Changes in the stand structure (1975–2000) of coastal Banksia forest in the long absence of fire

Abstract Revisitation studies enable long‐term changes in vegetation to be deciphered and insights into plant community succession to be gained. This is particularly important when assessing the effects of fire exclusion in ecosystems where fire is thought to have once been common. Using two adjacent coastal Banksia integrifolia forest stands in southern Victoria, Australia initially surveyed in 1975 by Hazard and Parsons, we document the changes that occurred in the stand structure between 1975 and 2000. Western Park (WP) has now remained unburnt for over 100 years while Cerberus Naval Base (CNB) was most recently burnt in 1942. Banksia integrifolia densities have decreased at both sites over the 25‐years period by an average of 42–77%, as have other coastal native shrubs (e.g. Leptospermum laevigatum, Leucopogon parviflorus). Trees at WP appear to have died due to old age while mortality at CNB is presumed to be due to stand thinning in response to intense competition for light. Successful recruitment by Banksia has been minimal; trees less than 9 cm girth over bark at breast height (GBBH) were absent at CNB while no trees <19 cm GBBH were observed at WP. The long‐term absence of disturbance such as fire is suspected to be one of the causes of regeneration failure of the stand at WP. Gap phase regeneration is not apparent in B. integrifolia and hence, long‐term succession to a more grassy community is likely when fire is excluded for long periods.     

CNB: requiescat in pace?

Despite its failure to predict variation in secondary chemistry for many metabolites and taxa, the Carbon/Nutrient Balance (CNB) hypothesis continues to be invoked with regularity. According to Lerdau and Coley (2002) , the value of the hypothesis is that it explains phytochemical phenotypic plasticity outside of an evolutionary context. We contend that the CNB hypothesis impedes a more comprehensive understanding of plant biology and that an approach divorcing plant chemistry from function is inherently limited in its ability to predict responses of plants to the environmental conditions in which they have evolved. Although it is possible for a mechanistically flawed hypothesis to predict phenomena, such hypotheses almost always suffer a lack of generality. Lerdau and Coley argue that the limitations of the CNB model are its strengths, not its weaknesses, and set forth refinements that, in essence, further limit its applicability. We address these refinements and explore alternative adaptive explanations for adjustments of secondary metabolism in relation to resource availability and environmental variation. In view of its flawed nature and the existence of alternative approaches, CNB no longer warrants consideration as a viable hypothesis.     

Out of the quagmire of plant defense hypotheses

Several hypotheses, mainly Optimal Defense (OD), Carbon: Nutrient Balance (CNB), Growth Rate (GR), and Growth-Differentiation Balance (GDB), have individually served as frameworks for investigating the patterns of plant defense against herbivores, in particular the pattern of constitutive defense. The predictions and tests of these hypotheses have been problematic for a variety of reasons and have led to considerable confusion about the state of the "theory of plant defense." The primary contribution of the OD hypothesis is that it has served as the main framework for investigation of genotypic expression of plant defense, with the emphasis on allocation cost of defense. The primary contribution of the CNB hypothesis is that it has served as the main framework for investigation of how resources affect phenotypic expression of plant defense, often with studies concerned about allocation cost of defense. The primary contribution of the GR hypothesis is that it explains how intrinsic growth rate of plants shaped evolutionarily by resource availability affects defensive patterns. The primary contribution of the expanded GDB hypothesis is that it recognizes the constant physiological tradeoff between growth and differentiation at the cellular and tissue levels relative to the selective pressures of resource availability, including explicitly taking into account plant tolerance of damage by enemies. A clearer understanding of these hypotheses and what we have learned from investigations that use them can facilitate development of well-designed experiments that address the gaps in our knowledge of plant defense.     

