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Estimates of global fungal diversity have varied widely, suggesting a range from fewer than one million to over 10 million species, with each of the estimates drawing data from various criteria. In 2022, Fungal Diversity published a special issue on fungal numbers. It had been hoped that the editorial would provide a more accurate account of the numbers of fungi. Instead, it was concluded that this was not possible based on present evidence and, some of the data necessary for accurate assessments was put forward, and the present paper expands on this short article. The review first looks at estimates of fungal numbers and what these estimates are based on. It then presents future research needs that will help us to gain a more accurate estimate of fungal numbers. This includes work that needs to be done in tropical rainforests, where the greatest diversity is expected, where whole rainforests, canopy diversity, and palm fungi are addressed. Case studies for lichens and associated fungi, soil and litter fungi, evidence from particle filtration, freshwater fungi, marine fungi, mushrooms, and yeasts will also be given. Once we have such information, we can obtain a more accurate estimate of fungal numbers. [ABSTRACT FROM AUTHOR]

Ecological niches and beta diversity are fundamental concepts providing insight into the structure and functioning of marine ecosystems. Both concepts help in understanding how communities are distributed in different habitats and how marine ecosystems respond to environmental change. Here, the study brings a functional approach to the relationship between phytoplankton ecological niches and beta diversity. Phytoplankton community (from pico- to microphytoplankton) was addressed during a spring bloom of Phaeocystis globosa and diatoms, from the eastern English Channel (EEC) toward the southern North Sea (SNS) in 8 distinct water bodies, from late-April 2017 to mid-May 2017. An automated flow cytometer was used to discriminate phytoplankton by their optical properties at the single-cell level from continuous subsurface pumping marine waters, allowing the characterization of 11 phytoplankton functional groups (PFGs) from pico- to microphytoplankton. The spatial segregation of PFGs was performed from total abundance and Local Contribution to Beta Diversity (LCBD) calculations, from the most abundant to the marginal PFGs, through niche's overlap. Nanoeukaryotes (RedNano) associated with Phaeocystis globosa and picophytoplankton associated with Synechococcus spp. (OraPicoProk) were the less marginal PFGs. However, the low niche overlap between these groups revealed they have contrasting habitat affinity. While nanoeukaryotes prefer estuarine habitats or at the vicinity of an estuary, Synechococcus spp. was more likely along the coasts without freshwater influence. Picoeukaryotes with high chlorophyll-a content (RedPico III), coccolithophores (HsNano), and Pseudo-nitzschia-like (RedMicro I) were highly marginal revealing a patchy distribution. Finally, the beta regression predicted changes in community composition (i.e., LCBD values) influenced positively by temperature and the distance to the coast and negatively by salinity. The overall contribution of the PFGs to these changes (i.e., Species Contribution to Beta Diversity) was positively linked to their niche position and negatively related to their environmental tolerance. [ABSTRACT FROM AUTHOR]

Purpose: Dicrocoeliosis can be an important cause of production loss in ruminants due to the cost of liver condemnation at slaughter. The aim of the present study was to determine the prevalence of Dicrocoelium infection and to predict the ecological niches and climatic variables that support dicrocoeliosis in the Himalayan ranges of Pakistan. Methods and Results: Dicrocoelium was detected in 33 of 381 liver samples and 238 of 6060 blood samples taken from sheep and goat herds in the area. The prevalence of dicrocoeliosis was higher in sheep than in goats and highest in females aged more than 3 years. An environmental risk map was created to predict active zones of transmission and showed the highest probability values in central parts of the Chitral district in the northwest of Pakistan. Climatic variables of the mean monthly diurnal temperature range (Bio2), annual precipitation (Bio12), and normalised difference vegetation index (NDVI) were found to be significantly (p < 0.05) associated with the presence of Dicrocoelium infection. Conclusion: Together, the findings of this study demonstrate the most suitable ecological niches and climatic variables influencing the risk of dicrocoeliosis in the Himalayan ranges of Pakistan. The methods and results could be used as a reference to inform the control of dicrocoeliosis in the region. [ABSTRACT FROM AUTHOR]

