RESUMO
Harrison's rule states that parasite body size and the body size of their hosts tend to be positively correlated. After it was proposed a century ago, a number of studies have investigated this trend, but the support level has varied greatly between parasite/host associations. Moreover, while the rule has been tested at the individual species level, we still lack knowledge on whether Harrison's rule holds at the scale of parasite and host communities. Here, we mapped flea (parasites) and rodent (hosts) body sizes across Mongolia and asked whether Harrison's rule holds for parasite/host assemblages (i.e. whether a parasite's average body size in a locality is positively correlated with its host's average body size). In addition, we attempted to disentangle complex relationships between flea size, host size and environmental factors by testing alternative hypotheses for the determinants of fleas' body size variation. We gathered occurrence data for fleas and rodents from 2,370 sites across Mongolia, constructed incidence matrices for both taxa and calculated the average body sizes of fleas and their hosts over half-degree cells. Then, we applied a path analysis, accounting for spatial autocorrelation, trying to disentangle the drivers of the correlation between parasite and host body sizes. We found a strong positive correlation between average flea and host size across assemblages. Surprisingly though, we found that environmental factors simultaneously affected the body sizes of both fleas and hosts in the same direction, leading to a most likely deceptive correlation between parasite and host size across assemblages. We suggest that environmental factors may, to a great extent, reflect the environmental conditions inside the hosts' burrows where fleas develop and attain their adult body size, thus influencing their larval growth. Similarly, rodent body size is strongly influenced by air temperature, in the direction predicted by Bergmann's rule. If our findings are valid in other host-parasite associations, this may explain the dissenting results of both support and lack thereof for Harrison's rule.
Assuntos
Parasitos , Sifonápteros , Animais , Tamanho Corporal , Interações Hospedeiro-ParasitaRESUMO
OBJECTIVES: This study sought to evaluate the potential clinical impact of using 3-dimensional echocardiography (3DE) to measure left ventricular ejection fraction (LVEF) in patients considered for implantable cardioverter-defibrillator (ICD) implantation and to assess the predictive value of 3DE LVEF for arrhythmic events. BACKGROUND: ICD therapy is currently recommended to prevent sudden cardiac death in patients with symptomatic heart failure and LVEF ≤35%, and in asymptomatic patients with ischemic heart disease and LVEF ≤30%. Two-dimensional echocardiography (2DE) is currently used to calculate LVEF. However, 3DE has been reported to be more reproducible and accurate than 2DE to measure LVEF. METHODS: The study prospectively enrolled 172 patients with LV dysfunction (71% ischemic). Both 2DE and 3DE LVEF were obtained during the same study. The outcome was the occurrence of major arrhythmic events (sudden cardiac death, aborted cardiac arrest, appropriate ICD therapy). RESULTS: After a median follow up of 56 (range 18 to 65) months, major arrhythmic events occurred in 30% of the patients. Compared with 2DE, 3DE changed the assignment above or below the LVEF thresholds for ICD implantation in 20% of patients, most of them having 2DE LVEFs within ± 10% from threshold. By cause-specific hazard model, 3DE LVEF was the only independent predictor of the occurrence of major arrhythmic events. CONCLUSIONS: LVEF by 3DE was an independent predictor of major arrhythmic events and improved arrhythmic risk prediction in patients with LV dysfunction. When compared with 2DE LVEF, 3DE measurement of LVEF may change the decision to implant an ICD in a sizable number of patients.