Reproductive biology and success of invasive Australian acacias in Portugal

Reproductive traits are crucial for the establishment and maintenance of populations in new areas, and therefore for the invasion process. This work aimed to study the reproductive biology of four aggressive invasive Australian Acacia spp. in Portugal. Fruit and seed set, seed weight and germinability, and seedling growth were assessed for self‐ and outcross treatments in invasive populations of A. dealbata, A. longifolia, A. melanoxylon and A. saligna. Acacia spp. showed different investments in the production of reproductive units and in natural reproductive success, with A. dealbata, the most aggressive species, having the highest investment and reproductive success. Acacia melanoxylon showed a different reproductive strategy, andromonoecy, contrasting with the other hermaphroditic species. Acacia spp. were shown to be predominantly self‐incompatible, but a low level of spontaneous selfing enabled the production of viable offspring. Acacia dealbata and A. longifolia suffered pollen limitation. Self‐progeny had lower viability than progeny from outcrossing for A. dealbata and A. melanoxylon. Acacia spp. did not show higher compatibility rates in comparison with the native area. They had low fruit set but, as a result of their massive flower production, their realized reproductive success was high and could have contributed to the invasion. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174 , 574–588.     

The biogeography of invasive alien plants in California: an application of GIS and spatial regression analysis

The spatial distribution of invasive alien plants has been poorly documented in California. However, with the increased availability of GIS software and spatially explicit data, the distribution of invasive alien plants can be explored. Using bioregions as defined in Hickman (1993 ), I compared the distribution of invasive alien plants (n = 78) and noninvasive alien plants (n = 1097). The distribution of both categories of alien plants was similar with the exception of a higher concentration of invasive alien plants in the North Coast bioregion. Spatial autocorrelation analysis using Moran's I indicated significant spatial dependence for both invasive and noninvasive alien plant species. I used both ordinary least squares (OLS) and spatial autoregressive (SAR) models to assess the relationship between alien plant species distribution and native plant species richness, road density, population density, elevation, area of sample unit, and precipitation. The OLS model for invasive alien plants included two significant effects; native plant species richness and elevation. The SAR model for invasive alien plants included three significant effects; elevation, road density, and native plant species richness. The SAR model for noninvasive alien plants resulted in the same significant effects as invasive alien plants. Both invasive and noninvasive alien plants are found in regions with low elevation, high road density, and high native‐plant species richness. This is in congruity with previous spatial pattern studies of alien plant species. However, the similarity in effects for both categories of alien plants alludes to the importance of autecological attributes, such as pollination system, dispersal system and differing responses to disturbance in the distribution of invasive plant species. In addition, this study emphasizes the critical importance of testing for spatial autocorrelation in spatial pattern studies and using SAR models when appropriate.     

Adaptations to water gradient in three Rorippa plant species correspond with plant resistance against insect herbivory under drought and waterlogged conditions

1. Plants live in environments where they are constantly, and often simultaneously, exposed to different types of biotic and abiotic stress, such as insect herbivory and water availability. How plants are adapted to abiotic conditions may determine how a surplus or shortage of water affects plant resistance to insect herbivory. Moreover, this effect may vary depending on the feeding mode of the herbivore.
2. We explored how three closely related Rorippa plant species that vary in adaptations to different water levels, resist herbivory by four different insects (aphids: Myzus persicae, Lipaphis erysimi, and caterpillars: Pieris brassicae, Plutella xylostella) under waterlogging or drought conditions. We hypothesized that plants that are differently adapted to water availability will be disparately affected by water availability in their resistance to insect herbivory.
3. On the semi-aquatic plant species Rorippa amphibia, both aphid species reached a larger colony size under drought conditions. This indicates that R. amphibia was compromised in resistance to aphid feeding when under drought conditions, to which it is less well adapted. Water conditions did not affect aphid performance on the flood-plain species Rorippa palustris. On the terrestrial plant species Rorippa sylvestris, aphids performed worse on waterlogged than drought-treated plants. Neither caterpillar species was significantly affected by the water availability of their food plant.
4. Our findings suggest that water availability can have distinct effects on plant–insect interactions. We propose that plant adaptations to water conditions can be a major predictor towards explaining the variation of effects that water availability can have on plant–insect interactions.

