Internal Eliminated Segments (IESs) of Oxytrichidae1

ABSTRACT Internal eliminated segments (IESs) are sequences that interrupt coding and noncoding regions of germline (micronuclear) genes of ciliated protozoa. IESs are flanked by short, unique repeat sequences, which are presumably required for precise IES excision during macronuclear development. Coding and noncoding segments of genes separated by IESs are called macronuclear-destined segments, or MDSs. We have compiled the characteristics of 89 individual IESs in 12 micronuclear genes in the Oxytricha and Stylonychia genera to define the IES phenomenon precisely, a first step in determining the origin, function and significance of IESs. Although all 89 IESs among the 12 different genes are AT-rich, they show no other similarity in sequence, length, position or number. Two main types of IESs are present. IESs that separate scrambled MDSs are significantly shorter and more frequent and have longer flanking repeat sequences than IESs that intervene between nonscrambled MDSs. A comparison of the nonscrambled gene encoding β-telomere binding protein in three species of hypotrichs shows that even in the same gene IESs are not conserved in sequence, length, position, or number from species to species. A comparison of IESs in the scrambled gene encoding actin I in the three species shows that the evolutionary behavior of IESs in a scrambled gene may be more constrained. However, IESs in the scrambled actin I gene have shifted along the DNA molecule during evolution. In total, the various studies show that IESs are hypermutable in sequence and length. They insert, excise, and shift along DNA molecules more or less randomly during evolution, with no discernible function or consequences.     

The Power of Black and Latina/o Counterstories: Urban Families and College-Going Processes

This article examines the diversity of practices utilized by working-class and poor black and Latina/o families to support their children's college-going processes. We employ the work of feminists, scholars of color, and critical ethnographers to critique the power undergirding the monolithic model establishing one entry point of parental involvement in urban schools. Then, drawing on data from a one-year critical ethnography of 27 black and Latina/o youth, we illustrate the ways counterstories expanded entry points of family involvement within the lives of black and Latina/o college-bound youth . [minorities, youth, college-going, family, counterstories]     

F-actin Distribution of Dictyostelium Myosin I Double Mutants

The roles of the myosin I class of mechanoenzymes have been investigated by single and double gene knockout studies in the amoeba Dictyostelium discoideum. Cells lacking different myosin I pairs (myoA^-/myoB^-, myoB^-/myoC^-, and myoA^-/myoC^-) were examined with respect to their cytoskeletal organization. F-actin localization by rhodamine-phalloidin staining of cells indicates that the myoA^-/myoB^-, myoB^-/myoC^-, and myoA^-/myoC^- cells appear to redistribute their F-actin more slowly than wild type cells upon adhesion to a substrate. These studies suggest that Dictyostelium myoA, myoB, and myoC may have overlapping roles in maintaining the integrity or organization of the cortical membrane cytoskeleton.     

Genetic consequences of introducing allopatric lineages of Bluestriped Snapper (Lutjanus kasmira) to Hawaii

A half century ago the State of Hawaii began a remarkable, if unintentional, experiment on the population genetics of introduced species, by releasing 2431 Bluestriped Snappers (Lutjanus kasmira) from the Marquesas Islands in 1958 and 728 conspecifics from the Society Islands in 1961. By 1992 L. kasmira had spread across the entire archipelago, including locations 2000 km from the release site. Genetic surveys of the source populations reveal diagnostic differences in the mtDNA control region (d = 3.8%; φ_ST = 0.734, P < 0.001) and significant allele frequency differences at nuclear DNA loci (F_ST = 0.49; P < 0.001). These findings, which indicate that source populations have been isolated for approximately half a million years, set the stage for a survey of the Hawaiian Archipelago (N = 385) to determine the success of these introductions in terms of genetic diversity and breeding behaviour. Both Marquesas and Society mtDNA lineages were detected at each survey site across the Hawaiian Archipelago, at about the same proportion or slightly less than the original 3.4:1 introduction ratio. Nuclear allele frequencies and parentage tests demonstrate that the two source populations are freely interbreeding. The introduction of 2431 Marquesan founders produced only a slight reduction in mtDNA diversity (17%), while the 728 Society founders produced a greater reduction in haplotype diversity (41%). We find no evidence of genetic bottlenecks between islands of the Hawaiian Archipelago, as expected under a stepping‐stone model of colonization, from the initial introduction site. This species rapidly colonized across 2000 km without loss of genetic diversity, illustrating the consequences of introducing highly dispersive marine species.     

