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Author |
Cameron, E.Z. |
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Title |
Facultative adjustment of mammalian sex ratios in support of the Trivers-Willard hypothesis: evidence for a mechanism |
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Journal Article |
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Year |
2004 |
Publication |
Proceedings. Biological sciences / The Royal Society |
Abbreviated Journal |
Proc Biol Sci |
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Volume |
271 |
Issue |
1549 |
Pages |
1723-1728 |
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Keywords |
Age Factors; Animals; Body Constitution; *Evolution; Female; Glucose/metabolism/physiology; Litter Size; Male; Mammals/*physiology; *Models, Biological; Reproduction/physiology; Seasons; Sex Factors; *Sex Ratio; Time Factors |
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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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Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa. ezcameron@zoology.up.ac.za |
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0962-8452 |
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PMID:15306293 |
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refbase @ user @ |
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413 |
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Author |
Etienne, A.S.; Maurer, R.; Seguinot, V. |
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Title |
Path integration in mammals and its interaction with visual landmarks |
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Journal Article |
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Year |
1996 |
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The Journal of Experimental Biology |
Abbreviated Journal |
J Exp Biol |
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Volume |
199 |
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Pt 1 |
Pages |
201-209 |
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Keywords |
Animals; Cognition/physiology; Cricetinae; Gerbillinae; Humans; Locomotion/*physiology; Mammals/*physiology; Mesocricetus; Mice; Proprioception/physiology; Rats; Visual Pathways/*physiology; Visual Perception/*physiology |
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Abstract |
During locomotion, mammals update their position with respect to a fixed point of reference, such as their point of departure, by processing inertial cues, proprioceptive feedback and stored motor commands generated during locomotion. This so-called path integration system (dead reckoning) allows the animal to return to its home, or to a familiar feeding place, even when external cues are absent or novel. However, without the use of external cues, the path integration process leads to rapid accumulation of errors involving both the direction and distance of the goal. Therefore, even nocturnal species such as hamsters and mice rely more on previously learned visual references than on the path integration system when the two types of information are in conflict. Recent studies investigate the extent to which path integration and familiar visual cues cooperate to optimize the navigational performance. |
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Laboratoire d'Ethologie, FPSE, Universite de Geneve, Carouge, Switzerland |
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0022-0949 |
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PMID:8576691 |
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Equine Behaviour @ team @ |
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2758 |
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Author |
Gallistel, C.R.; Cramer, A.E. |
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Title |
Computations on metric maps in mammals: getting oriented and choosing a multi-destination route |
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Journal Article |
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Year |
1996 |
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The Journal of Experimental Biology |
Abbreviated Journal |
J Exp Biol |
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199 |
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Pt 1 |
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211-217 |
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Keywords |
Animals; Brain/physiology; Cercopithecus aethiops; Cognition/*physiology; Humans; Mammals/*physiology; Movement; Orientation/*physiology; Rats; Space Perception; Visual Pathways/*physiology |
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Abstract |
The capacity to construct a cognitive map is hypothesized to rest on two foundations: (1) dead reckoning (path integration); (2) the perception of the direction and distance of terrain features relative to the animal. A map may be constructed by combining these two sources of positional information, with the result that the positions of all terrain features are represented in the coordinate framework used for dead reckoning. When animals need to become reoriented in a mapped space, results from rats and human toddlers indicate that they focus exclusively on the shape of the perceived environment, ignoring non-geometric features such as surface colors. As a result, in a rectangular space, they are misoriented half the time even when the two ends of the space differ strikingly in their appearance. In searching for a hidden object after becoming reoriented, both kinds of subjects search on the basis of the object's mapped position in the space rather than on the basis of its relationship to a goal sign (e.g. a distinctive container or nearby marker), even though they have demonstrably noted the relationship between the goal and the goal sign. When choosing a multidestination foraging route, vervet monkeys look at least three destinations ahead, even though they are only capable of keeping a maximum of six destinations in mind at once. |
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Department of Psychology, University of California, Los Angeles 90095, USA |
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0022-0949 |
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PMID:8576692 |
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Equine Behaviour @ team @ |
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2757 |
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Author |
Staunton, H. |
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Title |
Mammalian sleep |
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Journal Article |
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Year |
2005 |
Publication |
Die Naturwissenschaften |
Abbreviated Journal |
Naturwissenschaften |
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Volume |
92 |
Issue |
5 |
Pages |
203-220 |
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Animals; Brain/*physiology; Dreams/physiology; Electroencephalography; Humans; Mammals/*physiology; Sleep/*physiology; Sleep, REM/physiology; Wakefulness/physiology |
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This review examines the biological background to the development of ideas on rapid eye movement sleep (REM sleep), so-called paradoxical sleep (PS), and its relation to dreaming. Aspects of the phenomenon which are discussed include physiological changes and their anatomical location, the effects of total and selective sleep deprivation in the human and animal, and REM sleep behavior disorder, the latter with its clinical manifestations in the human. Although dreaming also occurs in other sleep phases (non-REM or NREM sleep), in the human, there is a contingent relation between REM sleep and dreaming. Thus, REM is taken as a marker for dreaming and as REM is distributed ubiquitously throughout the mammalian class, it is suggested that other mammals also dream. It is suggested that the overall function of REM sleep/dreaming is more important than the content of the individual dream; its function is to place the dreamer protagonist/observer on the topographical world. This has importance for the developing infant who needs to develop a sense of self and separateness from the world which it requires to navigate and from which it is separated for long periods in sleep. Dreaming may also serve to maintain a sense of 'I'ness or “self” in the adult, in whom a fragility of this faculty is revealed in neurological disorders. |
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Department of Clinical Neurological Sciences, Royal College of Surgeons in Ireland, Dublin 2, Ireland. hugh@iol.ie |
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0028-1042 |
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Notes |
PMID:15843983 |
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Call Number |
Equine Behaviour @ team @ |
Serial |
2796 |
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