     

Effect of elevated CO2 on tropical soda apple and its biological control agent Gratiana boliviana (Coleoptera: Chrysomelidae)

Rising atmospheric CO₂ levels could have drastic effects on the performance of invasive weeds and their insect herbivores. Despite the importance of biological control as an effective management tool for environmental weeds, there have been few studies on the potential impact of climate change on the future efficacy of biological control. The objective of the present study was to evaluate the effect of elevated CO₂ on the performance of tropical soda apple Solanum viarum (Solanaceae) and its biological control agent Gratiana boliviana (Coleoptera: Chrysomelidae). We established three levels of CO₂ in environmental growth chambers: ambient (400 ppm), medium (580 ppm) and high (780 ppm). Plants growing at the high level had greater biomass compared to those growing at the ambient and medium levels of CO₂. Leaf water content and the amount of leaf nitrogen were reduced at high compared to ambient or medium CO₂ levels. G. boliviana immature survival and developmental time were negatively affected at high CO₂ but not at medium or ambient levels. Adults were lighter and smaller when reared at the high CO₂ level compared to ambient and medium treatments, while adult fecundity was higher at the medium CO₂ level. Leaf area consumed by fifth instars was lower when feeding on plants grown at the high CO₂ level either inside a Petri dish or on potted plants. These results suggest that beetle performance may be diminished under future climate. However, further studies should incorporate other factors such as temperature and precipitation as well as the evolutionary potential of herbivores and plants to adapt to a changing climate.     

Host range validation,molecular identification and release and establishment of a Chinese biotype of the Asian leaf beetle Lilioceris cheni (Coleoptera: Chrysomelidae: Criocerinae) for control of Dioscorea bulbifera L. in the southern United States

Dioscorea bulbifera, an Asian vine, is invasive in the southeastern USA. It rarely flowers but propagates from potato-like bulbils formed in leaf axils, which persist into the subsequent growing season. Lilioceris cheni Gressitt and Kimoto, a foliage-feeding beetle (Coleoptera: Chrysomelidae: Criocerinae) from Nepal, had been tested, proven to be a specialist and approved for release as a biological control agent. Regulatory delays, however, resulted in the demise of quarantine-held colonies, and acquisition of new Nepalese stock proved untenable. Searches then undertaken in southern China resulted in the collection of over 300 similar beetles. Two Chinese Lilioceris species were identified: one confirmed to be L. cheni and the other identified as Lilioceris egena (Weise). Mitochondrial analysis revealed an exact DNA match between some Chinese and one of the two Nepalese c oxidase subunit I haplotypes and all Chinese L. cheni haplotypes clustered as a single species but the comingling of the two species aroused concerns over possible hybridisation. These concerns were allayed by nuclear D2 analysis showing the absence of dual parental sequences. Nonetheless, diligence was exercised to ensure that the Chinese strains were safe to release. Abridged host testing using critical test species verified specificity. Caged releases during autumn 2011 documented the ability of adult beetles to overwinter in south Florida despite a prolonged lack of foliage. Open releases the following year produced vigorous populations that caused extensive defoliation. Preliminary observations indicate that L. cheni now contributes to the control of D. bulbifera and the bulbil-feeding L. egena should complement these effects if its host range proves appropriate.     

Interactions between hawkmoths and flowering plants in East Africa: polyphagy and evolutionary specialization in an ecological context

