Variation in the ribosomal internal transcribed spacers and 5.8S rDNA among five species of Acropora (Cnidaria; Scleractinia): patterns of variation consistent with reticulate evolution

The ITS sequences of Acropora spp. are the shortest so far identified in any metazoan and are among the shortest seen in eukaryotes; ITS1 was 70-80 bases, and ITS2 was 100-112 bases. The ITS sequences were also highly variable, but base composition and secondary structure prediction indicate that divergent sequence variants are unlikely to be pseudogenes. The pattern of variation was unusual in several other respects: (1) two distinct ITS2 types were detected in both A. hyacinthus and A. cytherea, species known to hybridize in vitro with high success rates, and a putative intermediate ITS2 form was also detected in A. cytherea; (2) A. valida was found to contain highly (29%) diverged ITS1 variants; and (3) A. longicyathus contained two distinct 5.8S rDNA types. These data are consistent with a reticulate evolutionary history for the genus Acropora.      

Linking foraging decisions to residential yard bird composition

Urban bird communities have higher densities but lower diversity compared with wildlands. However, recent studies show that residential urban yards with native plantings have higher native bird diversity compared with yards with exotic vegetation. Here we tested whether landscape designs also affect bird foraging behavior. We estimated foraging decisions by measuring the giving-up densities (GUD; amount of food resources remaining when the final forager quits foraging on an artificial food patch, i.e seed trays) in residential yards in Phoenix, AZ, USA. We assessed how two yard designs (mesic: lush, exotic vegetation; xeric: drought-tolerant and native vegetation) differed in foraging costs. Further, we developed a statistical model to calculate GUDs for every species visiting the seed tray. Birds foraging in mesic yards depleted seed trays to a lower level (i.e. had lower GUDs) compared to birds foraging in xeric yards. After accounting for bird densities, the lower GUDs in mesic yards appeared largely driven by invasive and synanthropic species. Furthermore, behavioral responses of individual species were affected by yard design. Species visiting trays in both yard designs had lower GUDs in mesic yards. Differences in resource abundance (i.e., alternative resources more abundant and of higher quality in xeric yards) contributed to our results, while predation costs associated with foraging did not. By enhancing the GUD, a common method for assessing the costs associated with foraging, our statistical model provided insights into how individual species and bird densities influenced the GUD. These differences we found in foraging behavior were indicative of differences in habitat quality, and thus our study lends additional support for native landscapes to help reverse the loss of urban bird diversity.     

Structural analysis of the neuronal SNARE protein syntaxin-1A

Intracellular trafficking depends on the docking and fusion of transport vesicles with cellular membranes. Central to docking and fusion is the pairing of SNARE proteins (soluble NSF attachment protein receptors) associated with the vesicle and target membranes (v- and t-SNAREs, respectively). Here, the X-ray structure of an N-terminal conserved domain of the neuronal t-SNARE syntaxin-1A was determined to a resolution of 1.9 A using multiwavelength anomalous diffraction. This X-ray structure, which is in general agreement with an NMR structure of a similar fragment, provides new insight into the interaction surface between the N-terminal domain and the remainder of the protein. In vitro characterization of the intact cytoplasmic domain of syntaxin revealed that it forms dimers, and probably tetramers, at low micromolar concentrations, with concomitant structural changes that can be detected by limited proteolysis. These observations suggest that the promiscuity characteristic of pairing between v-SNAREs and t-SNAREs extends to the formation of homo-oligomeric t-SNARE complexes as well. They also suggest a potential role for the neuronal Sec1 protein (nSec1) in preventing the formation of syntaxin multimers.