The comparative ecology and biogeography of parasites

Comparative ecology uses interspecific relationships among traits, while accounting for the phylogenetic non-independence of species, to uncover general evolutionary processes. Applied to biogeographic questions, it can be a powerful tool to explain the spatial distribution of organisms. Here, we review how comparative methods can elucidate biogeographic patterns and processes, using analyses of distributional data on parasites (fleas and helminths) as case studies. Methods exist to detect phylogenetic signals, i.e. the degree of phylogenetic dependence of a given character, and either to control for these signals in statistical analyses of interspecific data, or to measure their contribution to variance. Parasite–host interactions present a special case, as a given trait may be a parasite trait, a host trait or a property of the coevolved association rather than of one participant only. For some analyses, it is therefore necessary to correct simultaneously for both parasite phylogeny and host phylogeny, or to evaluate which has the greatest influence on trait expression. Using comparative approaches, we show that two fundamental properties of parasites, their niche breadth, i.e. host specificity, and the nature of their life cycle, can explain interspecific and latitudinal variation in the sizes of their geographical ranges, or rates of distance decay in the similarity of parasite communities. These findings illustrate the ways in which phylogenetically based comparative methods can contribute to biogeographic research.     

A comparison of spatially explicit landscape representation methods and their relationship to stream condition

1. Biodiversity, water quality and ecosystem processes in streams are known to be influenced by the terrestrial landscape over a range of spatial and temporal scales. Lumped attributes (i.e. per cent land use) are often used to characterise the condition of the catchment; however, they are not spatially explicit and do not account for the disproportionate influence of land located near the stream or connected by overland flow. 2. We compared seven landscape representation metrics to determine whether accounting for the spatial proximity and hydrological effects of land use can be used to account for additional variability in indicators of stream ecosystem health. The landscape metrics included the following: a lumped metric, four inverse‐distance‐weighted (IDW) metrics based on distance to the stream or survey site and two modified IDW metrics that also accounted for the level of hydrologic activity (HA‐IDW). Ecosystem health data were obtained from the Ecological Health Monitoring Programme in Southeast Queensland, Australia and included measures of fish, invertebrates, physicochemistry and nutrients collected during two seasons over 4 years. Linear models were fitted to the stream indicators and landscape metrics, by season, and compared using an information‐theoretic approach. 3. Although no single metric was most suitable for modelling all stream indicators, lumped metrics rarely performed as well as other metric types. Metrics based on proximity to the stream (IDW and HA‐IDW) were more suitable for modelling fish indicators, while the HA‐IDW metric based on proximity to the survey site generally outperformed others for invertebrates, irrespective of season. There was consistent support for metrics based on proximity to the survey site (IDW or HA‐IDW) for all physicochemical indicators during the dry season, while a HA‐IDW metric based on proximity to the stream was suitable for five of the six physicochemical indicators in the post‐wet season. Only one nutrient indicator was tested and results showed that catchment area had a significant effect on the relationship between land use metrics and algal stable isotope ratios in both seasons. 4. Spatially explicit methods of landscape representation can clearly improve the predictive ability of many empirical models currently used to study the relationship between landscape, habitat and stream condition. A comparison of different metrics may provide clues about causal pathways and mechanistic processes behind correlative relationships and could be used to target restoration efforts strategically.     

Can seed dispersal by human activity play a useful role for the conservation of European grasslands?

Objective: To review the recent research into human‐mediated dispersal (HMD) in the European rural landscape, and explore the potential positive aspect of HMD for grassland conservation, in contrast to it's common association with the spread of invasive species. Methods: A literature search was undertaken to identify HMD vectors in the rural landscape for discussion regarding dispersal potential past and present, implications for management, and the identification of future research needs. Results: Grazing animals are important propagule dispersers, but the reduced movement of livestock through the landscape has also meant a reduction in seeds dispersed in this way. Other, non‐standard human‐mediated dispersal vectors such as clothing and motor vehicles can also transport seeds of many species, and HMD vectors often transport seeds with a variety of dispersal specialisations. Recommendations: There should be a greater movement of grazing animals throughout the landscape, either within larger grazing areas or between existing grasslands. Where this is not possible, other, more directed dispersal of propagules from species‐rich communities to target sites should be considered. The potential of non‐standard HMD vectors to make a positive contribution to biodiversity should be considered, but more research into all types of HMD vectors is important if we are to fully understand their role in the dispersal of plant species in fragmented landscapes.     