Does mother know best? The preference–performance hypothesis and parent–offspring conflict in aboveground–belowground herbivore life cycles

1. A substantial amount of research on host‐plant selection by insect herbivores is focused around the preference–performance hypothesis (PPH). To date, the majority of studies have primarily considered insects with aboveground life cycles, overlooking insect herbivores that have both aboveground and belowground life stages, for which the PPH could be equally applicable. 2. This study investigated the factors influencing the performance of the root‐feeding vine weevil (Otiorhynchus sulcatus) larvae and whether this was linked to the oviposition behaviour of the maternal adult living aboveground. 3. Maternal insects feeding aboveground reduced root biomass by 34% and increased root carbon by 4%. Larvae feeding on plants subjected to aboveground herbivory had reduced mass. Irrespective of the presence of maternal herbivory, larval mass was positively correlated with root biomass. 4. Larval mass was also reduced by conspecific larvae, previously feeding on roots (19% reduction). However, the mechanism underpinning this effect remains unclear, as in contrast to maternal herbivory aboveground, prior larval feeding did not significantly affect root biomass or root carbon concentrations. 5. Maternal insects did not distinguish between plants infested with larvae and those that were free of larvae, in terms of their egg‐laying behaviour. Conversely, maternal insects tended to lay eggs on plants with smaller root systems, a behaviour that is likely to negatively affect offspring performance. 6. The PPH is not supported by our findings for the polyphagous vine weevil feeding on the host plant raspberry (Rubus idaeus), and in fact our results suggest that there is the potential for strong parent–offspring conflict in this system.     

Choosy mothers pick challenging plants: maternal preference and larval performance of a specialist herbivore are not linked

1. Maternal preference is a dynamic process and interactions between preference and performance are fundamental for understanding evolutionary ecology and host association in insect–plant interactions. In the present study, the hypothesis of preference–performance was tested by offering solanaceous specialist Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) larvae and adult females four plant congeners that ranged in suitability. 2. Larval feeding, development, oviposition, plant glycoalkaloids, and headspace volatiles in the four plant species were analysed to examine the extent of variation, which might explain performance–preference differences. 3. It was found that larval performance was mismatched with adult oviposition preferences. Adults laid more eggs on Solanum immite Dunal plants, which were poor hosts for larval development, feeding, and survival, compared to the other three Solanum species. 4. Chemical plant defenses, in general, did not correlate with performance or preference, but some plant volatiles may have played a role in resolving female choice. Glycoalkaloids such as solanine and chaconine were detected in similar amounts in preferred and non‐preferred hosts, but there was significantly more limonene in the headspace of S. immite than in S. tuberosum L. 5. The present findings suggest that we must consider the risk‐spreading hypothesis in cases where preference and performance are not positively correlated, particularly in specialist herbivores that can feed on a diversity of congener plants and may attempt to expand their exploits to other solanaceae species.     

Selection of evolutionary models for phylogenetic hypothesis testing using parametric methods

Recent molecular studies have incorporated the parametric bootstrap method to test a priori hypotheses when the results of molecular based phylogenies are in conflict with these hypotheses. The parametric bootstrap requires the specification of a particular substitutional model, the parameters of which will be used to generate simulated, replicate DNA sequence data sets. It has been both suggested that, (a) the method appears robust to changes in the model of evolution, and alternatively that, (b) as realistic model of DNA substitution as possible should be used to avoid false rejection of a null hypothesis. Here we empirically evaluate the effect of suboptimal substitution models when testing hypotheses of monophyly with the parametric bootstrap using data sets of mtDNA cytochrome oxidase I and II (COI and COII) sequences for Macaronesian Calathus beetles, and mitochondrial 16S rDNA and nuclear ITS2 sequences for European Timarcha beetles. Whether a particular hypothesis of monophyly is rejected or accepted appears to be highly dependent on whether the nucleotide substitution model being used is optimal. It appears that a parameter rich model is either equally or less likely to reject a hypothesis of monophyly where the optimal model is unknown. A comparison of the performance of the Kishino–Hasegawa (KH) test shows it is not as severely affected by the use of suboptimal models, and overall it appears to be a less conservative method with a higher rate of failure to reject null hypotheses.     

