Interactions between seed predators/pollinators and their host plants: a first step towards mutualism?

The mutualisms between fig trees and their pollinator fig wasps and between yucca plants and yucca moths are spectacular examples of coevolution. The characteristics of these independently evolved mutualisms have resulted from long‐term processes, the first stages of which are unknown. A fundamental question in the study of mutualism is how these interactions evolve. Seed predator/pollinator and host plant interactions, which may initially be considered as mainly antagonistic, have the potential to provide good model systems for the study of the first stages of evolution towards mutualism. We present here theoretical models assessing the consequences of interactions between specialized seed predator insects and their host plants. These models describe the parameters that affect the fitness of an individual female seed predator and her influence on the fitness of the host plant. In an optimal strategy for the seed predator, the number of eggs laid in each flower depends on the interaction between the adult and larva survival. Along with a growing predation pressure on adults and larvae several eggs must be laid in each flower by the female seed predator to enhance her fitness. However, in a situation where the host plant selectively aborts flowers with a high number of eggs the fitness of the seed predator will seriously decrease. If the cost of selective abortion is less than the cost of seed predation the host plant will maintain fitness. In a mutualistic relationship a balance between the cost and the benefit of the parameters in the fitness models of the seed predator and the host plant has to occur so that the net seed output is larger than zero (0). Any unselfish behaviour or quality of the seed predator that would benefit the host plant in such a way that the net seed output increases might be a first stage in an interaction becoming mutualistic. The models presented here will not only provide a platform for empirical studies on interactions that may swing from parasitism to mutualism, but also for seed predator/pollinator and host plant interactions in general.     

Fortuitous infestation or wide host range? The case of Spinturnicidae and their bat hosts: reply to Guiller and Deunff (2010)

Defining the degree of host specificity in host-parasite studies can greatly inform cophylogenetic history. In a recent paper, Guiller and Deunff (2010) cast doubt on some points and conclusions drawn from a cophylogenetic study between European bats and Spinturnicid mites (Bruyndonckx et al., 2009a). Here we answer their criticisms and discuss the notion of specificity in Spinturnicid mites.     

En route to a genome-based classification of Archaea and Bacteria?

Given the considerable promise whole-genome sequencing offers for phylogeny and classification, it is surprising that microbial systematics and genomics have not yet been reconciled. This might be due to the intrinsic difficulties in inferring reasonable phylogenies from genomic sequences, particularly in the light of the significant amount of lateral gene transfer in prokaryotic genomes. However, recent studies indicate that the species tree and the hierarchical classification based on it are still meaningful concepts, and that state-of-the-art phylogenetic inference methods are able to provide reliable estimates of the species tree to the benefit of taxonomy. Conversely, we suspect that the current lack of completely sequenced genomes for many of the major lineages of prokaryotes and for most type strains is a major obstacle in progress towards a genome-based classification of microorganisms. We conclude that phylogeny-driven microbial genome sequencing projects such as the Genomic Encyclopaedia of Archaea and Bacteria (GEBA) project are likely to rectify this situation.     

Physiological host specificity: a model using the European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) and microsporidia of row crop and other stalk-boring hosts

We investigated vertical and horizontal transmission as means by which entomopathogenic microsporidia may be isolated in their hosts. Ostrinia nubilalis larvae were challenged with microsporidia isolated from other stalk-boring and row crop Lepidoptera and were susceptible to seven species. Two species were horizontally transmitted. A Nosema sp. from Eoreuma loftini was transmitted among O. nubilalis larvae but not among larvae of the E. loftini host. This species was also vertically transmitted to the offspring of infected O. nubilalis females. An rDNA sequence showed the E. loftini isolate to be Nosema pyrausta, a naturally occurring species in O. nubilalis. Our results suggest that both horizontal and vertical transmission provide physiological barriers to host switching in the microsporidia, thus restricting the natural host range.     

Phenological asynchrony between herbivorous insects and their hosts: signal of climate change or pre-existing adaptive strategy?

