Space Use Variation in Co-Occurring Sister Species: Response to Environmental Variation or Competition?

Coexistence often involves niche differentiation either as the result of environmental divergence, or in response to competition. Disentangling the causes of such divergence requires that environmental variation across space is taken into account, which is rarely done in empirical studies. We address the role of environmental variation versus competition in coexistence between two rodent species: Rhabdomys bechuanae (bechuanae) and Rhabdomys dilectus dilectus (dilectus) comparing their habitat preference and home range (HR) size in areas with similar climates, where their distributions abut (allopatry) or overlap (sympatry). Using Outlying Mean Index analyses, we test whether habitat characteristics of the species deviate significantly from a random sample of available habitats. In allopatry, results suggest habitat selection: dilectus preferring grasslands with little bare soil while bechuanae occurring in open shrublands. In sympatry, shrubland type habitats dominate and differences are less marked, yet dilectus selects habitats with more cover than bechuanae. Interestingly, bechuanae shows larger HRs than dilectus, and both species display larger HRs in sympatry. Further, HR overlaps between species are lower than expected. We discuss our results in light of data on the phylogeography of the genus and propose that evolution in allopatry resulted in adaptation leading to different habitat preferences, even at their distribution margins, a divergence expected to facilitate coexistence. However, since sympatry occurs in sites where environmental characteristics do not allow complete species separation, competition may explain reduced inter-species overlap and character displacement in HR size. This study reveals that both environmental variation and competition may shape species coexistence.     

Natural Genetic Variation in a Multigenerational Phenotype in C. elegans

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School Variation in Asthma: Compositional or Contextual?

Background

Childhood asthma prevalence and morbidity have been shown to vary by neighborhood. Less is known about between-school variation in asthma prevalence and whether it exists beyond what one might expect due to students at higher risk of asthma clustering within different schools. Our objective was to determine whether between-school variation in asthma prevalence exists and if so, if it is related to the differential distribution of individual risk factors for and correlates of asthma or to contextual influences of schools.

Methods

Cross-sectional analysis of 16,640 teens in grades 7–12 in Wave 1 (data collected in 1994–5) of the National Longitudinal Study of Adolescent Health. Outcome was current diagnosis of asthma as reported by respondents'' parents. Two-level random effects models were used to assess the contribution of schools to the variance in asthma prevalence before and after controlling for individual attributes.

Results

The highest quartile schools had mean asthma prevalence of 21.9% compared to the lowest quartile schools with mean asthma prevalence of 7.1%. In our null model, the school contributed significantly to the variance in asthma ( = 0.27, CI: 0.20, 0.35). Controlling for individual, school and neighborhood attributes reduced the between-school variance modestly ( = 0.19 CI: 0.13–0.29).

Conclusion

Significant between-school variation in current asthma prevalence exists even after controlling for the individual, school and neighborhood factors. This provides evidence for school level contextual influences on asthma. Further research is needed to determine potential mechanisms through which schools may influence asthma outcomes.     

Variation in Ambrosia pollen concentration in Southern and Central Poland in 1982–1999

The aim of the study was to investigate theAmbrosia pollen concentrations inselected Polish cities and for Kraków torelate it to some meteorological factors.Sampling was carried out in Kraków in1982–1997 and in Rabka in 1992–1996 with theuse of the gravimetric method. In Zakopane,Kraków, Ostrowiec witokrzyski,Warszawa and Pozna in 1995–1996 both thegravimetric and volumetric methods (Burkardtrap) were employed. In Kraków themonitoring has been performed since 1994 usingthe volumetric method. The results show theragweed pollen presence in August and Septemberwith the tendency to appear more frequently inAugust in some years. In Kraków (1994–1999)Ambrosia pollen was found either in thelast two weeks of August or in the first twoweeks of September which seems to be a regularand repeatable pattern every two years.Seasonal fluctuations of Ambrosia pollenconcentration do not show a clear increasingtendency except at Warszawa and Ostrowiecwitokrzyski in 1996 and at Krakówin 1999. Percentage of Ambrosia pollen inannual sums of total pollen is very low anddoes not exceed 1% except at Ostrowiecwitokrzyski in 1996 (1.2%) and atKraków in 1999 (2%). For Kraków theanalysis of some meteorological factors (Tmax,Tmin, precipitation, wind direction) wasperformed. High temperature and lack of rain orlow precipitation correlate well with ragweedpollen concentrations. During the Ambrosia pollen seasons ESE, E, S, SE, WSW, SWwind directions prevailed which could suggest along-distance transport from Ukraine, the CzechRepublic, Slovakia and also from Hungary, one ofthe most ragweed-polluted countries.     