Selection on intra‐individual variation in stigma–anther distance in the tropical tree Ipomoea wolcottiana (Convolvulaceae)

• It is well known that animals can exert strong selective pressures on plant traits. However, studies on the evolutionary consequences of plant–animal interactions have mainly focused on understanding how these interactions shape trait means, while overlooking its potential direct effect on the variability among structures within a plant (e.g. flowers and fruits). The degree of within‐plant variability can have strong fitness effects but few studies have evaluated its role as a potential target of selection.
• Here we reanalysed data on Ipomoea wolcottiana stigma–anther distance to test alternate mechanisms driving selection on the mean as well as on intra‐individual variance in 2 years. We found strong negative selection acting on intra‐individual variation but not on mean stigma–anther distance, suggesting independent direct selection on the latter.
• Our result suggests that intra‐individual variance has the potential to be an important target of selection in nature, and that ignoring it could lead to the wrong characterisation of the selection regime.
• We highlight the need for future studies to consider patterns of selection on the mean as well as on intra‐individual variance if we want to understand the full extent of plant–animal interactions as an evolutionary force in nature.

     

Intraspecific plant–soil feedback and intraspecific overyielding in Arabidopsis thaliana

Understanding the mechanisms of community coexistence and ecosystem functioning may help to counteract the current biodiversity loss and its potentially harmful consequences. In recent years, plant–soil feedback that can, for example, be caused by below‐ground microorganisms has been suggested to play a role in maintaining plant coexistence and to be a potential driver of the positive relationship between plant diversity and ecosystem functioning. Most of the studies addressing these topics have focused on the species level. However, in addition to interspecific interactions, intraspecific interactions might be important for the structure of natural communities. Here, we examine intraspecific coexistence and intraspecific diversity effects using 10 natural accessions of the model species Arabidopsis thaliana (L.) Heynh. We assessed morphological intraspecific diversity by measuring several above‐ and below‐ground traits. We performed a plant–soil feedback experiment that was based on these trait differences between the accessions in order to determine whether A. thaliana experiences feedback at intraspecific level as a result of trait differences. We also experimentally tested the diversity–productivity relationship at intraspecific level. We found strong differences in above‐ and below‐ground traits between the A. thaliana accessions. Overall, plant–soil feedback occurred at intraspecific level. However, accessions differed in the direction and strength of this feedback: Some accessions grew better on their own soils, some on soils from other accessions. Furthermore, we found positive diversity effects within A. thaliana: Accession mixtures produced a higher total above‐ground biomass than accession monocultures. Differences between accessions in their feedback response could not be explained by morphological traits. Therefore, we suggest that they might have been caused by accession‐specific accumulated soil communities, by root exudates, or by accession‐specific resource use based on genetic differences that are not expressed in morphological traits. Synthesis. Our results provide some of the first evidence for intraspecific plant–soil feedback and intraspecific overyielding. These findings may have wider implications for the maintenance of variation within species and the importance of this variation for ecosystem functioning. Our results highlight the need for an increased focus on intraspecific processes in plant diversity research to fully understand the mechanisms of coexistence and ecosystem functioning.     

Individual‐level differences in generalist caterpillar responses to a plant–plant cue

1. Plant–plant communication has been found to affect interactions between herbivores and plants in several model systems. In these systems, herbivore‐induced volatile chemical cues are emitted and perceived by other plants (receivers), which subsequently change their defensive phenotypes. Most studies have focused on how the effects of volatile cues affect plant damage, whereas herbivore performance has rarely been examined. 2. In this study, it is shown that plant–plant communication between willows reduced the growth rate, feeding rate, and conversion efficiency of some individuals but not others of a generalist caterpillar, Orgyia vetusta. 3. Using a paired, no‐choice trial design, there was substantial variation between caterpillar individuals in their response to willows that had been induced with a volatile plant–plant cue. This variation was explained by feeding parameters of the individual herbivores. Individuals behaved similarly when fed induced and non‐induced willow leaves. Specifically, growth rates of caterpillars that grew rapidly on non‐induced willow leaves were negatively affected by plant–plant cues, but growth rates of caterpillars that grew slowly on non‐induced willow leaves were not affected by the responses to volatiles from neighbouring willows. 4. Induction by volatile plant–plant cues reduced the growth rates of those individual herbivores that caused the greatest damage to willow, but had little effect on weak growers.     