Hawkmoths (Lepidoptera, Sphingidae) are considered important pollinators in tropical regions, but the frequency and degree of reciprocal specialization of interactions between hawkmoths and flowers remain poorly understood. Detailed observations at two sites in Kenya over a two‐year period indicate that adult hawkmoths are routinely polyphagous and opportunistic, regardless of their proboscis length. About 700 individuals of 13 hawkmoth species were observed visiting a wide range of plant species at the study sites, including 25 taxa that appear to be specifically adapted for pollination by hawkmoths. We estimate that 277 plant species in Kenya (c. 4.61% of the total angiosperm flora) are adapted for pollination by hawkmoths. Floral tube lengths of these plants have a bimodal distribution, reflecting the existence of two hawkmoth guilds differing in tongue length. Hawkmoths exhibited strongly crepuscular foraging patterns with activity confined to a 20‐min period at dusk and, in some cases, a similar period just before dawn. Corolla tube length appears to act as a mechanical filter as the longest‐tubed plants were visited by the fewest hawkmoth species and these were exclusively from the long‐tongued guild. Tube length showed a strong positive relationship with nectar volume, even after phylogenetic correction, which implies that plants with long corolla tubes are under selection to offer relatively large amounts of nectar to entice visits by polyphagous long‐tongued hawkmoths. Our study shows that diffusely co‐evolved pollination systems involving long‐tongued hawkmoths are clearly asymmetrical, with plants exhibiting a high degree of floral specialization, while hawkmoths exhibit polyphagous behaviour. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 199–213.     

Go forth,evolve and prosper: the genetic basis of adaptive evolution in an invasive species

Invasive species stand accused of a familiar litany of offences, including displacing native species, disrupting ecological processes and causing billions of dollars in ecological damage (Cox 1999 ). Despite these transgressions, invasive species have at least one redeeming virtue – they offer us an unparalleled opportunity to investigate colonization and responses of populations to novel conditions in the invaded habitat (Elton 1958 ; Sakai et al. 2001 ). Invasive species are by definition colonists that have arrived and thrived in a new location. How they are able to thrive is of great interest, especially considering a paradox of invasion (Sax & Brown 2000 ): if many populations are locally adapted (Leimu & Fischer 2008 ), how could species introduced into new locations become so successful? One possibility is that populations adjust to the new conditions through plasticity – increasing production of allelopathic compounds (novel weapons), or taking advantage of new prey, for example. Alternatively, evolution could play a role, with the populations adapting to the novel conditions of the new habitat. There is increasing evidence, based on phenotypic data, for rapid adaptive evolution in invasive species (Franks et al. 2012 ; Colautti & Barrett 2013 ; Sultan et al. 2013 ). Prior studies have also demonstrated genetic changes in introduced populations using neutral markers, which generally do not provide information on adaptation. Thus, the genetic basis of adaptive evolution in invasive species has largely remained unknown. In this issue of Molecular Ecology, Vandepitte et al. ( 2014 ) provide some of the first evidence in invasive populations for molecular genetic changes directly linked to adaptation.     

Differences in volatile composition and sexual morphs in rambutan (Nephelium lappaceum L.) flowers and their effect in the Apis mellifera L. (Hymenoptera,Apidae) attraction

We studied the volatile composition and sexual morphs of Nephelium lappaceum flowers from two orchards, and investigated the choice behavior of the honey bee, Apis mellifera toward the floral extracts from both locations. Our results showed significant differences in chemical composition and sexual morphs; only the hermaphrodite flowers from the Herradero orchard produced limonene and α-pinene and had longer peduncle and sepal than flowers from the Metapa orchard; on the other hand, the hermaphrodite flowers from the Metapa orchard had longer gynoecium. In the behavioral experiment the extracts from the Herradero orchard seemed to give A. mellifera foragers better cues for orientation to food sources, perhaps due to the presence of limonene and α-pinene, which are absent in the samples from Metapa. Such differences in both orchards could affect pollinator attraction and ultimately seed set and productivity.     

Differences in insect species richness and faunal composition of birch seedlings, saplings and trees: the importance of plant architecture

Abstract. 1. Data are presented on the species richness and faunal composition of herbivorous insects on birch seedlings, saplings and trees at one site in Northern England.
2. Species richness of insect herbivores in equal-sized samples from birch seedlings and trees was similar through most of the season.
3. Effects of plant architecture were confined to the first sampling date, when seedling faunas were species poor compared with trees – possibly due to safe overwintering sites on the extensive bark, twigs and buds of trees.
4. The faunal composition of birch seedlings, saplings and trees was also similar. Out of a total of 112 recorded species of herbivores, only one aphid species was confined to seedlings.
5. Similarly, no evidence for clear-cut vertical stratification of insects within trees was found.
6. Species turnover as host plants mature ('horizontal' stratification) and vertical stratification within trees add little to the high overall species richness of birch-feeding insects in Britain, contrary to the predictions of Lawton (1983).     

