Love is in the air: olfaction-based mate-odour identification by jumping spiders from the genus Cyrba

Jumping spiders (Salticidae) are known for having good eyesight, but the extent to which they rely on olfaction is poorly understood. Here we demonstrate for the first time that olfactory pheromones are used by two species from the salticid genus Cyrba (C. algerina and C. ocellata). Using a Y-shape olfactometer, we investigated the ability of adult males and females of both species to discriminate between mate and non-mate odour. A hidden spider or a spider’s draglines (no spider present) were used as odour sources. There was no evident response by females of either Cyrba species to any tested odour. Males of both species chose odour from conspecific females, or their draglines, significantly more often than the no-odour control, but there was no evident response by males to any of the other odours (conspecific male and heterospecific female). Our findings demonstrate that C. algerina and C. ocellata males can make sex- and species-specific discriminations even when restricted to using olfaction alone. Also, by showing that draglines can be a source of olfactory pheromones, our findings illustrate the difficulty of ruling out olfaction when attempting to test for chemotactile cues.     

Epidemiological landscape models reproduce cyclic insect outbreaks

Forest insect outbreaks can have large impacts on ecosystems and understanding the underlying ecological processes is critical for their management. Current process-based modeling approaches of insect outbreaks are often based on population processes operating at small spatial scales (i.e. within individual forest stands). As such, they are difficult to parameterize and offer limited applicability when modeling and predicting outbreaks at the landscape level where management actions take place. In this paper, we propose a new process-based landscape model of forest insect outbreaks that is based on stand defoliation, the Forest-Infected-Recovering-Forest (FIRF) model. We explore both spatially-implicit (mean field equations with global dispersal) and spatially-explicit (cellular automata with limited dispersal between neighboring stands) versions of this model to assess the role of dispersal in the landscape dynamics of outbreaks. We show that density-dependent dispersal is necessary to generate cyclic outbreaks in the spatially-implicit version of the model. The spatially-explicit FIRF model with local and stochastic dispersal displays cyclic outbreaks at the landscape scale and patchy outbreaks in space, even without density-dependence. Our simple, process-based FIRF model reproduces large scale outbreaks and can provide an innovative approach to model and manage forest pests at the landscape scale.     

Breeding dispersal of Northern Flickers Colaptes auratus in relation to natural nest predation and experimentally increased perception of predation risk

After nest predation, breeding dispersal can be an effective strategy to avoid local nest predators. Furthermore, encounters with predators at a nest during the pre-laying stage may be used by parents to judge future risk, such that they may abandon a nest when a nest predator has been encountered. We studied whether the between- and within-year breeding dispersal of Northern Flickers Colaptes auratus was dependent upon the outcome of the previous nesting attempt. We also tested whether pairs presented with a model predator prior to egg-laying were more likely to abandon their nests than were pairs presented with a control model. Between years, males moved significantly further after having their nest depredated than did successful males, and females showed the same trend. However, these movements did not result in greater reproductive success. More pairs switched sites within years after having their nest depredated, but those that remained and those that moved had equal subsequent nest success. Stressful encounters with predators involving nest defence may trigger dispersal both between and within years, although reproductive benefits are unclear. The proportion of pairs abandoning nests did not differ between parents presented with control or predator models, suggesting that a single encounter with a predator is not a sufficient deterrent against continued use of a particular nest.     

Responses of an araneophagic assassin bug,Stenolemus bituberus,to spider draglines

Abstract 1. Animals, as they move through their environment, leave traces of their passage that can be informative to others and convey significant advantages to the animal producing them. However, such traces may also reveal presence, location or identity to enemies. 2. We studied an araneophagic (‘spider‐eating’) assassin bug, Stenolemus bituberus (Heteroptera, Reduviidae), testing whether it associated with areas containing chemotactile traces (e.g. draglines, excreta) left behind by nine sympatric spider species. Stenolemus bituberus were presented with a choice between a substrate containing draglines and a clean substrate. Each hour, for a duration of 12 h, we recorded which substrate was occupied. 3. Stenolemus bituberus tended to associate especially with draglines left by spiders from the genus Achaearanea, their most common prey in nature. 4. These results suggest that S. bituberus exploits draglines from these spiders as cues for indicating prey presence. We also found an increasing tendency to associate with draglines from some spider species through the day, which may be related to circadian patterns or slower response times of some individuals.     