Patterns of diversification in two species of short‐tailed bats (Carollia Gray, 1838): the effects of historical fragmentation of Brazilian rainforests

The small‐sized frugivorous bat Carollia perspicillata is an understory specialist and occurs in a wide range of lowland habitats, tending to be more common in tropical dry or moist forests of South and Central America. Its sister species, Carollia brevicauda, occurs almost exclusively in the Amazon rainforest. A recent phylogeographic study proposed a hypothesis of origin and subsequent diversification for C. perspicillata along the Atlantic coastal forest of Brazil. Additionally, it also found two allopatric clades for C. brevicauda separated by the Amazon Basin. We used cytochrome b gene sequences and a more extensive sampling to test hypotheses related to the origin and diversification of C. perspicillata plus C. brevicauda clade in South America. The results obtained indicate that there are two sympatric evolutionary lineages within each species. In C. perspicillata, one lineage is limited to the Southern Atlantic Forest, whereas the other is widely distributed. Coalescent analysis points to a simultaneous origin for C. perspicillata and C. brevicauda, although no place for the diversification of each species can be firmly suggested. The phylogeographic pattern shown by C. perspicillata is also congruent with the Pleistocene refugia hypothesis as a likely vicariant phenomenon shaping the present distribution of its intraspecific lineages. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 527–539.     

Friend or foe? A parasitic wasp shifts the cost/benefit ratio in a nursery pollination system impacting plant fitness

Nursery pollination systems are species interactions where pollinators also act as fruit/seed herbivores of the plant partner. While the plants depend on associated insects for pollination, the insects depend on the plants’ reproductive structures for larval development. The outcome of these interactions is thus placed on a gradient between mutualism and antagonism. Less specialized interactions may fluctuate along this gradient with the ecological context, where natural enemies can play an important role. We studied whether a natural enemy may impact the level of seed consumption of a nursery pollinator and how this in turn may influence individual plant fitness. We used the plant Silene latifolia, its herbivore Hadena bicruris, and its ectoparasitoid Bracon variator as a model plant–herbivore–natural enemy system. We investigated seed output, germination, survival, and flower production as proxies for individual plant fitness. We show that B. variator decreases the level of seed consumption by H. bicruris larvae which in turn increased seed output in S. latifolia plants, suggesting that parasitism by B. variator may act as a regulator in the system. However, our results also show that plant survival and flower production decrease with higher seed densities, and therefore, an increase in seed output may be less beneficial for plant fitness than estimated from seed output alone. Our study should add another layer to the complex discussion of whether parasitoids contribute to plant fitness, as we show that taking simple proxies such as seed output is insufficient to determine the net effect of multitrophic interactions.     

Preference and performance of generalist and specialist herbivores on chemically defended host plants

1. Both the physiological efficiency (PE) hypothesis and the preference–performance (PP) hypothesis address the complex interactions between herbivores and host plants, albeit from different perspectives. The PE hypothesis contends that specialists are better physiologically adapted to their host plants than generalists. The PP hypothesis predicts that larvae perform best on the host plant preferred by ovipositing females. 2. This study tests components of both hypotheses using the specialist checkerspot, Euphydryas anicia, the generalist salt marsh caterpillar, Estigmene acrea, and host plants in the genus Penstemon, which are defended by iridoid glycosides. 3. In laboratory experiments, the generalist preferred and performed significantly better on the less well defended host plant species. This is consistent with results from a common garden experiment where the less well defended Penstemon species received more damage from the local community of generalists. Larvae of the specialist checkerspot preferred the more chemically defended species in the laboratory, but performed equally well on both hosts. However, field experiments demonstrated that adult checkerspot females preferred to oviposit on the less well defended host plant. 4. Components of the physiological efficiency hypothesis were supported in this system, as the specialist outperformed the generalist on the more iridoid glycoside‐rich host plant species. There was no support for the PP hypothesis, however, as there was no clear relationship between female preference in the field and offspring performance in the laboratory.     

