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931.
Nader MA Czoty PW Gould RW Riddick NV 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2008,363(1507):3223-3232
Animal models have provided valuable information related to trait and state variables associated with vulnerability to drug addiction. Our brain imaging studies in monkeys have implicated D2 receptors in cocaine addiction. For example, an inverse relationship between D2 receptor availability and rates of cocaine self-administration has been documented. Moreover, environmental variables, such as those associated with formation of the social hierarchy, can impact receptor availability and sensitivity to the abuse-related effects of cocaine. Similarly, both D2 receptor availability and cocaine self-administration can be altered by chronic drug administration and fluctuations in hormone levels. In addition, cocaine self-administration can be altered in an orderly fashion by presentation of an acute stressor, such as acting as an intruder into an unfamiliar social group, which can shift the cocaine dose-response curve to the left in subordinate monkeys and to the right in dominant animals, suggesting an interaction between social variables and acute stressors. Conversely, irrespective of social rank, acute environmental enrichment, such as increasing the size of the living space, shifts the cocaine dose-response curve to the right. These findings highlight a pervasive influence of the environment in modifying the reinforcing effects of cocaine and strongly implicate brain D2 receptors. 相似文献
932.
Grémillet D Pichegru L Kuntz G Woakes AG Wilkinson S Crawford RJ Ryan PG 《Proceedings. Biological sciences / The Royal Society》2008,275(1639):1149-1156
Worldwide fisheries generate large volumes of fishery waste and it is often assumed that this additional food is beneficial to populations of marine top-predators. We challenge this concept via a detailed study of foraging Cape gannets Morus capensis and of their feeding environment in the Benguela upwelling zone. The natural prey of Cape gannets (pelagic fishes) is depleted and birds now feed extensively on fishery wastes. These are beneficial to non-breeding birds, which show reduced feeding effort and high survival. By contrast, breeding gannets double their diving effort in an attempt to provision their chicks predominantly with high-quality, live pelagic fishes. Owing to a scarcity of this resource, they fail and most chicks die. Our study supports the junk-food hypothesis for Cape gannets since it shows that non-breeding birds can survive when complementing their diet with fishery wastes, but that they struggle to reproduce if live prey is scarce. This is due to the negative impact of low-quality fishery wastes on the growth patterns of gannet chicks. Marine management policies should not assume that fishery waste is generally beneficial to scavenging seabirds and that an abundance of this artificial resource will automatically inflate their populations. 相似文献
933.
Clucas B Owings DH Rowe MP 《Proceedings. Biological sciences / The Royal Society》2008,275(1636):847-852
Ground squirrels (Spermophilus spp.) have evolved a battery of defences against the rattlesnakes (Crotalus spp.) that have preyed on them for millions of years. The distinctive behavioural reactions by these squirrels to rattlesnakes have recently been shown to include self-application of rattlesnake scent-squirrels apply scent by vigorously licking their fur after chewing on shed rattlesnake skins. Here, we present evidence that this behaviour is a novel antipredator defence founded on exploitation of a foreign scent. We tested three functional hypotheses for snake scent application--antipredator, conspecific deterrence and ectoparasite defence--by examining reactions to rattlesnake scent by rattlesnakes, ground squirrels and ectoparasites (fleas). Rattlesnakes were more attracted to ground squirrel scent than to ground squirrel scent mixed with rattlesnake scent or rattlesnake scent alone. However, ground squirrel behaviour and flea host choice were not affected by rattlesnake scent. Thus, ground squirrels can reduce the risk of rattlesnake predation by applying rattlesnake scent to their bodies, potentially as a form of olfactory camouflage. Opportunistic exploitation of heterospecific scents may be widespread; many species self-apply foreign odours, but few such cases have been demonstrated to serve in antipredator defence. 相似文献
934.
935.
Geographical variation of genetic and phenotypic traits in the Mexican sailfin mollies, Poecilia velifera and P. petenensis 总被引:1,自引:1,他引:0
Comparing the patterns of population divergence using both neutral genetic and phenotypic traits provides an opportunity to examine the relative importance of evolutionary mechanisms in shaping population differences. We used microsatellite markers to examine population genetic structure in the Mexican sailfin mollies Poecilia velifera and P. petenensis. We compared patterns of genetic structure and divergence to that in two types of phenotypic traits: morphological characters and mating behaviours. Populations within each species were genetically distinct, and conformed to a model of isolation by distance, with populations within different geographical regions being more genetically similar to one another than were populations from different regions. Bayesian clustering and barrier analyses provided additional support for population separation, especially between geographical regions. In contrast, none of the phenotypic traits showed any type of geographical pattern, and population divergence in these traits was uncorrelated with that found in neutral markers. There was also a weaker pattern of regional differences among geographical regions compared to neutral genetic divergence. These results suggest that while divergence in neutral traits is likely a product of population history and genetic drift, phenotypic divergence is governed by different mechanisms, such as natural and sexual selection, and arises at spatial scales independent from those of neutral markers. 相似文献
936.