The sympatric complex of the northern Dolly Varden Salvelinus malma from the basin of Lake Azabachye is represented by four forms with a narrow long-term trophic specialization. Lake–river predators feed mainly on three-spined stickleback Gasterosteus aculeatus. Lake–river benthivorous are differentiated into two trophic groups; one of them (group G) feeds on amphipods and the other (group A) consumes mollusks (Mollusca) and caddis fly larvae (Trichoptera). Brook chars feed on amphibiotic insects (Insecta). The long-term food segregation of Dolly Varden forms is confirmed by differences in the degree of infection by parasites and in the ratios of stable isotopes, 15N/14N and 13C/12C, in the muscles. The indicator parasites are Eubothrium salvelini and Dibothriocephalus spp. for lake–river predators, Cystidicola farionis and Crepidostomum metoecus for lake–river benthivorous of group G, Diplostomum spp. for lake–river benthivorous of group A, and Salmonema ephemeridarum and Cucullanus truttae for brook chars. Predators and benthivorous of group G are characterized by high values of the 15N/14N ratio in the muscles, benthivorous of group A by high 13C/12C values, and brook chars by low values of 15N/14N and 13C/12C. Lake–river predators and benthivorous live together and are distributed throughout the lake and lake channel; brook chars inhabit tributaries. The sympatric complex of S. malma in the basin of Lake Azabachye is the second most diverse complex after the char complex in Lake Kronotskoe. [ABSTRACT FROM AUTHOR]

The differentiation by microsites of the population of dung beetles inhabiting horse droppings in the southern Sikhote-Alin, Primorsky krai, has been studied for the first time. The heterogeneity of the substrate has a significant effect on the distribution of beetles among microstations. The key factor affecting the seasonal dynamics of the species composition, abundance, and biomass of beetles in different parts of the droppings are the temperature and humidity regime. It is shown that the confinement of certain species of dung beetles to areas of horse manure can serve as a way of dividing their ecological niches and a way of avoiding competition within one functional group. [ABSTRACT FROM AUTHOR]

The architecture of rice plant represents important and complex agronomic traits, such as panicles morphology, which directly influence the microclimate of rice population and consequently grain yield. To enhance yield, modification of plant architecture to create new hybrid cultivars is considered a sustainable approach. The current study includes an investigation of yield and microclimate response index under low to high plant density of two indica hybrid rice R498 (curved panicles) and R499 (erect panicles), from 2017 to 2018. The split-plot design included planting densities of 11.9–36.2 plant/m2. The results showed that compared with R498, R499 produced a higher grain yield of 8.02–8.83 t/ha at a higher planting density of 26.5–36.2 plant/m2. The response index of light intensity and relative humidity to the planting density of R499 was higher than that of R498 at the lower position of the rice population. However, the response index of temperature to the planting density of R499 was higher at the upper position (0.2–1.4%) than at the lower position. Compared with R498, R499 at a high planting density developed lower relative humidity (78–88%) and higher light intensity (9900–15,916 lx) at the lower position of the rice population. Our finding suggests that erect panicles are highly related to grain yield microclimatic contributors under a highly dense rice population, such as light intensity utilization, humidity, and temperature. The application of erect panicle rice type provides a potential strategy for yield improvement by increasing microclimatic conditions in rice. [ABSTRACT FROM AUTHOR]

The diverse physicochemical conditions prevailing in the Arabian Sea are expected to result in marked spatial variations in heterotrophic flagellate (HF) and ciliate communities. Here, we report the environmental association of heterotrophic micro-eukaryotes, particularly the heterotrophic flagellates and ciliates, based on 18S rRNA gene survey in the region. High-throughput next-generation sequencing, using the V4 eukaryotic-specific primer, was employed to study the composition of these communities associated with low-O2 waters in both coastal and offshore settings. Canonical correspondence analysis (CCA) revealed a preference of the heterotrophic flagellates for nitrate- and nitrite-rich zones. Notably, the heterotrophic nanoflagellate genus Monosiga showed a strong positive correlation with NO3−, which suggests its potential denitrifying capability. Shannon's entropy analysis revealed a higher HF diversity in the hypoxic waters of the open ocean (depth 103 m), whereas ciliates were more diverse at oxygenated coastal stations. The estuarine waters exhibited a low diversity of both ciliates and flagellates. The UPGMA clusters of heterotrophic flagellates and ciliates in suboxic waters of the open ocean oxygen minimum zone were distinct from those found at other sites. Overall, CCA revealed the important relationship between nitrite, nitrate, salinity and chlorophyll a, which could be important factors for the partitioning of different ecological niches for specific HF and ciliate communities in the Arabian Sea. The community of heterotrophic protists that can adapt to varying biogeochemical regimes has been identified. [ABSTRACT FROM AUTHOR]

