Rattlesnake Rattles and Burrowing Owl Hisses: A Case of Acoustic Batesian Mimicry

Burrowing owls nest and roost in ground squirrel burrows, a refuge frequently used by rattlesnakes. When cornered, burrowing owls produce a vocal hiss that has been suggested to mimic a rattlesnake's rattle. To test this hypothesis, we conducted an experiment using two populations of Douglas ground squirrels that differ in their evolutionary histories with rattlesnakes. Both squirrel populations were sympatric with burrowing owls. Squirrels from a population subjected to natural selection by rattlesnakes treated the owl hiss as cautiously as they did the rattle, and responded with greater caution to the rattle and hiss than to two control sounds. Squirrels from a rattlesnake-free area, however, were less systematic in differentiating among the rattle, the hiss, and the control treatments. Such variation between ground-squirrel populations provides evidence that the burrowing owl's defensive hiss currently functions as an acoustic Batesian mimic of a rattlesnake's rattle.     

Context-dependent memory: colour versus odour

An olfactory stimulus and a visual stimulus were employed in a context- dependent memory study using a prose passage as the to-be-remembered item. Ninety-five university students (aged 17-35 years) learned the passage of prose in the presence of one of the stimuli and were then asked to recall the passage with the original context either reinstated or not reinstated. The results revealed a significant context-dependent memory effect for the olfactory cue but not for the visual cue. They demonstrate support for the effectiveness of odours as context cues and it is suggested that context-dependent memory processes may underlie the formation and retrieval of odour-evoked autobiographical memories.      

Shigella dysenteriae and Shigella boydii in England and Wales during 1972 and 1973

During 1972 and 1973 the Salmonella and Shigella Reference Laboratory examined 133 strains of Shigella dysenteriae and Shigella boydii isolated from patients in England and Wales. Of those infected 89 had recently travelled abroad and a further seven had been in close contact with travellers recently returned to this country. Though these subgroups were of little numerical significance they are of considerable epidemiological interest. The increase in tourism from the British Isles to North Africa and Asia is likely to lead to an increased incidence of infections due to these organisms, both in travellers infected abroad and in their contacts within the British Isles.     

Electrophoretic Heterogeneity of Bacterial Nicotinamide Adenine Dinucleotide Phosphate-Specific Isocitrate Dehydrogenases

The specific activities of the nicotinamide adenine dinucleotide phosphate-dependent isocitrate dehydrogenase in crude cell-free extracts of 15 different microorganisms, grown aerobically in simple mineral salts media containing glucose as the sole carbon source, ranged from a maximum of 0.820 in Pseudomonas aeruginosa to a minimum of 0.145 in Thiobacillus novellus. Polyacrylamide gel electrophoresis indicated that the bacterial species studied contained electrophoretically distinct proteins exhibiting isocitrate dehydrogenase activity. The electrophoretic mobilities, as well as the differences in stability of the enzyme observed in this study, indicate that the physical and chemical properties of isocitrate dehydrogenase may differ widely between bacterial species.     

Serological Relationship of the Tacaribe Complex of Viruses to Lymphocytic Choriomeningitis Virus

By means of the indirect fluorescent-antibody test, cross serological reactivity was demonstrated between lymphocytic choriomeningitis (LCM) virus and the viruses of the Tacaribe complex. Antisera to all members of the Tacaribe complex reacted with LCM virus; LCM antisera gave significant staining of Amapari virus, but minimal or inconsistent reactions with Tacaribe virus, and no reaction with two other viruses of the Tacaribe complex. A low level cross-reaction was observed in complement fixation tests of Machupo and Pichinde antisera against LCM antigen. Immunization with Tacaribe and Amapari viruses did not protect mice against challenge with LCM virus. Because of the identical appearance of the virions, the sharing of antigens, and the many biological similarities between LCM and the Tacaribe complex viruses, it is proposed that they be considered as constituting a new taxonomic group of viruses.