Lattice deformation and thermal stability of crystals in spider silk

The X-ray diffraction of dragline silks, produced by Nephila and Cyrtophora spiders, were measured by synchrotron radiation in their original states or in situ during stretching and heating. Nephila pilipes spiders construct a two-dimensional orb web that must be rebuilt in one or 2 days, but Cyrtophora spiders form a three-dimensional tent web that can exist for several weeks in a tropical forest. Diffraction patterns of N. pilipes and Cyrtophora draglines resemble each other. Crystals of two kinds are identified in these draglines; one is aligned parallel to the silk direction and another is less oriented. The less oriented crystal in Cyrtophora dragline is aligned better than that in N. pilipes dragline, which generates about three times stronger diffract intensity. Crystals in N. pilipes and C. moluccensis dragline silks have remarkable thermal stability. Equatorial reflections remain undiminished until 350 and 450 °C for N. pilipes and C. moluccensis, respectively. In contrast, the meridional reflections S and (0 0 2), which are parallel to the silk thread, disappear at a temperature less than 100 °C for C. moluccensis but remain for Nephila up to 100 °C. Meridional reflections S and (0 0 2) shift to a smaller angle during stretching, whereas equatorial reflections remain constant in a range 1.0–1.3 times the original length. The position of the S reflection shifts rapidly in the first 10% of elongation from the original length but remains constant during subsequent stretching, whereas the (0 0 2) reflection shifts rapidly during the first 5% elongation from the original length and continues to shift subsequently. In contrast, the features of N. pilipes dragline alter insignificantly during stretching. Examination of the composition of amino acids of the draglines of N. pilipes and C. moluccensis indicates that a dragline of N. pilipes contains more glycine, but much less alanine, than that of C. moluccensis.     

雌星豹蛛性信息素的行为学证据

采用星豹蛛(Pardosa astrigera)成熟雄蛛求偶时潜伏时间、静止时间、身体震动和第一墩步足伸展次数等行为参数,利用行为学方法测定了不同性别、日龄和生殖状态的星豹蛛雌蛛释放的拖丝对雄蛛求偶行为的影响。结果表明,雄蛛第一对步足伸展和身体震动等典型求偶行为是进行星豹蛛性信息素生物测定的可靠评价指标。星豹蛛雄蛛能通过拖丝上的性信息素辨别星豹蛛的性别、日龄和生殖状态。雄蛛在成熟3周未交配雌蛛拖丝处理过滤纸上潜伏时间和静止时间都相应最短,在交配未产卵雌蛛、雌亚成蛛和成熟雄蛛拖丝上时间中等,在卵孵化雌蛛拖丝处理滤纸上潜伏时间和静止时间都相应最长。成熟3周未交配雌蛛和交配未产卵雌蛛释放的拖丝都能引起雄蛛第一对步足伸展和身体震动等典型求偶行为,雄蛛对成熟3周未交配雌蛛拖丝典型求偶行为的频率都相应高于交配未产卵雌蛛。卵孵化雌蛛释放的拖丝虽也能引起雄蛛第一对步足伸展行为,但其伸展频率显著降低;而其它拖丝都不能引起雄蛛典型求偶行为。     

