Edge effects reduce the nesting success of Acadian Flycatchers in a moderately fragmented forest

ABSTRACT.   Forest fragmentation can create negative edge effects that reduce the reproductive success of birds nesting near the forest/nonforest interface, and threaten bird populations deeper in remnant forest habitats. Negative edge effects may be more pronounced in landscapes that are moderately fragmented, particularly where agriculture is the primary land-use fragmenting forests. Information about the extent and strength of edge effects at a site can help guide conservation actions, and determine their effectiveness. We examined edge effects for birds breeding in a nearly contiguous forest fragmented by relatively narrow agricultural corridors in Illinois (USA). We measured rates of nest predation and brood parasitism for Acadian Flycatchers ( Empidonax virescens ) over a continuum of distances from the edge of an agricultural inholding. Nest predation and brood parasitism were highest near the edge and decreased with increasing distance from the edge. Given the cumulative effects of nest predation and brood parasitism on reproductive success, we determined that forest within 600 m of the inholding was sink habitat. We found, however, that deeper forest interior areas currently serve as source habitat, and that conversion of the entire 205 ha agricultural corridor to forest would add 1350 ha of source habitat for Acadian Flycatchers. Such results provide support for a local conservation strategy of forest consolidation and establish baseline measures necessary to determine the relative effectiveness of any subsequent reforestation efforts.     

Studies of the biological properties of human beta-defensin 1

Defensins are small (30-45 amino acid residues) cationic proteins with broad antimicrobial activity against many bacteria and fungi, some enveloped viruses, and other activities such as chemoattraction of a range of different cell types to the sites of inflammation. These proteins represent attractive targets for developing novel antimicrobial agents and modulators of immune responses with therapeutic applicability. In this report, we present the results of functional and structural studies of 26 single-site mutants of human beta-defensin 1 (hBD1). All mutants were assayed for antimicrobial activity against Escherichia coli (ATCC strain 25922) and for chemotactic activity with CCR6-transfected HEK293 cells. To analyze the structural implications of mutagenesis and to verify the correctness of the disulfide connectivity, we used x-ray crystallography to conduct complete structural studies for 10 mutants in which the topology of disulfides was the same as in the native hBD1. Mutations did not induce significant changes of the tertiary structure, suggesting that the observed alterations of biological properties of the mutants were solely associated with changes in the respective side chains. We found that cationic residues located near the C terminus (Arg(29), Lys(31), Lys(33), and Lys(36)) of hBD1 define most of the anti-E. coli in vitro activity of this protein. In turn, nearly all mutations altering the CCR6-mediated chemotaxis are located at one area of the protein, defined by the N-terminal alpha-helical region (Asp(1)... Ser(8)) and a few topologically adjacent residues (Lys(22), Arg(29), and Lys(33)). These experimental results allow for the first time drafting of the CCR6-epitope for a defensin molecule.     

Intrastadial developmental resistance of third instar gypsy moths (Lymantria dispar L.) to L. dispar nucleopolyhedrovirus

Gypsy moth larvae become increasingly resistant to lethal infection by the Lymantria dispar M nucleopolyhedrovirus (LdMNPV) as they age within the fourth instar. Newly molted larvae are most sensitive to infection, mid-instars are least sensitive, and late-instars display intermediate sensitivity. This resistance occurs whether the virus is delivered orally or intrahemocoelically. The present study reveals a nearly identical pattern of resistance in third instar larvae. An LD₄₈ dose of polyhedra for newly molted third instars produced 18%, 10%, 8%, 25%, and 24% mortalities in larvae to which virus was orally administered at 12, 24, 48, 72, and 96 hours post-molt (hpm), respectively, which is a 6-fold reduction in mortality between newly molted larvae and mid-instars. An LD₄₄ dose of budded virus for newly molted third instars produced 33%, 23%, 17%, 31%, and 31% mortalities when injected into larvae that were 12, 24, 48, 72, and 96 hpm, respectively, which is a 2.6-fold reduction in mortality between newly molted larvae and mid-instars, indicating that approximately half of this resistance is midgut-based and half is systemically based. Doubling the viral dose did not overcome developmental resistance whether the virus was delivered orally or intrahemocoelically. In addition, time to death was significantly affected by the time post-molt at which the insect was inoculated with the virus. We suggest that intrastadial developmental resistance may affect both the ecology and management of the gypsy moth.     