南京地区外来植物一年蓬上访花昆虫的多样性及其访花选择性的影响因素分析

为揭示外来植物一年蓬Erigeron annuus上的本土访花昆虫多样性和影响访花行为的因素, 本研究在南京郊区进行了连续2年的野外调查, 采用跨栏模型分析了环境因素如何影响昆虫的访花选择性, 即接受概率（测度是否接受一年蓬花）和访问频数（测度接受一年蓬花的程度）。调查发现, 访问一年蓬花的昆虫共计9目54科145种, 其中, 科丰富度占优势的是膜翅目、 鳞翅目和鞘翅目（均占总科数的20.75%）, 其次是双翅目（18.87%）和半翅目（13.21%）; 物种丰富度占优势的是双翅目（26.39%）, 其次是膜翅目（18.75%）、 半翅目（18.75%）、 鞘翅目（17.36%）和鳞翅目（15.38%）。多数目的物种丰富度在6-7月最高, 9月最低, 仅双翅目（食蚜蝇为主）在5月最高。运用跨栏模型对物种优势度最大的半翅目、 膜翅目和双翅目等的访花个体数量及其影响因素的分析结果表明： 影响半翅目和膜翅目对一年蓬花访问倾向（接受概率）的因素多于影响其访问频数的因素, 由此预测这些访花昆虫可能参考较多因素做出是否接受一年蓬花, 而依据较少线索做出访问程度的访花行为决策; 一年蓬植株密度影响半翅目和膜翅目昆虫的接受概率, 而花密度影响半翅目和双翅目昆虫的接受概率和访问频数, 说明靶标植物花的特性可能对访花昆虫的访花行为决策起主要作用。     

Patterns of alien plant distribution at multiple spatial scales in a large national park: implications for ecology, management and monitoring

Aim Spatial scale is critical for understanding and managing biological invasions. In providing direction to managing alien plant invasions, much emphasis is placed on collecting spatially explicit data. However, insufficient thought is often given to how the data are to be used, frequently resulting in the incompatibility of the data for different uses. This paper explores the role of spatial scale in interpreting, managing and monitoring alien plant invasions in a large protected area. Location Kruger National Park, South Africa. Methods Using 27,000 spatially‐explicit records of invasive alien plants for the Kruger National Park (> 20,000 km²) we assessed alien plant species richness per cell at nine different scales of resolution. Results When assessing the patterns of alien plants at the various scales of resolution, almost identical results are obtained when working at scales of quarter‐degree grids and quaternary watersheds (the fourth level category in South Africa's river basin classification system). Likewise, insights gained from working at resolutions of 0.1–0.5 km and 1–5 km are similar. At a scale of 0.1 × 0.1 km cells, only 0.4% of the Kruger National Park is invaded, whereas > 90% of the park is invaded when mapped at the quarter‐degree cell resolution. Main conclusions Selecting the appropriate scale of resolution is crucial when evaluating the distribution and abundance of alien plant invasions, understanding ecological processes, and operationalizing management applications and monitoring strategies. Quarter‐degree grids and quaternary watersheds are most useful at a regional or national scale. Grid cells of 1 to 25 km² are generally useful for establishing priorities for and planning management interventions. Fine‐scale data are useful for informing management in areas which are small in extent; they also provide the detail appropriate for assessing patterns and rates of invasion.     

Reproducing under a warming climate: long winter flowering and extended flower longevity in the only Mediterranean and maritime Primula

Under the pressure of global warming, general expectations of species migration and evolution of adaptive traits should always be confirmed with species‐specific studies. Within this framework, some species can be used as study systems to predict possible consequences of global warming also on other relatives. Unlike its mountain congeneric, Primula palinuri Petagn. has endured all the climatic fluctuations since the Pleistocene, while surviving on Mediterranean coastal cliffs. The aim of this work was to investigate the possible evolution of reproductive biological and ecological traits in P. palinuri adaptation to a warmer environment. Data showed that flowering starts in mid‐winter; single flowers remain open for over a month, changing from pendulous to erect. The number of insects visiting flowers of P. palinuri increases during the flowering season, and pollination reduces flower longevity. Overall, the best pollen performances, in terms of viability and germinability, occur at winter temperatures, while pollinator activity prolongs flowering until spring. Moreover, extended longevity of single flowers optimises reproductive success. Both phenotypic plasticity and selective processes might have occurred in P. palinuri. However, we found that reproductive traits of the only Mediterranean Primula remain more associated with cold mountain habitats than warm coastal cliffs. Given the rapid trend of climate warming, migration and new adaptive processes in P. palinuri are unlikely. Response to past climate warming of P. palinuri provides useful indications for future scenarios in other Primula species.     