Ranking the ecological causes of dispersal in a butterfly

Dispersal, i.e. movements potentially leading to gene flow, is central in evolutionary ecology. Many factors can trigger dispersal, all linked to the social and/or the environmental context. Moreover, it is now widely demonstrated that phenotypes with contrasted dispersal abilities coexist within populations of a same species. The current challenge is to elucidate how social and environmental factors will influence the dispersal decision of individuals with distinct phenotypes. We have used the Metatron, a unique experimental mesocosm dedicated to the study of dispersal within fragmented landscapes, to analyze the relative and interactive roles played by ten potential dispersal triggers in experimental two‐patch metapopulations of butterflies. We demonstrate in our model species that some factors (flight performance and wing length) have direct effects on emigration decision, others act only through interactive effects (sex ratio), while a third class of factors presents both direct and interactive effects (weather conditions, habitat quality and sex). We also show that disperser and resident individuals have distinct behavioral and morphological attributes, revealing the existence of a dispersal syndrome. Finally, our results also suggest that the environmental context, and especially weather conditions and habitat quality, prevails over social factors and individual phenotypes in butterflies' decision to disperse. Our approach is applicable to many species facing medium to strong environmental fluctuations, and constitutes a new way to master the idiosyncrasy of the dispersal process. Our framework should also help prioritize the factors responsible for populations' spatial distribution, which is obviously crucial in the current era of global changes.     

The seed dimorphism of Spergularia marina in relation to dispersal by wind and water

Summary The seeds of the halophyte Spergularia marina differ both within and between individuals in that they either possess or lack a membranaceous border. This paper presents a morphological study of the length, weight and area of the seed types, and their dispersal characteristics under experimental conditions of wind and water dispersal. The winged seeds are shown to be larger both by length and by weight. Their rate of descent increases with wing loading. If the wing is lacking, however, the rate of descent increases with weight only. The distance of dispersal is equal for both seed types except at low wind speeds, when the winged seeds disperse farther. If the seed wing is removed, the excised seeds have shorter dispersal distances. When dispersed by water, a difference in the distance seeds are dispersed can only be detected in the presence of vegetation. The winged seeds are more frequently trapped in the vegetation as compared to the unwinged seeds. The hypothesis that the seed dimorphism is an adaptation for differential dispersal distances is discussed.     

Silk‐ and volatile‐based male mate choice in the genital plug‐producing spider

Female mating history can have a strong effect on male fertilization success. Although males often prefer to mate with virgin females, they often also engage with mated females. As the intensity of sperm competition can differ among mated females, males are expected to evolve means to identify their status. In spiders, males often use female silk to gather information about female quality. Males of many spider species deposit mating plugs into female genitalia to hinder further copulations. We tested whether males of the foliage‐dwelling, plug‐producing spider Philodromus cespitum, which is an important natural enemy of pests, discriminate between females of different mating status and whether they can determine the extent of genital plugging in mated females solely on the basis of cues gained from deposited female silk. We presented males with draglines of females that varied in either mating status (virgin vs. mated), the extent of plugging (small vs. big plug), or the age of the plug (fresh vs. old plug) and examined their mate preferences. Additionally, we tested whether males were attracted to volatile cues produced by female bodies. Our experiments revealed that males preferred draglines of virgin females to those of mated females, and mated females with small plugs to those with large plugs. They were also attracted to female volatile cues. This study suggests that males are able to extract fine‐scale information on mating status from female draglines.     

Investigating movement in the laboratory: dispersal apparatus designs and the red flour beetle,Tribolium castaneum

The natural dispersal of Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) has been emulated in the laboratory for more than 50 years, using a simple dispersal apparatus. This has typically comprised of a starting container (initial resource or patch) connected by tubing, which contains thread for the animals to climb into a tube and hence to an end container. That is, beetles move to a new viable resource or patch from an inter‐patch zone or non‐viable habitat. We modified this basic apparatus design to test the effect of tubing length and tubing insertion angle on the dispersal rate and proportion of successful dispersers. We expected that the proportion of successful dispersers would be repeatable within each apparatus design, and that increasing tubing length and steepness of the insertion angle would reduce dispersal rate and success across apparatus designs. Dispersal increased linearly through time, similarly so for both males and females. The design with the most vertical tubing insertion angle had a lower proportion of successful dispersers. Tubing length also had a negative relationship with dispersal success (as judged by insects reaching the end container), but a significant reduction in dispersal success was only apparent between the shortest and longest tubing between containers. We suggest that locating and climbing the vertical section of string before they can enter the tubing between containers restricts dispersal and that at higher densities, insects exhibit greater inclination to climb. This type of apparatus has flexible design tolerances and further potential to study the dispersal of other small insect species that primarily use pedestrian locomotion.     