Phenotypic properties of adult mouse intrinsic cardiac neurons maintained in culture

Intrinsic cardiac neurons are core elements of a complex neural network that serves as an important integrative center for regulation of cardiac function. Although mouse models are used frequently in cardiovascular research, very little is known about mouse intrinsic cardiac neurons. Accordingly, we have dissociated neurons from adult mouse heart, maintained these cells in culture, and defined their basic phenotypic properties. Neurons in culture were primarily unipolar, and 89% had prominent neurite outgrowth after 3 days (longest neurite length of 258 +/- 20 microm, n = 140). Many neurites formed close appositions with other neurons and nonneuronal cells. Neurite outgrowth was drastically reduced when neurons were kept in culture with a majority of nonneural cells eliminated. This finding suggests that nonneuronal cells release molecules that support neurite outgrowth. All neurons in coculture showed immunoreactivity for a full complement of cholinergic markers, but about 21% also stained for tyrosine hydroxylase, as observed previously in sections of intrinsic cardiac ganglia from mice and humans. Whole cell patch-clamp recordings demonstrated that these neurons have voltage-activated sodium current that is blocked by tetrodotoxin and that neurons exhibit phasic or accommodating patterns of action potential firing during a depolarizing current pulse. Several neurons exhibited a fast inward current mediated by nicotinic ACh receptors. Collectively, this work shows that neurons from adult mouse heart can be maintained in culture and exhibit appropriate phenotypic properties. Accordingly, these cultures provide a viable model for evaluating the physiology, pharmacology, and trophic factor sensitivity of adult mouse cardiac parasympathetic neurons.     

Laboratory test of suspended sediment effects on short‐term survival and swimming performance of juvenile Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus,Mitchill, 1815)

Tested was the hypothesis that juvenile Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) would exhibit no response in short‐term survival or swimming performance when exposed to varying concentrations of suspended sediment simulating dredge plumes in waterways where this species may be impacted by dredging operations. Sediment collected from Savannah Harbor, South Carolina, USA was used to simulate a worst‐case scenario. Juvenile sturgeon were contained for a 3‐day period in flow‐through aquaria, with limited opportunity for movement, in sediment of varying concentrations (100, 250 and 500 mg L^?1 total suspended solids [TSS]) mimicking prolonged exposure to suspended sediment plumes near an operating dredge. Of the 90 fish exposed, 86 (96%) survived the test. Of the four fish that died, one was exposed to 250 TSS and three to 500 TSS. Swimming performance results indicated that nearly all fish were positively rheotactic. Critical swim speeds (U_crits) were moderate, whether measured as absolute values (21–31 cm s^?1) or as relative values (1.4–2.1 body lengths s^?1), with no significant differences among treatments (F < 0.83, P ≥ 0.4874). Behavior was dominated by contact‐based locomotion and station‐holding. Absence of substantial or significant immediate effects on survival and swimming performance suggest that impacts of sediment plumes in nature, where fish have freedom of movement and the power to escape rapidly, are minimal.     

Relationship of aerobic and anaerobic parameters with 400 m front crawl swimming performance

The aims of the present study were to investigate the relationship of aerobic and anaerobic parameters with 400 m performance, and establish which variable better explains long distance performance in swimming. Twenty-two swimmers (19.1±1.5 years, height 173.9±10.0 cm, body mass 71.2±10.2 kg; 76.6±5.3% of 400 m world record) underwent a lactate minimum test to determine lactate minimum speed (LMS) (i.e., aerobic capacity index). Moreover, the swimmers performed a 400 m maximal effort to determine mean speed (S400m), peak oxygen uptake (V.O2PEAK) and total anaerobic contribution (C_ANA). The C_ANA was assumed as the sum of alactic and lactic contributions. Physiological parameters of 400 m were determined using the backward extrapolation technique (V.O2PEAK and alactic contributions of C_ANA) and blood lactate concentration analysis (lactic anaerobic contributions of C_ANA). The Pearson correlation test and backward multiple regression analysis were used to verify the possible correlations between the physiological indices (predictor factors) and S400m (independent variable) (p < 0.05). Values are presented as mean ± standard deviation. Significant correlations were observed between S400m (1.4±0.1 m·s^-1) and LMS (1.3±0.1 m·s^-1; r = 0.80), V.O2PEAK (4.5±3.9 L·min^-1; r = 0.72) and C_ANA (4.7±1.5 L·O₂; r= 0.44). The best model constructed using multiple regression analysis demonstrated that LMS and V.O2PEAK explained 85% of the 400 m performance variance. When backward multiple regression analysis was performed, C_ANA lost significance. Thus, the results demonstrated that both aerobic parameters (capacity and power) can be used to predict 400 m swimming performance.     

