Macroecological patterns of species richness in parasite assemblages

The diversity of parasite species exploiting a host population varies substantially among different host species. This review summarizes the main predictions generated by the two main theoretical frameworks used to study parasite diversity. The first is island biogeography theory, which predicts that host features, such as body size, that are associated with the probability of colonization by new parasite species, should covary with parasite species richness. The second predictive framework derives from epidemiological modelling; it predicts that host species with features that increase parasite transmission success among host individuals, such as high population density, will sustain a greater diversity of parasite species. A survey of comparative studies of parasite diversity among fish and mammalian host species finds support for most of the predictions derived from the above two theoretical perspectives. This empirical support, however, is not universal. It is often qualitative only, because quantitative predictions are lacking. Finally, the amount of variance in parasite diversity explained by host features is generally low. To move forward, the search for the determinants of parasite diversity will need to rely less on theories developed for free-living organisms, and more on its own set of hypotheses incorporating specific host–parasite interactions such as immune responses.

Zusammenfassung

Die Diversität der Parasitenarten, die eine Wirtspopulation nutzen, variiert erheblich zwischen verschiedenen Wirtsarten. Dieser Review fasst die hauptsächlichen Vorhersagen zusammen, die von den zwei wichtigsten theoretischen Rahmenkonzepten hervorgebracht werden, die für die Untersuchung der Parasitendiversität genutzt werden. Die erste ist die Inselbiogeografie, die vorhersagt, dass Wirtsmerkmale, die mit der Besiedlungswahrscheinlichkeit durch einen neuen Parasiten verknüpft sind, wie beispielsweise die Körpergröße, mit dem Artenreichtum der Parasiten kovariieren sollten. Das zweite Rahmenkonzept ist aus der epidemiologischen Modellierung abgeleitet. Es sagt vorher, dass Wirtsarten mit Merkmalen, die den Übertragungserfolg der Parasiten zwischen den Wirtsindividuen erhöhen, wie beispielsweise hohe Populationsdichten, eine größere Diversität von Parasitenarten erhalten werden. Eine Begutachtung von vergleichenden Untersuchungen über Parasitendiversität bei Fischen und Säugetieren als Wirtsarten unterstützt die meisten der Vorhersagen, die von den oben genannten zwei theoretischen Perspektiven abgeleitet sind. Diese empirische Bestätigung ist jedoch nicht allgemein gültig. Sie ist häufig nur qualitativ, da quantitative Vorhersagen fehlen. Schließlich ist der Anteil der Varianz in der Parasitendiversität, der durch die Wirtsmerkmale erklärt wird, normalerweise gering. Um vorwärts zu kommen muss sich die Suche nach den bestimmenden Faktoren der Parasitendiversität weniger auf Theorien, die für freilebende Organismen entwickelt wurden, und mehr auf ihre eigene Menge von Hypothesen verlassen, die spezifische Wirt-Parasit-Interaktionen, wie beispielsweise Immunreaktionen, mit einbeziehen.     

Physiological regulatory networks: ecological roles and evolutionary constraints

Ecological and evolutionary physiology has traditionally focused on one aspect of physiology at a time. Here, we discuss the implications of considering physiological regulatory networks (PRNs) as integrated wholes, a perspective that reveals novel roles for physiology in organismal ecology and evolution. For example, evolutionary response to changes in resource abundance might be constrained by the role of dietary micronutrients in immune response regulation, given a particular pathogen environment. Because many physiological components impact more than one process, organismal homeostasis is maintained, individual fitness is determined and evolutionary change is constrained (or facilitated) by interactions within PRNs. We discuss how PRN structure and its system-level properties could determine both individual performance and patterns of physiological evolution.     

Diversity,evolutionary contribution and ecological roles of aquatic viruses

Aquatic viruses include infected viruses in aquatic animals, plants and microorganisms, and free-floating viruses(virioplankton)in water environments. In the last three decades, a huge number of aquatic viruses, especially diverse free-floating viruses,including cyanophages, phycoviruses, archaea viruses, giant viruses, and even virophages, have been identified by virological experiments and metagenomic analyses. Based on a comprehensive introduction of aquatic virus classification and their morphological and genetic diversity, here, we summarize and outline main virus species, their evolutionary contribution to aquatic communities through horizontal gene transfer, and their ecological roles for cyanobacterial bloom termination and global biogeochemical cycling in freshwater and marine ecosystems. Thereby, some novel insights of aquatic viruses and virus-host interactions, especially their evolutionary contribution and ecological rolesin diverse aquatic communities and ecosystems, are highlighted in this review.     