Somaclonal Variation in a Food Legume—Lathyrus sativus

Somaclones of Lathyrus sativus cv P-24 were obtained from leaf, internode and root derived callus cultures. These showed significantly decreased neurotoxin (ODAP) content up to 0.03% compared to that of parent cultivar P-24 (0.3%). The somaclones also showed higher seed yield than parent P24. In addition. somaclone Bio 1–22 showed significantly decreased time for flowering. Other heritable morphological variant features were leaf length, leaf breadth, internode length, flower colour, seed colour, 100 seed weight, neurotoxin content of leaves and red markings on the pods.     

Variation in the fixation image of “Structured granules” in Anabaena

Summary The varied appearance of so-called structured granules in vegetative cells and akinetes of Anabaena sp. is dependent upon the length of primary glutaraldehyde fixation, the type and duration of secondary fixation, and the temperature during both fixations as well as possible changes under electron bombardment. The image produced may be one of an open hole, an area of low to medium electron opacity or that of a dense structured body and may include all intergradations. These structured granules represent the cyanophycin granules of light microscopy. Various cytochemical tests did not establish their chemical composition.     

Experimentelle Untersuchungen über individuelle Variation in der tierischen Entwicklung

Ohne ZusammenfassungDie Versuche, über die ich in dieser Arbeit berichtet habe, sind im März und April der Jahre 1905 und 1906 in der zoologischen Station zu Neapel ausgeführt worden. Im ersten Jahre wurde mir ein Arbeitsplatz von der Kgl. bayrischen Regierung, im zweiten von der Kgl. preußischen Regierung zur Verfügung gestellt. Die Kgl. Akademie der Wissenschaften bewilligte mir für die Ausführung meiner Arbeiten eine einmalige Dotation von 1200 Mark, wofür ich der hohen Körperschaft meinen ergebensten Dank ausspreche. Mein herzlichster Dank gebührt auch dem Leiter des altberühmten Instituts, Herrn GeheimratDohrn, der mir sogar persönlich gestattete, über die bewilligte Zeit hinaus in der Anstalt tätig zu sein. Den Herren Beamten des Instituts bin ich ebenfalls zu hohem Danke verpflichtet, da sie meine Arbeit in jeder Hinsicht förderten; Herr Dr.Lo BIANCO sorgte in liebenswürdiger Weise dafür, daß mir das Untersuchungs-material nie ausging. Endlich fügte es ein glücklicher Zufall, daß bei meinem ersten Aufenthalt Herr Prof.Boveri und die Herren Dr.Driesch und Prof.Herbst in Neapel anwesend waren, durch deren freundliche Ratschläge ich in den Stand gesetzt wurde, mich sehr bald in das mir gänzlich fremde Untersuchungsmaterial einzuarbeiten; auch diesen Herren herzlichsten Dank!     

Altitudinal Variation in Digestive Tract Length in Yunnan Pond Frog （Pelophylax pleuraden）

The digestive tract plays an important role in digestion and the acquisition of food energy. Understanding the impact of abiotic environments on digestive tract morphology is especially important for evolution of digestive tract across different environments. Here, we investigated altitudinal variation in digestive tract length in the Yunnan Pond Frog （Pelophylaxpleuraden） across five populations ranging from 1413 m to 1935 m a.s.1, in Ningnan County, Sichuan province in western China. Frogs were collected during the breeding season, from 1-5 June 2012. Our results revealed that females had longer digestive tract and relative digestive tract （i.e. digestive tract length / body size） lengths in com- parison to males, on average, but the differences between them decreased with increasing altitude. Digestive tract and relative digestive tract lengths increased with increasing altitude suggesting that a higher proportion of indigestible ma- terials may be consumed at high-altitude sites and result in a relative increase in digestive tract dimensions.     

