Arnold, K., & Zuberbuhler, K. (2006). Language evolution: semantic combinations in primate calls. Nature, 441(7091), 303.
Abstract: Syntax sets human language apart from other natural communication systems, although its evolutionary origins are obscure. Here we show that free-ranging putty-nosed monkeys combine two vocalizations into different call sequences that are linked to specific external events, such as the presence of a predator and the imminent movement of the group. Our findings indicate that non-human primates can combine calls into higher-order sequences that have a particular meaning.
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Ottoni, E. B., de Resende, B. D., & Izar, P. (2005). Watching the best nutcrackers: what capuchin monkeys (Cebus apella) know about others' tool-using skills. Anim. Cogn., 8(4), 215–219.
Abstract: The present work is part of a decade-long study on the spontaneous use of stones for cracking hard-shelled nuts by a semi-free-ranging group of brown capuchin monkeys (Cebus apella). Nutcracking events are frequently watched by other individuals--usually younger, less proficient, and that are well tolerated to the point of some scrounging being allowed by the nutcracker. Here we report findings showing that the choice of observational targets is an active, non-random process, and that observers seem to have some understanding of the relative proficiency of their group mates, preferentially watching the more skilled nutcrackers, which enhances not only scrounging payoffs, but also social learning opportunities.
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Skov-Rackette, S. I., & Shettleworth, S. J. (2005). What do rats learn about the geometry of object arrays? Tests with exploratory behavior. J Exp Psychol Anim Behav Process, 31(2), 142–154.
Abstract: Six experiments using habituation of exploratory behavior tested whether disoriented rats foraging in a large arena encode the shapes of arrays of objects. Rats did not respond to changes in position of a single object, but they responded to a change in object color and to a change in position of 1 object in a square array, as in previous research (e.g., C. Thinus-Blanc et al., 1987). Rats also responded to an expansion of a square array, suggesting that they encoded sets of interobject distances rather than overall shape. In Experiments 4-6, rats did not respond to changes in sense of a triangular array that maintained interobject distances and angles. Shapes of object arrays are encoded differently from shapes of enclosures.
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Krebs, J. R., Clayton, N. S., Hampton, R. R., & Shettleworth, S. J. (1995). Effects of photoperiod on food-storing and the hippocampus in birds. Neuroreport, 6(12), 1701–1704.
Abstract: Birds that store food have a relatively large hippocampus compared to non-storing species. The hippocampus shows seasonal differences in neurogenesis and volume in black-capped chikadees (Parus atricapillus) taken from the wild at different times of year. We compared hippocampal volumes in black-capped chickadees captured at the same time but differing in food-storing behaviour because of manipulations of photoperiod in the laboratory. Differences in food-storing behaviour were not accompanied by differences in the volume of the hippocampus. Hippocampal volumes also did not differ between two groups of a non-food-storing control species, house sparrows (Passer domesticus), exposed to the same conditions as the chickadees.
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Shettleworth, S. J., & Juergensen, M. R. (1980). Reinforcement and the organization of behavior in golden hamsters: brain stimulation reinforcement for seven action patterns. J Exp Psychol Anim Behav Process, 6(4), 352–375.
Abstract: Golden hamsters were reinforced with intracranial electrical stimulation of the lateral hypothalamus (ICS) for spending time engaging in one of seven topographically defined action patterns (APs). The stimulation used as reinforcer elicited hoarding and/or feeding and supported high rates of bar pressing. In Experiment 1, hamsters were reinforced successively for digging, open rearing, and face washing. Digging increased most in time spent, and face washing increased least. Experiments 2-5 examined these effects further and also showed that “scrabbling,” like digging, was performed a large proportion of the time, almost without interruption, for contingent ICS but that scratching the body with a hindleg and scent-marking showed relatively little effect of contingent ICS, the latter even in an environment that facilitated marking. In Experiment 6, naive hamsters received ICS not contingent on behavior every 30 sec (fixed-time 30-sec schedule). Terminal behaviors that developed on this schedule were APs that were easy to reinforce in the other experiments, but a facultative behavior, face washing, was one not so readily reinforced. Experiment 7 confirmed a novel prediction from Experiment 6--that wall rearing, a terminal AP, would be performed at a high level for contingent ICS. All together, the results point to both motivational factors and associative factors being involved in the considerable differences in performance among different reinforced activities.
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Shettleworth, S. J. (1978). Reinforcement and the organization of behavior in golden hamsters: Pavlovian conditioning with food and shock unconditioned stimuli. J Exp Psychol Anim Behav Process, 4(2), 152–169.
