Biomedical subjects

S Cahan

Publications and source records attributed to S Cahan.

5 recordsLinked to original sources

PubMed1999

Undertaking specialization in the desert leaf-cutter ant Acromyrmex versicolor.

We investigated undertaking behaviour in the desert leaf-cutter ant to determine whether colonies show undertaking specialization, how task specialization is regulated and the consequences of specialization on colony performance. Task specialization has been hypothesized to be a result of internal physiological or genetic factors that govern worker behaviour. On the other hand, it has been suggested that task specialization could be a result of spatial structuring of workers allowing only a subset to have the opportunity to perform certain tasks. To test between these two hypotheses, we experimentally introduced dead ants into laboratory colonies with individually marked workers, and recorded all encounters and undertaking behaviours. Workers demonstrated individual specialization, in that some workers removed the dead ant more frequently than expected from encounter rate. Although individual workers differed in their opportunity to perform undertaking, this did not account for the specialization. These results suggest that undertaking specialization is governed by internal differences among workers. In addition, undertaking specialists removed corpses more successfully, and in the largest colony, more quickly, than nonspecialist workers, indicating that internally governed specialization is an important part of overall colony efficiency. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1998

An abrupt transition in colony founding behaviour in the ant Messor pergandei.

Transitions in behaviour across a continuous distribution of organisms can provide valuable information on how variation in behaviour is maintained. We used analyses developed for interspecific hybrid zones to examine geographic variation in colony founding strategy in the desert seed-harvester ant, Messor pergandei. Newly mated females initiate new colonies either alone (haplometrosis) or cooperatively with other foundresses (pleometrosis). The incidence of these founding strategies were surveyed across the species' range and found to occur in geographically distinct regions joined by a narrow transition zone. Foundresses collected from haplometrotic sites were more likely to display aggression and found solitary nests than foundresses from pleometrotic sites, suggesting that geographical variation in metrosis is due to genotypic divergence. Foundresses from transitional sites were generally not aggressive and tended to co-found nests in the laboratory, yet rarely formed associations in the field. Such an abrupt shift in behaviour indicates that variation in colony founding strategy is maintained by selection rather than the result of secondary contact of neutral characters. Level of aggression displays a wider cline than founding strategy and is likely under selection only when accompanied by active strategy preference. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1989

Age versus schooling effects on intelligence development.

The effect of formal education, as opposed to chronological age, on intelligence development has suffered from inadequate empirical investigation. Most studies of this issue have relied on natural variation in exposure to school among children of the same age, thus confounding differences in schooling with differences in other intelligence-related variables. This difficulty can be overcome by a quasi-experimental paradigm involving comparison between children who differ in both chronological age and schooling. The present study applies this paradigm to the estimation of the independent effects of age and schooling in grades 5 and 6 on raw scores obtained on a variety of general ability tests. The sample included all students in Jerusalem's Hebrew-language, state-controlled elementary schools. The results unambiguously point to schooling as the major factor underlying the increase of intelligence test scores as a function of age and to the larger effect schooling has on verbal than nonverbal tests. These results contribute to our understanding of the causal model underlying intelligence development and call for reconsideration of the conceptual basis underlying the definition of deviation-IQ scores. Some implications of these results concerning the distinction between intelligence and scholastic achievement, the causal model underlying the development of "crystallized" and "fluid" abilities, and the notion of "culture-fair" tests are discussed.

Achievement↗

PubMed1977

Birth order and intellectual development: the confluence model in the light of cross-cultural evidence.

For Israeli eighth-grade students of Asian-African origin, achievement decreases as a function of birth order in small families and increases as a function of birth order in large families. This finding cannot be accounted for by differences in developmental rate or size of birth intervals. It can be accounted for by considering the effect of external influences, such as schooling, on intellectual development.

Achievement↗

PubMedDate not supplied

Evaluation of the effect of nitrous oxide and hydroxyzine in controlling the behavior of the pediatric dental patient.

This study evaluated and compared the effect of three different sedation combinations on the young dental patient: hydroxyzine alone, hydroxyzine with nitrous oxide, and nitrous oxide alone. Nineteen uncooperative children with mean age of 37 months needing at least three restorative visits were selected for this study. Crying, alertness, and general behavior were evaluated during the dental procedure. The combination of hydroxyzine and nitrous oxide was more effective than the others for the majority of the sessions in terms of controlling crying and alertness. The results in the present study indicate that the sedative effect of hydroxyzine on children's behavior is enhanced by the addition of nitrous oxide.

Analysis of Variance↗