Migratory divides and their consequences for dispersal, population size and parasite-host interactions

Populations of migratory birds differ in their direction of migration with neighbouring populations often migrating in divergent directions separated by migratory divides. A total of 26% of 103 passerine bird species in Europe had migratory divides that were located disproportionately often along a longitudinal gradient in Central Europe, consistent with the assumption of a Quaternary glacial origin of such divides in the Iberian and Balkan peninsulas followed by recolonization. Given that studies have shown significant genetic differentiation and reduced gene flow across migratory divides, we hypothesized that an absence of migratory divides would result in elevated rates of gene flow and hence a reduced level of local adaptation. In a comparative study, species with migratory divides had larger population sizes and population densities and longer dispersal distances than species without migratory divides. Species with migratory divides tended to be habitat generalists. Bird species with migratory divides had higher richness of blood parasites and higher growth rates of Staphylococcus on their eggs during the incubation period. There was weaker cell-mediated immunity in adults and stronger cell lysis in species with migratory divides. These findings may suggest that migratory divides constitute barriers to dispersal with consequences for ecology and evolution of distributions, population sizes, habitats and parasite-host interactions. They also suggest that migratory divides may play a role in local adaptation in host-parasite interactions.     

沙地生境和平茬年限对沙柳叶功能特征的影响

研究了毛乌素沙地南缘水滨边丘间地和干旱丘顶两种生境下沙柳平茬后不同年限(1、2、3～4和5～6年)对沙柳叶片光合气体交换、水分利用效率、结构特性及氮、磷养分含量等叶功能特征的影响.结果表明:水滨边丘间地沙柳叶片的净光合速率、气孔导度、瞬时和长期水分利用效率均高于丘顶,但N、P养分含量低于丘顶;两种生境下沙柳的叶结构性状无显著差异.干旱生境下沙柳主要通过增加养分含量、降低光合和水分利用来生存.随平茬年限增加,叶片净光合速率和气孔导度显著下降,氮含量和瞬时水分利用效率亦呈下降趋势,且二者之间呈显著正相关;平茬后1年的叶面积最高,比叶质量和叶干物质含量最低,此后比叶质量增加,叶面积和干物质含量不变;叶结构性状与光合及养分特性之间无显著相关性.叶光合活性和氮含量的下降是沙柳随平茬年限增加而衰败的重要原因.     

Using demographic data to better interpret pitfall trap catches

The results of pitfall trapping are often interpreted as abundance in a particular habitat. At the same time, there are numerous cases of almost unrealistically high catches of ground beetles in seemingly unsuitable sites. The correlation of catches by pitfall trapping with the true distribution and abundance of Carabidae needs corroboration. During a full year survey in 2006/07 in the Lake Elton region (Volgograd Area, Russia), 175 species of ground beetles were trapped. Considering the differences in demographic structure of the local populations, and not their abundances, three groups of species were recognized: residents, migrants and sporadic. In residents, the demographic structure of local populations is complete, and their habitats can be considered "residential". In migrants and sporadic species, the demographic structure of the local populations is incomplete, and their habitats can be considered "transit". Residents interact both with their prey and with each other in a particular habitat. Sporadic species are hardly important to a carabid community because of their low abundances. The contribution of migrants to the structure of carabid communities is not apparent and requires additional research. Migrants and sporadic species represent a "labile" component in ground beetles communities, as opposed to a "stable" component, represented by residents. The variability of the labile component substantially limits our interpretation of species diversity in carabid communities. Thus, the criteria for determining the most abundant, or dominant species inevitably vary because the abundance of migrants in some cases can be one order of magnitude higher than that of residents. The results of pitfall trapping adequately reflect the state of carabid communities only in zonal habitats, while azonal and disturbed habitats are merely transit ones for many species of ground beetles. A study of the demographic structure of local populations and assessment of the migratory/residential status of particular carabid species are potential ways of increasing the reliability of pitfall trap information.     