Climate change alters phenological relations between interacting species. We might expect the historical baseline, or starting-point, for such effects to be precise synchrony between the season at which a consumer most requires food and the time when its resources are most available. We synthesize evidence that synchrony was not the historical condition in two insect–plant interactions involving Edith''s checkerspot butterfly (Euphydryas editha), the winter moth (Operophtera brumata) and their host plants. Initial observations of phenological mismatch in both systems were made prior to the onset of anthropogenically driven climate change. Neither species can detect the phenology of its host plants with precision. In both species, evolution of life history has involved compromise between maximizing fecundity and minimizing mortality, with the outcome being superficially maladaptive strategies in which many, or even most, individuals die of starvation through poor synchrony with their host plants. Where phenological asynchrony or mismatch with resources forms the starting point for effects of anthropogenic global warming, consumers are particularly vulnerable to impacts that exacerbate the mismatch. This vulnerability likely contributed to extinction of a well-studied metapopulation of Edith''s checkerspot, and to the skewed geographical pattern of population extinctions underlying a northward and upward range shift in this species.     

Parasite infectivity to hybridising host species: a link between hybrid resistance and allopolyploid speciation?

Variation in host-specific infectivity was studied in monogenean polystome parasites (Protopolystoma spp.) of the interfertile, parapatric anurans Xenopus laevis laevis and Xenopus muelleri. Laboratory-raised host F1 hybrids were resistant to parasites respectively specific to each parent taxon in nature. This resistance occurred against parasite isolates from both inside and outside a host hybrid/sympatric zone (and no isolate was compatible with the foreign host species under experimental conditions). Geographical Protopolystoma xenopodis isolates showed variable infectivity to a single full-sib group of their usual host, X. l. laevis, and strains with high or low infectivity to these sibs co-occurred in spatially distant local areas (separated by 1,700 km). The host compatibility of P. xenopodis was also subject to host genotypexparasite genotype interactions. Refractoriness to some parasites or pathogens, as a consequence of hybridisation, may have conferred a selective advantage on the allopolyploid pathway by which most Xenopus spp. are believed to have evolved.     

Do floral odor profiles geographically vary with the degree of specificity for pollinators? Investigation in two sapromyophilous Arum species (Araceae)

We compared floral odour profiles among populations of two Arum species which show different degrees of specificity for their fly pollinators. Insects were collected from inflorescences in four populations of Arum italicum and two populations of Arum maculatum. In six Arum populations, we compared inflorescences odour profiles collected by Solid Phase Micro Extraction (SPME) and analysed by gas chromatography. We confirmed that from a pollination point of view, A. italicum is an opportunist species, as it is mainly pollinated by insects of the families Psychodidae, Chironomidae and Sciaridae, whereas A. maculatum is a specialist species, as it is 90% pollinated by Psychodidae. In all populations, Arum italicum was less attractive to pollinators than Arum maculatum. Floral odour profiles of A. italicum were not geographically structured among populations, suggesting a high gene flow or adaptation to a fluctuant guild of pollinators. On the contrary, odour profiles of A. maculatum varied between the two populations studied suggesting a lower gene flow or adaptation to different local pollinator preferences     

How does an animal behave like a plant? Physiological and molecular adaptations of zooxanthellae and their hosts to symbiosis

Cnidarians (corals and sea anemones) harbouring photosynthetic microalgae derive several benefits from their association. To allow this association, numerous symbiotic-dependent adaptations in both partners, resulting from evolutionary pressures, have been selected. The dinoflagellate symbionts (zooxanthellae) are located inside a vesicle in the cnidarian host cell and are therefore exposed to a very different environment compared to the free-living state of these microalgae in terms of ion concentration and carbon content and speciation. In addition, this intracellular localization imposes that they rely completely upon the host for their nutrient supply (nitrogen, CO₂). Symbiotic-dependent adaptations imposed to the animal host by phototrophic symbiosis are more relevant to photosynthetic organisms than to metazoans: indeed, the cnidarian host often harbours diurnal changes of morphology to adapt itself to the amount of light and possesses carbon-concentrating mechanisms, antioxidative defences and UV sunscreens similar to that present in phototrophs. These adaptations and the contrasting fragility of the association are discussed from both ecological and evolutionary points of view.     

Does chemical aposematic (warning) signaling occur between host plants and their potential parasitic plants?

Aposematism (warning) signaling is a common defensive mechanism toward predatory or herbivorous animals, i.e., interactions between different trophic levels. I propose that it should be considered at least as a working hypothesis that chemical aposematism operates between certain host plants and their plant predators, parasitic plants, and that although they are also plants, they belong to a higher trophic level. Specific host plant genotypes emit known repelling chemical signals toward parasitic plants, which reduce the level of, slow the directional parasite growth (attack) toward the signaling hosts, or even cause parasitic plants to grow away from them in response to these chemicals. Chemical host aposematism toward parasitic plants may be a common but overlooked defense from parasitic plants.     

