Red leaves, insects and coevolution: a red herring?

W.D. (Bill) Hamilton proposed that coevolution between plants and herbivorous insects explains the bright autumnal colouration of leaves. Accordingly, plants invest in bright signals to reduce their herbivore load, whereas insects use these bright signals to identify less-defended hosts more efficiently. Archetti and Brown have recently revisited this theory by explaining its basic predictions and providing new research perspectives. Their work presents an important basis to our understanding of non-green leaf colouration, provided that alternative adaptive explanations on the photoprotective and antioxidant role of leaf pigments, or their possible function in crypsis to herbivores are incorporated into future research.     

Do qualifiers of ASCUS distinguish between low- and high-risk patients?

OBJECTIVE: To evaluate the qualification of a Pap smear classified as atypical squamous cells of undetermined significance (ASCUS) favor reactive or neoplasia as recommended by the Bethesda System. STUDY DESIGN: The smears from 105 concurrent patients with a cytologic diagnosis of ASCUS not otherwise qualified were reviewed and subclassified as ASCUS favor reactive, low grade squamous intraepithelial lesion (LSIL) or high grade squamous intraepithelial lesion (HSIL) based on the Bethesda System criteria. The cervical biopsy diagnoses were correlated. RESULTS: Of the 105 cases classified as ASCUS, 37 were subclassified as favor reactive, 51 as favor LSIL and 17 as favor HSIL on cytologic review. In the ASCUS favor reactive group, 19 (51%) had reactive changes on biopsy, 17 (46%) had cervical intraepithelial neoplasia (CIN) 1, and 1 (2%) had CIN 3. A total of 48% patients had CIN. In the favor LSIL group, there was CIN 1 in 28 cases (55%), CIN 2 or 3 in 12 (23%) and benign changes in 11 (22%) on biopsy. Seventy-eight percent had CIN. In the 17 cases classified as ASCUS favor HSIL group, all had CIN. CONCLUSION: Of the total 105 cases of ASCUS, 71% had CIN, 29% had reactive changes on follow-up biopsies, and 48% of patients in the ASCUS favor reactive group had CIN. Qualifiers of ASCUS have questionable utility in patient management.     

Do plant mites commonly prefer the underside of leaves?

The adaxial (upper) and abaxial (lower) surfaces of a plant leaf provide heterogeneous habitats for small arthropods with different environmental conditions, such as light, humidity, and surface morphology. As for plant mites, some agricultural pest species and their natural enemies have been observed to favor the abaxial leaf surface, which is considered an adaptation to avoid rain or solar ultraviolet radiation. However, whether such a preference for the leaf underside is a common behavioral trait in mites on wild vegetation remains unknown. The authors conducted a 2-year survey on the foliar mite assemblage found on Viburnum erosum var. punctatum, a deciduous shrub on which several mite taxa occur throughout the seasons, and 14 sympatric tree or shrub species in secondary broadleaf-forest sites in Kyoto, west–central Japan. We compared adaxial–abaxial surface distributions of mites among mite taxa, seasons, and morphology of host leaves (presence/absence of hairs and domatia). On V. erosum var. punctatum, seven of 11 distinguished mite taxa were significantly distributed in favor of abaxial leaf surfaces and the trend was seasonally stable, except for Eriophyoidea. Mite assemblages on 15 plant species were significantly biased towards the abaxial leaf surfaces, regardless of surface morphology. Our data suggest that many mite taxa commonly prefer to stay on abaxial leaf surfaces in wild vegetation. Oribatida displayed a relatively neutral distribution, and in Tenuipalpidae, the ratio of eggs collected from the adaxial versus the abaxial side was significantly higher than the ratio of the motile individuals, implying that some mite taxa exploit adaxial leaf surfaces as habitat.     

Do plant and human pathogens have a common pathogenicity strategy?

Recently, a novel 'two-step' model of pathogenicity has been described that suggests host-cell-derived vasculoproliferative factors play a crucial role in the pathogenesis of bacillary angiomatosis, a disease caused by the human pathogenic bacterium Bartonella henselae. The resulting proliferation of endothelial cells could be interpreted as bacterial pathogens triggering the promotion of their own habitat: the host cell. Similar disease mechanisms are well known in the plant pathogen Agrobacterium tumefaciens, which causes crown gall disease. There are notable similarities between the pathogenicity of A. tumefaciens leading to tumourous disease in plants and to the B. henselae-triggered proliferation of endothelial cells in humans. Here, we hypothesize that this pathogenicity strategy might be common to several bacterial species in different hosts owing to shared pathogenicity factors.     

