Abstract. The expense and ineffectiveness of drift-based insecticide aerosols to control dengue epidemics has led to suppression strategies based on eliminating larval breeding sites. With the notable but short-lived exceptions of Cuba and Singapore, these source reduction efforts have met with little documented success; failure has chiefly been attributed to inadequate participation of the communities involved. The present work attempts to estimate transmission thresholds for dengue based on an easily-derived statistic, the standing crop of Aedes aegypti pupae per person in the environment. We have developed these thresholds for use in the assessment of risk of transmission and to provide targets for the actual degree of suppression required to prevent or eliminate transmission in source reduction programs. The notion of thresholds is based on 2 concepts: the mass action principal-the course of an epidemic is dependent on the rate of contact between susceptible hosts and infectious vectors, and threshold theory-the introduction of a few infectious individuals into a community of susceptible individuals will not give rise to an outbreak unless the density of vectors exceeds a certain critical level. We use validated transmission models to estimate thresholds as a function of levels of pre-existing antibody levels in human populations, ambient air temperatures, and size and frequency of viral introduction. Threshold levels were estimated to range between about 0.5 and 1.5 Ae. aegypti pupae per person for ambient air temperatures of 28ЊC and initial seroprevalences ranging between 0% to 67%. Surprisingly, the size of the viral introduction used in these studies, ranging between 1 and 12 infectious individuals per year, was not seen to significantly influence the magnitude of the threshold. From a control perspective, these results are not particularly encouraging. The ratio of Ae. aegypti pupae to human density has been observed in limited field studies to range between 0.3 and Ͼ60 in 25 sites in dengue-endemic or dengue-susceptible areas in the Caribbean, Central America, and Southeast Asia. If, for purposes of illustration, we assume an initial seroprevalence of 33%, the degree of suppression required to essentially eliminate the possibility of summertime transmission in Puerto Rico, Honduras, and Bangkok, Thailand was estimated to range between 10% and 83%; however in Mexico and Trinidad, reductions of Ͼ90% would be required. A clearer picture of the actual magnitude of the reductions required to eliminate the threat of transmission is provided by the ratio of the observed standing crop of Ae. aegypti pupae per person and the threshold. For example, in a site in Mayaguez, Puerto Rico, the ratio of observed and threshold was 1.7, meaning roughly that about 7 of every 17 breeding containers would have to be eliminated. For Reynosa, Mexico, with a ratio of approximately 10, 9 of every 10 containers would have to be eliminated. For sites in Trinidad with ratios averaging approximately 25, the elimination of 24 of e...

Morphometric estimates of body condition are widely used by ornithologists, but which estimates work best is a matter of debate. We review morphometric approaches (body mass, ratio and residual condition indices, predictive regression models, fat scoring, and abdominal profiles) for estimating body condition (defined as fat mass) in birds. We describe the strengths and weaknesses of each approach. Across diverse indices and species (*200 estimates total), the mean r 2 relating condition indices to mass of body fat was 0.55, and 64% of the r 2 values were greater than 0.50. But despite their generally good performance, condition indices sometimes perform poorly (i.e., r 2 is low). The data indicate that: (1) no single index was clearly best, (2) on average body mass alone, fat scores, and predictive multiple regression equations explained slightly more than 50% of the variation in fat content, (3) on average, ratio and residual indices explained slightly less than 50% of the variation in fat content, and (4) body mass alone, a variable that can be easily and reliably measured, is as good or nearly as good an indicator of fat content as any other condition index. We recommend that: (1) morphometric indicators of condition be empirically validated, (2) researchers publish their body composition data in sufficient detail that they can be used in future analyses exploring the relative merits of different condition indices, and (3) multiple regression directly on measured traits be used instead of condition indices whenever the condition index is not empirically validated.

Urban dengue is common in most countries of the Americas, but has been rare in the United States for more than half a century. In 1999 we investigated an outbreak of the disease that affected Nuevo Laredo, Tamaulipas, Mexico, and Laredo, Texas, United States, contiguous cities that straddle the international border. The incidence of recent cases, indicated by immunoglobulin M antibody serosurvey, was higher in Nuevo Laredo, although the vector, Aedes aegypti, was more abundant in Laredo. Environmental factors that affect contact with mosquitoes, such as air-conditioning and human behavior, appear to account for this paradox. We conclude that the low prevalence of dengue in the United States is primarily due to economic, rather than climatic, factors.

