Adaptive mate-guarding by males ofOntholestes cingulatus (Coleoptera: Staphylinidae)

Males of the staphylinid beetle Ontholestes cingulatusremain close by their mates following copulation while the mated females oviposit. The hypothesis that male behavior constitutes adaptive mate-guarding was tested by examining three predictions: (1) receptive females would be scarce, (2) some females would mate multiply, and (3) males that stayed with their mates would often be able to repel rivals intent on takeovers. All three predictions were confirmed. These results and additional comparative evidence suggest that postcopulatory associations have evolved in the Staphylinidae only when the reproductive costs of this form of mate-guarding are outweighed by its benefits.     

Respiratory poliomyelitis: a follow-up study.

Data from the medical records of 113 patients living in Manitoba who had contracted respiratory poliomyelitis between 1952 and 1959 were compared with information obtained from interviews with these patients in 1980. The study was designed to determine whether the patients'' respiratory function, mobility, ability to perform daily tasks, and employment, residential and marital status had changed between 1 year after the onset of polio and 1980. The patients'' dependence on mechanical aids and other people was also studied. More than half (56%) of the patients perceived their respiratory impairment to be the same as it was 1 year after the onset of polio, 27% perceived the impairment to be increased, and 17% perceived it to be decreased. There was an association between level of respiratory function, mobility and ability to perform daily tasks. The 69 patients who lived at home had better respiratory function, mobility and ability to perform daily tasks than the 24 patients who were assisted by a home care program and the 20 who lived in hospital. The latter group had the lowest levels of respiratory and functional ability.     

LEARNING AND THE FORAGING PERSISTENCE OF WHITE-CROWNED SPARROWS ZONOTRICHIA LEUCOPHRYS

Ten White-crowned Sparrows Zonotrichia leucophrys took part in an experiment of 24 trials in which they foraged for food hidden in one of four blocks. Each block had six depressions covered with sunflower seed shells. On each trial three of the blocks were empty while one contained six sunflower seed particles. Initially the birds removed most of the covers from the empty blocks as well as from the baited blocks. However, as the experiment progressed, many of the birds learned to displace only a few covers from the empty blocks they encountered before leaving to search for the block with sunflower seeds. In other words, the sparrows proved capable of learning to adjust the time spent foraging in areas of identical appearance on the basis of the results of their initial “test” pecks. The ability to alter foraging persistence on the basis of test probes could contribute to the efficient exploitation of hidden food by bird predators.     

The Nesting Behavior of Dawson's Burrowing Bee, Amegilla dawsoni (Hymenoptera: Anthophorini), and the Production of Offspring of Different Sizes

Females of Dawson's burrowing bees have a well-defined brood cell cycle involving cell construction, waxing, provisioning, egg laying, and cell capping. In one study population, nesting bees built smaller brood cells for offspring of lower weight and larger ones for heavier offspring, demonstrating their ability to anticipate the desired size of an offspring at the outset of a brood cell cycle. Furthermore, individual females varied the number of provisioning trips made per brood cell cycle by a factor of two or more, apparently exercising control over the amount of brood provisions supplied to an offspring. The size distribution of emerging males at two widely separated locations in 1997 was nearly identical to that recorded in 1995. These findings suggest that the production of small males (minors) is the result of active female control rather than the product of food shortages that force females to undersupply some brood cells. Female foraging decisions resulted in a bimodal distribution of weights of mature dormant larvae at one site in 1997. However, the times required to complete brood cell cycles at this site were not distributed bimodally. This result stemmed in part from daily variation among females in the duration of their provisioning trips as well as from seasonal variation in provisioning trip times. When provisioning trips lasted longer, females tended to make fewer trips per brood cell cycle, and so were presumably more likely to produce minor sons. As a result, the weight of an offspring was not tightly linked to the time investment required to produce it, making it difficult to compare the relative costs of minors and majors in terms of maternal time investments.