Speciation in the highlands of Mexico: genetic and phenotypic divergence in the Mexican jay (Aphelocoma ultramarina)

The pine-oak woodlands of the Mexican highlands harbour significant biological diversity, yet little is known about the evolutionary history of organisms inhabiting this region. We assessed genetic and phenotypic differentiation in 482 individuals representing 27 populations of the Mexican jay ( Aphelocoma ultramarina ) — a widespread bird species of the Mexican highlands — to test whether populations in the central and northern Mexican sierras display discrete breaks between groups, which would be consistent with a role for the different mountain chains in divergence and speciation. We found abrupt breaks in mitochondrial DNA (mtDNA; ND2 and control region) delineating four major genetic groups found in the Sierra Madre Occidental, Sierra Madre Oriental, southern Central Plateau (Bajio), and Transvolcanic Belt. These mtDNA groups were largely corroborated by data from nuclear microsatellites and phenotypic data, except that clades from the Central Plateau and Sierra Madre Oriental showed clinal change in these data sets. Uncertainty about the mutation rate for our mitochondrial markers warrants considerable caution with regard to estimating divergence times, but the major genetic groups appear to have split before the most extreme period of glacial cycling that marked the last 0.7 million years and after Mexico's period of major mountain formation. The fact that some genetic breaks do not coincide with well-known geographic barriers suggests a role for ecology in divergence and speciation, and we discuss implications for taxonomy and conservation.     

Spatially explicit models of divergence and genome hitchhiking

Strong barriers to genetic exchange can exist at divergently selected loci, whereas alleles at neutral loci flow more readily between populations, thus impeding divergence and speciation in the face of gene flow. However, ‘divergence hitchhiking’ theory posits that divergent selection can generate large regions of differentiation around selected loci. ‘Genome hitchhiking’ theory suggests that selection can also cause reductions in average genome‐wide rates of gene flow, resulting in widespread genomic divergence (rather than divergence only around specific selected loci). Spatial heterogeneity is ubiquitous in nature, yet previous models of genetic barriers to gene flow have explored limited combinations of spatial and selective scenarios. Using simulations of secondary contact of populations, we explore barriers to gene flow in various selective and spatial contexts in continuous, two‐dimensional, spatially explicit environments. In general, the effects of hitchhiking are strongest in environments with regular spatial patterning of starkly divergent habitat types. When divergent selection is very strong, the absence of intermediate habitat types increases the effects of hitchhiking. However, when selection is moderate or weak, regular (vs. random) spatial arrangement of habitat types becomes more important than the presence of intermediate habitats per se. We also document counterintuitive processes arising from the stochastic interplay between selection, gene flow and drift. Our results indicate that generalization of results from two‐deme models requires caution and increase understanding of the genomic and geographic basis of population divergence.     

Life history traits variation in heterogeneous environment: The case of a freshwater snail resistance to pond drying

Ecologists and population geneticists have long suspected that the diversity of living organisms was connected to the structure of their environment. In heterogeneous environments, diversifying selection combined to restricted gene flow may indeed lead to locally adapted populations. The freshwater snail, Galba truncatula, is a good model to address this question because it is present in a heterogeneous environment composed of temporary and permanent waters. In order to test the selective importance of those environments, we proposed here to measure survival of lineages from both habitats during drought episodes. To this purpose, we experimentally submitted adults and juveniles individuals from both habitats to drought. We found a difference in desiccation resistance between temporary and permanents waters only for adults. Adults from temporary habitats were found more resistant to drought. This divergence in desiccation resistance seems to explain the unexpected life history traits differences between habitats observed.     