水流对莲草直胸跳甲种群存活和扩散的影响

【背景】水流是外来入侵生物传播蔓延的重要方式之一,特别是水生生物。水生杂草在水流传播过程中也经常携带其天敌从一个地方传播到另一个地方,如莲草直胸跳甲经常随着空心莲子草在水流中传播。研究水流对莲草直胸跳甲存活的影响及其对种群迁移的间接协助作用,可为解析该天敌抵御洪涝灾害和借助水流传播的能力提供科学依据。【方法】本研究以莲草直胸跳甲为研究对象,在室内进行水流模拟,比较水流转速（1000、1250和1750r.min-1）和时间（30、60、90和120min）对不同虫态莲草直胸跳甲（雌雄成虫、幼虫和卵）存活率的影响,并推算莲草直胸跳甲成虫和幼虫在野外随水流传播的最大距离。【结果】水流速度对昆虫的存活和发育具有一定影响。在不同旋转时间和转速下,雌雄成虫的存活率较高,幼虫次之,卵的存活率最低;雌虫随水流传播能达到的最远距离最大,雄虫次之,传播距离最小的是幼虫。【结论与意义】莲草直胸跳甲可随水流进行远距离传播和自然扩散,对于利用莲草直胸跳甲防治空心莲子草,缓解水渠和河道的堵塞非常有利。     

Evidence for the transmission of information through electric potentials in injured avocado trees

Electrical excitability and signaling, frequently associated with rapid responses to environmental stimuli, have been documented in both animals and higher plants. The presence of electrical potentials (EPs), such as action potentials (APs) and variation potentials (VPs), in plant cells suggests that plants make use of ion channels to transmit information over long distances. The reason why plants have developed pathways for electrical signal transmission is most probably the necessity to respond rapidly, for example, to environmental stress factors.We examined the nature and specific characteristics of the electrical response to wounding in the woody plant Persea americana (avocado). Under field conditions, wounds can be the result of insect activity, strong winds or handling injury during fruit harvest. Evidence for extracellular EP signaling in avocado trees after mechanical injury was expressed in the form of variation potentials. For tipping and pruning, signal velocities of 8.7 and 20.9 cm/s, respectively, were calculated, based on data measured with Ag/AgCl microelectrodes inserted at different positions of the trunk. EP signal intensity decreased with increasing distance between the tipping and pruning point and the electrode. Recovery time to pre-tipping or pre-pruning EP values was also affected by the distance and signal intensity from the tipping or pruning point to the specific electrode position. Real time detection of remote EP signaling can provide an efficient tool for the early detection of insect attacks, strong wind damage or handling injury during fruit harvest.Our results indicate that electrical signaling in avocado, resulting from microenvironment modifications, can be quantitatively related to the intensity and duration of the stimuli, as well as to the distance between the stimuli site and the location of EP detection. These results may be indicative of the existence of a specific kind of proto-nervous system in plants.     

