Evolutionary and ecological implications of cardenolide sequestration in the monarch butterfly

Summary Monarch butterflies sequester cardenolides from their larval host plants in the milkweed genusAsclepias for use in defense against predation. Of 108Asclepias species in North America, monarchs are known to feed as larvae on 27. Research on 11 of these has shown that monarchs sequester cardenolides most effectively, to an asymptote of approximately 350 g/0.1 g dry butterfly, from plants with intermediate cardenolide contents rather than from those with very high or very low cardenolide contents. SinceAsclepias host plant species are distributed widely in space and time across the continent, monarchs exploit them by migration between breeding and overwintering areas. After overwintering in central Mexico, spring migrants east of the Rocky Mountains exploit three predominantAsclepias species in the southern USA that have moderately high cardenolide contents. Monarchs sequester cardenolides very effectively from these species. First generation butterflies are thus well protected against predators and continue the migration north. Across the northern USA and southern Canada most summer breeding occurs on a fourthAsclepias species and in autumn most of these monarchs migrate back to Mexican overwintering sites. The ecological implications of this cycle of cardenolide sequestration for the evolution of monarch migration are discussed.     

Heat shock-induced gynandromorphism in the pharaoh's ant,Monomorium pharaonis (L.)

Summary The ability of ants to reacting to sublethal high temperatures with production of gynandromorphs is reported for the first time. The abnormal forms produced in the pharaoh's ant range from ergatandromorphs to classical halfsidegynanders.Thanks are due to Drs V. Rupe (Prague), and B. Styczýnska (Warsaw) for providing the ant strains mentioned and to Mrs G. Hilzbrich for technical assistance.     

From model to mimic: Age-dependent unpalatability in monarch butterflies

Monarch butterflies (Danaus plexippus) are unpalatable to various vertebrate predators because their larvae sequester bitter and emetic cardiac glycosides (CGs) from milkweed plants (Asclepias spp.). Here we show that the concentration of the defensive CGs decrease as individual butterflies age, regardless of the CGs' initial amounts or specific chemical structures. Consequently, individual monarch butterflies can change from being unpalatable models to palatable mimics during their lifetime. Since monarchs breed continuously over the spring and summer in North America, freshly emerged adult butterflies may serve as noxious models for older individuals which become automimics as they age.     

Slavery in the subfamily dolichoderinae (F. Formicidae) and its ecological consequences

Summary Evidence of slave-making habits in 2 species of the subfamily Dolichoderinae has been found in arid habitats of western North America. The enslaved species are of the subfamilies Myrmicinae and Formicinae. In previously reported cases of slavery in ants, both the slave-making and enslaved species are of the subfamily Formicinae., In the 2 new cases of slavery reported here, presence of slaves of another species in a colony significantly increases the breadth of diet and/or the range of temperatures at which the colony forages.     

Roles of glial cells in synapse development

Brain function relies on communication among neurons via highly specialized contacts, the synapses, and synaptic dysfunction lies at the heart of age-, disease-, and injury-induced defects of the nervous system. For these reasons, the formation—and repair—of synaptic connections is a major focus of neuroscience research. In this review, I summarize recent evidence that synapse development is not a cell-autonomous process and that its distinct phases depend on assistance from the so-called glial cells. The results supporting this view concern synapses in the central nervous system as well as neuromuscular junctions and originate from experimental models ranging from cell cultures to living flies, worms, and mice. Peeking at the future, I will highlight recent technical advances that are likely to revolutionize our views on synapse–glia interactions in the developing, adult and diseased brain.     

Control of the behaviour of leaf-cutting ants by their ‘symbiotic’ fungus

There is an obligatory relationship between leaf-cutting ants of the generaAtta andAcromyrmex (Hymenoptera; Attini) and the fungus,Attamyces bromatificus Kreisel, for which they provide a substrate of cut plant material. We show that the ants learn to reject plant material that contains chemicals injurious to the fungus. After an initial period of acceptance, ants from laboratory nests stopped harvesting granular bait containing a fungicidal agent (cycloheximide) and orange peel. This rejection was maintained for many weeks. These colonies also rejected control bait containing no cycloheximide. Some generalisation of the response was observed; colonies rejecting orange granules also rejected grapefruit granules, although they still accepted blackcurrant granules. Rejection of fungicidal bait by colonies in the field was restricted to ants on foraging trails exposed to experimental bait. We conclude that a semiochemical from the fungus, circulated by trophallaxis and grooming, regulates the selection of plant material by foragers. The fungus gains more advantages from the symbiotic relationship than is often realised. The ants provide the fungus with housing, sanitation, defence against disease and predators, pre-selected food, and a means of dissemination, at the cost to itself of providing food for the ant brood.     