Bird Assemblages in Anthropogenic Habitats: Identifying a Suitability Gradient for Native Species in the Atlantic Forest

Traditional approaches to the study of species persistence in fragmented landscapes generally consider a binary classification of habitat being suitable or unsuitable; however, the range of human‐modified habitats within a region may offer a gradient of habitat suitability (or conservation value) for species. We identified such a gradient by comparing bird assemblages among contrasting land uses (pine plantations of different age, annual crops, clear cuts and cattle pastures) in the Upper Parana Atlantic forest. Bird assemblages and vegetation structure were characterized in an extensive area of 4400 km² in Argentina and Paraguay during the breeding seasons of 2005–2010. Similarity of bird assemblages between anthropogenic habitats and the native forest and the proportion of forest species increased with vegetation vertical structure, while the proportion of open‐area species decreased. As a consequence, mature tree plantations were the most suitable habitats for forest species and were mainly used by frugivores and bark insectivores. In contrast, open habitats were the least suitable habitat for forest species and were used primarily by insectivores. Human‐created habitats that are structurally complex can be used by a subset of forest species, and may improve functional connectivity and mitigate edge effects. The conservation of large tracks of native forests, however, is critical for the long‐term persistence of the entire bird assemblage, especially for native forest dependent species.     

Linking woodland key habitat inventory and forest inventory data to prioritize districts needing conservation efforts

Woodland key habitat (WKH) inventories have been conducted in northern European countries, with the aim to create networks of minimally disturbed forest stands for protection. The goal of national forest inventory is to provide information relevant to forest management, such as on forest types, trees species composition, age structure and wood volume. The aim of this study was to link these two inventory databases to identify districts of Latvia most deficient in connectivity and habitat quality, in order to prioritize districts needing conservation effort. As an example, the area of deciduous forest with nemoral tree species (oak, ash, lime, maple and elm) and aspen was chosen. These forests provide habitat for a specific community of epiphytes. Using information in the WKH database, habitat quality in different districts of Latvia was estimated by the frequencies of occurrence of structural elements and selected indicator epiphyte species in nemoral tree species and aspen WKHs. Using digital data in the national forest inventory database, fragmentation metrics were determined for forests that, according to age and tree species composition, could potentially be nemoral tree and aspen WKHs. On a regional level, the lowest habitat quality in WKH occurred in districts that had the least fragmentation of potential WKH forest. In the less fragmented areas, the habitat quality of the existing WKH will likely increase in the future, and could be promoted by management to create structural elements typical of natural forests. The districts with the most fragmented nemoral and aspen forests, contained WKHs with the best habitat quality. A focus on protection should be given to these stands as they are the most likely to support source populations, and there is a need to improve spatial continuity of suitable tree substrate in these areas.     

Integrating spatial data and shorebird nesting locations to predict the potential future impact of global warming on coastal habitats: A case study on Farasan Islands,Saudi Arabia

One of the expected effects of the global warming is changing coastal habitats by accelerating the rate of sea level rise. Coastal habitats support large number of marine and wetland species including shorebirds (plovers, sandpipers and allies). In this study, we investigate how coastal habitats may be impacted by sea level rise in the Farasan Islands, Kingdom of Saudi Arabia. We use Kentish plover Charadrius alexandrinus – a common coastal breeding shorebird – as an ecological model species to predict the influence of sea level rise. We found that any rise of sea level is likely to inundate 11% of Kentish plover nests. In addition, 5% of the coastal areas of Farasan Islands, which support 26% of Kentish plover nests, will be flooded, if sea level rises by one metre. Our results are constrained by the availability of data on both elevation and bird populations. Therefore, we recommend follow-up studies to model the impacts of sea level rise using different elevation scenarios, and the establishment of a monitoring programme for breeding shorebirds and seabirds in Farasan Islands to assess the impact of climate change on their populations.     

近海潮间带植物及其生境中微生物的特性及药用前景

近海潮间带植物生境的微生物是最富有生物多样性的海洋种群,其生境的独特性决定了该区域微生物较高的药用价值.本文介绍了我国南北方海域近海潮间带植物生境和微生物的特性及药用前景,为该区域微生物的开发利用提供参考.