The ideal free distribution as an evolutionarily stable strategy

We examine the evolutionary stability of strategies for dispersal in heterogeneous patchy environments or for switching between discrete states (e.g. defended and undefended) in the context of models for population dynamics or species interactions in either continuous or discrete time. There have been a number of theoretical studies that support the view that in spatially heterogeneous but temporally constant environments there will be selection against unconditional, i.e. random, dispersal, but there may be selection for certain types of dispersal that are conditional in the sense that dispersal rates depend on environmental factors. A particular type of dispersal strategy that has been shown to be evolutionarily stable in some settings is balanced dispersal, in which the equilibrium densities of organisms on each patch are the same whether there is dispersal or not. Balanced dispersal leads to a population distribution that is ideal free in the sense that at equilibrium all individuals have the same fitness and there is no net movement of individuals between patches or states. We find that under rather general assumptions about the underlying population dynamics or species interactions, only such ideal free strategies can be evolutionarily stable. Under somewhat more restrictive assumptions (but still in considerable generality), we show that ideal free strategies are indeed evolutionarily stable. Our main mathematical approach is invasibility analysis using methods from the theory of ordinary differential equations and nonnegative matrices. Our analysis unifies and extends previous results on the evolutionary stability of dispersal or state-switching strategies.     

Phenological responses to small-scale spatial variation in snowmelt timing reveal compensatory and conservative strategies in subarctic-alpine plants

Background: In tundra ecosystems, the adjustment of phenological events, such as bud burst, to snowmelt timing is crucial to the climatic adaptation of plants. Natural small-scale variations in microclimate potentially enable plant populations to persist in a changing climate.

Aims: To assess how plant phenology responds to natural differences in snowmelt timing.

Methods: We observed the timing of eight vegetative and reproductive phenophases in seven dwarf-shrub species in relation to differences in snowmelt timing on a small spatial scale in an alpine environment in subarctic Finland.

Results: Some species and phenophases showed accelerated development with later snowmelt, thus providing full or partial compensation for the shorter snow-free period. Full compensation resulted in synchronous occurrence of phenophases across the snowmelt gradient. In other species, there was no acceleration of development. The timing of phenophases varied between two consecutive years and two opposing mountain slope aspects.

Conclusions: The results have shown three distinct patterns in the timing of phenophases in relation to snowmelt and suggest alternative strategies for adaptation to snowmelt timing. These strategies potentially apply to other species and tundra ecosystems and provide a framework, enabling one to compare and generalise phenological responses to snowmelt timing under different future climate scenarios.     

Stochastic models for the Trojan Y-Chromosome eradication strategy of an invasive species

The Trojan Y-Chromosome (TYC) strategy, an autocidal genetic biocontrol method, has been proposed to eliminate invasive alien species. In this work, we develop a Markov jump process model for this strategy, and we verify that there is a positive probability for wild-type females going extinct within a finite time. Moreover, when sex-reversed Trojan females are introduced at a constant population size, we formulate a stochastic differential equation (SDE) model as an approximation to the proposed Markov jump process model. Using the SDE model, we investigate the probability distribution and expectation of the extinction time of wild-type females by solving Kolmogorov equations associated with these statistics. The results indicate how the probability distribution and expectation of the extinction time are shaped by the initial conditions and the model parameters.     

Varying foraging patterns in response to competition? A multicolony approach in a generalist seabird

Reducing resource competition is a crucial requirement for colonial seabirds to ensure adequate self‐ and chick‐provisioning during breeding season. Spatial segregation is a common avoidance strategy among and within species from neighboring breeding colonies. We determined whether the foraging behaviors of incubating lesser black‐backed gulls (Larus fuscus) differed between six colonies varying in size and distance to mainland, and whether any differences could be related to the foraging habitats visited. Seventy‐nine incubating individuals from six study colonies along the German North Sea coast were equipped with GPS data loggers in multiple years. Dietary information was gained by sampling food pellets, and blood samples were taken for stable isotope analyses. Foraging patterns clearly differed among and within colonies. Foraging range increased with increasing colony size and decreased with increasing colony distance from the mainland, although the latter might be due to the inclusion of the only offshore colony. Gulls from larger colonies with consequently greater density‐dependent competition were more likely to forage at land instead of at sea. The diets of the gulls from the colonies furthest from each other differed, while the diets from the other colonies overlapped with each other. The spatial segregation and dietary similarities suggest that lesser black‐backed gulls foraged at different sites and utilized two main habitat types, although these were similar across foraging areas for all colonies except the single offshore island. The avoidance of intraspecific competition results in colony‐specific foraging patterns, potentially causing more intensive utilization of terrestrial foraging sites, which may offer more predictable and easily available foraging compared with the marine environment.     

Environmental variability and population dynamics: do European and North American ducks play by the same rules?

Density dependence, population regulation, and variability in population size are fundamental population processes, the manifestation and interrelationships of which are affected by environmental variability. However, there are surprisingly few empirical studies that distinguish the effect of environmental variability from the effects of population processes. We took advantage of a unique system, in which populations of the same duck species or close ecological counterparts live in highly variable (north American prairies) and in stable (north European lakes) environments, to distinguish the relative contributions of environmental variability (measured as between‐year fluctuations in wetland numbers) and intraspecific interactions (density dependence) in driving population dynamics. We tested whether populations living in stable environments (in northern Europe) were more strongly governed by density dependence than populations living in variable environments (in North America). We also addressed whether relative population dynamical responses to environmental variability versus density corresponded to differences in life history strategies between dabbling (relatively “fast species” and governed by environmental variability) and diving (relatively “slow species” and governed by density) ducks. As expected, the variance component of population fluctuations caused by changes in breeding environments was greater in North America than in Europe. Contrary to expectations, however, populations in more stable environments were not less variable nor clearly more strongly density dependent than populations in highly variable environments. Also, contrary to expectations, populations of diving ducks were neither more stable nor stronger density dependent than populations of dabbling ducks, and the effect of environmental variability on population dynamics was greater in diving than in dabbling ducks. In general, irrespective of continent and species life history, environmental variability contributed more to variation in species abundances than did density. Our findings underscore the need for more studies on populations of the same species in different environments to verify the generality of current explanations about population dynamics and its association with species life history.     