The roles of ecological and behavioral observation in species recognition among primates

Closely related living mammal species present numerous difficulties of recognition and delineation, not least because populations as well as individual organisms fulfill both genetic and economic functions. However, since species are often distributed geographically across multiple ecosystems or environments, it is evident that species as wholes, except where coterminous with the local populations of which they are composed, cannot be said to play unitary ecological roles. Aspects of the economic activity of organisms thus may not be admitted as elements in species recognition. Those who study the behavior of mammals in their natural habitats must therefore focus upon behaviors which preserve the genetic integrity of species if they wish to contribute to the systematic question of species identification. «Isolation» concepts of species are not served by data of this kind, since they emphasize interspecies discontinuities; the «recognition» concept of species, however, specifically focuses upon behaviors of this kind as they contribute to the «Specific-Mate Recognition System». Among primates such behaviors are likely to involve signalling of various kinds; where this is visual it is reasonable to expect to find morphological or chromatic correlates; where such cues are auditory or, to a lesser extent, olfactory, it is less probable that such correlates will be found to exist.     

Response of epilithic diatom assemblages to urbanization influences

Urbanization has long been recognized to alter the hydrology, water quality and channel form of waterways. Recently, consideration of urban impacts on waterways has expanded to include assessment of the aquatic biota, generally focusing upon the macroinvertebrate fauna. This study compares the impacts of urbanization on the structure of stream benthic diatom communities in 16 first- and second-order streams in the east of Melbourne, Australia. Relationships between the physical elements of urbanization, water quality and diatom communities were examined using multivariate analyses with compositional similarity, and univariate analyses with selected diatom species and indices,. There was a strong negative correlation between urban density and the diatom indices of water quality. The element of urbanization most strongly related to the measured decline in the diatom community was drainage connection. Electrical conductivity was the most influential water quality variable. It is hypothesized that, in addition to increasing electrical conductivity, drainage connection may be impacting the diatom community by increasing the delivery of phosphorus during small storm events. The study suggests that reducing directly piped drainage connection using infiltration and retention is a logical step in the mitigation of urban impacts upon receiving streams. A corollary part of the project indicated strong potential for using overseas diatom indices in studies on water quality in southeastern Australia.     

Local and regional influences on patterns of parasite species richness of central European fishes

Local, regional and global influences on the patterns of parasite species richness of 39 freshwater fish species from Central Europe were investigated. Host local abundance and host occurrence were considered respectively as local and regional factors, while host geographical range in longitude and latitude was considered as a global factor. Influences of size, ecology and behavior of hosts were also included in a comparative analysis using the independent contrasts method. We considered host habitat, host diet, host shoaling behavior and mobility. We found a positive relationship between local occurrence of fish and global range of their distribution. We confirmed previous findings showing the importance of host behavior and ecology on the variability of parasite species richness. Second, we showed how a global pattern, such as host geographical range, may affect the variability in parasite species richness through its effects on local abundance and distribution of hosts. A negative relationship between endoparasite species richness and host longitudinal range was found. This suggests that fish with eastern distribution live in the boundary of their distribution in Central Europe far from their center of distribution, which should also be characterized by a higher diversity of parasites.     

Tallgrass prairie ants: their species composition,ecological roles,and response to management

Ants are highly influential organisms in terrestrial ecosystems, including the tallgrass prairie, one of the most endangered ecosystems in North America. Through their tunneling, ants affect soil properties and resource availability for animals and plants. Ants also have important ecological roles as consumers of plant tissue and seeds. In the last several decades, various organizations, agencies, and agricultural producers have attempted to create wildlife habitat or reduce soil erosion by seeding thousands of hectares of bare cropland in the central United States with tallgrass prairie seed mixes. Although initially, monitoring of these restorations and of unplowed prairie remnants focused on plants and birds, in recent years the response of invertebrates such as ants has increasingly been the subject of research. An understanding of tallgrass prairie ant communities can help land managers and scientists better monitor the ecological condition of tallgrass prairie and guide management and restoration efforts. Here I review our current knowledge of ant species found within tallgrass prairie, their ecological roles, and their response to management.     

