Why are there more species in the tropics than in temperate regions? In recent years, this long-standing question has been addressed primarily by seeking environmental correlates of diversity. But to understand the ultimate causes of diversity patterns, we must also examine the evolutionary and biogeographic processes that directly change species numbers (i.e., speciation, extinction, and dispersal). With this perspective, we dissect the latitudinal diversity gradient in hylid frogs. We reconstruct a phylogeny for 124 hylid species, estimate divergence times and diversification rates for major clades, reconstruct biogeographic changes, and use ecological niche modeling to identify climatic variables that potentially limit dispersal. We find that hylids originated in tropical South America and spread to temperate regions only recently (leaving limited time for speciation). There is a strong relationship between the species richness of each region and when that region was colonized but not between the latitudinal positions of clades and their rates of diversification. Temperature seasonality seemingly limits dispersal of many tropical clades into temperate regions and shows significant phylogenetic conservatism. Overall, our study illustrates how two general principles (niche conservatism and the time-for-speciation effect) may help explain the latitudinal diversity gradient as well as many other diversity patterns across taxa and regions.

Problem statement:A goal during weight loss is to reduce body fat while maintaining body protein. We hypothesized that an increased dietary lysine: calorie might be beneficial during periods of caloric restriction. Approach: Two experiments were conducted to determine if changing the ratio of lysine: calories (lysine g/kg: Mcal ME/kg) while maintaining an ideal profile of amino acids will change nitrogen metabolism and weight loss in obese mature dogs. Results: The results of these experiments imply that if all essential amino acids are in adequate supply in the food, foods with an optimal balance of nutrients can reduce muscle degradation during periods of caloric restriction. Conclusion: Our optimum food for decreasing protein degradation was the food containing 3.0 lysine: calorie. However, the present experiments were relatively short and these results may not be sustained over longer periods of restriction.

Exposures to UV radiation from solaria and sunlight have potentially damaging and beneficial effects that are not yet fully quantified. Here we compare weighted UV irradiances relevant to erythema (sunburn) and vitamin-D production from 2 phototherapy units and 2 commercial solaria with those under clear-skies in summer and winter at Lauder New Zealand (45°S). We find that weighted irradiances from one solarium are an order-of-magnitude greater than for summer sunlight whereas the others are comparable with summer sunlight, and an order-of-magnitude greater than winter sunlight. For most solaria, UV-A irradiances far exceed those in sunlight, constituting a potentially serious health risk. The calculated vitamin D benefit to erythema risk ratios for the solaria are comparable to, or greater than for with summer sunlight, and significantly greater for one of the phototherapy booths (the predominantly UV-B booth). Exposure times to maintain sufficient vitamin-D without inducing erythema are extremely short for the latter solarium, whereas for the others they are comparable to, or less than, those for summer sunlight. For winter sunlight, deduced exposure times for vitamin-D sufficiency are impractically long. In conclusion, the solaria tested should be capable of helping to maintain vitamin-D sufficiency. However there is an attendant risk of erythema; and exposure times are sensitive to the choice of action spectrum. For all solaria the spectrum differs greatly from sunlight with unnaturally high irradiances at some wavelengths, which could have adverse health effects. Their use is not advocated as a way of ensuring vitamin-D sufficiency.

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