Edaphic,Nutritive, and Species Assemblage Differences between Hotspots and Matrix Vegetation: Two African Case Studies

Areas of locally intense and frequent grazing, or ‘hotspots’, are pervasive features in tropical grasslands and savannas. In some ecosystems, hotspot presence is clearly associated with edaphic factors (e.g., high clay content and elevated soil fertility), such as those that develop in abandoned cattle bomas. Studies in a range of other savanna ecosystems, however, have failed to find intrinsic soil differences between hotspots and the surrounding matrix. Also, it remains unclear to what extent hotspots are associated with specific assemblages of nutrient‐rich plant species, as opposed to being a manifestation of intraspecific variation in nutritive quality. We conducted simultaneous studies in Kruger (South Africa) and Serengeti (Tanzania) National Parks to re‐evaluate the role of edaphic correlates of hotspot occurrence and to test whether intraspecific variation in plant quality occurs across hotspot‐matrix boundaries. We sampled soils and plants in paired hotspot and matrix plots at multiple sites within each ecosystem to test our a priori hypothesis that hotspots would be associated with distinct species assemblages and differences in soil fertility. We found clear hotspot‐matrix differences in foliar N, particularly within species, despite finding no differences in any soil or plant–soil variables, including N mineralization potential and mycorrhizal inoculation levels. We found only weak differences in community composition across the boundary, suggesting that intraspecific variation in foliar N rather than species turnover is mainly responsible for the enhanced nutritive value of hotspot vegetation. We propose that grazer–plant interactions may be stronger drivers of hotspot maintenance in these systems than plant–soil interactions.     

Density and assemblage influence the nature of the species richness–productivity relationship in Australian dry sclerophyll forest species

The relationship between species richness and productivity is important from both a basic, theoretical perspective and also because it has important ramifications for applied ecology including ecosystem restoration and the design of carbon offset plantings. While a more species‐rich community is often believed to be more productive than a species‐poor community, findings from observational and experimental studies differ and our understanding of the relationship comes largely from grasslands. Consequently, we aimed to determine for the first time the nature of the species richness–productivity relationship in a southern‐hemisphere dry sclerophyll ecosystem. We investigated the impact of species richness on productivity, plant density and mean plant biomass at three sowing densities in three species assemblages. Eucalyptus globulus, Acacia mearnsii and Allocasuarina verticillata were each grown as monocultures and included in every subsequent level of species richness, forming three distinct species assemblages. Communities were grown in a glasshouse pot experiment for four months, then harvested and above‐ground biomass measured. We found no general species richness–productivity relationship in the communities studied. There were no overall increases in productivity as species richness increased and in fact in most cases the productivity of communities with 4 and 8 species was lower than monocultures of the dominants. Importantly, density influenced the way richness affected productivity and this effect was dependent upon assemblage, indicating that species identity is a key determinant of productivity. These results demonstrate important ecological principles in a previously untested system. A key outcome of this experiment is that density alters the relationship between species richness and initial productivity in assemblages of Australian dry sclerophyll species.     

Liberation of amino acids by heterotrophic nitrogen fixing bacteria

Summary. Large amounts of amino acids are produced by nitrogen-fixing bacteria such as Azotobacter, Azospirillum, Rhizobium, Mesorhizobium and Sinorhizobium when growing in culture media amended with different carbon and nitrogen sources. This kind of bacteria live in close association with plant roots enhanced plant growth mainly as a result of their ability to fix nitrogen, improving shoot and root development suppression of pathogenic bacteria and fungi, and increase of available P concentration. Also, it has been strongly evidenced that production of biologically substances such as amino acids by these rhizobacteria are involved in many of the processes that explain plant-grown promotion. This paper reviews literature concerning amino acids production by nitrogen-fixing bacteria. The role of amino acids in microbial interactions in the rhizosphere and establishment of plant bacterial association is also discussed.     