Mechanisms of optimal defense patterns in Nicotiana attenuata: flowering attenuates herbivory-elicited ethylene and jasmonate signaling

To defend themselves against herbivore attack, plants produce secondary metabolites, which are variously inducible and constitutively deployed, presumably to optimize their fitness benefits in light of their fitness costs. Three phytohormones, jasmonates (JA) and their active forms, the JA-isoleucine (JA-Ile) and ethylene (ET), are known to play central roles in the elicitation of induced defenses, but little is known about how this mediation changes over ontogeny. The Optimal Defense Theory (ODT) predicts changes in the costs and benefits of the different types of defenses and has been usefully extrapolated to their modes of deployment. Here we studied whether the herbivore-induced accumulation of JA, JA-Ile and ET changed over ontogeny in Nicotiana attenuata, a native tobacco in which inducible defenses are particularly well studied. Herbivore-elicited ET production changed dramatically during six developmental stages, from rosette through flowering, decreasing with the elongation of the first corollas during flower development. This decrease was largely recovered within a day after flower removal by decapitation. A similar pattern was found for the herbivore-induced accumulation of JA and JA-Ile. These results are consistent with ODT predictions and suggest that the last steps in floral development control the inducibility of at least three plant hormones, optimizing defense-growth tradeoffs.     

Elevational gradients in plant defences and insect herbivory: recent advances in the field and prospects for future research

Classic research on elevational gradients in plant–herbivore interactions holds that insect herbivore pressure is stronger under warmer, less seasonal climates characteristic of low elevations, and that this in turn selects for increased defence in low‐ (relative to high‐) elevation plants. However, recent work has questioned this paradigm, arguing that it overly simplifies the ecological complexity in which plant–insect herbivore interactions are embedded along elevational gradients. Numerous biotic and abiotic factors vary with elevation, and their simultaneous influences are the focus of current work on elevational gradients in insect herbivory and plant defences. The present review 1) synthesizes current knowledge on elevational gradients in plant–insect herbivore interactions; 2) critically analyses research gaps and highlights recent advances that contribute to filling these gaps; and 3) outlines new research opportunities to uncover underlying mechanisms and build towards a unified theory on elevational gradients. We conclude that the next generation of studies should embrace community complexity – including multi‐trophic dynamics and the multivariate nature of plant defence – and to do so by combining observational data, manipulative experiments and emerging analytical tools.     

Invasive plants and their ecological strategies: prediction and explanation of woody plant invasion in New England

Effective management of introduced species requires the early identification of species that pose a significant threat of becoming invasive. To better understand the invasive ecology of species in New England, USA, we compiled a character data set with which to compare non-native species that are known invaders to non-native species that are not currently known to be invasive. In contrast to previous biological trait-based models, we employed a Bayesian hierarchical analysis to identify sets of plant traits associated with invasiveness for each of three growth forms (vines, shrubs, and trees). The resulting models identify a suite of 'invasive traits' highlighting the ecology associated with invasiveness for each of three growth forms. The most effective predictors of invasiveness that emerged from our model were 'invasive elsewhere', 'fast growth rate', 'native latitudinal range', and 'growth form'. The contrast among growth forms was pronounced. For example, 'wind dispersal' was positively correlated with invasiveness in trees, but negatively correlated in shrubs and vines. The predictive model was able to correctly classify invasive plants 67% of the time (22/33), and non-invasive plants 95% of the time (204/215). A number of potential future invasive species in New England that deserve management consideration were identified.     