Do plasma proteins distinguish between liposomes of varying charge density?

Cationic liposomes (CLs) are one of the most employed nonviral nanovector systems in gene therapy. However, their transfection efficiency is strongly affected by interactions with plasma components, that lead to the formation of a “protein corona” onto CL surface. The interactions between nanoparticles entering the body and biomolecules have an essential role for their biodistribution. Because the knowledge of proteins adsorbed onto vector surface could be useful in the screening of new, more efficient and more biocompatible liposomal formulations, the behavior of three CLs with different membrane charge densities was investigated. The proteins of the three coronas were identified by nano-liquid chromatography-tandem mass spectrometry, and quantified with label-free spectral counting strategy. Fibrinogen displayed higher association with CLs with high membrane charge density, while apolipoproteins and C4b-binding protein with CLs with low membrane charge density. These results are discussed in terms of the different lipid compositions of CLs and may have a deep biological impact for in vivo applications. Surface charge of nanoparticles is emerging as a relevant factor determining the corona composition after interaction with plasma proteins. Remarkably, it is also shown that the charge of the protein corona formed around CLs is strongly related to their membrane charge density.     

Phenolic compounds in black currant leaves – an interaction between the plant and foliar diseases?

Interactions between phenolic compounds in black currant leaves and foliar diseases may be important in breeding for resistant genotypes with a nutritional high profile for human applications. For increased understanding of such interactions, we evaluated the presence of major fungal diseases by visual inspection, and content of phenolic compounds by HPLC in leaves of five segregating black currant breeding populations. Eight individual flavonols (e.g. quercetin-3-O-glucoside, quercetin-3-O-rutinoside and kaempferol-malonylgucoside), three flavan-3-ols (epigallocatechin, catechin and epicatechin) and two chlorogenic acids (neochlorogenic acid and chlorogenic acid) were significantly correlated to the leaf diseases. Rib-0701 was the population possessing the highest content for several of the compounds, while genotype differences existed for content of various phenolic compounds and resistance to the diseases. The high variability of content of phenolic compounds opens up for opportunities to breed resistant genotypes with improved health properties of the leaves for functional food products.     

Do pollinators influence the assembly of flower colours within plant communities?

The co-occurrence of plant species within a community is influenced by local deterministic or neutral processes as well as historical regional processes. Floral trait distributions of co-flowering species that share pollinators may reflect the impact of pollinator preference and constancy on their assembly within local communities. While pollinator sharing may lead to increased visitation rates for species with similar flowers, the receipt of foreign pollen via interspecific pollinator movements can decrease seed set. We investigated the pattern of community flower colour assembly as perceived by native honeybee pollinators within 24 local assemblages of co-flowering Oxalis species within the Greater Cape Floristic Region, South Africa. To explore the influence of pollinators on trait assembly, we assessed the impact of colour similarity on pollinator choices and the cost of heterospecific pollen receipt. We show that flower colour is significantly clustered within Oxalis communities and that this is not due to historical constraint, as flower colour is evolutionarily labile within Oxalis and communities are randomly structured with respect to phylogeny. Pollinator observations reveal that the likelihood of pollinators switching between co-flowering species is low and increases with flower colour similarity. Interspecific hand pollination significantly reduced seed set in the four Oxalis species we investigated, and all were dependant on pollinators for reproduction. Together these results imply that flower colour similarity carries a potential fitness cost. However, pollinators were highly flower constant, and remained so despite the extreme similarity of flower colour as perceived by honeybees. This suggests that other floral traits facilitate discrimination between similarly coloured species, thereby likely resulting in a low incidence of interspecific pollen transfer (IPT). If colour similarity promotes pollinator attraction at the community level, the observed clustering of flower colour within communities might result from indirect facilitative interactions.     

Do thyroid hormones function in insects?