Abstract: The effects of Pavlovian conditioned stimuli (CSs) for food or shock on a variety of behaviors of golden hamsters were observed in three experiments. The aim was to see whether previously reported differences among the behaviors produced by food reinforcement and punishment procedures could be accounted for by differential effects of Pavlovian conditioning on the behaviors. There was some correspondence between the behaviors observed to the CSs and the previously reported effects of instrumental training. However, the Pavlovian conditioned responses (CRs) alone would not have predicted the effects of instrumental training. Moreover, CRs depended to some extent on the context in which training and testing occurred. These findings, together with others in the literature, suggest that the results of Pavlovian conditioning procedures may not unambiguously predict what system of behaviors will be most readily modified by instrumental training with a given reinforcer.
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Plotnik, J. M., de Waal, F. B. M., & Reiss, D. (2006). Self-recognition in an Asian elephant. Proc. Natl. Acad. Sci. U.S.A., 103(45), 17053–17057.
Abstract: Considered an indicator of self-awareness, mirror self-recognition (MSR) has long seemed limited to humans and apes. In both phylogeny and human ontogeny, MSR is thought to correlate with higher forms of empathy and altruistic behavior. Apart from humans and apes, dolphins and elephants are also known for such capacities. After the recent discovery of MSR in dolphins (Tursiops truncatus), elephants thus were the next logical candidate species. We exposed three Asian elephants (Elephas maximus) to a large mirror to investigate their responses. Animals that possess MSR typically progress through four stages of behavior when facing a mirror: (i) social responses, (ii) physical inspection (e.g., looking behind the mirror), (iii) repetitive mirror-testing behavior, and (iv) realization of seeing themselves. Visible marks and invisible sham-marks were applied to the elephants' heads to test whether they would pass the litmus “mark test” for MSR in which an individual spontaneously uses a mirror to touch an otherwise imperceptible mark on its own body. Here, we report a successful MSR elephant study and report striking parallels in the progression of responses to mirrors among apes, dolphins, and elephants. These parallels suggest convergent cognitive evolution most likely related to complex sociality and cooperation.
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Cameron, E. Z. (2004). Facultative adjustment of mammalian sex ratios in support of the Trivers-Willard hypothesis: evidence for a mechanism. Proc Biol Sci, 271(1549), 1723–1728.
Abstract: Evolutionary theory predicts that mothers of different condition should adjust the birth sex ratio of their offspring in relation to future reproductive benefits. Published studies addressing variation in mammalian sex ratios have produced surprisingly contradictory results. Explaining the source of such variation has been a challenge for sex-ratio theory, not least because no mechanism for sex-ratio adjustment is known. I conducted a meta-analysis of previous mammalian sex-ratio studies to determine if there are any overall patterns in sex-ratio variation. The contradictory nature of previous results was confirmed. However, studies that investigated indices of condition around conception show almost unanimous support for the prediction that mothers in good condition bias their litters towards sons. Recent research on the role of glucose in reproductive functioning have shown that excess glucose favours the development of male blastocysts, providing a potential mechanism for sex-ratio variation in relation to maternal condition around conception. Furthermore, many of the conflicting results from studies on sex-ratio adjustment would be explained if glucose levels in utero during early cell division contributed to the determination of offspring sex ratios.
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Clutton-Brock, T. H., Russell, A. F., Sharpe, L. L., Brotherton, P. N., McIlrath, G. M., White, S., et al. (2001). Effects of helpers on juvenile development and survival in meerkats. Science, 293(5539), 2446–2449.
Abstract: Although breeding success is known to increase with group size in several cooperative mammals, the mechanisms underlying these relationships are uncertain. We show that in wild groups of cooperative meerkats, Suricata suricatta, reductions in the ratio of helpers to pups depress the daily weight gain and growth of pups and the daily weight gain of helpers. Increases in the daily weight gain of pups are associated with heavier weights at independence and at 1 year of age, as well as with improved foraging success as juveniles and higher survival rates through the first year of life. These results suggest that the effects of helpers on the fitness of pups extend beyond weaning and that helpers may gain direct as well as indirect benefits by feeding pups.
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Hemelrijk, C. K., & Wantia, J. (2005). Individual variation by self-organisation. Neurosci Biobehav Rev, 29(1), 125–136.
Abstract: In this paper, we show that differences in dominance and spatial centrality of individuals in a group may arise through self-organisation. Our instrument is a model, called DomWorld, that represents two traits that are often found in animals, namely grouping and competing. In this model individual differences grow under the following conditions: (1) when the intensity of aggression increases and grouping becomes denser, (2) when the degree of sexual dimorphism in fighting power increases. In this case the differences among females compared to males grow too, (3) when, upon encountering another individual, the tendency to attack is 'obligate' and not conditional, namely 'sensitive to risks'. Results resemble phenomena described for societies of primates, mice, birds and pigs.
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