Female "dispersal" in hamadryas baboons: transfer among social units in a multilevel society

Unlike most cercopithecines, hamadryas baboons (Papio hamadryas hamadryas) are characterized by female-biased dispersal. To clarify this pattern within the context of their hierarchical social system (comprising one-male units, clans, bands, and troops), we report here 7 years of data on female transfers among social units in wild hamadryas baboons in Ethiopia. Female tenure in one-male units (OMUs) ranged from 1 to 2,556 days (N = 208) and survival analysis revealed a median tenure length of 1,217 days (40 months). Changes in OMU membership consisted almost exclusively of takeovers by males, not voluntary transfer. Of 130 takeovers, 67% occurred within the band and 33% across bands, and, of the 22 takeovers for which we have clan membership data, 77% occurred within, not between, clans. These results reinforce the notion that hamadryas female dispersal is not analogous to sex-biased dispersal in other taxa, because (1) at least in Ethiopian populations, females do not disperse voluntarily but are transferred, often forcibly, by males; (2) only dispersal between bands will promote gene flow, whereas females are most often rearranged within bands; (3) hamadryas females undergo social dispersal but not usually locational dispersal; and (4) while male hamadryas are far more philopatric than females, they have been observed to disperse. It thus appears that the ancestral baboon pattern of female philopatry and male dispersal has evolved into a system in which neither sex is motivated to disperse, but females are forcibly transferred by males, leading to female-mediated gene flow, and males more rarely disperse to find females.     

Intergall migration in aphids; a model and a test of ESS dispersal rate

Summary I present an inclusive-fitness model for the evolution of dispersal rates of the offspring of asexual organisms living in discrete sites, which vary in available resources. I also assume a stable and saturated condition and that the offspring can respond to the variation in the capacity (amount of resources) of their natal sites. The model was tested using data obtained from the intergall migration in the yezo-spruce gall aphid,Adelges japonicus. All the parameters needed for the model, which included the cost of dispersal, both dispersal rates and available resources in each site, were estimated from field examinations. The data fit the model well, suggesting the importance of kin selection in determining the dispersal rates. Both actual and ESS dispersal rates are shown as concave functions of site capacity with a minimum rate for intermediate site capacity. The effect of both actual and ESS dispersal is to reduce, but not eliminate sibling competition within natal sites, which is most severe in intermediate site capacity.     

应用细胞自动机对一年生植物种群扩散进行理论研究

应用细胞自动机方法构造了用于研究一年生植物扩散的理论模型并应用该模型模拟了一年生植物（杂草）种群在同质环境中的扩散。一年生杂草种子的扩散距离和分布是其种群扩散的主要方式,故本文将其种子扩散分布作为构建邻域细胞函数的基础。根据Howard(1991)^[1]提供的某一年生杂草种子的扩散数据,本文导出了一个25邻的邻域细胞函数和相关的转移函数。建立了一个受控的细胞自动机模型。通过模拟,发现在同质环境中聚集在一起的一年生植物杂草越多就需要越大的控制力才能限制它们扩散;生长于农田边缘的杂草更容易被控制。这些模拟结果表明该模型能较好地表现生态学中的两个众所周知的现象;生物的聚集效应和边缘效应。希望自动机方法和在本文获得的知识将有助于我们制订植物种群的最优管理策略。     

Starvation affects pre-dispersal behaviour of Erigone spiders

Population studies often focus on demographic and genetic consequences of dispersal strategies, generally within an evolutionary framework. Adaptive investment in dispersal is generally assessed from single types of (pre-)dispersal behaviour that are presumed to reliably reflect the dispersal strategy adopted. Various spider families show a striking and quantifiable display, known as tiptoe behaviour that prepares individuals for take-off prior to (passive) aerial dispersal (ballooning). The lack of efficient control mechanisms during ballooning prevents individuals from actively selecting a suitable habitat for landing. Ballooning dispersal is therefore often regarded as a wind lottery preceded by individual-based risk assessment. Our laboratory experiments showed that the duration of tiptoe behaviour can be used as an indicator of silk thread length, which is related to the potential dispersal distance. For two related species, Erigone arctica and E. dentiplapis, tiptoe duration decreased independently of sex after starvation, while more complex reaction norms were observed for tiptoe frequency.