Genetic variation in an ephemeral mudflat species: The role of the soil seed bank and dispersal in river and secondary anthropogenic habitats

Many ephemeral mudflat species, which rely on a soil seed bank to build up the next generation, are endangered in their natural habitat due to the widespread regulation of rivers. The aim of the present study was to elucidate the role of the soil seed bank and dispersal for the maintenance of genetic diversity in populations of near‐natural river habitats and anthropogenic habitats created by traditional fish farming practices using Cyperus fuscus as a model. Using microsatellite markers, we found no difference in genetic diversity levels between soil seed bank and above‐ground population and only moderate differentiation between the two fractions. One possible interpretation is the difference in short‐term selection during germination under specific conditions (glasshouse versus field) resulting in an ecological filtering of genotypes out of the reservoir in the soil. River populations harbored significantly more genetic diversity than populations from the anthropogenic pond types. We suggest that altered levels and patterns of dispersal together with stronger selection pressures and historical bottlenecks in anthropogenic habitats are responsible for the observed reduction in genetic diversity. Dispersal is also supposed to largely prohibit genetic structure across Europe, although there is a gradient in private allelic richness from southern Europe (high values) to northern, especially north‐western, Europe (low values), which probably relates to postglacial expansion out of southern and/or eastern refugia.     

Pollen limitation in the endangered Chinese endemic species Sinocalycanthus chinensis

Pollen limitation negatively impacts endangered and endemic plants with small fragmented populations, such as Sinocalycanthus chinensis, an endangered plant endemic to China. In this study, we analyzed the pollen limitation of the S. chinensis Damingshan (DMS) population in 2006, 2009, and 2010, and crossed plants with mates separated by different distances, both within and between populations. The DMS population exhibited strong pollen limitation in fruit set, seed set, and seeds per fruit in 2006, 2009, and 2010. The average accumulated pollen limitation (for fruit set times seeds per fruit) was 0.510 ± 0.180. Progeny crossed with pollen from intermediate neighboring plants within the same population (separated by 30–50 m from pollen recipients) had the lowest fitness. No optimal outcrossing distance was found within the DMS population. Progeny from crosses with the Shunxiwu (SXW) and Daleishan (DLS) populations performed relatively better, while those from crosses with Qingliangfeng (QLF) and Longxushan (LXS) populations performed worse. Compared with average reproductive success, outbreeding depression was found in progeny from crosses with the LXS and QLF populations. Reproductive success from pure self‐pollination indicated S. chinensis is self‐compatible. Geitonogamous selfing increased reproductive success. Based on geitonogamous selfing, the proportion of selfed offspring was relatively high. These results provide basic references for the conservation of this species.     

救护白鹤与野生白鹤迁徙路线和活动规律差异分析

受伤和体弱白鹤的救护及放归是白鹤保护的重要方式之一。2014—2016年间,先后对8只救护白鹤和2只野生白鹤进行环志并安装卫星跟踪器,根据所获得的卫星跟踪数据来分析比较救护白鹤与野生白鹤在秋季迁徙路线和在重要中途停歇地的最大日活动距离、活动区分布和面积、生境类型等方面的异同。结果显示,救护白鹤放归当年与放归次年以及救护白鹤放归当年与野生白鹤的秋季迁徙路线和活动规律之间存在明显差异,但救护白鹤放归次年与野生白鹤之间差异不明显。(1)放归当年,4只救护白鹤在农田和水塘停歇1个月左右,停歇时长明显高于野生白鹤和放归次年的救护白鹤。(2)救护白鹤放归当年在跨海方式、登陆地点、停歇地点以及登陆后的迁徙方向上表现出多样性和不确定性,其中部分个体在迁徙过程中有停顿徘徊、迷失迁徙方向的现象,且跨越渤海和大别山的距离大于放归次年的救护白鹤和野生白鹤。(3)救护白鹤放归后4天内每日最大活动距离小,而后高低分化明显,无明显规律,而救护白鹤放归次年的每日最大活动距离规律变化与野生白鹤较一致。(4)与救护白鹤放归次年以及野生白鹤的活动规律相比,救护白鹤放归当年的栖息地位点变化频繁,具体表现为生境类型选择的多样化,且无明显规律,同时活动区面积较小。探索救护白鹤放归野外后与野生白鹤迁徙路线和活动规律的差异,对救护白鹤的科学放归具有指导意义。