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Kirkpatrick, J. F., Vail, R., Devous, S., Schwend, S., Baker, C. B., & Wiesner, L. (1976). Diurnal variation of plasma testosterone in wild stallions. Biol Reprod, 15(1), 98–101.
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Hertsch, B., & Becker, C. (1986). [Occurrence of aseptic necrosis of the palmar and plantar ligament in the horse--a contribution to the differentiation of sesamoid bone diseases]. Dtsch Tierarztl Wochenschr, 93(6), 263–266.
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Kraus-Hansen, A. E., Fackelman, G. E., Becker, C., Williams, R. M., & Pipers, F. S. (1992). Preliminary studies on the vascular anatomy of the equine superficial digital flexor tendon. Equine Vet J, 24(1), 46–51.
Abstract: The vascular and microvascular anatomy of normal equine superficial digital flexor tendons was studied by dissection of vinyl-perfused specimens and by microangiography on high detail film. The presence of an extensive intratendinous vascular latticework was confirmed, and a 'nutrient artery' described closely associated with the accessory ligament of the superficial digital flexor tendon (proximal check ligament). Circumferential stripping of the paratenon from the tendon to eliminate afferent vessels was performed bilaterally in three horses and unilaterally in a fourth, followed by a treadmill training regimen. No resulting intratendinous lesions could be documented on gross post mortem and histological examination at three, 10, or 35 days post operatively. There was mild paratendinous proliferation in all instances. In one horse, four intratendinous ligatures were placed within the medial and lateral borders of the contralateral tendon to isolate further from its blood supply a 10 cm segment. Gross lesions at 35 days post operatively included a marked paratendinous response involving the entire 10 cm segment, and a darkened, soft focus within the core of the tendon. Histopathology and electron microscopy demonstrated focal degeneration. It was concluded that the blood supply of the normal equine superficial digital flexor tendon is primarily intratendinous, rather than paratendinous as previously thought. The lesions in one horse similar to those in naturally occurring tendinitis supported a vascular aetiology of the disease, and set the groundwork for studies aimed at the development of a clinically relevant tendinitis model.
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de Waal, F. B. M., Dindo, M., Freeman, C. A., & Hall, M. J. (2005). The monkey in the mirror: hardly a stranger. Proc. Natl. Acad. Sci. U.S.A., 102(32), 11140–11147.
Abstract: It is widely assumed that monkeys see a stranger in the mirror, whereas apes and humans recognize themselves. In this study, we question the former assumption by using a detailed comparison of how monkeys respond to mirrors versus live individuals. Eight adult female and six adult male brown capuchin monkeys (Cebus apella) were exposed twice to three conditions: (i) a familiar same-sex partner, (ii) an unfamiliar same-sex partner, and (iii) a mirror. Females showed more eye contact and friendly behavior and fewer signs of anxiety in front of a mirror than they did when exposed to an unfamiliar partner. Males showed greater ambiguity, but they too reacted differently to mirrors and strangers. Discrimination between conditions was immediate, and blind coders were able to tell the difference between monkeys under the three conditions. Capuchins thus seem to recognize their reflection in the mirror as special, and they may not confuse it with an actual conspecific. Possibly, they reach a level of self-other distinction intermediate between seeing their mirror image as other and recognizing it as self.
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Flack, J. C., Krakauer, D. C., & de Waal, F. B. M. (2005). Robustness mechanisms in primate societies: a perturbation study. Proc Biol Sci, 272(1568), 1091–1099.
Abstract: Conflict management mechanisms have a direct, critical effect on system robustness because they mitigate conflict intensity and help repair damaged relationships. However, robustness mechanisms can also have indirect effects on system integrity by facilitating interactions among components. We explore the indirect role that conflict management mechanisms play in the maintenance of social system robustness, using a perturbation technique to 'knockout' components responsible for effective conflict management. We explore the effects of knockout on pigtailed macaque (Macaca nemestrina) social organization, using a captive group of 84 individuals. This system is ideal in addressing this question because there is heterogeneity in performance of conflict management. Consequently, conflict managers can be easily removed without disrupting other control structures. We find that powerful conflict managers are essential in maintaining social order for the benefit of all members of society. We show that knockout of components responsible for conflict management results in system destabilization by significantly increasing mean levels of conflict and aggression, decreasing socio-positive interaction and decreasing the operation of repair mechanisms.
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Brosnan, S. F., Schiff, H. C., & de Waal, F. B. M. (2005). Tolerance for inequity may increase with social closeness in chimpanzees. Proc Biol Sci, 272(1560), 253–258.
