Evidence for multiple introductions of Centaurea stoebe micranthos (spotted knapweed,Asteraceae) to North America

Invasive species’ success may depend strongly on the genetic resources they maintain through the invasion process. We ask how many introductions have occurred in the North American weed Centaurea stoebe micranthos (Asteraceae), and explore whether genetic diversity and population structure have changed as a result of introduction. We surveyed individuals from 15 European native range sites and 11 North American introduced range sites at six polymorphic microsatellite loci. No significant difference existed in the total number of alleles or in the number of private alleles found in each range. Shannon–Weaver diversity of phenotype frequencies was also not significantly different between the ranges, while expected heterozygosity was significantly higher in the invasive range. Population structure was similar between the native range and the invasive range, and isolation by distance was not significant in either range. Traditional assignment methods did not allocate any North American individuals to the sampled European populations, while Bayesian assignment methods grouped individuals into nine genetic clusters, with three of them shared between North America and Europe. Invasive individuals tended to have genetically admixed profiles, while natives tended to assign more strongly to a single cluster. Many North American individuals share assignment with Romania and Bulgaria, suggesting two separate invasions that have undergone gene flow in North America. Samples from three other invasive range sites were genetically distinct, possibly representing three other unique introductions. Multiple introductions and the maintenance of high genetic diversity through the introduction process may be partially responsible for the invasive success of C. stoebe micranthos.     

Geographic variation and genetic structure in Spotted Owls

We examined genetic variation, populationstructure, and definition of conservation unitsin Spotted Owls (Strix occidentalis). Spotted Owls are mostly non-migratory,long-lived, socially monogamous birds that havedecreased population viability due to theiroccupation of highly-fragmented latesuccessional forests in western North America. To investigate potential effects of habitatfragmentation on population structure, we usedrandom amplified polymorphic DNA (RAPD) toexamine genetic variation hierarchicallyamong local breeding areas, subregionalgroups, regional groups, and subspeciesvia sampling of 21 breeding areas (276individuals) among the three subspecies ofSpotted Owls. Data from 11 variable bandssuggest a significant relationship betweengeographic distance among local breeding groupsand genetic distance (Mantel r = 0.53, P< 0.02) although multi-dimensional scaling ofthree significant axes did not identifysignificant grouping at any hierarchical level. Similarly, neighbor-joining clustering ofManhattan distances indicated geographicstructure at all levels and identified MexicanSpotted Owls as a distinct clade. RAPDanalyses did not clearly differentiate NorthernSpotted Owls from California Spotted Owls. Among Northern Spotted Owls, estimates ofpopulation differentiation (F_ST) rangedfrom 0.27 among breeding areas to 0.11 amongregions. Concordantly, within-group agreementvalues estimated via multi-response permutationprocedures of Jaccard's distances ranged from0.22 among local sites to 0.11 among regions. Pairwise comparisons of F_ST andgeographic distance within regions suggestedonly the Klamath region was in equilibrium withrespect to gene flow and genetic drift. Merging nuclear data with recent mitochondrialdata provides support for designation of anEvolutionary Significant Unit for MexicanSpotted Owls and two overlapping ManagementUnits for Northern and California Spotted Owls.     

Increased seed consumption by biological control weevil tempers positive CO2 effect on invasive plant (Centaurea diffusa) fitness

Predicted increases in atmospheric CO₂ and temperature may benefit some invasive plants, increasing the need for effective invasive plant management. Biological control can be an effective means of managing invasive plants, but the anticipated range in responses of plant–insect interactions to climate change make it difficult to predict how effective biological control will be in the future. Field experiments that manipulate climate within biological control systems could improve predictive power, but are challenging to implement and therefore rare to date. Here, we show that free air CO₂ enrichment in the field increased the fitness of Centaurea diffusa Lam., a problematic invader in much of the western United States. However, CO₂ enrichment also increased the impact of the biological control agent Larinus minutus (Coleoptera: Curculionidae) on C. diffusa fitness. C. diffusa plants flowered earlier and seed heads developed faster with both elevated CO₂ and increased temperature. Natural dispersal of L. minutus into the experimental plots provided a unique opportunity to examine weevil preference for and effects on C. diffusa grown under the different climate change treatments. Elevated CO₂ increased both the proportion of seed heads infested by L. minutus and, correspondingly, the amount of seed removed by weevils. Warming had no detectable effect on weevil utilization of plants. Higher weevil densities on elevated CO₂ plants reduced, but did not eliminate, the positive effects of CO₂ on C. diffusa fitness. Correlations between plant development time and weevil infestation suggest that climate change increased weevil infestation by hastening plant phenology. Phenological mismatches are anticipated with climate change in many plant–insect systems, but in the case of L. minutus and C. diffusa in mixed-grass prairie, a better phenological match may make the biological control agent more effective as CO₂ levels rise.     

