Native parasitic plants: Biological control for plant invasions?

Plant invasions cause biodiversity loss and degradation in ecosystems worldwide. The invasive species involved may be introduced, or native invaders, and controlling them is a major global challenge. Here, we highlight an emerging role for native parasitic plants in suppressing invasive species, thus aiding in restoration of affected habitats. Compelling empirical evidence is provided by three study systems located in Central Europe, southern Australia and eastern China. Further cases of parasitism of invasive plants have been recorded across five continents. We propose including the interactions between parasitic and invasive plants into the theoretical framework of the biotic resistance hypothesis concerning generalist interactions between invaders and native biota. Among parasitic plants, numerous root hemiparasites, mistletoes and parasitic vines show low host specificity and exert substantial negative effects on their hosts. These parasitic plants may interfere with key traits of invaders such as symbiotic nitrogen fixation or clonal propagation which provide them with competitive advantage over native species. We contend that some parasitic plants may present a cost‐effective environmentally sustainable component of invasion management schemes. Therefore, we encourage exploration of this potential and the development of methods for practical applications in ecological restoration and nature conservation.     

Crepidula fornicata is not a first intermediate host for trematodes: who is?

Trematode larvae must generally invade a molluscan intermediate host, usually a gastropod, before they can reach reproductive maturity in another definitive host. The research literature to date has focused almost exclusively on the documented specificity between particular trematode species and particular molluscan hosts; little attention has been paid to gastropod species that do not appear to serve as hosts. We sampled Rhode Island and Massachusetts populations of the marine gastropod Crepidula fornicata to determine whether this widespread species serves as a first intermediate host for trematodes. We also sampled from the same habitat populations of Littorina littorea and Ilyanassa obsoleta, gastropods known to serve as first intermediate hosts for several trematode species. All individuals were examined by dissection for the presence of sporocysts, rediae, or developing cercariae. Although 4-28% of L. littorea (N=112) and I. obsoleta (N=84) were infected by larvae of at least one trematode species, no individuals of C. fornicata sampled from the same locations were so infected (N=136). A survey of the Biological Abstracts computer database indicates that snails in only about 10% of marine gastropod families are known to serve as first intermediate hosts for trematodes. We suggest that more attention be paid to marine gastropods that appear not to be infected by trematode miracidia. Such species may productively serve as new models for understanding trematode host specificity and gastropod resistance to infection.     

Native topology or specific interactions: what is more important for protein folding?

Fifty-five molecular dynamics runs of two three-stranded antiparallel beta-sheet peptides were performed to investigate the relative importance of amino acid sequence and native topology. The two peptides consist of 20 residues each and have a sequence identity of 15 %. One peptide has Gly-Ser (GS) at both turns, while the other has d-Pro-Gly ((D)PG). The simulations successfully reproduce the NMR solution conformations, irrespective of the starting structure. The large number of folding events sampled along the trajectories at 360 K (total simulation time of about 5 micros) yield a projection of the free-energy landscape onto two significant progress variables. The two peptides have compact denatured states, similar free-energy surfaces, and folding pathways that involve the formation of a beta-hairpin followed by consolidation of the unstructured strand. For the GS peptide, there are 33 folding events that start by the formation of the 2-3 beta-hairpin and 17 with first the 1-2 beta-hairpin. For the (D)PG peptide, the statistical predominance is opposite, 16 and 47 folding events start from the 2-3 beta-hairpin and the 1-2 beta-hairpin, respectively. These simulation results indicate that the overall shape of the free-energy surface is defined primarily by the native-state topology, in agreement with an ever-increasing amount of experimental and theoretical evidence, while the amino acid sequence determines the statistically predominant order of the events.     

Plants,microbes, and odorants involved in host plant location by a specialist moth: who's making the message?

The grape berry moth (GBM), Paralobesia viteana (Clemens) (Lepidoptera: Tortricidae), is a specialist pest insect of cultivated grape, Vitis spp. (Vitaceae), in the eastern USA. A blend of volatile compounds has been isolated from plant material that attracts female GBM in the flight tunnel and field. However, the origin of the volatile cue is potentially complicated by the presence of microbes (bacteria and fungi) living on the surface of the plant. Microbial volatile organic compounds can affect insect behavior, and therefore must be considered to fully understand olfaction‐mediated behaviors. We report here the chemical and behavioral analysis of the volatile profiles produced from both the sanitized and control shoot treatments. The sanitization treatment removed 96.4% of the surface microbes up to 24 h, covering the duration of the behavioral assays and volatile collections. Overall, the surface microbes did not significantly contribute to the volatile profile of the grape shoots, as all of the peaks in the volatile profile of sanitized shoots were found in the profile of control shoots. In flight tunnel assays, female GBM displayed the same level of upwind oriented flight to sanitized shoots (flew upwind 57.4%, landed 30.9%) as they did to control shoots (flew upwind 57.8%, landed 31.0%), suggesting further that surface microbes did not contribute to the production of the previously identified blend of behaviorally active volatiles for GBM.     

What is life? Prerequisites for a definition

Biologists view life as transient while theologians see it as eternal. An unbiased definition for life would respect both views until one or both were eliminated by evidence. This paper identifies pre-requisites for such a definition. First among these is that all assumptions be made explicit. Currently "life" is surrounded by implicit assumptions, e.g., that it is what organisms lose at death or that it is eternal, that its quality is inversely related to personal distress, that it originated some four billion years ago, and that animate matter can be distinguished from inanimate matter. None of these assumptions are supported by data. It is possible therefore that "life" is as meaningless as phlogiston. If life has meaning, i.e., if it is true, it must be as permanent as buoyancy, gravity, electricity, and the other truths of nature. Any definition for life that would permit such truth to be seen must be free of unwarranted assumptions. For the moment, at least, such a definition would need to be loosely structured and broadly focused. It would need to describe the long and convoluted process by which matter and energy form organisms which then evolve to form conscious organisms which then explore nature and eventually discover truth. Such a definition would include all the reactions and interactions of matter and energy and all the aspects of conscious discovery. It would suffer from superficiality, but, by being free from bias, provide a foundation for dialogue between biologists and theologians.     