Hydroxyproline-rich glycoproteins in plant reproductive tissues: structure, functions and regulation

The plant reproductive process of pollination involves a series of interactions between the male gametophyte (the pollen grain or pollen tube) and extracellular matrix (ECM) molecules secreted by different cell types along the pollen tube growth pathway in the female organ, the pistil. These interactions are believed to signal and regulate the pollen tube growth process to effect successful delivery of the sperm cells to the ovules where fertilization takes place. Hydroxyproline-rich glycoproteins secreted by plant cells are believed to play a broad range of functions, ranging from providing structural integrity to mediating cell-cell interactions and communication. The pistil and pollen tube ECM is enriched in these highly glycosylated proteins. Our discussions here will focus on a number of these proteins for which most information has been available, from Nicotiana tabacum, its self-incompatible relative N. alata, and Zea mays. In addition, the regulation of the synthesis and glyco-modification of one of these proteins, TTS (transmitting tissue-specific) protein from N. tabacum will be discussed in the light of how differential glycosylation may be used to regulate molecular interactions within the ECM.     

Membrane-shed vesicles from the parasite <Emphasis Type="Italic">Trichomonas vaginalis</Emphasis>: characterization and their association with cell interaction

Trichomonas vaginalis is a common sexually transmitted parasite that colonizes the human urogenital tract, where it remains extracellular and adheres to epithelial cells. Infections range from asymptomatic to highly inflammatory, depending on the host and the parasite strain. Despite the serious consequences associated with trichomoniasis disease, little is known about parasite or host factors involved in attachment of the parasite-to-host epithelial cells. Here, we report the identification of microvesicle-like structures (MVs) released by T. vaginalis. MVs are considered universal transport vehicles for intercellular communication as they can incorporate peptides, proteins, lipids, miRNA, and mRNA, all of which can be transferred to target cells through receptor–ligand interactions, fusion with the cell membrane, and delivery of a functional cargo to the cytoplasm of the target cell. In the present study, we demonstrated that T. vaginalis release MVs from the plasma and the flagellar membranes of the parasite. We performed proteomic profiling of these structures demonstrating that they possess physical characteristics similar to mammalian extracellular vesicles and might be selectively charged with specific protein content. In addition, we demonstrated that viable T. vaginalis parasites release large vesicles (LVs), membrane structures larger than 1 µm that are able to interact with other parasites and with the host cell. Finally, we show that both populations of vesicles present on the surface of T vaginalis are induced in the presence of host cells, consistent with a role in modulating cell interactions.     

Oxygen consumption and the evolution of order: negentropy criteria applied to the evolution of ants

Optimization of energy use by evolving organisms, predicted by theoretical extensions of the neo-Darwinian theory, i. contrasted with that of irreversible thermodynamics, which predicts an increase in orderliness and thus an increase in energy consumption per unit of biomass. We compared this index with estimates of social complexity among ant genera and species. Our results show that simple optimization models cannot explain experimental data, and that social complexity correlates differently with negentropy at different levels of analysis. Comparing the genera among Formicidae, workers (not colonies) from genera with highly social species are less negentropic than those of socially primitive ones. At the sub-generic level, social complexity correlated positively with negentropy among species, for major workers inAcromyrmex and for minor workers inAtta. The results illustrate the complexity of thermodynamic criteria in the study of evolution but also hint at their usefulness. In this case, they show that two different evolutionary routes to the complex Attini ant societies may exist.     