高粱可溶性酸性转化酶基因(SAI-1)PCR克隆方法

可溶性酸性转化酶(SAI)是蔗糖代谢途径中的关键酶,对植物生长发育起着至关重要的调节作用,研究简捷快速克隆可溶性酸性转化酶基因方法,对于育种材料和品种资源的基因分型具有重要意义。本研究通过已知的高粱可溶性酸性转化酶基因序列及高粱基因组中该基因序列片段,设计引物,比较了分段克隆、基因全长克隆、巢式PCR克隆等方法克隆高粱SAI-1基因的效果,结果表明,直接扩增全长,扩增产物极其不稳定且扩增产物纯化、连接,转化后得不到阳性克隆;采用均等分段克隆,前半段扩增产物纯化、连接转化后得不到阳性克隆,但后半段克隆成功;针对高粱基因组信息中SAI-1基因上游的未知序列部分设计引物,进行单独克隆(635 bp),再单独克隆其其余序列,两段序列拼接后得到SAI-1基因全长。序列分析发现,SAI-1前段635 bp的扩增片段GC含量高达69.6%,而其后GC含量急剧下降至30%以下,所以推测全长克隆、均等片段克隆以及巢式PCR克隆失败的原因可能是SAI-1基因中GC分布不均匀,克隆高粱SAI-1基因较为适宜的方法为利用2对引物进行不均等分段扩增克隆,前段PCR退火温度较后段高1℃。该方法将为其他研究人员提供有益参考。     

医药 CRO 专题报告——蓝海市场，强者恒强

随着全球制药企业研发投资成本加大、研发周期变长、研发成功率降低,作为社会分工专业化的产物,CRO 企业凭借其低成本、高效率、 多服务的特点,快速发展,且服务范畴已涵盖药物研发的整个过程,成为医药研发产业链中不可缺少的环节。报告采用文献调研、数据库检索、 数据统计与分析等定性定量研究方法,从发展概况、发展策略、竞争格局、企业布局等角度对国内外医药 CRO 领域进行多角度、多层次的 分析,旨在为相关企业确定产品研发思路、制定市场策略提供线索和参考。     

毕赤酵母GS115表达HSA-GCSFm的诱导工艺研究

本文探讨了甲醇流加控制、添加胰蛋白胨和甲醇/山梨醇共混诱导对重组毕赤酵母GS115/pPIC9K-HSA-GCSFm表达HSA-GCSFm的影响.结果显示:甲醇供应充足条件下HSA-GCSFm表达水平仅为37 mg·L-1,而甲醇添加受限条件下HSA-GCSFm表达水平可达到239mg·L-1;甲醇添加受限并添加胰蛋白胨条件下,HSA-GCSFm表达水平可以提高到266 mg·L-1;在此基础上,流加山梨醇作为辅助碳源,表达水平可大幅提高至424 mg·L-1.通过对各诱导条件下OUR、胞外蛋白酶及碳流分配进行分析后发现,将甲醇限制在低浓度同时添加胰蛋白胨与山梨醇,可以改善细胞代谢活性,增加细胞用于HSA-GCSFm合成的碳流分配量,降低胞外蛋白酶活性,从而提高了HSA-GCSFm的表达水平并缓解了HSA-GCSFm的降解.因此,该诱导工艺适于毕赤酵母高效表达HSA-GCSFm.     

生境异质性对鼎湖山常绿阔叶林群落功能多样性的影响

物种共存机制一直以来是群落生态学的研究热点。为了探讨异质生境条件下鼎湖山常绿阔叶林群落功能多样性变化,找到其变化的主要环境驱动因子,该研究利用位于鼎湖山20 hm~2监测样地第2次群落调查数据并选择代表不同生境(海拔和地形)的27个样方(20 m×20 m),于2013年夏季在样地内所选样方中测定所有胸径≥1 cm树种的叶片功能性状。所测性状包括形态学性状(比叶面积、叶片干物质含量、叶面积以及叶片长宽比)和化学计量学性状(叶片碳、氮、磷的含量),结合地形和土壤数据并通过分析功能多样性随环境梯度的变化,探讨了环境过滤和竞争在鼎湖山群落物种共存中的相对重要性。结果表明:功能分歧度和群落权重平均值与环境因素关系密切,尤其是海拔、凹凸度和土壤养分。环境条件较好区域(微尺度高海拔、高凹凸度和土壤养分含量)的植物采取统一的养分有效保存(低SLA,高LDMC)的适应策略(功能分歧度低),环境过滤所起作用更强;植物在相反的环境条件下,采取快速生长策略(高SLA,低LDMC),能够更好地适应环境的变化,且性状变化是多样的(功能分歧度高),在该条件下竞争作用更为显著。叶面积和叶片氮含量的分歧度在环境条件较好的区域增大,这与其他功能性状不一致,说明不同生态位轴(环境因素)影响不同性状的分歧度变化,并且在局域尺度上植物为了更好地适应环境变化采取了多样的适应策略。