Context: Island Biogeography Theory and Habitat Amount Hypothesis postulate species richness and densities to increase with connectivity and habitat amount, while niche theory highlights the importance of environmental heterogeneity for species coexistence. Additional ecological niches in heterogeneous landscapes increase species richness and functional and phylogenetic diversity, but larger, less isolated habitats are expected to enlarge species densities by mass effects without effects on functional or phylogenetic diversity. Objectives: We assessed the relative contribution of habitat amount, isolation and environmental heterogeneity on taxonomic, functional and phylogenetic diversity of the particular canga vegetation, i.e., rupestrian savannas associated to banded ironstone outcrops from the Carajás Massif, Eastern Amazon. Methods: We sampled vegetation at 48 sampling points comprising different physiognomies from 5 canga patches. Diversity measures were modelled as response variables in linear mixed models, using non-collinear predictors of habitat amount, isolation and environmental heterogeneity. Results: Diversity and species composition differed among canga physiognomies, indicating that environmental filters segregate canga plant metacommunity in physiognomy-specific species pools. Landscape roughness, a proxy for heterogeneity on the landscape level, increases species densities and functional richness. Additionally, habitat amount was positively associated with the degree of phylogenetic relatedness and functional diversity in communities. Conclusions: Our results suggest that configurational landscape heterogeneity increases the number of available ecological niches, while larger habitat amounts select for functionally and phylogenetically convergent species. These different underlying mechanisms need to be considered for management plans and reserve design for canga ecosystems, so that functional canga portions can be protected. [ABSTRACT FROM AUTHOR]

The fungal P450s catalyze vital monooxygenation reactions in primary and secondary metabolism, which may lead to the production of diverse secondary metabolites. Many of these, such as from the family of trichothecenes, involve in biocontrol activities. The diversified nature of fungal P450 monooxygenases makes their host organisms adoptable to various ecological niches. The available genome data analysis provided an insight into the activity and mechanisms of the fungal P450s. However, still more structural and functional studies are needed to elucidate the details of its catalytic mechanism, and the advance studies are also required to decipher further about their dynamic role in various aspects of trichothecene oxygenations. This mini review will provide updated information on different fungal P450 monooxygenases, their genetic diversity, and their role in catalyzing various biochemical reactions leading to the production of plant growth promoting secondary metabolites. [ABSTRACT FROM AUTHOR]

Understanding how climate and land cover currently shape species distributions and community structure is crucial to inform conservation decisions. Unfortunately, limited information is available for the relative importance of climatic and land use variables in determining the distribution of amphibians and reptiles. Here, we studied amphibian and reptile communities from the Carpathian Mountains, asking (i) to what extent is the distribution of reptiles and amphibians determined by environmental gradients, (ii) does the response to these factors differ between amphibians and reptiles, and (iii) are reptile and amphibian communities at higher altitudes more similar to each other than communities from lower altitudes. We found that forests, pastures, and heterogeneous arable land best explain the composition of the herpetofauna, with mountain communities associated with coniferous forests, and lowland species with mixed or broad-leaved forests and pastures. Our results also suggest that reptiles and amphibians respond idiosyncratically to the influence of climate and land use. Reptiles responded more to land use and less to climate variables compared with amphibians. Of the three amphibian hybrids registered, one (Bombina) was associated with heterogeneous arable land. These results have potential implications for future conservation planning, especially in the light of global climate change and changes in land use. Hence, local and regional processes are important in shaping amphibian and reptile communities. [ABSTRACT FROM AUTHOR]

With the advent of powerful parallel computers, efforts have commenced to simulate complete mammalian brains. However, so far none of these efforts has produced outcomes close to explaining even the behavioral complexities of animals. In this article, we suggest four challenges that ground this shortcoming. First, we discuss the connection between hypothesis testing and simulations. Typically, efforts to simulate complete mammalian brains lack a clear hypothesis. Second, we treat complications related to a lack of parameter constraints for large-scale simulations. To demonstrate the severity of this issue, we review work on two small-scale neural systems, the crustacean stomatogastric ganglion and the Caenorhabditis elegans nervous system. Both of these small nervous systems are very thoroughly, but not completely understood, mainly due to issues with variable and plastic parameters. Third, we discuss the hierarchical structure of neural systems as a principled obstacle to whole-brain simulations. Different organizational levels imply qualitative differences not only in structure, but in choice and appropriateness of investigative technique and perspective. The challenge of reconciling different levels also undergirds the challenge of simulating and hypothesis testing, as modeling a system is not the same thing as simulating it. Fourth, we point out that animal brains are information processing systems tailored very specifically for the ecological niches the respective animals live in. [ABSTRACT FROM AUTHOR]