Earlier work demonstrated that phenoxy-phenyl compounds such as fenoxycarb and thyroxine mimicked the effects of JH III in causing a reduction in volume of the follicle cells of Locusta migratoria. While these compounds were only moderately effective, a derivative of thyroxine, 3,3',5-triiodothyronine (T3) was as effective as JH III, and T3 has been shown to bind to the same membrane receptor and activate the same pathway as JH III. The current paper shows that other thyroxine derivatives vary in activity. 3,3', 5'-Triiodothyronine (reverse T3) is inactive. 3,5-Diiodothyronine (T2) is more active than JH III, while its relatives (iodines at 3', 5' or at 3,3') are inactive. When follicles are exposed in vitro to rhodamine conjugated T3, the fluorescent compound can be seen to enter the cells and accumulate there: this process is inhibited by cycloheximide or by a temperature of 0 degrees C. The accumulation is antagonised by JH III but not JH I (which does not bind to the JH III membrane receptor) and by an antiserum raised against the putative membrane receptor protein. The action of T3, but not T2, is inhibited by 6-n-propyl-2-thiouracil or by aurothioglucose, both known to inhibit deiodinases. The activity of T3, but not of T2, increases with time of exposure to the follicle cells. These facts suggest that T3 enters the cells by receptor mediated endocytosis and is converted to a more active compound. Immunoreactivity to T3, but not thyroxine, can be detected in the haemolymph of locusts, and the titre varies slightly with the gonotrophic cycle. The food shows immunoreactivity for both thyroxine and T3. These findings suggest that thyroid hormones are ingested by locusts and have the potential to be used as hormonal signals in the control of egg production.     

Does asymmetric specialization differ between mutualistic and trophic networks?

Recently, plant–pollinator networks have been found to be highly structured in a nested pattern in which specialists interact with generalist species. This structure is often assumed to be particular to mutualistic interactions in opposition to the compartmentalized pattern expected for antagonistic networks. We investigated the presence of asymmetric specialization in a data set assembled from the literature of 20 highly resolved plant–insect herbivore networks and compared them with 24 plant–pollinator networks. Our results indicate that these two types of networks differ, but not in the way it is generally assumed. Asymmetric specialization is present in plant–herbivore networks even if it appears less frequently than in plant–pollinator networks. Indeed, mean and median percentages of species showing asymmetric specialisation in herbivory webs are 33% and 14% respectively, compared to 57% and 60% in pollination webs. Furthermore, the amount of asymmetry is linked with species diversity and not to connectance in plant-pollinator networks whereas the opposite pattern is found in plant–herbivore networks. Our results offer promising perspectives for understanding both the mechanisms that structure ecological communities and their impact on community dynamics depending on the type of interaction.     

What physiological processes permit insects to eat Eucalyptus leaves?

Many species of insects eat Eucalyptus foliage despite its relatively low nutritional value and the many plant secondary metabolites (PSMs) present, for example, terpenes, phenols and formylated phloroglucinols (FPGs). Formylated phloroglucinols are a new class of PSMs that act as antifeedants for possums and koalas. What physiological processes are present that permit insects to eat eucalypt foliage and how do PSMs influence insect feeding or digestion? Some trees seem to be repeatedly infested with eucalypt‐feeding insects, possibly as a result of previous chemosensory cues remaining from parental selection of a plant. Avoidance or storage of PSMs permit jarrah leafminers (Perthida glyphopa) and sawflies (Perga sp.) to consume eucalypt foliage without dealing with the majority of these compounds. Some PSMs can be metabolized by polysubstrate membrane oxidases as found in caterpillars or sawflies that feed on eucalypts. High midgut pH may be advantageous for nutrient extraction and PSM metabolism, and midgut pH ranges between 8.5 and 8.9 for caterpillars of Hyalarcta huebneri. Plant secondary metabolites may not be absorbed as a result of the combined presence of the peritrophic matrix and endogenous surfactants. Excretion of PSMs can be as metabolites or intact compounds. Both putative metabolites and sideroxylonal‐A, an FPG, are present in the faeces of larvae of the case moth, H. huebneri. The presence of sideroxylonal‐A in the food had an effect on the presence of 5‐hydroxytryptamine (5HT) in the central nervous system of caterpillars, as larvae fed leaves with a high concentration of sideroxylonal‐A had relatively more 5HT in the brain and central nervous system ganglia than larvae fed leaves containing a low concentration. Further work is necessary to clarify how PSMs are handled by eucalypt‐feeding insects and what effect FPGs have on feeding and digestion.     