Soil pathogen communities associated with native and non‐native Phragmites australis populations in freshwater wetlands

Soil pathogens are believed to be major contributors to negative plant–soil feedbacks that regulate plant community dynamics and plant invasions. While the theoretical basis for pathogen regulation of plant communities is well established within the plant–soil feedback framework, direct experimental evidence for pathogen community responses to plants has been limited, often relying largely on indirect evidence based on above‐ground plant responses. As a result, specific soil pathogen responses accompanying above‐ground plant community dynamics are largely unknown. Here, we examine the oomycete pathogens in soils conditioned by established populations of native noninvasive and non‐native invasive haplotypes of Phragmites australis (European common reed). Our aim was to assess whether populations of invasive plants harbor unique communities of pathogens that differ from those associated with noninvasive populations and whether the distribution of taxa within these communities may help to explain invasive success. We compared the composition and abundance of pathogenic and saprobic oomycete species over a 2‐year period. Despite a diversity of oomycete taxa detected in soils from both native and non‐native populations, pathogen communities from both invaded and noninvaded soils were dominated by species of Pythium. Pathogen species that contributed the most to the differences observed between invaded and noninvaded soils were distributed between invaded and noninvaded soils. However, the specific taxa in invaded soils responsible for community differences were distinct from those in noninvaded soils that contributed to community differences. Our results indicate that, despite the phylogenetic relatedness of native and non‐native P. australis haplotypes, pathogen communities associated with the dominant non‐native haplotype are distinct from those of the rare native haplotype. Pathogen taxa that dominate either noninvaded or invaded soils suggest different potential mechanisms of invasion facilitation. These findings are consistent with the hypothesis that non‐native plant species that dominate landscapes may “cultivate” a different soil pathogen community to their rhizosphere than those of rarer native species.     

Congruent population genetic structures and divergence histories in anther‐smut fungi and their host plants Silene italica and the Silene nutans species complex

Study of the congruence of population genetic structure between hosts and pathogens gives important insights into their shared phylogeographical and coevolutionary histories. We studied the population genetic structure of castrating anther‐smut fungi (genus Microbotryum) and of their host plants, the Silene nutans species complex, and the morphologically and genetically closely related Silene italica, which can be found in sympatry. Phylogeographical population genetic structure related to persistence in separate glacial refugia has been recently revealed in the S. nutans plant species complex across Western Europe, identifying several distinct lineages. We genotyped 171 associated plant–pathogen pairs of anther‐smut fungi and their host plant individuals using microsatellite markers and plant chloroplastic single nucleotide polymorphisms. We found clear differentiation between fungal populations parasitizing S. nutans and S. italica plants. The population genetic structure of fungal strains parasitizing the S. nutans plant species complex mirrored the host plant genetic structure, suggesting that the pathogen was isolated in glacial refugia together with its host and/or that it has specialized on the plant genetic lineages. Using random forest approximate Bayesian computation (ABC‐RF), we found that the divergence history of the fungal lineages on S. nutans was congruent with that previously inferred for the host plant and probably occurred with ancient but no recent gene flow. Genome sequences confirmed the genetic structure and the absence of recent gene flow between fungal genetic lineages. Our analyses of individual host–pathogen pairs contribute to a better understanding of co‐evolutionary histories between hosts and pathogens in natural ecosystems, in which such studies remain scarce.     