The genus Scedosporium, which comprises at least five clinically relevant species, i.e. Scedosporium apiospermum, Scedosporium boydii, Scedosporium aurantiacum, Scedosporium dehoogii and Scedosporium minutisporum, ranks the second among the filamentous fungi colonizing the airways of patients with cystic fibrosis (CF). This colonization of the airways is thought to contribute to the inflammatory reaction leading to a progressive deterioration of the lung function. Additionally, these colonizing fungi may lead to severe disseminated infections in case of lung transplantation. Therefore, considering the low susceptibility of Scedosporium species to all current antifungal drugs, preventive measures should be defined to reduce the risk of exposure to these fungi for non-colonized CF patients. With this in mind, several studies have been conducted to elucidate the ecology of these fungi and to define possible sources of patient contamination. This review will summarize the major outcomes of those studies, including: the clear demonstration that ecological niches of Scedosporium species are strongly impacted by human activities, and the ability of Scedosporium species to degrade aliphatic and aromatic pollutants which supports the high occurrence of these species in contaminated soils and polluted waters and makes them promising candidates for bioremediation purposes. Finally, prospects for future research in this field are proposed. [ABSTRACT FROM AUTHOR]

Context: Competitive interactions potentially play an important role in structuring bird communities. It is unclear how differences in functional traits influence the niche dimensions of highly mobile waterbird species, particularly when they co-exist in spatiotemporally heterogeneous communities. Objectives: We investigated the inter-relationships between waterbird trait groupings (movement, dietary and foraging habitat) and environmental variable groupings (rainfall, land cover, vegetation structure and water quality). Specifically, we tested whether the scale of environmental variables filtered movement traits and whether these traits operated in conjunction with dietary and foraging habitat traits to form distinct ecological niches in waterbirds. Methods: We conducted waterbird and environmental variable surveys in 60 sites, sampled seven times each at bimonthly intervals, in KwaZulu-Natal, South Africa. Trait-environment relationships were tested using a combination of RLQ and fourth-corner analyses. Results: Several significant trait-environment relationships emerged in bivariate correlations and multivariate ordination space. Movement traits correlated with the scale of environmental variables; migrant and nomadic species responded to broad scale environmental variables. Vegetation structure and land cover were particularly important in explaining the abundance of species foraging in emergent vegetation. Three groups emerged along a gradient in multivariate ordination space providing evidence for ecological niche separation of waterbirds with different movement traits. Conclusions: Our findings suggest that the scale of landscape resources can act as a filter of movement traits, and that in conjunction with dietary and foraging traits, waterbirds with different movement traits occupy distinct ecological niches. [ABSTRACT FROM AUTHOR]

Here, we investigated the patterns of microbial nitrogen cycling communities along a chronosequence of soil development in a salt marsh. The focus was on the abundance and structure of genes involved in N fixation ( nifH), bacterial and archaeal ammonium oxidation ( amoA; AOB and AOA), and the abundances of genes involved in denitrification ( nirS, nirK, nosZ). Potential nitrification and denitrification activities were also measured, and increases in nitrification were found in soils towards the end of succession, whereas denitrification became maximal in soils at the intermediate stages. The nifH, nirK and nirS gene markers revealed increases in the sizes of the respective functional groups towards the intermediate stage (35 years), remaining either constant (for nifH) or slightly declining towards the latest stage of succession (for nirK and nirS). Moreover, whereas the AOB abundance peaked in soils at the intermediate stage, that of AOA increased linearly along the chronosequence. The abundance of nosZ was roughly constant, with no significant regression. The drivers of changes in abundance and structure were identified using path analysis; whereas the ammonia oxidizers (AOA and AOB) showed patterns that followed mainly N availability, those of the nitrogen fixers followed plant diversity and soil structure. The patterns of denitrifiers were group-dependent, following the patterns of plant diversity ( nirK and nirS) and belowground shifts ( nosZ). The variation observed for the microbial groups associated with the same function highlights their differential contribution at different stages of soil development, revealing an interplay of changes in terms of niche complementarity and adaptation to the local environment. [ABSTRACT FROM AUTHOR]

