Large Differences in Livelihood Responses and Outcomes to Increased Conservation Enforcement in a Protected Area

Human Ecology - Despite the popularity of integrated conservation and development approaches to protected area management, adjacent communities increasingly face livelihood dilemmas. Yet...     

Water structure around a left-handed Z-DNA fragment analyzed by cryo neutron crystallography

Even in high-quality X-ray crystal structures of oligonucleotides determined at a resolution of 1 Å or higher, the orientations of first-shell water molecules remain unclear. We used cryo neutron crystallography to gain insight into the H-bonding patterns of water molecules around the left-handed Z-DNA duplex [d(CGCGCG)]₂. The neutron density visualized at 1.5 Å resolution for the first time allows us to pinpoint the orientations of most of the water molecules directly contacting the DNA and of many second-shell waters. In particular, H-bond acceptor and donor patterns for water participating in prominent hydration motifs inside the minor groove, on the convex surface or bridging nucleobase and phosphate oxygen atoms are finally revealed. Several water molecules display entirely unexpected orientations. For example, a water molecule located at H-bonding distance from O6 keto oxygen atoms of two adjacent guanines directs both its deuterium atoms away from the keto groups. Exocyclic amino groups of guanine (N2) and cytosine (N4) unexpectedly stabilize waters H-bonded to O2 keto oxygens from adjacent cytosines and O6 keto oxygens from adjacent guanines, respectively. Our structure offers the most detailed view to date of DNA solvation in the solid-state undistorted by metal ions or polyamines.     

Contribution of peeling host for epiphyte abundance in two tropical dry forests in the “El Cielo Biosphere Reserve”, Mexico

Host traits partly determine the abundance and species richness of epiphytes in tropical forests. It has been proposed that older trees with rough bark and evergreens often house more individuals and more epiphytic species than those with thin, smooth, and peeling bark, which harbor few epiphytes. We hypothesize (i) that epiphytes are more abundant and species-rich in the more shaded forest, which is related to bark roughness, and (ii) that epiphytes are distributed in the middle of the host, where microenvironmental conditions are more favorable to survival. We evaluated abundance, species richness, and vertical distribution of epiphytes in two tropical dry forests, according to the deciduousness and basal area of the trees. Moreover, we selected the most abundant epiphytes to test whether their distribution is related to a specific bark type and examine their vertical distribution in two dry forests. We distinguished a high abundance and species richness of epiphytes in the deciduous forest, although basal area and host species richness were higher in the semi-deciduous forest. In both forests, we found a positive relationship between epiphyte abundance and basal area. Higher abundance of epiphytes was related to the predominance of Tillandsia schiedeana, a drought-adapted species, in both forests. Unexpectedly, epiphytes abundantly colonized Bursera simaruba, a host with peeling bark and a very branched crown, where small individuals of T. schiedeana colonized abundantly toward the top of the crown. Our results show the importance of the tropical dry forest, particularly, B. simaruba, in maintaining epiphyte diversity in terms of T. schiedeana colonization.