Taxonomic distinctness and species richness as measures of functional structure in bird assemblages

Most traditional "biodiversity" indices have an uncertain ecological interpretation, unfavourable sampling properties, and excessive data requirements. A new index of taxonomic distinctness (the average evolutionary distance between species in an assemblage) has many advantages over traditional measures, but its ecological interpretation remains unclear. We used published behavioural species data in conjunction with bird atlas data to quantify simple functional metrics (the fraction of species engaged in non-competitive interactions, and the average between-species disparity in habitat preferences) for breeding-bird assemblages in Europe and North America. We then analysed correlations of functional metrics with taxonomic distinctness and species richness, respectively. All functional metrics had weak, positive correlations with species richness. In contrast, correlations between functional metrics and taxonomic distinctness ranged from slightly negative to strongly positive, depending on the relative habitat heterogeneity, and on the resource involved in the between-species interaction. Strong positive correlations between taxonomic distinctness and the fraction of interactive species occurred for resources with few producer species per consumer species, and we suggest that taxonomic distinctness is consistently correlated with conservation worth. With its favourable sampling properties and data requirements, this taxonomic distinctness measure is a promising tool for biodiversity research and for environmental monitoring and management.     

The glucosinolate-myrosinase system in an ecological and evolutionary context

Functional analysis of natural variation in the model species Arabidopsis thaliana has enabled the cloning of many glucosinolate biosynthesis and hydrolysis genes. Variation in these genes is central to understanding the ecological role of the glucosinolate-myrosinase defense system, and allows us to dissect the evolutionary and ecological forces that shape polymorphism at underlying loci. These same genes are also variable in other crucifer species, suggesting the presence of recurring selection, possibly mediated by insects. By utilizing the genomic tools available in A. thaliana to investigate these loci fully, it might be possible to generate detailed evolutionary or ecological models to apply to other species.     

The analysis of plant growth in ecological and evolutionary studies

Plant growth rate is often assumed to be an ecologically important life history trait. However, conventional plant growth analysis, while providing a useful accounting of rates of weight gain and its components, is ill-suited for testing relationships between growth and fitness, particularly in natural populations. Two new approaches that are suitable for testing such relationships have evolved over the past several years. The first - the population biology of plant parts, or 'modular demography' - permits non-destructive measures of growth rate in natural field populations. When modular demography is performed using matrix population models, controls over growth rate can be examined, as well as consequences of growth variation for reproduction. The second - demographic growth analysis - provides growth parameters analogous to those of conventional growth analysis, but can be performed in natural field populations. Demographic growth analysis allows measures of individual growth-rate variation, which, in turn, can be related to plant performance.     

The genotypic structure of a multi-host bumblebee parasite suggests a role for ecological niche overlap

The genotypic structure of parasite populations is an important determinant of ecological and evolutionary dynamics of host-parasite interactions with consequences for pest management and disease control. Genotypic structure is especially interesting where multiple hosts co-exist and share parasites. We here analyze the natural genotypic distribution of Crithidia bombi, a trypanosomatid parasite of bumblebees (Bombus spp.), in two ecologically different habitats over a time period of three years. Using an algorithm to reconstruct genotypes in cases of multiple infections, and combining these with directly identified genotypes from single infections, we find a striking diversity of infection for both data sets, with almost all multi-locus genotypes being unique, and are inferring that around half of the total infections are resulting from multiple strains. Our analyses further suggest a mixture of clonality and sexuality in natural populations of this parasite species. Finally, we ask whether parasite genotypes are associated with host species (the phylogenetic hypothesis) or whether ecological factors (niche overlap in flower choice) shape the distribution of parasite genotypes (the ecological hypothesis). Redundancy analysis demonstrates that in the region with relatively high parasite prevalence, both host species identity and niche overlap are equally important factors shaping the distribution of parasite strains, whereas in the region with lower parasite prevalence, niche overlap more strongly contributes to the distribution observed. Overall, our study underlines the importance of ecological factors in shaping the natural dynamics of host-parasite systems.     

DNA hybridization to compare species compositions of natural bacterioplankton assemblages.