Bois noir of grapevines is attributed to infection by ' Candidatus Phytoplasma solani' strains, taxonomic subgroups 16SrXII-A, -F, and -G. Plant-to-plant transmission by polyphagous leafhoppers determined that ' Ca. Phytoplasma solani' strains exist in diverse plant hosts in varied ecosystems, where selection conceivably influences intra-species strain diversity. In this study, virtual restriction fragment length polymorphism (RFLP) and single nucleotide polymorphism (SNP) analyses of 16S rDNA nucleotide sequences, amplified from grapevines and bindweeds in central-eastern Italy, revealed the presence of two new subgroups (16SrXII-J and 16SrXII-K) in the 16SrXII group, and of genetically distinct SNP lineages. Findings from the present and related works report the extensive intra-species diversity among ' Ca. Phytoplasma solani' strains in vineyards, underscoring the need for further studies to investigate relationships between diverse phytoplasma strains and dynamics of bois noir epidemiology. [ABSTRACT FROM AUTHOR]

Egypt is the only country in Africa where domestic buffalo have a long-term presence and constitute an important part of the array of domestic animal resources. Attempts to introduce buffalo to other African countries have been made since at least the 1920s. Nine such attempted introductions are documented in this paper, although for most cases, there is very limited information. Buffalo have disappeared without trace in some countries and were slaughtered in at least two because of lack of adaptation or susceptibility to disease. In addition to Egypt, only Tanzania and Mozambique are known to have buffalo in 2012. There are suitable ecological niches for buffalo in many African countries. Failure to provide sufficient financial resources by governments, initially small numbers of animals and probable lack of interest by the private sector are among the reasons for the failure of buffalo to become a contributor to African livestock production. Policy makers and development agencies should very carefully consider the overall benefits against the overall costs of attempted introductions of buffalo (and of other exotic livestock species) in to African countries. [ABSTRACT FROM AUTHOR]

In this study we investigated the temporal variability of N-source utilization of pioneer plant species in different early successional stages of dry acidic grasslands. Current theory states that plant species occupy distinct ecological niches and that there are species-specific, temporal N-uptake patterns. We hypothesized that small-scale dynamics in the natural habitat may affect niche differentiation among plant species. We investigated N-uptake patterns of two co-occurring plant species from different functional groups ( Corynephorus canescens, Rumex acetosella) under natural conditions using N-labeled nitrate and ammonium in three different early successional stages during early and late summer. We found (1) marked seasonal dynamics with respect to N-uptake and N-source partitioning, and (2) different uptake rates across successional stages but a similar N-form utilization of both species. Nitrate was the main N-source in the early and later successional stages, but a shift towards enhanced ammonium uptake occurred at the cryptogam stage in June. Both species increased N-uptake in the later successional stage in June, which was associated with increasing plant biomass in C. canescens, whereas R. acetosella showed no significant differences in plant biomass and root/shoot-ratio between successional stages. Ammonium uptake decreased in both species across all stages with increasing drought. Nevertheless, the peak time of N-uptake differed between the successional stages: in the early successional site, with the lowest soil N, plants were able to extend N-uptake into the drier season when uptake rates in the other successional stages had already declined markedly. Hence, we found a pronounced adjustment in the realized niches of co-occurring plant species with respect to N-uptake. Our results indicate that ecological niches can be highly dynamic and that niche sharing between plant species may occur instead of niche partitioning. [ABSTRACT FROM AUTHOR]

From September 2007 to September 2009, we studied the species of ticks present in the Summit Municipal Park. Ticks were extracted from zoo animals, free-living wild mammals and reptiles trapped, dead mammals on the roads and environment (ground and zoo burrows). A total of 2,649 ticks were collected: 2,167 immature stages (1,345 larvae and 822 nymphs) and 482 adults. Seventeen species were identified: Ornithodoros puertorricensis (Argasidae), Amblyomma auricularium, A. cajennense, A. calcaratum, A. dissimile, A. geayi, A. naponense, A. nodosum, A. oblongoguttatum, A. ovale, A. pecarium, A. sabanerae, A. tapirellum, A. varium, Ixodes luciae, Haemaphysalis juxtakochi and Rhipicephalus sanguineus (Ixodidae), representing 36% of the species reported in Panama. Amblyomma ovale was the species most commonly infesting animals from the zoo. [ABSTRACT FROM AUTHOR]

