HOLARCTIC PHYLOGEOGRAPHY OF AN ASEXUAL SPECIES COMPLEX I. MITOCHONDRIAL DNA VARIATION IN ARCTIC DAPHNIA

Pleistocene glacial cycles undoubtedly altered the evolutionary trajectories of many taxa, yet few studies have examined the impact of such events on genetic differentiation and phylogeography at large geographic scales. Here we present the results of a circumarctic survey of mitochondrial DNA diversity in members of the Daphnia pulex complex. The analysis involved the survey of restriction site polymorphisms in a 2100-bp fragment of the NADH-4 (ND4) and NADH-5 (ND5) genes for 276 populations representing the two major groups (tenebrosa and pulicaria) in this complex across their Holarctic range. A comparison of the distribution patterns for seven clades in this complex revealed very clear phylogeographic structuring. Most notably, pulicaria group lineages were restricted primarily to the Nearctic, with some colonization of formerly glaciated portions of northern Europe. This group was not detected from vast expanses of northern Eurasia, including the Beringian glacial refuge. In contrast, tenebrosa group haplotypes showed considerable intercontinental divergence between Eurasian and North American lineages, but were absent from Greenland and Iceland, as well as the Canadian arctic archipelago. Dispersal in Eurasia was primarily in a westerly direction from Beringia, whereas dispersal in the Nearctic followed proglacial drainage patterns. Long-distance dispersal of certain lineages was observed in both groups, and variation in haplotype richness and nucleotide diversity allowed us to make inferences about the positioning of putative glacial refugia. Overall, the phylogeographic pattern of diversification in this arctic complex is characterized by the apparently unique postglacial histories for each clade, indicating that even closely allied taxa can respond independently to the allopatric effects of glacial cycles. This is in sharp contrast to other phylogeographic studies of species assemblages from more southern (unglaciated) latitudes, which are often characterized by concordant patterns.     

Studies on the flight activity of the Viburnum whitefly, a reluctant flyer

Dispersal of adult Viburnum whitefly,Aleurotrachelus jelinekii (Frauenf.) was assessed over a period of 6 years, both in the field and in the laboratory. Flight activity did not appear to be strongly affected by normal variation in either temperature or windspeed. The aerial density of flying adults decreased rapidly with distance from the host plant. Movement up to 5 m from the host plant was found to be density dependent, although there is no suggestion that longer flights become more frequent at higher population densities. More males were caught at the beginning of the season and the number of males flying increased as the population density rose. Insects were flight mature after about 3 h, but flew readily only after 2 days. Longer flights were observed from younger females at a time when they would move from old to young leaves. Landing site preference was not recorded, which contrasts with the behaviour of the cabbage whitefly. Flight in the Viburnum whitefly appears to redistribute the population within the immediate habitat, but migration did not appear to be a significant demographic factor in the isolated populations studied.

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Etude de l'activité de vold d'Aleurotrachelus jelinekii peu enclin au vol

Résumé La dispersion des adultes d'Aleurotrachelus jelinekii Frauenf, tant dans la nature qu'au laboratoire, a été estimée sur une période de 6 ans. L'activité de vol n'a pas paru être fortement modifiée par les variations de la température et de la vitesse du vent. Le nombre d'adultes en vol a diminué rapidement jusqu'à 5 m de la plante hôte, et il était density-dependent, bien que rien ne prouve que les vols les plus longs deviennent plus fréquents à des densités de population plus élevées. Plus de mâles ont été capturés au début de la saison et le nombre de mâles en vol s'est accru avec la densité de la population. Les insectes étaient aptes au vol 3 heures après la mue imaginale, mais ne volaient normalement que 2 jours après. Les vols les plus longs ont été observés chez les plus jeunes femelles au moment où elles devaient migrer de feuilles âgées à des feuilles jeunes. Les lieux d'atterrissage préférés n'ont pas été décelés. Le vol chezA. jelinekii semble redistribuer la population dans l'habitat immédiat et la migration n'apparaît pas être un paramètre démographique significantif dans les populations isolées étudiées.