Post‐fire vegetation dynamics in nutrient‐enriched and non‐enriched sclerophyll woodland

Abstract Exotic plant invasions are a significant problem in urban bushland in Sydney, Australia. In low‐nutrient Hawkesbury Sandstone communities, invasive plants are often associated with urban run‐off and subsequent increases in soil nutrients, particularly phosphorus. Fire is an important aspect of community dynamics in Sydney vegetation, and is sometimes used in bush regeneration projects as a tool for weed control. This study addressed the question: ‘Are there differences in post‐fire resprouting and germination of native and exotic species in nutrient‐enriched communities, compared with communities not disturbed by nutrient enrichment?’ We found that in non‐enriched areas, few exotic species emerged, and those that did were unable to achieve the rapid growth that was seen in exotic plants in the nutrient‐enriched areas. Therefore, fire did not promote the invasion of exotic plants into areas that were not nutrient‐enriched. In nutrient‐enriched areas after fire, the diversity of native species was lower than in the non‐enriched areas. Some native species were able to survive and compete with the exotic species in terms of abundance, per cent cover and plant height. However, these successful species were a different suite of natives to those commonly found in the non‐enriched areas. We suggest that although fire can be a useful tool for short‐term removal of exotic plant biomass from nutrient‐enriched areas, it does not promote establishment of native species that were not already present.     

Forested Buffer Strips and Breeding Bird Communities in Southeast Alaska

Abstract: Forested buffer strips are used to mitigate fragmentation and habitat loss and are a common feature in management of riparian landscapes. Low-elevation, old-growth coastal forests are a rare riparian habitat that can benefit from similar conservation measures. We evaluated the effectiveness of postlogging, forested buffer strips for forest-dwelling birds in the coastal temperate rainforest of southeast Alaska, USA. Our objective was to compare bird composition and density among forested buffer strips of differing widths and controls at the stand and landscape scales. We applied a 2-stage sampling design stratified by forested buffer width and randomly selected 24 managed and 18 control sites to sample over 2 breeding seasons. We estimated abundance of birds using the paired-observer, variable-circular plot method. We modeled combined effects of buffer width and vegetation and landscape characteristics on bird density at 2 spatial scales. Species richness and diversity were greatest in the narrowest buffers, but species composition in the largest buffers (≥400 m) was most similar to that in control blocks. Abundance of 3 of 10 common species differed across forested buffer treatments and controls. Densities of red-breasted sapsucker (Sphyrapicus ruber) and Pacific-slope flycatcher (Empidonax difficilis) were positively related to buffer width, whereas density of ruby-crowned kinglet (Regulus calendula) was negatively associated with buffer width. Parameter estimates for buffer width effects at both spatial scales were similar within species. We found few habitat and landscape variables that clearly affected density of our focal species, and among species no predictor variables affected density in a similar fashion. We recommend retaining forested buffers ≥400 m to support composition and abundance of forest-dwelling birds, particularly those species that rely on interior forest conditions. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):674-681; 2008)     

Ecological impacts of invasive African olive (Olea europaea ssp. cuspidata) in Cumberland Plain Woodland,Sydney, Australia

African olive (Olea europaea ssp. cuspidata) is a small evergreen tree which has become highly invasive at a landscape scale in the western Sydney and Hunter Valley regions of New South Wales, Australia. African olive invasion results in the formation of a dense and permanent mid‐canopy in grassy woodland vegetation. We investigated the relationship between African olive and native species establishment, abundance and diversity, using field surveys and a manipulative shading experiment. There were 78% fewer native species beneath African olive canopy in the field compared to uninvaded woodland sites. The shading experiment showed that simulated dense African olive shade levels produced the lowest dry weight for the three native species studied, with simulated canopy edge light providing optimal conditions for the native shrub Bursaria spinosa and African olive. Dense African olive shade levels produced the highest mortality rate for native species; however, African olive was able to maintain an 88% survival rate under dense canopy shade. This study confirms the adaptability of African olive and its capacity to decrease native plant diversity and substantially modify native vegetation at the community level.     

Life stage specific variation in the occupancy of ponds by Litoria aurea,a threatened amphibian

Breeding aggregations are a reproductive strategy to increase mate finding opportunity. However, because aggregations skew the distribution of mature animals through conspecific attraction, rather than resource availability, the distribution of breeding sites may be reduced, so that not all suitable breeding sites are used. To examine the relationship between landscape and reproductive strategies of a threatened frog, Litoria aurea, we studied its distribution at Sydney Olympic Park over two breeding seasons. We aimed to: (i) determine the distribution and predictors of breeding ponds; and (ii) assess the significance of dispersal in the juvenile age‐class. We found that the distribution of the calling males was highly skewed and occurred in large, well‐connected ponds. Despite this, breeding ponds were not aggregated; pond size was the single factor explaining the distribution of breeding ponds. Juvenile frogs dispersed from breeding ponds and were not associated with a specific pond characteristic. Less breeding occurred in the second season during which fewer ponds were used for breeding including many different ponds from the previous year. These changes suggest that breeding effort and breeding pond choice are dynamic and therefore knowledge of the factors that drive breeding events will be a powerful tool in managing species, particularly in light of changing climatic regimes.