A combination of culture-dependent and independent methods was used to study the co-existence of different sulfate-reducing bacteria (SRB) in an upflow anaerobic sludge bed reactor treating sulfate-rich wastewater. The wastewater was fed with ethanol as an external electron donor. Twenty six strains of SRB were randomly picked and isolated from the highest serial dilution that showed growth (i.e. 108). Repetitive enterobacterial palindromic polymerase chain reaction and whole cell protein profiling revealed a low genetic diversity, with only two genotypes among the 26 strains obtained in the pure culture. The low genetic diversity suggests the absence of micro-niches within the reactor, which might be due to a low spatial and temporal micro-heterogeneity. The total 16S rDNA sequencing of two representative strains L3 and L7 indicated a close relatedness to the genus Desulfovibrio. The two strains differed in as many as five physiological traits, which might allow them to occupy distinct niches and thus co-exist within the same habitat. Whole cell hybridisation with fluorescently labeled oligonucleotide probes was performed to characterise the SRB community in the reactor. The isolated strains Desulfovibrio L3 and Desulfovibrio L7 were the most dominant SRB, representing 30–35% and 25–35%, respectively, of the total SRB community. Desulfobulbus-like bacteria contributed for 20–25%, and the Desulfobacca acetoxidans-specific probe targeted approximately 15–20% of the total SRB. The whole cell hybridisation results thus revealed a consortium of four different species of SRB that can be enriched and maintained on a single energy source in a full-scale sulfidogenic reactor. [ABSTRACT FROM AUTHOR]

The paper deals with a comparative analysis of the serological and ecological properties of Pseudomonas syringae pv. atrofaciens strains from the collections of microbial cultures at the Malkov Institute for Plant Genetic Resources and Zabolotny Institute of Microbiology and Virology. All of the strains from the Bulgarian collection, except for one, fall into five serogroups (II through VI) of the classification system of Pastushenko and Simonovich. The P. syringae pv. atrofaciens strains isolated from Bulgarian and Ukrainian wheats belong mainly to serogroups II and IV, respectively. The strains that were isolated from rye plants belong to serogroup I. The strains isolated from sorghum and Sudan grass belong to serogroups II, IV, and VI. Serogroup III includes the P. syringae pv. atrofaciens strains that were isolated from cereals in the United Kingdom but not in Ukraine. [ABSTRACT FROM AUTHOR]

This paper analyses the life strategies, the dominance patterns and the diversity in phytoplankton communities in large and deep lakes. The study was carried out on the largest Italian Lake (Lake Garda) from 1995 to 2000. Different statistical analyses were applied. For phytoplankton the time variable represents a complex environmental gradient driving annual succession; this gradient was made explicit by the application of PCA analyses to the environmental data. The use of Non Metric Multi Dimensional Scaling applied to Bray-Curtis dissimilarity matrices revealed an ordered and cyclic development of phytoplankton every year; the Bray-Curtis index, calculated between pairs of chronologically contiguous samples, was also used as a measure of the community change rate (βt) over the temporal succession. A significant relationship between βt and the complex environmental gradient was assessed. Finally, for every phytoplankton species, the optimum conditions for growth and the realised niches were determined. The positioning of the species on the complex environmental gradient, and the contemporaneous application of cluster analysis based on the different specific environmental optima, highlighted primarily the existence of two groups at the extreme of the complex environmental gradient. The first group included the large late winter/spring diatoms, which developed during high water turbulence and strong physical control, high nutrient concentrations, low light conditions and reduced competition. The second group was composed by many heterogeneous summer species characterised by the ability to contrast losses by grazing and sinking in stratified and stable conditions, and the ability of tolerating nutrient deficiency. A third group of species developed during environmental conditions in the middle of the two previous extremes. These included the three master species Mougeotia sp., Fragilaria crotonensis and Planktothrix rubescens/agardhii. The endogenous and exogenous mechanisms promoting species coexistence are discussed, along with the applicability of competitive and equilibrium/non-equilibrium theories to phytoplankton dynamics. [ABSTRACT FROM AUTHOR]

We have investigated interspecific divergence in a eucaryotic gene family, the Balbiani ring genes of the dipteran genus Chironomus. In general, our data show that C. pallidivittatus and C. tentans possess virtually identical Balbiani ring gene sequences, whereas C. thummi represents a more distantly related member of the genus. These results are consistent with phylogenetic relationships for the three species based on polytene chromosome banding patterns. However, one Balbiani ring gene sequence displays an evolutionarily anomalous behavior. A 16-kilobase-pair Balbiani ring gene 1 sequence in C. pallidivittatus that we show to be transcribed is absent in the sibling species C. tentans. We propose that this sequence was deleted in C. tentans after divergence of the species. Considering the importance of Balbiani ring genes for feeding and protection of the Chironomus larvae, we suggest that the pronounced interspecific genetic difference contributes to a difference in ecological niche between the two sympatrically distributed species. [ABSTRACT FROM AUTHOR]