The binding of mycolic acids to galectin-3: a novel interaction between a host soluble lectin and trafficking mycobacterial lipids?

Understanding the molecular mechanism of host-pathogen interactions is the basis for drug design and vaccine development. The fine composition of mycolic acids (MA), the major constituents of Mycobacterium tuberculosis (Mtb) cell envelope, as well as other cell wall-associated lipids, contribute to determine the virulence of a given strain. However, endogenous receptors for mycolic acids on susceptible cells exposed to mycobacterial infections have not been fully identified. Here, we show that galectin-3, a multifunctional beta-galactoside binding lectin present mainly in the cytoplasm of inflammatory cells and also present on the cell surface, can recognize mycobacterial mycolic acids. MA can inhibit the lectin self-association but not its carbohydrate-binding abilities and can selectively interfere in the interaction of the lectin with its receptors on temperature-sensitive dendritic cell line, suggesting that galectin-3 could be involved in the recognition of trafficking mycolic acids and participate in their interaction with host cells.     

Olfactory responses of Neoseiulus cucumeris (Acari: Phytoseiidae) to odors of host plants and Frankliniella occidentalis (Thysanoptera: Thripidae)�Cplant complexes

We studied the olfactory responses of Neoseiulus cucumeris (Acari: Phytoseiidae) to odors from eggplant (Solanum melongena L.), pepper (Capsicum aunuum), and tomato (Solanum lycopersicum), three host plants, and their complexes with different treatments (undamaged, mechanically damaged, infested, pre-infested) in an olfactometer. The results showed that N. cucumeris preferred the odors of undamaged eggplant, pepper, and tomato to clean air. N. cucumeris preferred the volatiles from eggplant infested with Frankliniella occidentalis (Thysanoptera: Thripidae) over undamaged, mechanically damaged, and pre-infested with F. occidentalis eggplant volatiles. The same results were observed with pepper and tomato. N. cucumeris adults preferred the odors of undamaged eggplant and tomato to undamaged pepper. Similarly, same results were observed with mechanically damaged eggplant, pepper, tomato, and same plants pre-infested with F. occidentalis. Compared with odors of tomato infested with F. occidentalis, N. cucumeris adults significantly responded to odors of eggplant and pepper infested with F. occidentalis. There was no significant difference of N. cucumeris in making choice between eggplant infested with F. occidentalis and pepper infested with F. occidentalis.     

Rats’ (Rattus norvegicus) temporal discrimination of brief auditory stimuli: How does it compare with that of humans (Homo sapiens) and zebra finches (Taeniopygia guttata)?

The present study with rats replicated an experiment on the ability of zebra finches and humans to discriminate among brief auditory stimuli (see Weisman et al., 1999, Experiment 2). We trained rats with 27 3-kHz tones that varied in duration from 10 ms to 1420 ms. Reinforcement was contingent on responding (approaching the food well) to the nine medium-durations range tones (56-255 ms) but not to the nine short-durations range (10-46 ms) or long-durations range tones (309-1420 ms). Rats also received post-discrimination transfer tests with 2 kHz and 4 kHz tones that varied over the same durations as the 3 kHz tones. Rats acquired the temporal discrimination to a slightly lower level of accuracy than seen in finches or humans by Weisman et al. (1999). We tested for transfer of the temporal discrimination to find that rats, similar to humans (data from Weisman et al., 1999), transferred to untrained 2-kHz and 4-kHz tones at levels approaching accuracy to that achieved to the trained 3-kHz tone. By contrast, zebra finches (data from Weisman et al., 1999) failed to transfer their discrimination to the trained tone. We conclude that (a) rats discriminate among tone durations at least as well as they do among auditory frequencies and (b) rats like humans, but unlike finches, are insensitive to absolute pitch in their temporal discrimination.     

Three species of Mytilus and their hybrids identified in a Scottish Loch: natives, relicts and invaders?