Genomic evidence of genetic variation with pleiotropic effects on caterpillar fitness and plant traits in a model legume

Plant–insect interactions are ubiquitous, and have been studied intensely because of their relevance to damage and pollination in agricultural plants, and to the ecology and evolution of biodiversity. Variation within species can affect the outcome of these interactions. Specific genes and chemicals that mediate these interactions have been identified, but genome‐ or metabolome‐scale studies might be necessary to better understand the ecological and evolutionary consequences of intraspecific variation for plant–insect interactions. Here, we present such a study. Specifically, we assess the consequences of genome‐wide genetic variation in the model plant Medicago truncatula for Lycaeides melissa caterpillar growth and survival (larval performance). Using a rearing experiment and a whole‐genome SNP data set (>5 million SNPs), we found that polygenic variation in M. truncatula explains 9%–41% of the observed variation in caterpillar growth and survival. Genetic correlations among caterpillar performance and other plant traits, including structural defences and some anonymous chemical features, suggest that multiple M. truncatula alleles have pleiotropic effects on plant traits and caterpillar performance (or that substantial linkage disequilibrium exists among distinct loci affecting subsets of these traits). A moderate proportion of the genetic effect of M. truncatula alleles on L. melissa performance can be explained by the effect of these alleles on the plant traits we measured, especially leaf toughness. Taken together, our results show that intraspecific genetic variation in M. truncatula has a substantial effect on the successful development of L. melissa caterpillars (i.e., on a plant–insect interaction), and further point toward traits potentially mediating this genetic effect.     

Molecular characterization of the ligand–receptor interaction of the neuropeptide Y family

Neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) belong to the NPY hormone family and activate a class of receptors called the Y‐receptors, and also belong to the large superfamily of the G‐protein coupled receptors. Structure–affinity and structure–activity relationship studies of peptide analogs, combined with studies based on site‐directed mutagenesis and anti‐receptor antibodies, have given insight into the individual characterization of each receptor subtype relative to its interaction with the ligand, as well as to its biological function. A number of selective antagonists at the Y₁‐receptor are available whose structures resemble that of the C‐terminus of NPY. Some of these compounds, like BIBP3226, BIBO3304 and GW1229, have recently been used for in vivo investigations of the NPY‐induced increase in food intake. Y₂‐receptor selective agonists are the analog cyclo‐(28/32)‐Ac‐[Lys²⁸‐Glu³²]‐(25–36)‐pNPY and the TASP molecule containing two units of the NPY segment 21–36. Now the first antagonist with nanomolar affinity for the Y₂‐receptor is also known, BIIE0246. So far, the native peptide PP has been shown to be the most potent ligand at the Y₄‐receptor. However, by the design of PP/NPY chimera, some analogs have been found that bind not only to the Y₄‐, but also to the Y₅‐receptor with subnanomolar affinities, and are as potent as NPY at the Y₁‐receptor. For the characterization of the Y₅‐receptor in vitro and in vivo, a new class of highly selective agonists is now available. This consists of analogs of NPY and of PP/NPY chimera which all contain the motif Ala³¹‐Aib³². This motif has been shown to induce a 3₁₀‐helical turn in the region 28–31 of NPY and is suggested to be the key motif for high Y₅‐receptor selectivity. The results of feeding experiments in rats treated with the first highly specific Y₅‐receptor agonists support the hypothesis that this receptor plays a role in the NPY‐induced stimulation of food intake. In conclusion, the selective compounds for the different Y‐receptor subtypes known so far are promising tools for a better understanding of the physiological properties of the hormones of the NPY family and related receptors. Copyright © 2000 European Peptide Society and John Wiley & Sons, Ltd.     

The zebrafish as a model for gastrointestinal tract–microbe interactions

The zebrafish (Danio rerio) has become a widely used vertebrate model for bacterial, fungal, viral, and protozoan infections. Due to its genetic tractability, large clutch sizes, ease of manipulation, and optical transparency during early life stages, it is a particularly useful model to address questions about the cellular microbiology of host–microbe interactions. Although its use as a model for systemic infections, as well as infections localised to the hindbrain and swimbladder having been thoroughly reviewed, studies focusing on host–microbe interactions in the zebrafish gastrointestinal tract have been neglected. Here, we summarise recent findings regarding the developmental and immune biology of the gastrointestinal tract, drawing parallels to mammalian systems. We discuss the use of adult and larval zebrafish as models for gastrointestinal infections, and more generally, for studies of host–microbe interactions in the gut.