Abstract: Economic decision-making depends on our social environment. Humans tend to respond differently to inequity in close relationships, yet we know little about the potential for such variation in other species. We examine responses to inequity in several groups of chimpanzees (Pan troglodytes) in a paradigm similar to that used previously in capuchin monkeys (Cebus apella). We demonstrate that, like capuchin monkeys, chimpanzees show a response to inequity of rewards that is based upon the partner receiving the reward rather than the presence of the reward alone. However, we also found a great amount of variation between groups tested, indicating that chimpanzees, like people, respond to inequity in a variable manner, which we speculate could be caused by such variables as group size, the social closeness of the group (as reflected in length of time that the group has been together) and group-specific traditions.
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Flack, J. C., Jeannotte, L. A., & de Waal, F. B. M. (2004). Play signaling and the perception of social rules by juvenile chimpanzees (Pan troglodytes). J Comp Psychol, 118(2), 149–159.
Abstract: Prescriptive social rules are enforced statistical regularities. The authors investigated whether juvenile chimpanzees (Pan troglodytes) recognize and use enforced statistical regularities to guide dyadic play behavior. They hypothesized (a) that proximity of adults, especially mothers of younger play partners, to play bouts will increase the play signaling of older partners and (b) that when juvenile-juvenile play bouts occur in proximity to adults, older partners will play at a lower intensity than when no adults are present. They found that older and younger partners increase their play signaling in the presence of the mothers of younger partners, particularly as the intensity of play bouts increases. In contrast to their hypothesis, older partners played more roughly when the mothers of younger partners were in proximity. These results suggest that juvenile chimpanzees increase play signaling to prevent termination of the play bouts by mothers of younger partners.
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Akins, C. K., Klein, E. D., & Zentall, T. R. (2002). Imitative learning in Japanese quail (Coturnix japonica) using the bidirectional control procedure. Anim Learn Behav, 30(3), 275–281.
Abstract: In the bidirectional control procedure, observers are exposed to a conspecific demonstrator responding to a manipulandum in one of two directions (e.g., left vs. right). This procedure controls for socially mediated effects (the mere presence of a conspecific) and stimulus enhancement (attention drawn to a manipulandum by its movement), and it has the added advantage of being symmetrical (the two different responses are similar in topography). Imitative learning is demonstrated when the observers make the response in the direction that they observed it being made. Recently, however, it has been suggested that when such evidence is found with a predominantly olfactory animal, such as the rat, it may result artifactually from odor cues left on one side of the manipulandum by the demonstrator. In the present experiment, we found that Japanese quail, for which odor cues are not likely to play a role, also showed significant correspondence between the direction in which the demonstrator and the observer push a screen to gain access to reward. Furthermore, control quail that observed the screen move, when the movement of the screen was not produced by the demonstrator, did not show similar correspondence between the direction of screen movement observed and that performed by the observer. Thus, with the appropriate control, the bidirectional procedure appears to be useful for studying imitation in avian species.
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Akins, C. K., & Zentall, T. R. (1996). Imitative learning in male Japanese quail (Coturnix japonica) using the two-action method. J Comp Psychol, 110(3), 316–320.
Abstract: The study of imitative learning in animals has suffered from the presence of a number of confounding motivational and attentional factors (e.g., social facilitation and stimulus enhancement). The two-action method avoids these problems by exposing observers to demonstrators performing a response (e.g., operating a treadle) using 1 of 2 distinctive topographies (e.g., by pecking or by stepping). Japanese quail (Coturnix japonica) observers exposed to conspecific demonstrators showed a high correlation between the topography of the response they observed and the response they performed. These data provide strong evidence for the existence of true imitative learning in an active, precocious bird under conditions that control for alternative accounts.
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Zentall, T. R., Hogan, D. E., Edwards, C. A., & Hearst, E. (1980). Oddity learning in the pigeon as a function of the number of incorrect alternatives. J Exp Psychol Anim Behav Process, 6(3), 278–299.
Abstract: Pigeons' rate of learning a two-color oddity task increased as a function of the number of incorrect alternatives from 2 to 24 in Experiments 1, 2, and 3. In general, pigeons that were transferred from many-incorrect-alternative to two-incorrect-alternative oddity performed better than controls, but considerably below baseline (Experiments 2 and 3). In Experiment 4, pigeons showed no unconditioned tendency to peck the odd stimulus among 24 incorect alternatives, when pecks were nondifferentially reinforced, and in Experiment 5, when this procedure was preceded by oddity training, a progressive drop in odd-stimulus pecking was found. In Experiment 6, pigeons exposed to a nine-stimulus array in which the odd stimulus appeared (a) in the center or (b) separate from the array learned faster than when the odd stimulus was at the edge. This outcome suggests ththe figure-ground relation between the odd stimulus and the incorrect alternatives plays a role in the facilitation produced by increasing the number of incorrect alternatives but that poor performance on the standard, three-alternative oddity task appears to be due to center-odd trials which provide a difficult size or number discrimination.
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