What is a quasispecies?

A quasispecies is a well-defined distribution of mutants that is generated by a mutation-selection process. Selection does not act on a single mutant but on the quasispecies as a whole. Experimental systems have been designed to study quasispecies evolution under laboratory conditions. More recently, virus populations have been called quasispecies to indicate their extensive genetic heterogeneity. The most prominent examples are probably the human immunodeficiency viruses HIV-1 and HIV-2. The quasispecies nature of HIV has formed the basis of a model that provides a mechanism for the pathogenesis of acquired immunodeficiency syndrome (AIDS) in humans. This article focuses on the nature of the quasispecies concept and its implications for evolutionary biology and virology.     

What is a genome?

The field of genomics is expanding rapidly, yet the meanings of the word ‘genome’ have yet to be conceptualized in explicit, coherent and useful frameworks. We develop and apply an evolutionary conceptualization of the genome, which represents a logical extension of the evolutionary definition of a gene developed by George C. Williams. An evolutionary genome thus represents a set of genetic material, in a lineage, that due to common interests tends to favour the same or similar phenotypes. This conceptualization provides novel perspectives on genome functions, boundaries and evolution, which should help to guide theoretical and empirical genomics research.     

Revisiting the dietary niche: When is a mammalian herbivore a specialist?

Understanding dietary specialization in herbivores has theoretical and practical implications in ecology, yet defining niche breadth consistently has been problematic. To increase clarity and communication among ecologists and among disciplines (i.e., chemists, pharmacologists), we propose a specialization key for mammalian herbivores that assigns "obligatory" and "facultative" modifiers to the terms "specialist" and "generalist". These modifiers are assigned based on (1) relative breadth of the animal's realized niche and diet (what it eats), (2) relative breadth of the fundamental niche and available diet (what it could eat), (3) the extent of chemical or physical characteristics, termed "difficulty", that make food items either low in value or unpalatable to most herbivores, and (4) relevant temporal and spatial scales at which diets and niche breadth were measured. Obligatory specialists always have a narrow realized niche consisting of difficult food items, and morphological adaptations and/or the loss of redundant behavioral flexibility that effectively limit their fundamental niches, precluding them from expanding their diet under changed environmental conditions. Facultative specialists have a consistently narrow realized niche for difficult foods during at least one spatial or temporal scale, but have a broad enough fundamental niche to allow them to expand their diet to include less difficult foods when environmental conditions allow. Facultative generalists have the broadest fundamental niche, allowing them to consume a wide variety of foods. However, they may occasionally demonstrate a narrow realized niche, focused on less difficult plants than is the case with specialists. Finally, the obligatory generalists always have a wide realized niche because of a relatively narrow fundamental niche, precluding them from eating much of any difficult plant. We summarize hypothesized characteristics of mammalian herbivores in each of the four categories of specialization. We demonstrate the need for further work on defining the realized and fundamental niches, comparing among herbivores across categories conducted under similar conditions, and understanding the nature of trade-offs required for specialization and generalization for both community and phylogenetically based analyses.     

Growing with siblings: a common ground for cooperation or for fiercer competition among plants?

Recent work has shown that certain plants can identify their kin in competitive settings through root recognition, and react by decreasing root growth when competing with relatives. Although this may be a necessary step in kin selection, no clear associated improvement in individual or group fitness has been reported to qualify as such. We designed an experiment to address whether genetic relatedness between neighbouring plants affects individual or group fitness in artificial populations. Seeds of Lupinus angustifolius were sown in groups of siblings, groups of different genotypes from the same population and groups of genotypes from different populations. Both plants surrounded by siblings and by genotypes from the same population had lower individual fitness and produced fewer flowers and less vegetative biomass as a group. We conclude that genetic relatedness entails decreased individual and group fitness in L. angustifolius. This, together with earlier work, precludes the generalization that kin recognition may act as a widespread, major microevolutionary mechanism in plants.     

Selection of large host plants for oviposition by a monophagous leaf beetle: nutritional quality or enemy‐free space?

Abstract.  1. Oviposition site selection is crucial for the reproductive success of herbivorous insects. According to the preference–performance hypothesis, females should oviposit on host plants that enhance the performance of their offspring. More specifically, the plant vigour hypothesis predicts that females should prefer large and vigorously growing host plants for oviposition and that larvae should perform best on these plants.
2. The present study examined whether females of the monophagous leaf beetle Cassida canaliculata Laich. (Coleoptera: Chrysomelidae) prefer to oviposit on large host plant individuals of the meadow clary and whether large host plants are of higher nutritional quality than small host plants. Subsequently, it was tested whether the female preference correlates with offspring performance and survival.
3. In the field, females preferred large host plant individuals for oviposition and host plant quality, i.e. leaf nitrogen content, was significantly higher in leaves of large than of small host plants.
4. In the laboratory, larval development time was shorter on leaves of large host plant individuals than on small host plant individuals, but this could not be shown in the field.
5. However, a predator-exclusion experiment in the field resulted in a higher survival of larvae on large host plants than on small host plants when all predators had free access to the plants. On caged host plants there was no difference in survival of larvae between plant size categories.
6. It is concluded that females of C. canaliculata select oviposition sites that enhance both performance and survival of their offspring, which meets the predictions of the plant vigour hypothesis.