Little is known about the species composition and variability of natural bacterial communities, mostly because conventional identification requires pure cultures, but less than 1% of active natural bacteria are cultivable. This problem was circumvented by comparing species compositions via hybridization of total DNA of natural bacterioplankton communities for the estimation of the fraction of DNA in common between two samples (similarity). DNA probes that were labeled with 35S by nick translation were hybridized to filter-bound DNA in a reciprocal fashion; similarities (in percent) were calculated by normalizing the values to self-hybridizations. In tests with DNA mixtures of pure cultures, the experimentally observed similarities agreed with expectations. However, reciprocal similarities (probe and target reversed) were often asymmetric, unlike those of DNA from single strains. This was due to the relative complexity and G + C content of DNA, which provided a means to interpret the asymmetry that was occasionally observed in natural samples. Natural bacteria were collected by filtration from Long Island Sound (LIS), N.Y., the Caribbean and Sargasso seas, and a coral reef lagoon near Bermuda. The samples showed similarities of less than 10 to 95%. The LIS and Sargasso and Caribbean sea samples were 20 to 50% similar to each other. The coral reef sample was less than 10% similar to the others, indicating its unique composition. Seasonality was also observed; an LIS sample obtained in the autumn was 40% similar to two LIS samples obtained in the summer; these latter two samples were 95% similar. We concluded that total DNA hybridization is a rapid, simple, and unbiased method for investigating the variation of bacterioplankton species composition over time and space, avoiding the need of culturing.     

Taxonomic, evolutionary and ecological implications of the leaf anatomy of rhizomatous Iris species

The leaf anatomy of the rhizomatous Iris species with ensiform leaves and the related genera Pardanthopsis and Belamcanda is described. Their isobilateral leaves may or may not have a pseudo-dorsiventral structure. Variable characters of their leaf blades include: outline in transverse section, height and shape of papillae, form and structure of stomata, transverse section outline of marginal fibre strands and sclerenchy matous inner bundle sheath at phloem and xylem poles, forms of mesophyll arrangement, mesophyll structure and air canals, vascular bundle arrangement and the detailed structure of the larger vascular bundles, distribution of tannin, size and distribution of crystals. The taxonomic and ecological significance of these characters has been evaluated.
The anatomical characteristics of 25 supraspecific taxa in three genera are presented and compared in tables. The relationships and evolutionary position of these taxa are discussed. Each of the three subgroups within Iris appears to be correlated with a syndrome of anatomical characters. Some species currently of uncertain taxonomic position are discussed, and their classification based on anatomical data is suggested.
Some characters related to xeromorphy or helomorphy are mentioned.     

The importance of evolutionary constraints in ecological time scales

Summary The importance of constraints, defined as factors that retard or prevent a population from reaching its immediate adaptive peak on an ecological time scale is analysed. This is done by means of simple quantitative genetic models, which if anything underestimate the importance of constraints. The results show that even in the simplest case the response to selection will not generally be in the same direction as the selection vector, i.e. the direction to the nearest optimum. Adding complexity identifies cases where selection may lead the population in suboptimal directions. It is concluded that information about univariate genetic variances is not sufficient to predict evolutionary responses and may even be misleading. However, genetic covariances are not always acting as constraints, but can under certain circumstances promote evolution towards the nearest optimum. This can be understood by a spectral decomposition of the genetic variance—covariance matrix, where it is shown that the eigenvector associated with the largest amount of variance will to various degrees determine the outcome of selection. A literature survey of the pattern of character covariation in morphological characters in natural populations shows a wide variety of correlation patterns, but quite often shows a high level of covariance between traits. This suggests that constraints to short-term evolution may be more common than generally appreciated.     

The evolutionary and ecological roots of human social organization

Social organization among human foragers is characterized by a three-generational system of resource provisioning within families, long-term pair-bonding between men and women, high levels of cooperation between kin and non-kin, and relatively egalitarian social relationships. In this paper, we suggest that these core features of human sociality result from the learning- and skill-intensive human foraging niche, which is distinguished by a late age-peak in caloric production, high complementarity between male and female inputs to offspring viability, high gains to cooperation in production and risk-reduction, and a lack of economically defensible resources. We present an explanatory framework for understanding variation in social organization across human societies, highlighting the interactive effects of four key ecological and economic variables: (i) the role of skill in resource production; (ii) the degree of complementarity in male and female inputs into production; (iii) economies of scale in cooperative production and competition; and (iv) the economic defensibility of physical inputs into production. Finally, we apply this framework to understanding variation in social and political organization across foraging, horticulturalist, pastoralist and agriculturalist societies.