Three species of the mussel, Mytilus, occur in the North Atlantic region, M. edulis, M. galloprovincialis and M. trossulus, and hybrid zones are present where their distributions overlap. M. edulis is a native species in the UK. M. galloprovincialis originated in the Mediterranean and its distribution extends northwards along the Atlantic seaboard to Scotland. Baltic Sea mussels have a M. trossulus ancestry but are highly introgressed by M. edulis. In recent decades, farming of mussels on long-line rope culture systems has been introduced into Scotland. On farms in Loch Etive, a form of mussel with a fragile shell and a different shape to either M. edulis or M. galloprovincialis has been increasing in frequency over recent years. Samples of fragile shelled, normal strong shelled and intermediate mussel types were sampled from two farms in 2006 and compared with samples of M. edulis, M. galloprovincialis and M. trossulus from other sources where their species identity is well established. Abundance relative to depth, shell strength, condition index and shell morphology were analysed together with 5 allozyme loci and one nuclear DNA genetic marker (Me 15/16). The fragile shelled mussels, and many of those classed as intermediate, were identified as a mixture of M. trossulus and M. trossulus x M. edulis hybrids. This identification was strongly supported by both morphological and genetic data and is the first record of the presence of M. trossulus in UK waters. M. trossulus in Loch Etive are most likely to be a post-glacial relict population restricted to the low salinity area of the Loch that has recently increased in abundance due to commercial mussel growing activity. In addition, individual mussels of all three species and their hybrids were detected amongst Loch Etive mussels. This is the first genetic demonstration of all three species and their hybrids occurring together in one location in the Atlantic region and provides a unique opportunity to study the processes of speciation, divergence, and introgression in the genus Mytilus.     

How to spend a token? Trade-offs between food variety and food preference in tufted capuchin monkeys (Cebus apella)

Humans and non-human animals often choose among different alternatives by seeking variety. Here we assessed whether variety-seeking, i.e. the tendency to look for diversity in services and goods, occurs in capuchin monkeys - South-American primates which - as humans - are omnivorous and susceptible to food monotony. Capuchins chose between a Variety-token, that allowed to select one among 10 different foods (one more-preferred and nine less-preferred) and a Monotony-token, that - upon exchange with the experimenter - either allowed to select one among 10 units of the same more-preferred food or gave access to one unit of the more-preferred food. To examine how food preference affects variety-seeking, in the B-condition we presented nine moderately preferred foods, whereas in the C-condition we presented nine low-preferred foods. Overall, capuchins preferred the Variety-token over the Monotony-token and often selected one of the less-preferred foods. These results suggest that variety-seeking is rooted in our evolutionary history, and that it satisfies the need of experiencing stimulation from the environment; at the ultimate level, variety-seeking may allow the organism to exploit novel foods and obtain a correct nutritional intake. Finally, variety-seeking could have contributed to the transition from barter to money in many human cultures.     

Isolation,identification and subtyping of Campylobacter: Where to from here?

Campylobacter species are widely regarded as the most frequent bacterial cause of gastroenteritis in humans worldwide. Their main transmission routes are via contaminated food and water. For interventions to be effective, methods for the detection, identification and epidemiological subtyping must be sensitive, accurate and rapid. As yet, methods are not perfect, although several significant advances have been made in these areas in recent years. This paper provides a brief review and commentary on the current state of the art in the hope that it will help provide context for others in selecting, improving or developing these vital tools for research and diagnoses.     

Cytolethal distending toxin (CDT): a bacterial weapon to control host cell proliferation?

Cytolethal distending toxins (CDT) constitute a family of genetically related bacterial protein toxins able to stop the proliferation of numerous cell lines. This effect is due to their ability to trigger in target cells a signaling pathway that normally prevents the transition between the G2 and the M phase of the cell cycle. Produced by several unrelated Gram-negative mucosa-associated bacterial species, CDTs are determined by a cluster of three adjacent genes (cdtA, cdtB, cdtC) encoding proteins whose respective role is not yet fully elucidated. The CDT-B protein presents sequence homology to several mammalian and bacterial phosphodiesterases, such as DNase I. The putative nuclease activity of CDT-B, together with the activation by CDT of a G2 cell cycle checkpoint, strongly suggests that CDT induces an as yet uncharacterized DNA alteration. However, the effective entry of CDT into cells and subsequent translocation into the nucleus have not yet been demonstrated by direct methods. The relationship between the potential DNA-damaging properties of this original family of toxins and their role as putative virulence factors is discussed.