Variation of seed α-amylase inhibitors in the common bean

Variation of seed -amylase inhibitors was investigated in 1 154 cultivated and 726 non-cultivated (wild and weedy) accessions of the common bean, Phaseolus vulgaris L. Four -amylase inhibitor types were recognized based on the inhibtion by seed extracts of the activities of porcine pancreatic -amylase and larval -amylase and larval -amylase of the Mexican bean weevil, Zabrotes subfasciatus Boheman. Of the 1 880 accessions examined most (1 734) were able to inhibit porcine pancreatic -amylase activity, but were inactive against the Z. subfasciatus larval -amylase; 41 inhibited only the larval -amylase activity, 52 inhibited the activities of the two -amylases, and 53 did not inhibit the activity of either of the -amylases. The four different inhibitor types were designated as AI-1, AI2, AI-3, and AI-0, respectively. These four inhibitor types were identified by the banding patterns of seed glycoproteins in the range of 14–20 kDa by using SDSpolyacrylamide gel electrophoresis. Additionally, four different banding patterns were recognized in accessions with AI-1, and were designated as AI-1a, 1b, 1c, and 1d. Two different patterns of the accessions lacking an -amylase inhibitory activity were identified and designated as AI-0a and AI-0b. The largest diversity for seed -amylase inhibitors was observed in non-cultivated accessions collected from Mexico where all eight inhibitor types were detected. The possible relationships between the variation of seed -amylase inhibitors and bruchid resistance are discussed.     

Consequences of Interspecific Competition on the Virulence and Genetic Composition of a Nucleopolyhedrovirus in Spodoptera frugiperda Larvae Parasitized by Chelonus insularis

Nucleopolyhedroviruses ( Baculoviridae ) are virulent insect pathogens that generally show a high degree of host specificity and have recognized potential as biological insecticides. Whenever viruses are applied for pest control, a proportion of the infected insects will also be parasitized by hymenopteran or dipteran parasitoids and interspecific competition for host resources will occur; the severity of such competition is likely to be modulated to a large degree by the virulence of each type of parasite. We examined the impact of parasitism by the solitary egg-larval endoparasitoid Chelonus insularis (Hymenoptera: Braconidae) on the speed of kill of nucleopolyhedrovirus-infected Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae and the pattern of host growth and virus production in infected and/or parasitized hosts. We also examined the effect of parasitism on the virulence, infectivity and genetic composition of serially passaged virus. Both parasitism and viral infection resulted in a marked reduction in host growth. When third instar larvae were dually parasitized and virus-infected, the growth rate was even more severely affected compared to parasitized larvae. There was a significant increase in virus production in larvae infected at later instars. Interspecific competition resulted in a substantial decrease in pathogen production in parasitized larvae infected at the fourth instar, but not in parasitized larvae infected at earlier instars. The serial passage experiment resulted in the appearance of four distinct genetic isolates of the virus detected by restriction endonuclease analysis. Of the three isolates that appeared in nonparasitized larvae, two showed increased virulence, expressed by mean time to death, and for one of these the infectivity, expressed as LC 50 , was reduced. One isolate that appeared in parasitized larvae (isolate D) had increased virulence and infectivity. Southern blot analysis indicated that virus isolate D was most likely generated by point mutation of a restriction site or by alterations such as duplications, deletions or by recombination of two or more genotypic variants present in the wild-type nucleopolyhedrovirus isolate. Our study provides clear evidence of interspecific competition within the host, since, depending on the timing of inoculation, adverse effects were observed upon both the parasitoid and the virus.     

Characterization of Vibrio cholerae O1 isolates responsible for cholera outbreaks in Kenya between 1975 and 2017

Kenya is endemic for cholera with different waves of outbreaks having been documented since 1971. In recent years, new variants of Vibrio cholerae O1 have emerged and have replaced most of the traditional El Tor biotype globally. These strains also appear to have increased virulence, and it is important to describe and document their phenotypic and genotypic traits. This study characterized 146 V. cholerae O1 isolates from cholera outbreaks that occurred in Kenya between 1975 and 2017. Our study reports that the 1975–1984 strains had typical classical or El Tor biotype characters. New variants of V. cholerae O1 having traits of both classical and El Tor biotypes were observed from 2007 with all strains isolated between 2015 and 2017 being sensitive to polymyxin B and carrying both classical and El Tor type ctxB. All strains were resistant to Phage IV and harbored rstR, rtxC, hlyA, rtxA and tcpA genes specific for El Tor biotype indicating that the strains had an El Tor backbone. Pulsed field gel electrophoresis (PFGE) genotyping differentiated the isolates into 14 pulsotypes. The clustering also corresponded with the year of isolation signifying that the cholera outbreaks occurred as separate waves of different genetic fingerprints exhibiting different genotypic and phenotypic characteristics. The emergence and prevalence of V. cholerae O1 strains carrying El Tor type and classical type ctxB in Kenya are reported. These strains have replaced the typical El Tor biotype in Kenya and are potentially more virulent and easily transmitted within the population.     