Evidence of climatic niche shift during biological invasion

Niche-based models calibrated in the native range by relating species observations to climatic variables are commonly used to predict the potential spatial extent of species' invasion. This climate matching approach relies on the assumption that invasive species conserve their climatic niche in the invaded ranges. We test this assumption by analysing the climatic niche spaces of Spotted Knapweed in western North America and Europe. We show with robust cross-continental data that a shift of the observed climatic niche occurred between native and non-native ranges, providing the first empirical evidence that an invasive species can occupy climatically distinct niche spaces following its introduction into a new area. The models fail to predict the current invaded distribution, but correctly predict areas of introduction. Climate matching is thus a useful approach to identify areas at risk of introduction and establishment of newly or not-yet-introduced neophytes, but may not predict the full extent of invasions.     

四川南充市区珠颈斑鸠的繁殖生态学和巢址选择

2002年11月~2004年4月在四川省南充市区内对珠颈斑鸠(Streptopelia chinensis)繁殖生态和巢址选择进行了研究。结果表明:珠颈斑鸠3月初开始求偶交配,求偶行为复杂,有“婚飞”行为;雌雄参与筑巢,营巢期7~8 d。影响巢址选择的主要因素有6种:栖位与巢周隐蔽因子、巢下隐蔽因子、光照因子、人为活动因子、食物因子和营巢树因子;窝卵数2枚,雌雄轮流孵卵,孵卵期17~18 d,孵化率86.67%;雌雄均参与育雏,育雏期18~20 d,雏离巢率73.08%,繁殖生产力1.82,种群育雏高峰期为7月和8月中上旬。     

The importance of analytical techniques in allelopathy studies with the reported allelochemical catechin as an example

Allelopathy can be challenging to demonstrate. Developing rigorous analytical techniques to detect and quantify compound(s) of interest from soil or liquid media lays the foundation for designing ecologically relevant experiments that incorporate candidate allelochemicals. In this paper, fundamental components of analytical techniques, including method development, validation, and appropriate controls are discussed. Research on the candidate allelochemical from spotted knapweed, catechin, is used as an example to demonstrate the importance of including these components both during data collection and in subsequent publications. This example shows how contrasting results between research groups can be difficult to interpret when information on controls and method validation are not included in publications. Recent research suggests that catechin is not likely driving spotted knapweed’s invasion, and thus future research on this system should focus on alternate candidate toxins from spotted knapweed. By employing appropriate analytical techniques, such as those outlined here, a strong foundation can be laid for ecologically oriented experiments that examine the role of allelochemicals in structuring communities.     

The rickettsia surface cell antigen 4 applies mimicry to bind to and activate vinculin

Pathogenic Rickettsia species cause high morbidity and mortality, especially R. prowazekii, the causative agent of typhus. Like many intracellular pathogens, Rickettsia exploit the cytoskeleton to enter and spread within the host cell. Here we report that the cell surface antigen sca4 of Rickettsia co-localizes with vinculin in cells at sites of focal adhesions in sca4-transfected cells and that sca4 binds to and activates vinculin through two vinculin binding sites (VBSs) that are conserved across all Rickettsia. Remarkably, this occurs through molecular mimicry of the vinculin-talin interaction that is also seen with the IpaA invasin of the intracellular pathogen Shigella, where binding of these VBSs to the vinculin seven-helix bundle head domain (Vh1) displaces intramolecular interactions with the vinculin tail domain that normally clamp vinculin in an inactive state. Finally, the vinculin·sca4-VBS crystal structures reveal that vinculin adopts a new conformation when bound to the C-terminal VBS of sca4. Collectively, our data define the mechanism by which sca4 activates vinculin and interacts with the actin cytoskeleton, and they suggest important roles for vinculin in Rickettsia pathogenesis.