Dynamical Transitions in a Pollination–Herbivory Interaction: A Conflict between Mutualism and Antagonism

Plant-pollinator associations are often seen as purely mutualistic, while in reality they can be more complex. Indeed they may also display a diverse array of antagonistic interactions, such as competition and victim–exploiter interactions. In some cases mutualistic and antagonistic interactions are carried-out by the same species but at different life-stages. As a consequence, population structure affects the balance of inter-specific associations, a topic that is receiving increased attention. In this paper, we developed a model that captures the basic features of the interaction between a flowering plant and an insect with a larval stage that feeds on the plant’s vegetative tissues (e.g. leaves) and an adult pollinator stage. Our model is able to display a rich set of dynamics, the most remarkable of which involves victim–exploiter oscillations that allow plants to attain abundances above their carrying capacities and the periodic alternation between states dominated by mutualism or antagonism. Our study indicates that changes in the insect’s life cycle can modify the balance between mutualism and antagonism, causing important qualitative changes in the interaction dynamics. These changes in the life cycle could be caused by a variety of external drivers, such as temperature, plant nutrients, pesticides and changes in the diet of adult pollinators.     

Mutualism in a community context: the positive feedback between an ant–aphid mutualism and a gall-making midge

Although mutualisms are widespread and often described in natural history accounts, their ecological influences on other community members remain largely unexplored. Many of these influences are likely a result of indirect effects. In this field study, we investigated the indirect effects of an ant–aphid mutualism on the abundance, survival rates and parasitism rates of a co-occurring herbivore. Rabdophaga salicisbrassicoides (Diptera: Cecidomyiidae) induces rosette galls on the developing shoots of Salix exigua trees, and populations can reach outbreak densities (up to 1,000 galls/stem) in central Washington State (USA). Ant-tended aphids feed on these same stems and often feed on gall tissue. In this study we used a combination of manipulative experiments and observational surveys to test the hypothesis that the abundances of aphids, ants, and galls have positive and reciprocal effects on one another, in a manner that would create a positive feedback loop in population growth. In addition, we examined whether the combined presence of ants and aphids reduces parasitism rates for the gallers. In support of the positive feedback loop hypothesis, aphids enjoyed higher population growth rates in the presence of ants and galls, the presence of ants and aphids resulted in increased abundance of galls, and the abundances of ants, aphids and galls were all positively correlated with one another. However, the mechanism underlying the positive effect of ants and aphids on galler density remains unknown, as the mutualism did not affect parasitism rates. More broadly, this study demonstrates that mutualisms can have significant and complex indirect effects on community and population ecology.     

Animal personality: what are behavioural ecologists measuring?

The discovery that an individual may be constrained, and even behave sub‐optimally, because of its personality type has fundamental implications for understanding individual‐ to group‐level processes. Despite recent interest in the study of animal personalities within behavioural ecology, the field is fraught with conceptual and methodological difficulties inherent in any young discipline. We review the current agreement of definitions and methods used in personality studies across taxa and systems, and find that current methods risk misclassifying traits. Fortunately, these problems have been faced before by other similar fields during their infancy, affording important opportunities to learn from past mistakes. We review the tools that were developed to overcome similar methodological problems in psychology. These tools emphasise the importance of attempting to measure animal personality traits using multiple tests and the care that needs to be taken when interpreting correlations between personality traits or their tests. Accordingly, we suggest an integrative theoretical framework that incorporates these tools to facilitate a robust and unified approach in the study of animal personality.     

How do plant ecologists use matrix population models?

Matrix projection models are among the most widely used tools in plant ecology. However, the way in which plant ecologists use and interpret these models differs from the way in which they are presented in the broader academic literature. In contrast to calls from earlier reviews, most studies of plant populations are based on < 5 matrices and present simple metrics such as deterministic population growth rates. However, plant ecologists also cautioned against literal interpretation of model predictions. Although academic studies have emphasized testing quantitative model predictions, such forecasts are not the way in which plant ecologists find matrix models to be most useful. Improving forecasting ability would necessitate increased model complexity and longer studies. Therefore, in addition to longer term studies with better links to environmental drivers, priorities for research include critically evaluating relative/comparative uses of matrix models and asking how we can use many short-term studies to understand long-term population dynamics.     

Mutualism or parasitism? The variable outcome of cleaning symbioses

The exact nature of many interspecific interactions remains unclear, with some evidence suggesting mutualism and other evidence pointing to parasitism for the same pair of interacting species. Here, we show spatial variation in the outcome of the cleaning relationship between Caribbean cleaning gobies (Elacatinus evelynae) and longfin damselfish (Stegastes diencaeus) over the distribution range of these species, and link this variation to the availability of ectoparasites. Cleaning interactions at sites with more ectoparasites were characterized by greater reductions in ectoparasite loads on damselfish clients and lower rates of removal of scales and mucus (i.e. cheating) by cleaning gobies, whereas the opposite was observed at sites where ectoparasite abundance was lower. For damselfish clients, cleaning was therefore clearly mutualistic in some locations, but sometimes neutral or even parasitic in others. Seasonal variability in ectoparasite abundance may ensure that locally low parasite availability, which promotes cleanerfish cheating, may be a transient condition at any given site. Conflicting conclusions about the nature of cleaning symbioses may, therefore, be explained by variation in ectoparasite abundance.     

