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Biomedical subjects

J R Krebs

Publications and source records attributed to J R Krebs.

12 recordsLinked to original sources
PubMed1992

Delayed-matching-to-sample by marsh tits and great tits.

The ability of two species of tits to remember the location and/or features of an object was tested in a delayed-matching-to-sample procedure. Three values of retention interval between presentation of the sample stimulus and the choice--30 sec, 5 min, and 15 min--were used. Both species performed at above-chance level at all retention intervals, and there was no significant decline in accuracy with increasing interval. A pool of 100 stimulus objects was used, but the results of control trials indicated that the birds responded primarily to location rather than stimulus features of the object itself. Although the food-storing marsh tit tended to perform at a higher level than the non-storing great tit, the only significant difference between the species was in the first 50 trials of the first treatment, when the birds were acquiring the task. The results are discussed in relation to the hypothesized special memory capacity of food-storing birds.

Animals↗
PubMed1991

The distribution of neurotransmitters and neurotransmitter-related enzymes in the dorsomedial telencephalon of the pigeon (Columba livia).

Immunoreactivity to four neurotransmitters/transmitter-related enzymes was found in the dorsomedial telencephalon (hippocampal region) of the pigeon. Putative afferent fibers containing choline acetyltransferase-like, serotonin-like, and tyrosine hydroxylase-like immunoreactivity were seen in a fiber tract passing through the septo-hippocampal junction and along the medial wall of the hippocampal region. The most intensive labeling of neuropil and terminals of all four substances was found in the dorsomedial area of the hippocampal region. Glutamic acid decarboxylase-like immunoreactivity was seen in sparsely scattered cells throughout the region. These results are discussed in relation to hypotheses about the boundaries and subdivisions of the hippocampal region of the pigeon.

Afferent Pathways↗
PubMed1991

The distribution of neuropeptides in the dorsomedial telencephalon of the pigeon (Columba livia): a basis for regional subdivisions.

The distribution of six neuropeptides [substance P (SP), leucine (leu5-) enkephalin (LENK), vasoactive intestinal polypeptide (VIP), cholecystokinin (CCK), neuropeptide Y (NPY), and somatostatin (SS)] in the dorsomedial telencephalon (hippocampal region) of the pigeon was studied by immunohistochemistry. All six peptides were found in fibers passing through the septo-hippocampal junction and along the medial wall of the hippocampal region. NPY-, SS-, and VIP-like staining of fibers was seen in the hippocampal commissure. NPY and SS had similar distributions within the hippocampal region, both being most conspicuous in cell bodies, terminals, and fibers of the medial hippocampal region. VIP-positive cells were found in an area dorsal to the SS/NPY cell region. CCK-like immunoreactivity was found in terminal baskets surrounding large cells of a v-shaped structure in the ventromedial hippocampal region. SP- and LENK-like immunoreactivity was found in neuropils in a lateral-dorsal region, the two substances showing similar distributions. This region is thought to lie lateral to the limit of the hippocampal region. Parallels with the distribution of immunoreactivity in the mammalian hippocampus are used to suggest possible equivalent subdivisions of the avian and mammalian hippocampal regions.

Animals↗
PubMed1991

The effect of constant light and phase shifts on a learned time-place association in garden warblers (Sylvia borin): hourglass or circadian clock?

Garden warblers are able to learn an association between time of day and feeding place. In constant dim light and constant food availability, the learned feeding pattern (successive visits to four feeding rooms for approximately 3 hr each) persisted for at least 1 day in three birds and for at least 6 days in one bird. The free-running feeding rhythm had a period of slightly greater than 23 hr. In response to a 6-hr phase advance of the light-dark cycle, the birds advanced their learned feeding pattern by 2.6 hr on the first day, whereas a 6-hr phase delay had no significant effect. These results are consistent with the hypothesis that the birds use a circadian clock rather than an hourglass mechanism of timing. This conclusion is further supported by the response of birds to forced interruptions of the daily feeding pattern (Krebs and Biebach, 1989).

Animals↗
PubMed1990

Food-storing birds: adaptive specialization in brain and behaviour?

Among the passerine birds, species that store food have an enlarged hippocampal region (dorso-medial cortex), relative to brain and body size, when compared with the non-storers. The volume of one of the major afferent-efferent pathways (the septo-hippocampal pathway) is also greater in food storing species. This specialization of brain structure is discussed in relation to behavioural studies in which the spatial memory of storing and non-storing species has been compared.

Adaptation, Physiological↗
PubMed1990

Comparing brains.

Some animals have larger brains than others, but it is not yet known why. Species differences in life-style, including dietary habits and patterns of development of the young, are associated with variation in brain weight, independently of the effects of body weight and evolutionary history. Taken together with behavioral and neuroanatomical analyses, these studies begin to suggest the evolutionary pressures that favor different sized brains and brain components.

Animals↗
PubMed1989

Hippocampal specialization of food-storing birds.

In a study of 52 individuals belonging to 35 species or subspecies of passerine birds it was shown that the volume of the hippocampal complex relative to brain and body size is significantly larger in species that store food than in species that do not. Retrieval of stored food relies on an accurate and long-lasting spatial memory, and hippocampal damage disrupts memory for storage sites. The results suggest, therefore, that food-storing species of passerines have an enlarged hippocampal complex as a specialization associated with the use of a specialized memory capacity. Other life-history variables were examined and found not to be correlated with hippocampal volume.

Animals↗
PubMed1989

Treating the chemically impaired medical family.

This is the second of a two-part series on impairment in medical families. Here the authors describe how the family can participate in the recognition, treatment, and recovery of a chemically impaired physician. Last month they examined the stresses put on a family by having a physician for a spouse or parent.

Combined Modality Therapy↗
PubMed1979

Arms races between and within species.

An adaptation in one lineage (e.g. predators) may change the selection pressure on another lineage (e.g. prey), giving rise to a counter-adaptation. If this occurs reciprocally, an unstable runaway escalation or 'arms race' may result. We discuss various factors which might give one side an advantage in an arms race. For example, a lineage under strong selection may out-evolve a weakly selected one (' the life-dinner principle'). We then classify arms races in two independent ways. They may be symmetric or asymmetric, and they may be interspecific or intraspecific. Our example of an asymmetric interspecific arms race is that between brood parasites and their hosts. The arms race concept may help to reduce the mystery of why cuckoo hosts are so good at detecting cuckoo eggs, but so bad at detecting cuckoo nestlings. The evolutionary contest between queen and worker ants over relative parental investment is a good example of an intraspecific asymmetric arms race. Such cases raise special problems because the participants share the same gene pool. Interspecific symmetric arms races are unlikely to be important, because competitors tend to diverge rather than escalate competitive adaptations. Intraspecific symmetric arms races, exemplified by adaptations for male-male competition, may underlie Cope's Rule and even the extinction of lineages. Finally we consider ways in which arms races can end. One lineage may drive the other to extinction; one may reach an optimum, thereby preventing the other from doing so; a particularly interesting possibility, exemplified by flower-bee coevolution, is that both sides may reach a mutual local optimum; lastly, arms races may have no stable and but may cycle continuously. We do not wish necessarily to suggest that all, or even most, evolutionary change results from arms races, but we do suggest that the arms race concept may help to resolve three long-standing questions in evolutionary theory.

Adaptation, Biological↗