A new quorum‐sensing system (TprA/PhrA) for Streptococcus pneumoniae D39 that regulates a lantibiotic biosynthesis gene cluster

The Phr peptides of the Bacillus species mediate quorum sensing, but their identification and function in other species of bacteria have not been determined. We have identified a Phr peptide quorum‐sensing system (TprA/PhrA) that controls the expression of a lantibiotic gene cluster in the Gram‐positive human pathogen, Streptococcus pneumoniae. Lantibiotics are highly modified peptides that are part of the bacteriocin family of antimicrobial peptides. We have characterized the basic mechanism for a Phr‐peptide signaling system in S. pneumoniae and found that it induces the expression of the lantibiotic genes when pneumococcal cells are at high density in the presence of galactose, a main sugar of the human nasopharynx, a highly competitive microbial environment. Activity of the Phr peptide system is not seen when pneumococcal cells are grown with glucose, the preferred carbon source and the most prevalent sugar encountered by S. pneumoniae during invasive disease. Thus, the lantibiotic genes are expressed under the control of both cell density signals via the Phr peptide system and nutritional signals from the carbon source present, suggesting that quorum sensing and the lantibiotic machinery may help pneumococcal cells compete for space and resources during colonization of the nasopharynx.     

A generalist brood parasite modifies use of a host in response to reproductive success

Avian obligate brood parasites, which rely solely on hosts to raise their young, should choose the highest quality hosts to maximize reproductive output. Brown-headed cowbirds (Molothrus ater) are extreme host generalists, yet female cowbirds could use information based on past reproductive outcomes to make egg-laying decisions thus minimizing fitness costs associated with parasitizing low-quality hosts. We use a long-term (21 years) nest-box study of a single host, the prothonotary warbler (Protonotaria citrea), to show that local cowbird reproductive success, but not host reproductive success, was positively correlated with the probability of parasitism the following year. Experimental manipulations of cowbird success corroborated that female cowbirds make future decisions about which hosts to use based on information pertaining to past cowbird success, both within and between years. The within-year pattern, in particular, points to local cowbird females selecting hosts based on past reproductive outcomes. This, coupled with high site fidelity of female cowbirds between years, points to information use, rather than cowbird natal returns alone, increasing parasitism rates on highly productive sites between years.     

Synapse-Assembly Proteins Maintain Synaptic Vesicle Cluster Stability and Regulate Synaptic Vesicle Transport in Caenorhabditis elegans

The functional integrity of neurons requires the bidirectional active transport of synaptic vesicles (SVs) in axons. The kinesin motor KIF1A transports SVs from somas to stable SV clusters at synapses, while dynein moves them in the opposite direction. However, it is unclear how SV transport is regulated and how SVs at clusters interact with motor proteins. We addressed these questions by isolating a rare temperature-sensitive allele of Caenorhabditis elegans unc-104 (KIF1A) that allowed us to manipulate SV levels in axons and dendrites. Growth at 20° and 14° resulted in locomotion rates that were ∼3 and 50% of wild type, respectively, with similar effects on axonal SV levels. Corresponding with the loss of SVs from axons, mutants grown at 14° and 20° showed a 10- and 24-fold dynein-dependent accumulation of SVs in their dendrites. Mutants grown at 14° and switched to 25° showed an abrupt irreversible 50% decrease in locomotion and a 50% loss of SVs from the synaptic region 12-hr post-shift, with no further decreases at later time points, suggesting that the remaining clustered SVs are stable and resistant to retrograde removal by dynein. The data further showed that the synapse-assembly proteins SYD-1, SYD-2, and SAD-1 protected SV clusters from degradation by motor proteins. In syd-1, syd-2, and sad-1 mutants, SVs accumulate in an UNC-104-dependent manner in the distal axon region that normally lacks SVs. In addition to their roles in SV cluster stability, all three proteins also regulate SV transport.