative locations. Using a global database documenting the outcome of >600 introduction events, we confirm that avian species with larger brains, relative to their body mass, tend to be more successful at establishing themselves in novel environments. Moreover, we provide evidence that larger brains help birds respond to novel conditions by enhancing their innovation propensity rather than indirectly through noncognitive mechanisms. These findings provide strong evidence for the hypothesis that enlarged brains function, and hence may have evolved, to deal with changes in the environment.
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