Structural diversity of trypsin from different mosquito species feeding on vertebrate blood

Mosquito trypsin was purified using a combination of ion exchange and affinity chromatography with the ligand soybean trypsin inhibitor. Three Aedes and three Anopheles species were tested, all of which are specialized in the digestion of vertebrate blood. Amino-terminal sequences of HPLC-purified trypsins from Aedes aegypti and Anopheles quadrimaculatus revealed homologies of 30-40% with vertebrate and other invertebrate proteases previously identified as serine-proteases. The purified mosquito trypsins have molecular masses between 25 kDa and 36 kDa, as determined by denaturing polyacrylamide electrophoresis, and are heterogeneous in size and number in the various species. The number of SDS-bands varies between 3 and 6 in Aedes and between 1 and 3 in Anopheles. The specific activities, determined with the substrate TAME, range from 240 U/mg in Aedes aegypti to 1065 U/mg in Anopheles quadrimaculatus. All mosquito trypsins tested have acidic isoelectric points between pH 3.5 and pH 5.4. No alkaline proteases were detected. Polyclonal antisera against Aedes aegypti and Anopheles albimanus trypsin do not cross-react with bovine trypsin. Cross-reactivity of the two sera with trypsin from six mosquito species suggests the presence of at least 2 enzyme families.     

Molecular recognition of microbial lipid-based antigens by T cells

The immune system has evolved to protect hosts from pathogens. T cells represent a critical component of the immune system by their engagement in host defence mechanisms against microbial infections. Our knowledge of the molecular recognition by T cells of pathogen-derived peptidic antigens that are presented by the major histocompatibility complex glycoproteins is now well established. However, lipids represent an additional, distinct chemical class of molecules that when presented by the family of CD1 antigen-presenting molecules can serve as antigens, and be recognized by specialized subsets of T cells leading to antigen-specific activation. Over the past decades, numerous CD1-presented self- and bacterial lipid-based antigens have been isolated and characterized. However, our understanding at the molecular level of T cell immunity to CD1 molecules presenting microbial lipid-based antigens is still largely unexplored. Here, we review the insights and the molecular basis underpinning the recognition of microbial lipid-based antigens by T cells.     

Pyrrolizidine alkaloid storage in African and australian danaid butterflies

Summary 8 species of African and Australian danaid butterflies, captured in the field, were analyzed and found to contain pyrrolizidine alkaloids. It is suggested that these alkaloids, which are gathered by the adults from plants, contribute significantly to the chemical defences of the danaids.     

Visual spatial memory in desert ants,Cataglyphis bicolor (Hymenoptera: Formicidae)

Summary For navigation, desert ants apply piloting and dead-reckoning strategies based on terrestrial and celestial visual cues, respectively. Visual spatial memories, rather than general concepts derived from landmark constellations, are most probably used to define points on earth by nearby landmarks. The visual field of a specialized dorsal part of the ant's retina is mapped on to the celestial sphere to consider the possibility that similar mechanisms are used to define directions on earth by exploiting skylight patterns present at infinity.Supported by the Hescheler Foundation (Zurich) and the Swiss National Science Foundation grants Nos 3.529-0.75 and 3.313-0.78.     

First identification of a trail pheromone of an army ant (Aenictus species)

Totally blind army ants carry out massive and highly organised foraging raids, apparently guided by chemical stimuli. Until now, this phenomenon has not been closely analysed. The existence of a trail pheromone in a postpygidial gland of anAenictus species has been demonstrated and the substances identified as methyl anthranilate and methyl nicotinate The pheromone consists of two parts: a primer effect, caused by methyl nicotinate, which prepares workers to follow trails, but is not itself followed, and a releaser effect, due to methyl anthranilate, which causes trail-following only in conjunction with the primer substance.     

Syndecan family of cell surface proteoglycans: Developmentally regulated receptors for extracellular effector molecules