Adaptive explanations that rely on physiological arguments are common, but tests of hypotheses about the significance of whole-animal physiological performance (e.g., aerobic capacities) are rare. We studied phenotypic selection on the thermogenic capacity (i.e., maximal rate of oxygen consumption [V0 2 max] elicited via cold exposure) of high-altitude (-3800 m) deer mice (Peromyscus maniculatus). A high V0 2 max equates to a high capacity for heat production and should favor survival in the cold environments prevalent at high altitude. Strong directional selection favored high V0 2 max, at least in one year. The selection for increased V0 2 max is consistent with predictions derived from incorporating our physiological data into a biophysical model. During another year, we found weak evidence of selection for decreased body mass. Nonlinear selection was not significant for any of the selection episodes we studied. The strong directional selection for V0 2 max that we observed suggests that-given ample genetic variation-aerobic metabolism and perhaps endothermy may have evolved rapidly on the geological time scale.

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Body condition indices are widely used by ecologists, but many indices are used without empirical validation. To test the validity of a variety of indices, we compared how well a broad range of body condition indices predicted body fat mass, percent body fat and residual fat mass in mice Mus musculus. We also compared the performance of these condition indices with the multiple regression of several morphometric variables on body fat mass, percent body fat and residual fat mass. In our study population, two ratio based condition indices – body mass/body length and log body mass/log body length – predicted body fat mass as well as or better than other ratio and residual indices of condition in females. In males one ratio based condition index (log body mass/log body length) and one residual index (residuals from a regression of pelvic circumference on body length) were best at predicting body fat mass. All indices were better at estimating body fat mass, and residual fat mass than at estimating percent body fat. The predictions of body fat were much better for females than for males. Multiple regressions incorporating pelvic circumference (i.e. girth at the iliac crests) were the best predictors of body fat mass, residual fat mass, and percent body fat, and these multiple regressions were better than any of the condition indices. We recommend 1) that condition be precisely defined, 2) that predictors of condition be empirically validated, 3) that pelvic circumference be considered as a potential predictor of fat content, and 4) that, in general, multiple regression be considered as an alternative to condition indices.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. American Society of Mammalogists is collaborating with JSTOR to digitize, preserve and extend access to Journal of Mammalogy.The study of individual variation offers an underexploited wealth of opportunities for mammalogists. This paper addresses recent developments in the study of both intra-and interindividual variation. After reviewing several methods (e.g., intraclass correlation, productmoment correlation, and confirmatory factor analysis) for quantifying intra-individual consistency or repeatability, we discuss how these measures of repeatability can serve as guides for appropriately defining traits and how they may be helpful in ensuring that appropriate statistical models are used (e.g., in accounting for measurement errors in regression analyses). We discuss three aspects of inter-individual variation; phenotypic selection, alternative individual strategies and phenotypic integration, and quantitative genetic analyses. The value of these approaches for studying inter-individual variation is illustrated with recent examples from the literature. Finally, we discuss how many field studies of mammals may be well poised to exploit the unique insights that can be gained from studying individual variation. Speakman et al., 1994). The study of individual variation has an illustrious history, forming one of the cornerstones of Darwin's theory of evolution by natural selection (Darwin, 1958). While much has been written about individual variation since Darwin's time (Schmalhausen, 1949; Yablokov, 1974), many biological insights remain to be gained by studying it. Indeed, stimulated by physiologists (Bennett, 1987), population biologists (Clutton-Brock, 1988), and behaviorists (Boake, 1989), the study of individual variation is undergoing a renaissance, to which mammalogists are paying increasing attention (BlankIndividual variation can be defined in many ways but, most broadly defined, it is synonymous with intraspecific variation. Accordingly, individual variation would include differences related to group attributes (e.g., all members of a rodent population oc-cupying habitat with dark volcanic soils might have dark pelage, while their conspecifics occupying pale-colored sands might all have pale pelage-Benson, 1933). In this example, as in many comparisons among populations (Garland and Adolph, 1991), the variation (i.e., in pelage color) is more usefully attributed to variation among groups than to variation among individuals. Among-group variation is important, but we believe it is fruitfully considered separately from variation within populations. Consequently, for this paper, we define individual variation as differences among individuals within a population, following Darw...

Application of molecular diagnostic technology in the past 10 years has resulted in the discovery of several new species of pathogenic rickettsiae, including Rickettsia felis. As more sequence information for rickettsial genes has become available, the data have been used to reclassify rickettsial species and to develop new diagnostic tools for analysis of mixed rickettsial pathogens. R. felis has been associated with opossums and their fleas in Texas and California. Because R. felis can cause human illness, we investigated the distribution dynamics in the murine typhus–endemic areas of these two states. The geographic distribution of R. felis-infected opossum populations in two well-established endemic foci overlaps with that of the reported human cases of murine typhus. Descriptive epidemiologic analysis of 1998 human cases in Corpus Christi, Texas, identified disease patterns consistent with studies done in the 1980s. A close geographic association of seropositive opossums (22% R. felis; 8% R. typhi) with human murine typhus cases was also observed.