Because these two aspects of dispersal behaviours show different responses towards a simple stress-factor (starvation) in two related spider species, we conclude that the level of plasticity in dispersal investment can be subject to selective forces affecting different dispersal properties in different ways. Our results, hence, plead for a more holistic approach when addressing evolutionary and applied questions related to dispersal.     

Dispersal of Galerucella pusilla and G. calmariensis via passive water transport in the Columbia River Estuary

Dispersal of biological control agents and their subsequent population growth can be a major determinant of the success of landscape-scale weed control programs. Biocontrol agents must be able to disperse across the distances between patches of host plants in order to colonize and control their targets. The presence of three species of biocontrol agents for purple loosestrife (Lythrum salicaria L.): Galerucella calmariensis L. (Coleoptera: Chrysomelidae), Galerucella pusilla Duftschmid (Coleoptera: Chrysomelidae), and Nanophyes marmoratus Goeze (Coleoptera: Brentidae), on relatively remote islands in the Columbia River Estuary (CRE) indicate that these organisms have the ability to disperse across large expanses of open flowing water to colonize remote sites. Previous studies suggest that colonization of these islands by active flight is highly unlikely; therefore, some other dispersal mechanism must be responsible for colonization. A spatial database of all known biocontrol agent release sites for purple loosestrife within 68 river kilometers of our CRE study area was developed and field surveys for biocontrol agents were conducted. A GIS was used to model dispersal distances between biocontrol agent recovery sites and the nearest conspecific release site. Tidal water flow within the CRE was assessed as a potential dispersal mechanism across the modeled distances. The ability of the biocontrol agents to withstand submersion was evaluated in field tests. Our results indicate that it is highly likely that passive water transport has been responsible for some of the long-distance open-water dispersal that would have been necessary for colonization of the remote islands where biocontrol agents were recovered.     

Colonization genetics of an animal-dispersed plant (Vaccinium membranaceum) at Mount St Helens, Washington

Population founding and spatial spread may profoundly influence later population genetic structure, but their effects are difficult to quantify when population history is unknown. We examined the genetic effects of founder group formation in a recently founded population of the animal-dispersed Vaccinium membranaceum (black huckleberry) on new volcanic deposits at Mount St Helens (Washington, USA) 24 years post-eruption. Using amplified fragment length polymorphisms and assignment tests, we determined sources of the newly founded population and characterized genetic variation within new and source populations. Our analyses indicate that while founders were derived from many sources, about half originated from a small number of plants that survived the 1980 eruption in pockets of remnant soil embedded within primary successional areas. We found no evidence of a strong founder effect in the new population; indeed genetic diversity in the newly founded population tended to be higher than in some of the source regions. Similarly, formation of the new population did not increase among-population genetic variance, and there was no evidence of kin-structured dispersal in the new population. These results indicate that high gene flow among sources and long-distance dispersal were important processes shaping the genetic diversity in this young V. membranaceum population. Other species with similar dispersal abilities may also be able to colonize new habitats without significant reduction in genetic diversity or increase in differentiation among populations.     

Non‐equilibrium in plant distribution models – only an issue for introduced or dispersal limited species?