Phenotypic variation and genomic variation in insect virulence traits reveal patterns of intraspecific diversity in a locust-specific fungal pathogen

Intraspecific pathogen diversity is crucial for understanding the evolution and maintenance of adaptation in host–pathogen interactions. Traits associated with virulence are often a significant source of variation directly impacted by local selection pressures. The specialist fungal entomopathogen, Metarhizium acridum, has been widely implemented as a biological control agent of locust pests in tropical regions of the world. However, few studies have accounted for natural intraspecific phenotypic and genetic variation. Here, we examine the diversity of nine isolates of M. acridum spanning the known geographic distribution, in terms of (1) virulence towards two locust species, (2) growth rates on three diverse nutrient sources, and (3) comparative genomics to uncover genomic variability. Significant variability in patterns of virulence and growth was shown among the isolates, suggesting intraspecific ecological specialization. Different patterns of virulence were shown between the two locust species, indicative of potential host preference. Additionally, a high level of diversity among M. acridum isolates was observed, revealing increased variation in subtilisin-like proteases from the Pr1 family. These results culminate in the first in-depth analysis regarding multiple facets of natural variation in M. acridum, offering opportunities to understand critical evolutionary drivers of intraspecific diversity in pathogens.     

Detection of double stranded RNA in phytopathogenic <Emphasis Type="Italic">Macrophomina phaseolina</Emphasis> causing charcoal rot in <Emphasis Type="Italic">Cyamopsis tetragonoloba</Emphasis>

One hundred one isolates of Macrophomina phaseolina from various hosts and eco-geographical locations were employed for elucidating relationships among genetic diversity and virulence. Highly pathogenic, moderately pathogenic, and hypovirulent cluster bean specific isolates were identified. In order to correlate respective phenotypes of plant pathogenic fungus multiple and complex patterns of dsRNA elements were analyzed. Double-stranded ribonucleic acids (dsRNA) are ubiquitous in all major groups and most of them have vast potential as biological control agents for fungi. Rate of virulence and its further association could ascertain by host plant and their fungal genotypes. Variability of the fungal genotypes decides the link between the complexity of dsRNA with different variants and the change in virulence pattern. Double-stranded RNA was identified in approximately 21.7% of M. phaseolina isolates from charcoal rot infected cluster bean varieties. After recurrent laboratory transfer on culture media, the preponderance of the isolates harboring dsRNAs developed degenerate culture phenotypes and showed reduced virulence (hypovirulence) to cluster bean. Macrophomina has successfully showed diversified and reproducible banding profile in dsRNA containing/free isolates. This is the first report of hypovirulence and detection of dsRNA in Macrophomina phaseolina isolates of cluster bean origin.     

Antigenic variation of pilin regulates adhesion of Neisseria meningitidis to human epithelial cells

Pili have been shown to play an essential role in the adhesion of Neisseria meningitidis to epithelial cells. However, among piliated strains, both inter- and intrastrain variability exist with respect to their degree of adhesion to epithelial cells in vitro (Virji et al., 1992). This suggests that factors other than the presence of pili per se are involved in this process. The N. meningitidis pilin subunit undergoes extensive antigenic variation. Piliated low- and high-adhesive derivatives of the same N. meningitidis strain were selected and the nucleotide sequence of the pilin gene expressed in each was determined. The highly adhesive derivatives had the same pilin sequence. The alleles encoding the pilin subunit of the low-adhesive derivatives were completely different from the one found in the high-adhesive isolates. Using polyclonal antibodies raised against one hyperadhesive variant, it was confirmed that the low-adhesive piliated derivatives expressed pilin variants antigenically different from the highly adhesive strains. The role of antigenic variation in the adhesive process of N. meningitidis was confirmed by performing allelic exchanges of the pilE locus between low-and high-adhesive isolates. Antigenic variation has been considered a means by which virulent bacteria evade the host immune system. This work provides genetic proof that a bacterial pathogen, N. meningitidis, can use antigenic variation to modulate their degree of virulence.     