Interactions between metals and alpha-synuclein--function or artefact?

alpha-synuclein is one of a family of proteins whose function remains unknown. This protein has become linked to a number of neurodegenerative disease although its potential causative role in these diseases remains mysterious. In diseases such as Parkinson's disease and Lewy body dementias, alpha-synuclein becomes deposited in aggregates termed Lewy bodies. Also, some inherited forms of Parkinson's diseases are linked to mutations in the gene for alpha-synuclein. Studies have mostly focussed on what causes the aggregation of the protein but, like many amyloidogenic proteins associated with a neurodegenerative disorder, this protein has now been suggested to bind copper. This finding is currently controversial. This review examines the evidence that alpha-synuclein is a copper binding protein and discusses whether this has any significance in determining the function of the protein or whether copper binding is at all necessary for aggregation.     

Genetic relationship between Mongolian and Norwegian horses?

Human populations of Central Asian origin have contributed genetic material to northern European populations. It is likely that migrating humans carried livestock to ensure food and ease transportation. Thus, eastern genes could also have dispersed to northern European livestock populations. Using microsatellite data, we here report that the essentially different genetic distances DA and (deltamu)2 and their corresponding phylogenetic trees show close associations between the Mongolian native horse and northern European horse breeds. The genetic distances between the northern European breeds and Standardbred/Thoroughbred, representing a southern-derived source of horses, were notably larger. We suggest that contribution of genetic material from eastern horses to northern European populations is likely to have occurred.     

Do the evolutionary interactions between moths and bats promote niche partitioning between bats and birds?

Ecological theory suggests that the coexistence of species is promoted by the partitioning of available resources, as in dietary niche partitioning where predators partition prey. Yet, the mechanisms underlying dietary niche partitioning are not always clear. We used fecal DNA metabarcoding to investigate the diets of seven nocturnal insectivorous bird and bat species. Low diet overlap (2%–22%) supported resource partitioning among all species. Differences in diet corresponded with species identity, prey detection method, and foraging behavior of predators. Insects with ultrasonic hearing capabilities were consumed significantly more often by birds than bats, consistent with an evolved avoidance of echolocating strategies. In turn, bats consumed a greater proportion of noneared insects such as spruce budworms. Overall, our results suggest that evolutionary interactions among bats and moths translate to dietary niche partitioning and coexistence among bats and nocturnal birds.     

How much variance is explained by ecologists? Additional perspectives

Oecologia - A recent meta-analysis of meta-analyses by Møller and Jennions (2002, Oecologia 132:492–500) suggested that ecologists using statistical models are explaining between 2.5%...     

Chromatin: a connection between loops and barriers?

A genetic screen for proteins that can block the spread of silenced heterochromatin has identified components of the nuclear pores with potential barrier activity. These results suggest that formation of loops of chromatin anchored to the pore could be one mechanism of barrier function.     

Myzostomida: a link between trochozoans and flatworms?

Myzostomids are obligate symbiotic invertebrates associated with echinoderms with a fossil record that extends to the Ordovician period. Due to their long history as host-specific symbionts, myzostomids have acquired a unique anatomy that obscures their phylogenetic affinities to other metazoans: they are incompletely segmented, parenchymous, acoelomate organisms with chaetae and a trochophore larva. Today, they are most often classified within annelids either as an aberrant family of polychaetes or as a separate class. We inferred the phylogenetic position of the Myzostomida by analysing the DNA sequences of two slowly evolving nuclear genes: the small subunit ribosomal RNA and elongation factor-1alpha. All our analyses congruently indicated that myzostomids are not annelids but suggested instead that they are more closely related to flatworms than to any trochozoan taxon. These results, together with recent analyses of the myzostomidan ultrastructure, have significant implications for understanding the evolution of metazoan body plans, as major characters (segmentation, coeloms, chaetae and trochophore larvae) might have been independently lost or gained in different animal phyla.     

AMPK: a link between metabolism and reproduction?

5'AMP-activated protein kinase (AMPK) is a serine/threonine kinase that acts as a fuel gauge in regulating energy metabolism. It restores cellular ATP levels by switching on catabolic pathways and switching off anabolic pathways. Some evidence indicates that AMPK could be also implicated in reproductive functions such as granulosa cell steroidogenesis and nuclear oocyte maturation in several species. Some metabolic hormones such as leptin, resistin, adiponectin (three adipokines) and ghrelin may in part act through the AMPK signaling. These hormones are also involved in the control of the reproductive functions at the hypothalamus-pituitary-gonadal axis level in both male and female. Thus, AMPK could be one of the signaling pathways controlling the interactions between energy balance and reproduction. The reproductive system is tightly coupled with energy balance, and thereby metabolic abnormalities can lead to the development of some physiopathological situations such as the polycystic ovary syndrome (PCOS). Women with PCOS show altered fertility mostly associated with metabolic disorders such as insulin-resistance, hyperinsulinemia and/or dyslipidemia. Metformin, an insulin-sensitizer, is used for the treatment of women with PCOS. It restores subnormal fertility and energy balance. Recent studies show that AMPK is involved in the mechanism of action of metformin. Thus, it may be a therapeutic target. However, further investigations are necessary to elucidate the functions of AMPK in both metabolic and reproductive tissues.     

Is communication improving between general practitioners and psychiatrists?

General practitioners and psychiatrists communicate mainly by letter. To ascertain the most important items of information that should be included in these letters ("key items") questionnaires were sent to 80 general practitioners and 80 psychiatrists. A total of 120 referral letters sent to psychiatric clinics in 1973 and 1983 were studied, together with the psychiatrists'' replies, and these were rated for the inclusion of "key items." General practitioners'' letters contain less information about the family but more about psychiatric history than they did a decade ago. Overall, psychiatrists'' letters have not changed. Registrars, however, now include noticeably more "key items" than they did 10 years ago, but their letters remain twice the length of those written by consultants. It is suggested that letter writing skills are vital to good patient management and should be taught to postgraduate trainees in general practice and psychiatry.