Species distribution models rely on the assumption that species' distributions are at equilibrium with environmental conditions within a region – i.e. they occur in all suitable habitats. If this assumption holds, species occurrence should be predictable from measures of the environment. Introduced species may be poor candidates for distribution models due to their presumed lack of equilibrium within the landscapes they occupy, although predicting their potential distributions is often of critical importance to natural resource managers. We determined if the accuracy of species distribution models differed between 17 native and 17 introduced riparian plant species in the western United States. We also assessed if model accuracy was associated with both environmental and biological factors that can influence dispersal. We used Random Forests to model species distributions and linear regression to determine if model accuracy was associated with dispersal‐related traits. Model accuracy for introduced species was higher than that for native species. Dispersal‐related traits did not affect model accuracy or improvement, though two other traits, family affiliation and rarity on the landscape, did have an effect. Distance‐based measures of dispersal potential improved model fit equally for both native and introduced species and for species with a variety of dispersal traits, suggesting that the importance of regional propagule pressure is relatively constant across species with different dispersal opportunities. Several lines of future questioning are suggested by our results, including why introduced species may in some cases produce more accurate distribution models than native species and how species dispersal traits relate to distribution model accuracy at different spatial scales.     

Evolution of stepping-stone dispersal rates

We present a general model of the evolution of dispersal in a population with any distribution of dispersal distance. We use this model to analyse evolutionarily stable (ES) dispersal rates for the classical island model of dispersal and for three different stepping-stone models. Using general techniques to compute relatedness coefficients in the different dispersal models which we consider, we find that the distribution of dispersal distance may affect the ES dispersal rate when the cost of dispersal is low. In this case the ES dispersal rate increases with the number of demes that can be reached by one dispersal event. However, for increasing cost the ES dispersal rate converges to a value independent of the distribution of dispersal distance. These results are in contrast to previous analyses of similar models. The effects of the size (number of demes) and shape (ratio between the width and the length) of the population on the evolution of dispersal are also studied. We find that larger and more elongated populations lead generally to higher ES dispersal rates. However, both of these effects can only be observed for extreme parameter values (i.e. for very small and very elongated populations). The direct fitness method and the analytical techniques used here to compute relatedness coefficients provide an efficient way to analyse ES strategies in subdivided populations.     

Dispersal stochasticity mediates species richness in source–sink metacommunities

Although it is well‐known that dispersal of organisms within a metacommunity will influence patterns of coexistence and richness, theoretical and experimental studies generally assume that dispersal rates are constant through time. However, dispersal is often a highly variable process that can vary seasonally and/or when stochastic events (e.g. wind storms, droughts, floods) occur. Using a well‐known source–sink metacommunity model, we present novel predictions for local and regional species richness when stochasticity in dispersal is expressly considered. We demonstrate that dispersal stochasticity alters some of the predictions obtained with constant dispersal; the peak of the predicted hump‐shaped relationship between dispersal and local species richness is diminished and shifted towards higher values of dispersal. Dispersal stochasticity increases extinction probabilities of inferior competitor species particularly in metacommunities subjected to severe isolation events (i.e. decreases of dispersal) or homogenization events (i.e. sudden increases of dispersal). Our results emphasize how incorporating dispersal stochasticity into theoretical predictions will broaden our understanding of metacommunities dynamics and their responses to natural and human‐related disturbances.     

Ocean circulation model predicts high genetic structure observed in a long‐lived pelagic developer

Understanding the movement of genes and individuals across marine seascapes is a long‐standing challenge in marine ecology and can inform our understanding of local adaptation, the persistence and movement of populations, and the spatial scale of effective management. Patterns of gene flow in the ocean are often inferred based on population genetic analyses coupled with knowledge of species' dispersive life histories. However, genetic structure is the result of time‐integrated processes and may not capture present‐day connectivity between populations. Here, we use a high‐resolution oceanographic circulation model to predict larval dispersal along the complex coastline of western Canada that includes the transition between two well‐studied zoogeographic provinces. We simulate dispersal in a benthic sea star with a 6–10 week pelagic larval phase and test predictions of this model against previously observed genetic structure including a strong phylogeographic break within the zoogeographical transition zone. We also test predictions with new genetic sampling in a site within the phylogeographic break. We find that the coupled genetic and circulation model predicts the high degree of genetic structure observed in this species, despite its long pelagic duration. High genetic structure on this complex coastline can thus be explained through ocean circulation patterns, which tend to retain passive larvae within 20–50 km of their parents, suggesting a necessity for close‐knit design of Marine Protected Area networks.