Rick S Loewenstein G 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2008,363(1511):3813-3824
Since the advent of the discounted utility (DU) model, economists have thought about intertemporal choice in very specific terms. DU assumes that people make explicit trade-offs between costs and benefits occurring at different points in time. While this explicit trade-off perspective is simple and tractable, and has stimulated productive research, it does not provide a very realistic representation of a wide range of the most important intertemporal trade-offs that people face in daily life. If one considers the most important and commonly discussed examples of intertemporal choices, a striking pattern emerges: in almost all cases, early outcomes tend to be concrete (e.g. purchasing this latte), but later outcomes tend to be much less tangible (e.g. the unknown item that could have been purchased later with the money spent on this latte). We propose that people rely on anticipatory emotions as a proxy for intangible outcomes when trade-offs are implicit. This paper reviews neuroeconomic evidence that has begun to elucidate the role of anticipatory emotions in decisions involving intangible outcomes. Although most progress has been made in the domain of spending and saving, we discuss how the existing neuroeconomic research could be extended to other domains where trade-offs are ill defined. 相似文献
937.
Parasites can fundamentally alter the cost–benefit ratio of living in a group, e.g. if infected individuals increase the predation
risk of shoal mates. Here, the effect of an infection with a trematode, Uvulifer sp. (Diplostomatidae) on the shoaling behaviour of female western mosquitofish, Gambusia affinis, was investigated. The parasite examined causes a direct phenotypical change of the host by forming black spots on its body
surface. When given a choice between a stimulus shoal and no shoal, we found shoaling tendencies to be significantly reduced
in infected focal fish. In another experiment, we tested for association preferences relative to the infection status of the
stimulus fish. Given the choice between an infected and a healthy stimulus fish, both infected and healthy focal fish preferred
to associate with non-infected stimulus fish. Our results suggest that (1) the cost–benefit ratio of shoaling might be different
for infected and non-infected individuals. Infected fish may be more affected by competition for food within a shoal. (2)
Associating with infected conspecifics appears to be costly for female mosquitofish, maybe due to increased predation risk. 相似文献
938.
Martina Hrušková-Martišová Stano Pekár Alexandr Gromov 《Journal of Insect Behavior》2008,21(5):440-449
Stridulation in solifuges has not been investigated yet. We performed a comparative analysis of the stridulatory organs and
sounds produced by juveniles of various developmental stages and adults (both sexes) of Galeodes caspius subfuscus Birula. The stridulatory organ is of similar morphology in all developmental stages. The sound that they produced was a broad
frequency hissing, composed of one or two chirps with maximum at 2.4 kHz. The intensity of the sound was found to increase
with body size. Otherwise, no differences were observed between stridulation in juvenile, male and female individuals. Therefore,
we suggest that the stridulation in solifuges has primarily a defensive role. As solifuges are neither venomous nor unpalatable,
they might imitate an accoustically aposematic organism that shares the same habitat and has similar circadian activity, e.g.
vipers. It may also have an intraspecific function in reduction of cannibalistic tendencies. 相似文献
939.
940.
Rob Vreeker Liangbin Li Yapeng Fang Ingrid Appelqvist Eduardo Mendes 《Food biophysics》2008,3(4):361-369
In this paper, we study the rehydration properties of air-dried calcium alginate gel beads. Rehydration is shown to depend
on alginate source (i.e. mannuronic to guluronic acid ratio) and the salt concentration in the rehydration medium. Rehydration
curves are described adequately by the empirical Weibull equation. Wide-angle X-ray diffraction measurements are performed
to obtain information on the microstructure of dried alginate gels. The X-ray diffraction patterns provide evidence for formation
of ordered domains in which alginate polymers are laterally associated. Formation of ordered structures during drying is found
to have a large impact on rehydration properties. Lateral association of alginate chains is reduced (and rehydration improved)
by removing excess calcium ions from the gel beads in a washing step prior to air drying. In addition, rehydration properties
of mixed alginate–carboxymethyl cellulose (CMC) gel beads are investigated. The presence of CMC in the gel matrix is found
to reduce lateral association of alginate chains during drying and to improve rehydration properties. 相似文献