An in situ enclosure experiment to test the solar UVB impact on plankton in a high-altitude mountain lake. I. Lack of effect on phytoplankton species composition and growth

The effect of solar UVB radiation on the growth and speciescomposition of phytoplankton from a high-mountain lake (2417m a.s.l.) was studied in situ for 16 days in two enclosuresof 1 m receiving either full sunlight or sunlight without UVB.A total of 20 species were identified in both enclosures, consistingmainly of dinoflagellates, chrysophytes and diatoms. Duringthe experiment, there were no significant differences in phytoplanktonspecies composition between the two enclos ures. In both treatments,the abundance of phytoplankton increased continuously, and chlorophylla changed by -5-fold. We observed high fluctuations in the abundanceof several species. However, these fluctuations occurred inboth enclosures, and hence they were not related to UVB radiation.Some species were affected by daily fluctuations of radiation(UVA + photosynthetically active radi ation). Cyclotella aff.gordonensis showed a robust positive correlation, whereas speciesof Gymno dinium were negatively correlated. For most species,the sensitivity to radiation found during the experiment wasconsistent with their diurnal vertical distribution in the lake.Our findings suggest that the phytoplankton from this very clearlake (10% of the surface UVB radiation at 305 nm reached 9.6m depth) were well adapted to the high UVB radiation charactensticof high-elevation sites.     

Frontal sinus ontogeny and covariation with bone structures in a modern human population

In humans, the frontal sinus (FS) is located in the medial part of the supraorbital region, sometimes expanded throughout the frontal squama. It exhibits high morphological variability, but its general form appears to be constrained by surrounding structures. The goal of this study is to analyze FS growth and test for covariation between FS volume and the glabellar region, upper nasal region, bone thickness and endocranial size in a human sample from Argentina. The sample comprises 149 reconstructions derived from computed tomography images of individuals aged 0–31 years. Volume of the FS and measurements of the surrounding structures were recorded. The FS growth trajectory was assessed by parametric and nonparametric methods, and covariation was determined using correlations and partial correlations. The FS volume could be measured at an age of about 6 years and older; adults had no aplasia but hyperplasia was found in some cases. Since the most conspicuous characteristic found was variation among individuals, the nonparametric smoothing spline produced very poor fitting. The modified logistic function was the only parametric method providing significant parameters. Sexes differed in the age at which FS growth began and ended, with FS developing earlier but at a slower rate in females than in males. The FS volume did not correlate with either upper nasal width or endocranial volume, but it correlated with bone thickness measurements (mainly from the glabellar region), even when age was held constant. Expansion of the FS at the frontal poles also correlated with frontal bone thickness. Despite the difficulty in modeling and predicting the trajectory and morphology of FS, our results suggest that it is affected by its surrounding bony environment.