     

Interactions between spatial and temporal scales in the evolution of dispersal rate

The evolution of dispersal rate is studied with a model of several local populations linked by dispersal. Three dispersal strategies are considered where all, half or none of the offspring disperse. The spatial scale (number of patches) and the temporal scale (probability of local extinction) of the environment are critical in determining the selective advantage of the different dispersal strategies. The results from the simulations suggest that an interaction between group selection and individual selection results in a different outcome in relation to the spatial and temporal scales of the environment. Such an interaction is able to maintain a polymorphism in dispersal strategies. The maintenance of this polymorphism is also scale-dependent. This study suggests a mechanism for the short-term evolution of dispersal, and provides a testable prediction of this hypothesis, namely that loss of dispersal abilities should be more frequent in spatially more continuous environments, or in temporally more stable environments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evolution of helping and harming in heterogeneous populations

There has been much interest in understanding how demographic factors can mediate social evolution in viscous populations. Here, we examine the impact of heterogeneity in patch quality--that is, the availability of reproductive resources for each breeder--upon the evolution of helping and harming behaviors. We find that, owing to a cancellation of relatedness and kin competition effects, the evolution of obligate and facultative helping and harming is not influenced by the degree of viscosity in populations characterized by either spatial or temporal heterogeneity in patch quality. However, facultative helping and harming may be favored when there is both spatial and temporal heterogeneity in patch quality, with helping and harming being favored in both high-quality and low-quality patches. We highlight the prospect for using kin selection theory to explain within-population variation in social behavior, and point to the need for further theoretical and empirical investigation of this topic.     

秦岭南北坡森林鼠类对板栗和锐齿栎种子扩散的影响

森林鼠类的种子贮藏行为对植物的扩散及更新会产生积极的影响。2012和2013年秋季,分别在秦岭北坡的周至国家级自然保护区和南坡的佛坪国家级自然保护区内,调查了森林鼠类对板栗(Castanea mollissima)和锐齿栎(Quercus aliena)种子的取食和扩散差异。结果显示:1)秦岭南北坡的环境因素,特别是植被因素,对鼠类扩散板栗和锐齿栎种子具有重要的影响。南坡较为丰富的壳斗科植被种类,导致2种种子在南坡存留时间均长于北坡,而北坡的扩散取食和丢失率均高于南坡。2)种子特征影响鼠类的取食或贮藏偏好。由于较高的蛋白、脂肪等营养含量,鼠类更喜好取食或搬运贮藏板栗种子。然而,低营养但高丹宁含量的锐齿栎种子仍然被鼠类大量贮藏。3)2种种子在南北坡的扩散历程在两个年份间有很大差异,在食物相对匮乏的年份(2012年),种子被扩散的速度更快且丢失的比率更高。这种差异反映了种子大小年现象对森林鼠类取食和贮藏策略的影响。4)无论在秦岭南坡还是北坡,营养价值含量(如蛋白和脂肪)较高的板栗种子的取食和贮藏距离都明显大于营养价值含量较低的锐齿栎种子,这与最优贮藏空间分布模型的预测一致。     

Mathematical modeling of the population dynamics of a distinct interactions type system with local dispersal

Distinct biotic interactions in multi-species communities are a ubiquitous force in the natural ecosystem, and this force is an essential determinant of community stability and species coexistence outcomes. We conduct numerical simulations and bifurcation analysis of partial differential equations to gain better understanding and ecological insights into how predation (a), predator handling time (h), and local dispersal affect multi-species community dynamics. This system consists of resource-mutualist-exploiter-competitor interactions and local dispersal. From the inspection of our numerical simulations and co-dimension one bifurcation analysis findings, we discover several critical values that correspond to transcritical bifurcation, subcritical and supercritical Hopf bifurcations. This occurs as we vary the bifurcation parameters a and h in this complex ecological system under symmetric and asymmetric dispersal scenarios. Furthermore, the interplay between these local bifurcation points results in an exciting co-dimension two bifurcations, i.e., Bogdanov-Takens and cusp bifurcation points, respectively, which act as the synchronization points in this complex ecological system. From an ecological viewpoint, we find that (i) the effect of the no-dispersal scenario supports the maintenance of species biodiversity when the predation strength is moderate; (ii) symmetric dispersal induces both subcritical and supercritical Hopf bifurcation and support species diversity for moderate predation strength; and (iii) asymmetric dispersal promotes species diversity as it simplifies the bifurcation changes in dynamics by eliminating the subcritical bifurcations that trigger uncertainty, and this dispersal mechanism mediates species coexistence outcomes. Fundamentally, stable limit cycles have been reported as predator handling time varies in some ecological models; however, we observed in our bifurcation analysis the emergence of the unstable limit cycle as predator handling time changes. We discover that intense predator handling time destabilizes this complex ecological community. In general, our results demonstrate the influential roles of predation, predator handling time, and local dispersal in determining this system’s coexistence dynamics. This knowledge provides a better understanding of species conservation and biological control management.     