The influence of host plant genotype on variation in population densities of the gorse thrips,Sericothrips staphylinus (Thysanoptera: Thripidae), and its consideration in relation to release strategies

Large variations in population densities of Sericothrips staphylinus were observed between gorse bushes at a field site in an earlier Tasmanian study. A replicated potted plant experiment was conducted to assess whether genetic variation between gorse bushes could affect densities of S. staphylinus. There were significant differences in the number of S. staphylinus recovered from the individual bushes sampled within sites and individual bushes across all sites. This provides evidence that genetic variation between gorse bushes is at least partly responsible for the observed variability in field populations. The result validates the current release strategy used for the field establishment of S. staphylinus in south-eastern Australia. This strategy involves making multiple small releases (ca. 250 adults per bush per site) instead of a small number of large releases (ca. 1000 per bush per site), thereby reducing variation in numbers due to genetic affects. Genetic variation between individual plants of the same species and associated effects on herbivore densities should be considered when devising release strategies for biological control agents.     

No evidence for local adaptation in an invasive alien plant: field and greenhouse experiments tracing a colonization sequence

Background and Aims

Local adaptation enables plant species to persist under different environmental conditions. Evolutionary change can occur rapidly in invasive annual species and has been shown to lead to local adaptation. However, the patterns and mechanisms of local adaptation in invasive species along colonization sequences are not yet understood. Thus, in this study the alien annual Impatiens glandulifera was used to investigate local adaptation to distinct habitats that have been consecutively invaded in central Europe.

Methods

A reciprocal transplant experiment was performed using 15 populations from alluvial deciduous forests, fallow meadows and coniferous upland forests, and a greenhouse experiment was performed in which plants from these habitats were grown under treatments reflecting the main habitat differentiators (shade, soil acidity, competition).

Key Results

Biomass production, specific leaf area, plant height and relative growth rate differed between habitats in the field experiment and between treatments in the greenhouse, but not between seed origins. Overall, there was no indication of local adaptation in either experiment.

Conclusions

Since I. glandulifera is a successful invader in many habitats without showing local adaptation, it is suggested that the species is coping with environmental variation by means of high phenotypic plasticity. The species seems to follow a ‘jack-and-master’ strategy, i.e. it is able to maintain high fitness under a wide range of environmental conditions, but performs particularly well in favourable habitats. Therefore, the proposed colonization sequence is likely to be based primarily on changes in propagule pressure. It is concluded that invasive alien plants can become dominant in distinct habitats without local adaptation.     

Cross-correlation analysis of invasive mango mealybug and its associated natural enemies in relation to meteorological factors: implications for biological control

Damage caused by invasive downey snow line mealybug, Rastrococcus iceryoides Green (Hemiptera: Pseudococcidae) has been reported to vary between 30% to complete crop loss where no control measure is applied. The current studies seek to determine factors influencing R. iceryoides population outbreaks, parasitoid – host and predator–prey relationships as well as predict optimal management strategies through weather modelling over a period of 28 months from 2008 to 2010 in Tanzania. The highest incidence of R. iceryoides was recorded during the dry season coinciding with the major mango fruiting season. The relationship between R. iceryoides and the parasitoid was positive but not significant, which implies the influence on outbreaks was negligible probably due to low percent parasitism (<12%). However, the predator abundance was directly and significantly related to that of R. iceryoides. Average temperature, average relative humidity, rainfall, and R. iceryoides abundance were autocorrelated to each other. Cross-correlation coef?cients vary significantly from ?0.286 to 0.589 for the pair-variable between R. iceryoides, temperature, relative humidity, rainfall, parasitism and predators. Our findings showed that temperature was the key climatic variable that significantly influenced R. iceryoides outbreaks while rainfall was significantly negatively associated with the pest. Time series analyses show R. iceryoides population increased 4 months after an increase in average temperature in all the sites, 11 months after rainfall and 11 months after relative humidity in Kibaha and Dar es Salaam, respectively. Our findings revealed that R. iceryoides is an excellent target for classical biological control. Thus, the importation of promising co-evolved parasitoid specific to R. iceryoides from the aboriginal home is crucial in formulating an efficient and sustainable management approaches against the invasive mealybug pest in mango agro-ecosystems.     

Larval Exposure to Parasitic Varroa destructor Mites Triggers Specific Immune Responses in Different Honey Bee Castes and Species

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