Syndecans are a family of integral membrane proteoglycans with conserved membrane-spanning and intracellular domains but with structurally distinct extracellular domains (ectodomains). They are known to function as heparan sulphate co-receptors in fibroblast growth factor signalling as well as to link cells directly to the extracellular matrix. These and other biological activities of syndecans involve specific interactions of the heparan sulphate side chains of syndecans with cytokines and extracellular matrix proteins. Four different vertebrate syndecans, designated as syndecans 1–4 (or syndecan, fibroglycan, N-syndecan and amphiglycan, respectively), are known. During embryonic development, syndecans have specific and highly regulated expression patterns that are distinct from the expression in adult tissue, suggesting an active role in morphogenetic processes. The developmental expression of syndecans is particularly intense in mesenchymal condensates and at epithelium mesenchyme interfaces, where a number of heparan sulphate-binding cytokines and matrix components are also expressed in a regulated manner, ofter spatially and temporally co-ordinated with the syndecan expression. Recent evidence indicates that the regulation of heparan sulphate fine structure (mainly the number and arrangement of sulphate groups along the polymer) provides a mechanism for the cellular control of syndecan-protein interactions. Furthermore, morphogenetically active cytokines such as fibroblast growth factor-2 and transforming growth factor-β participate in the regulation of syndecan expression and glycosaminoglycan structure. This review discusses the developmental expression and binding functions of syndecans as well as the molecular regulation of specific heparan sulphate-protein interactions.     

Structural diversity of trypsin from different mosquito species feeding on vertebrate blood

Summary Mosquito trypsin was purified using a combination of ion exchange and affinity chromatography with the ligand soybean trypsin inhibitor. ThreeAedes and threeAnopheles species were tested, all of which are specialized in the digestion of vertebrate blood. Amino-terminal sequences of HPLC-purified trypsins fromAedes aegypti andAnopheles quadrimaculatus revealed homologies of 30–40% with vertebrate and other invertebrate proteases previously identified as serine-proteases. The purified mosquito trypsins have molecular masses between 25 kDa and 36 kDa, as determined by denaturing polyacrylamide electrophoresis, and are heterogeneous in size and number in the various species. The number of SDS-bands varies between 3 and 6 inAedes and between 1 and 3 inAnopheles. The specific activities, determined with the substrate TAME, range from 240 U/mg inAedes aegypti to 1065 U/mg inAnopheles quadrimaculatus. All mosquito trypsins tested have acidic isoelectric points between pH 3.5 and pH 5.4. No alkaline proteases were detected. Polyclonal antisera againstAedes aegypti andAnopheles albimanus trypsin do not cross-react with bovine trypsin. Cross-reactivity of the two sera with trypsin from six mosquito species suggests the presence of at least 2 enzyme families.     

Reproductive competition and colony fragmentation in the guest-ant,Formicoxenus provancheri

Aggressive reproductive conflicts and dominance interactions among queens are involved in establishing functional monogyny in the ant,Formicoxenus provancheri. Competition among potential reproductives may lead to the founding of new societies by budding or colony fragmentation.     

Two related butterfly species avoid oviposition near each other's eggs

Summary Some butterfly species avoid egg-laying on plants which already bear conspecific eggs, and thus reduce food competition between their offspring. In twoPieris species the females produce in their accessory glands an oviposition-deterring pheromone (ODP), which is combined with the egg during oviposition. The ODP collected from eggs or accessory glands ofP. brassicae inhibits oviposition byP. rapae and vice versa. The ODP of either species stimulates tarsal receptors in both species. The antennae of the two pierids respond to the volatiles of their own and each other's eggs. Thus the ODPs of the two species may reduce not only intraspecific, but also interspecific food competition between their larvae.     

Recently discovered functions of glucosylceramides in plants and fungi

Glycosphingolipids are ubiquitous membrane lipids of eukaryotic organisms and a few bacteria. Whereas inositol-containing glycosphingolipids are restricted to plants and fungi, galactosylceramide occurs only in fungi and animals. In contrast, glucosylceramide is the unique glycosphingolipid which plants, fungi and animals have in common. However, there are specific differences in the structure of the ceramide backbone of glucosylceramides from these organisms. A comparison of the structural features and the biosynthesis of glucosylceramides from plants, fungi and animals will contribute to our understanding of their functions, which so far have been analysed mainly in animals. The availability of nearly all genes involved in the biosynthesis of glucosylceramides enables the specific manipulation of glycosphingolipid metabolism by techniques of forward and reverse genetics. Application of this approach to unicellular organisms like yeasts, multicellular filamentous fungi, as well as to complex organisms like plants will reveal common and different glucosylceramide functions in these organisms. These glycolipids play a role both in intracellular processes and in cell-to-cell interactions. These interactions may occur between cells of a multicellular organism or between cells of different species, as in host-pathogen interactions.