Phenological match drives pollen‐mediated gene flow in a temporally dimorphic tree

• Variation in flowering phenology is common in natural populations, and is expected to be, together with inter‐mate distance, an important driver of effective pollen dispersal. In populations composed of plants with temporally separated sexual phases (i.e. dichogamous or heterodichogamous populations), pollen‐mediated gene flow is assumed to reflect phenological overlap between complementary sexual phases. In this study, we conducted paternity analyses to test this hypothesis in the temporally dimorphic tree Acer opalus.
• We performed spatially explicit analyses based on categorical and fractional paternity assignment, and included tree size, pair‐wise genetic relatedness and morph type as additional predictors. Because differences between morphs in flowering phenology may also influence pollination distances, we modelled separate pollen dispersal kernels for the two morphs.
• Extended phenological overlap between male and female phases (mainly associated with inter‐morph crosses) resulted in higher siring success after accounting for the effects of genetic relatedness, morph type and tree size, while reduced phenological overlap (mainly associated with intra‐morph crosses) resulted in longer pollination distances achieved. Siring success also increased in larger trees.
• Mating patterns could not be predicted by phenology alone. However, as heterogeneity in flowering phenology was the single morph‐specific predictor of siring success, it is expected to be key in maintaining the temporal dimorphism in A. opalus, by promoting not only a prevalent pattern of inter‐morph mating, but also long‐distance pollination resulting from intra‐morph mating events.

     

Warming increases plant biomass and reduces diversity across continents,latitudes, and species migration scenarios in experimental wetland communities

Atmospheric warming may influence plant productivity and diversity and induce poleward migration of species, altering communities across latitudes. Complicating the picture is that communities from different continents deviate in evolutionary histories, which may modify responses to warming and migration. We used experimental wetland plant communities grown from seed banks as model systems to determine whether effects of warming on biomass production and species richness are consistent across continents, latitudes, and migration scenarios. We collected soil samples from each of three tidal freshwater marshes in estuaries at three latitudes (north, middle, south) on the Atlantic coasts of Europe and North America. In one experiment, we exposed soil seed bank communities from each latitude and continent to ambient and elevated (+2.8 °C) temperatures in the greenhouse. In a second experiment, soil samples were mixed either within each estuary (limited migration) or among estuaries from different latitudes in each continent (complete migration). Seed bank communities of these migration scenarios were also exposed to ambient and elevated temperatures and contrasted with a no‐migration treatment. In the first experiment, warming overall increased biomass (+16%) and decreased species richness (?14%) across latitudes in Europe and North America. Species richness and evenness of south‐latitude communities were less affected by warming than those of middle and north latitudes. In the second experiment, warming also stimulated biomass and lowered species richness. In addition, complete migration led to increased species richness (+60% in North America, + 100% in Europe), but this higher diversity did not translate into increased biomass. Species responded idiosyncratically to warming, but Lythrum salicaria and Bidens sp. increased significantly in response to warming in both continents. These results reveal for the first time consistent impacts of warming on biomass and species richness for temperate wetland plant communities across continents, latitudes, and migration scenarios.     

Effects of transportation direction of photosynthate on soil microbial processes in the rhizosphere of Phyllostachys bissetii北大核心CSCD

Aims Clonal integration contributes greatly to the adaption of clonal plants to heterogeneous habitats. However, effects of transportation direction of photosynthate on microbial processes need to be further investigated in the rhizosphere. The purpose of this study is to determine the effects of directional differences in photosynthate transport on microbial processes in the rhizosphere of clonal plant Phyllostachys bissetii. Methods By removing the aboveground parts of the ramets, acropetal treatment and basipetal treatment were applied in this study to control the transportation direction of photosynthate. In acropetal treatment, aboveground parts of distal ramets were cut off (with 20 cm above ground kept), and proximal ramets were left intact. While in basipetal treatment, aboveground parts of proximal ramets were cut off (with 20 cm above ground kept), and distal ramets were left intact. Rhizomes between the two ramets were either connected or severed. Carbon (C) and nitrogen (N) availabilities, and enzyme activities in the rhizosphere soils were measured. Important findings In acropetal treatment, total organic carbon (TOC), dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and soil inorganic nitrogen (NH4 +-N and NO3 --N) content in the rhizosphere soil of distal ramets with connected rhizomes were significantly higher than those with severed rhizome. The activities of urease, polyphenol oxidase (POXase), N-acetyl-β-D-Glucosaminidase (NAGase) were significantly enhanced. Further, clonal integration had a significant effect on C and N availability, and microbial processes in the rhizosphere soil of neighbouring ramets. In basipetal treatment, clonal integration did not show a significant effect on C availability in the rhizosphere soil of proximal ramets, but microbial processes along with soil enzyme activities were altered accordingly. Effects of transportation direction of photosynthate on microbial processes in the rhizosphere of P. bissetii provides insights into the adaptation mechanisms of clonal plant populations. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.