Selection analysis on the rapid evolution of a secondary sexual trait

Evolutionary analyses of population translocations (experimental or accidental) have been important in demonstrating speed of evolution because they subject organisms to abrupt environmental changes that create an episode of selection. However, the strength of selection in such studies is rarely measured, limiting our understanding of the evolutionary process. This contrasts with long-term, mark–recapture studies of unmanipulated populations that measure selection directly, yet rarely reveal evolutionary change. Here, we present a study of experimental evolution of male colour in Trinidadian guppies where we tracked both evolutionary change and individual-based measures of selection. Guppies were translocated from a predator-rich to a low-predation environment within the same stream system. We used a combination of common garden experiments and monthly sampling of individuals to measure the phenotypic and genetic divergence of male coloration between ancestral and derived fish. Results show rapid evolutionary increases in orange coloration in both populations (1 year or three generations), replicating the results of previous studies. Unlike previous studies, we linked this evolution to an individual-based analysis of selection. By quantifying individual reproductive success and survival, we show, for the first time, that males with more orange and black pigment have higher reproductive success, but males with more black pigment also have higher risk of mortality. The net effect of selection is thus an advantage of orange but not black coloration, as reflected in the evolutionary response. This highlights the importance of considering all components of fitness when understanding the evolution of sexually selected traits in the wild.     

A salt on the bioenergy and biological invasions debate: salinity tolerance of the invasive biomass feedstock Arundo donax

Arundo donax L., commonly known as giant reed, is promising biomass feedstock that is also a notorious invasive plant in freshwater ecosystems around the world. Heretofore, the salt tolerance of A. donax had not been quantified even though anecdotal evidence suggests halophytic qualities. To test whole-plant and leaf level responses, we established a pot experiment on 80 scions propagated from an A. donax population that has naturalized on the shore of the San Francisco Bay Estuary. To quantify growth and physiological responses to salinity (NaCl), A. donax scions were divided into eight treatments and grown for 60 days across a range of salinities (0–42 dS m⁻¹). Classic growth analysis showed >80% reduction in overall growth at the highest salinities. Yet, there was zero mortality indicating that A. donax is able to tolerate high levels of salt. Declining photosynthesis rates were strongly correlated (R² > 0.97) with decreasing stomatal conductance, which was in turn closely related to increasing salinity. Leaf gas exchange revealed that stomata and leaf limitations of carbon dioxide were three times greater at high salinities. Nonetheless, even when salinities were 38–42 dS m⁻¹ A. donax was able to maintain assimilation rates 7–12 μmol m⁻² s⁻¹. Further, by maintaining 50% relative growth at salinities ~12 dS m⁻¹ A. donax can now be classified as ‘moderately salt tolerant’. A. donax leaf gas exchange and whole-plant salt tolerance are greater than many important food crops (i.e. maize, rice), the bioenergy feedstock Miscanthus × giganteus, as well as some uncultivated plant species (i.e. Populus and Salix) that are indigenous in regions A. donax currently invades. The results of this study have implications for both agronomists wishing to expand A. donax to fields dominated by saline soils, and for others who are concerned about the spread of A. donax with altered stream hydrology or sea-level rise.     

Seasonal home range dynamics and sex differences in habitat use in a threatened,coastal marsh bird

A comprehensive understanding of spatiotemporal ecology is needed to develop conservation strategies for declining species. The king rail (Rallus elegans) is a secretive marsh bird whose range historically extended across the eastern United States. Inland migratory populations have been greatly reduced with most remaining populations inhabiting the coastal margins. Our objectives were to determine the migratory status of breeding king rails on the mid‐Atlantic coast and to characterize home range size, seasonal patterns of movement, and habitat use. Using radiotelemetry, we tracked individual king rails among seasons, and established that at least a segment of this breeding population is resident. Mean (±SE) home range size was 19.8 ± 5.0 ha (95% kernel density) or 2.5 ± 0.9 (50% kernel density). We detected seasonal variation and sex differences in home range size and habitat use. In the nonbreeding season, resident male home ranges coincided essentially with their breeding territories. Overwintering males were more likely than females to be found in natural emergent marsh with a greater area of open water. Females tended to have larger home ranges than males during the nonbreeding season. We report for the first time the use of wooded natural marsh by overwintering females. Brood‐rearing king rails led their young considerable distances away from their nests (average maximum distance: ~600 ± 200 m) and used both wooded natural and impounded marsh. King rails moved between natural marsh and managed impoundments during all life stages, but the proximity of these habitat types particularly benefitted brood‐rearing parents seeking foraging areas with shallower water in proximity to cover. Our results demonstrate the importance of interspersion of habitat types to support resident breeders. Summer draining of impounded wetlands that are seasonally flooded for wintering waterfowl allows regrowth of vegetation and provides additional habitat at a critical time for wading birds.     