Do interactions between plant and soil biota change with elevation? A study on Fagus sylvatica

Theoretical models predict weakening of negative biotic interactions and strengthening of positive interactions with increasing abiotic stress. However, most empirical tests have been restricted to plant-plant interactions. No empirical study has examined theoretical predictions of interactions between plants and below-ground micro-organisms, although soil biota strongly regulates plant community composition and dynamics. We examined variability in soil biota effects on tree regeneration across an abiotic gradient. Our candidate tree species was European beech (Fagus sylvatica L.), whose regeneration is extremely responsive to soil biota activity. In a greenhouse experiment, we measured tree survival in sterilized and non-sterilized soils collected across an elevation gradient in the French Alps. Negative effects of soil biota on tree survival decreased with elevation, similar to shifts observed in plant-plant interactions. Hence, soil biota effects must be included in theoretical models of plant biotic interactions to accurately represent and predict the effects of abiotic gradient on plant communities.     

Do food‐plant preferences of modern families of phytophagous insects and mites reflect past evolution with plants?

The evolutionary history of phytophagous insects and mites and of their food-plants is traced in the conservative preferences of modern-day insects for plants. Based on UK data in the Phytophagous Insects Data Bank, a correspondence analysis displays 182 insect families and 117 plant families in a bi-variate plot. The overall pattern suggests the expansion of diversity of insects and host plants from Gymnosperms to Dicots. Plots for phytophagous insect orders and major plant clades are described, with families provisionally ranked as evolutionarily basal, intermediate or advanced. There are blurred patterns of evolutionary advancement from basal insect families with more species on conifers and on ferns and Eurosid I trees. Intermediate families are commoner on Malpighiales and Fabales, and advanced insects more frequent on later evolved euasterids II (Asterales and Lamiales), Caryophyllales and Gramineae. Basal Hymenoptera have associations with conifers, basal Lepidoptera to Eurosid I trees, and Diptera are mainly advanced families on commelinids (grasses) and Asteraceae. Blurred traces of similar phylogenetic sequences are described for subfamilies within eight example insect families. Basal families and clades tend to have fewer species than derived advanced clades. Insect communities on plants should be seen in the light of this linked past evolutionary background.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78 , 51–83.     

Do high-tannin leaves require more roots?

The well-known deceleration of nitrogen (N) cycling in the soil resulting from addition of large amounts of foliar condensed tannins may require increased fine-root growth in order to meet plant demands for N. We examined correlations between fine-root production, plant genetics, and leaf secondary compounds in Populus angustifolia, P. fremontii, and their hybrids. We measured fine-root (<2mm) production and leaf chemistry along an experimental genetic gradient where leaf litter tannin concentrations are genetically based and exert strong control on net N mineralization in the soil. Fine-root production was highly correlated with leaf tannins and individual tree genetic composition based upon genetic marker estimates, suggesting potential genetic control of compensatory root growth in response to accumulation of foliar secondary compounds in soils. We suggest, based on previous studies in our system and the current study, that genes for tannin production could link foliar chemistry and root growth, which may provide a powerful setting for external feedbacks between above- and belowground processes.     

Coevolution between interspecific plant competitors?

The most important aspect of an individual's environment may be its individual neighbours; if so, microevolutionary selection pressure could be dominated by the competitors. Since biotic differentiation and coevolution of plant populations is a developing field in which there is strong interest, it has provoked keen discussion. Trifolium repens represents a particularly suitable example for an overview of the advances and criticism voiced in this research field.     

What determines the relationship between plant diversity and habitat productivity?

The relationship between biodiversity and habitat productivity has been a fundamental topic in ecology. Although the relationship between these parameters may exhibit different shapes, the unimodal shape has been frequently encountered. The decrease in diversity at high productivity has usually been attributed to competitive exclusion. We suggest that evolutionary history and dispersal limitation may be even more important in shaping the diversity–productivity relationship. On a global scale, unimodal diversity–productivity relationships dominate in temperate regions, whereas positive relationships are more common in the tropics. This difference can be accounted for by contrasting evolutionary history. Temperate regions have smaller species pools for productive habitats since these habitats have been scarce historically for speciation, while the opposite is true for the tropics. In addition, dispersal within a region may limit diversity either due to the lack of dispersal syndromes at low productivity or the low number of diaspores at high productivity. Thereafter, biotic interactions (competition and facilitation) can shape the relationship. All these processes can act independently or concurrently. We recommend that the common approach to examining empirical diversity–environmental relationships should start with the role of large‐scale processes such as evolutionary history and dispersal limitation, followed by influences associated with ecological interactions.