Plant evolution and urbanization: quantifying the effects of natural selection in shaping shepherd’s purse (capsella bursa-pastoris) populations in New York City

The aim of this study is to quantify the effects of natural selection in shaping Capsella bursa-pastoris populations along an urban-rural gradient in New York City. A reciprocal transplant experiment with 168 lab-germinated C. bursa-pastoris seedlings from both urban and rural populations are grown in eight paired home and away sites distributed throughout the New York metropolitan area. Sites are visited approximately thirteen times to record plant fitness. There is evidence for local adaptation of urban populations: urban plants have longer reproductive durations and produce more seed pods in urban environments. These findings suggest that urban plants are better adapted to the stressful abiotic conditions found in urban areas. Water stress laboratory trials test if urban populations are shaped by urban water stress regimes. The trials use 392 lab-germinated seedlings representing urban and rural populations from the New York metropolitan area, and include four water-stress treatments: drought, flood, cyclic drought and flood, and a well-watered control. Leaf traits from plants in the drought and control treatments are quantified to examine their role in water stress response. Both plant types appear unaffected by water stress, and demonstrate plasticity in leaf traits in response to drought. Leaf traits predict final plant size in the drought treatment but not in the control. A salt stress trial tests if urban populations are shaped by urban soil salt stress. The trial includes 288 plants representing urban and rural populations from the New York metropolitan area. Plants are grown under different salt treatments (0, 20, 40, 50, 60, 100, and 150 mM NaCl) for five weeks. Both plant types demonstrate salt-sensitivity, having high rates of mortality at high salt concentrations. However, plants that survive high salt treatments are significantly larger than controls, indicating some individuals are salt tolerant. Leaf trait analysis demonstrates that different plastic responses occur in plants grown in salt stress compared to those grown in drought. The reciprocal transplant experiment shows evidence of local adaptation in urban populations, whereas the laboratory trials find that the species is highly plastic in leaf trait responses to drought and salinity

Comments on environmental effects in the origin of angular momenta in galaxies

We examine the orientations of galaxies in 43 rich Abell galaxy clusters belonging to superclusters and containing at least 100 members in the considered area as a function of supercluster multiplicity. It is found that the orientation of galaxies in the analyzed clusters is not random and the alignment decreases with supercluster richness, although the effect is statistically significant only for azimuthal angles. The dependence of galaxy alignment on cluster location inside or outside a supercluster and on supercluster multiplicity clearly shows the importance of environmental effects on the origin of galaxy angular momenta. The comparison with alignment of galaxies in a sample of rich Abell clusters not belonging to superclusters is made too.Comment: accepted in Odessa Astronomical Publications 2012 vol.25 p.2

On the existence of young embedded clusters at high Galactic latitude

Careful analyses of photometric and star count data available for the nine putative young clusters identified by Camargo et al. (2015, 2016) at high Galactic latitudes reveal that none of the groups contain early-type stars, and most are not significant density enhancements above field level. 2MASS colours for stars in the groups match those of unreddened late-type dwarfs and giants, as expected for contamination by (mostly) thin disk objects. A simulation of one such field using only typical high latitude foreground stars yields a colour-magnitude diagram that is very similar to those constructed by Camargo et al. (2015, 2016) as evidence for their young groups as well as the means of deriving their reddenings and distances. Although some of the fields are coincident with clusters of galaxies, one must conclude that there is no evidence that the putative clusters are extremely young stellar groups.Comment: Accepted for publication (MNRAS