长江口滨海湿地潮间带生态系统的多稳态特征

多稳态现象普遍存在于多种生态系统中,它与生态系统的健康和可持续发展密切相关,已成为生态学研究的热点与难点,但是目前有关滨海湿地生态系统多稳态的形成机制还缺乏深入研究.本文以崇明东滩鸟类自然保护区的潮间带生态系统为研究对象,通过以下内容,开展滨海湿地多稳态研究: 1)通过验证多稳态的判定依据“双峰”和“阈值”特征,证实长江口潮间带生态系统存在多稳态,并确定其稳态类型;2)通过监测潮间带生态系统水动力过程、沉积动力过程以及盐沼植物生长和扩散情况,分析盐沼植被与沉积地貌之间的正反馈作用,进而探讨潮间带生态系统多稳态的形成机制.结果表明: 1)潮间带生态系统的归一化植被指数(NDVI)频度分布存在明显的双峰特征,且盐沼植物成活存在生物量阈值效应,均证实潮间带生态系统存在多稳态,“盐沼”和“光滩”是潮间带生态系统的两种相对稳定状态;2)崇明东滩盐沼前沿的沉积地貌表现出泥沙快速淤积的趋势,显著促进了盐沼植物的生长,盐沼植物与泥沙淤积之间的这种正反馈作用是潮间带生态系统形成多稳态的主要原因;3)盐沼植被扩散格局监测结果在景观尺度上也表明,泥沙淤积作用促进了潮间带生态系统“盐沼”和“光滩”多稳态的形成.本研究既丰富了滨海湿地稳态转换的机理研究,也为我国开展海岸带保护、修复和管理提供了科学依据,具有重要的理论和实践意义.     

人工湿地对胡子鲇养殖水体循环净化的研究

以大型观光植物美人蕉-砾石为基础的垂直流人工湿地对胡子鲇养殖水体进行净化处理和回流使用,在胡子鲇养殖中测定了水体主要水质指标的变化,表明人工湿地对养殖水体净化效果显著,养殖期间BOD5、COD、TN的平均去除率分别为81.77%、55.55%和65%,净化后水质部分符合渔业用水标准,可以循环利用.对照池水体由于BOD5、COD、TN得不到去除而持续增加,混浊度显著高于实验池,并出现水华.这种水体循环养殖模式具结构简单和易推广等优点.     

周边区域湿地景观变化对洪河保护区涉禽栖息地的影响

以三江平原洪河国家级保护区及其周边3个农场为研究区域，利用GIS技术和栖息地评价模型方法，探讨了周边区域湿地景观变化对保护区内景观结构以及丹顶鹤、东方白鹳栖息地的影响。结果显示：（1）自1983年区域土地开发以来，周边区域湿地景观面积减少了63％，景观类型多样性趋于单一化；（2）保护区内湿地景观结构改变明显，类型多样性呈降低趋势，丹顶鹤和东方白鹳栖息地面积和空间分布均发生变化；（3）保护区与周边区域湿地景观连通度降低了70％，其结果严重改变了保护区与周边区域的景观生态联系，削弱了保护区原有湿地景观多样性和涉禽栖息地功能；（4）必须从景观尺度，恢复保护区周边一定面积的湿地景观结构，维持保护区与周边区域适当的景观生态联系，是有效管理和维护保护区可持续发展的最佳手段之一。     

Evaluation of past and potential phosphorus uptake at the Orlando Easterly Wetland

The Orlando Easterly Wetland (OEW), located near Christmas, Florida, USA, is among the longer-lived treatment wetlands in the United States. It was established in the late 1980s to reduce nitrogen and phosphorus concentrations from tertiary treated wastewater bound for the St. Johns River. A goal of 0.07 mg/l total phosphorus concentration has been set by the regulating agency (St. Johns River Water Management District). In order to understand and define the operating conditions for which this target could be met, a systematic study of historic phosphorus uptake was performed using a traditional first-order model. Phosphorus uptake performance is shown to correlate well with hydraulic performance for two parallel upstream cells. The first-order model is enhanced with predictive capabilities that acknowledge the correlation between the phosphorus uptake rate constant and the hydraulic loading rate observed in the system. Inherent limitations with the first-order modeling approach are addressed and uncertainty in model performance is used to bound predictions.     

Ecological thresholds of Suaeda salsa to the environmental gradients of water table depth and soil salinity

The responses of Suaeda salsa to the environmental gradients of water table depth and soil salinity in the Yellow River Delta, China were analyzed from the aspect of ecological thresholds which were developed from the Gaussian model. Based on the correlation analysis of population biomass, density, height, coverage and abundance of Suaeda salsa, population biomass was selected as the population index for further analysis. The results indicated that the optimum water table depth for the growth of Suaeda salsa was about −0.42 m, the ecological thresholds were from −0.92 m to 0.08 m, and the optimum ecological thresholds were from −0.67 m to −0.17 m. To the soil salinity gradient, the optimum was about 12.71 g/kg, the ecological thresholds were from 5.17 g/kg to 20.25 g/kg, and the optimum ecological thresholds were from 8.94 g/kg to 16.48 g/kg. However, the effect of water-salinity interaction seemed to be important to the growth of Suaeda salsa, which was discussed through analyzing the water table depth-soil salinity relationship and their interactions. By using Ward cluster analysis and Gamma distances, 69 sampling sites were classified into 7 kinds of Suaeda salsa communities. It was found that there was a remarkable response of the community structure of Suaeda salsa to the water table depth and soil salinity gradients, which can be a switchover from xeromorphic and saline-alkali plants to limnophytes, and vice versa.