FINE-SCALE GENETIC AND PHENOTYPIC STRUCTURE IN NATURAL POPULATIONS OF BACILLUS SUBTILIS AND BACILLUS LICHENIFORMIS: IMPLICATIONS FOR BACTERIAL EVOLUTION AND SPECIATION

The genetic and phenotypic structure of sympatric populations of wild bacteria traditionally identified as Bacillus subtilis and B. licheniformis was analyzed. Small soil samples were taken from a single, tiny site in the Sonoran Desert of Arizona, USA, to provide a true population analysis, in contrast to many analyses of genetic structure using bacterial strain collections of widely heterogeneous origin. Genetic analyses of isolates used multilocus enzyme electrophoresis, mismatches in restriction fragment length polymorphism, and variants from Southern hybridization with B. subtilis DNA probes. Phenotypic analyses of isolates used the API test system for detection of growth and acid production on specific carbon sources. The two species were distinct both phenotypically and genetically, despite their known potential for genetic exchange in laboratory experiments. Genic and genotypic diversity were high in both species, and only 16% of observed allozyme variants might possibly be common to both species. Hence, there is probably modest genetic exchange, if any, between the species in nature. Clear hierarchies of population-genetic structure were found for both species. Different types of genetic data yield concordant population structures for B. subtilis. For both species, two-locus and multilocus statistical analyses of linkage demonstrated modest to strong disequilibrium at the species level but truly panmictic subunits within each species. The evidence for extensive genetic recombination within these fine-scale subdivisions is unequivocal, indicating that the sexuality of these bacteria can be well expressed in nature. The relation of these results to processes of bacterial evolution and speciation is discussed.     

Cellular Reaction to Mycobacterium avium Complex (MAC) Clinical Isolates Differing in Hemolytic Activity and Virulence for C57BL/6 Mice

In this study we showed that Mycobacterium avium complex (MAC) clinical isolates differed by the expression of hemolytic activity. Two hemolytic MAC strains were less susceptible to the mycobactericidal effect of murine macrophages than two unhemolytic MAC isolates. In vivo, hemolytic MAC bacilli survived in the spleens of infected mice for a longer time than unhemolytic MAC strains. This suggested a role of hemolysins in the virulence of MAC strains. There was no difference in the cytotoxicity of T cells from mice immunized with M. bovis BCG towards macrophages infected in vitro with MAC strains expressing or not expressing hemolytic activity.     

Genetic variation in a host-parasite association: potential for coevolution and frequency-dependent selection

Abstract.— Models of host‐parasite coevolution assume the presence of genetic variation for host resistance and parasite infectivity, as well as genotype‐specific interactions. We used the freshwater crustacean Daphnia magna and its bacterial microparasite Pasteuria ramosa to study genetic variation for host susceptibility and parasite infectivity within each of two populations. We sought to answer the following questions: Do host clones differ in their susceptibility to parasite isolates? Do parasite isolates differ in their ability to infect different host clones? Are there host clone‐parasite isolate interactions? The analysis revealed considerable variation in both host resistance and parasite infectivity. There were significant host clone‐parasite isolate interactions, such that there was no single host clone that was superior to all other clones in the resistance to every parasite isolate. Likewise, there was no parasite isolate that was superior to all other isolates in infectivity to every host clone. This form of host clone‐parasite isolate interaction indicates the potential for coevolution based on frequency‐dependent selection. Infection success of original host clone‐parasite isolate combinations (i.e., those combinations that were isolated together) was significantly higher than infection success of novel host clone‐parasite isolate combinations (i.e., those combinations that were created in the laboratory). This finding is consistent with the idea that parasites track specific host genotypes under natural conditions. In addition, correspondence analysis revealed that some host clones, although distinguishable with neutral genetic markers, were susceptible to the same set of parasite isolates and thus probably shared resistance genes.     

Genotypic and phenotypic diversity of a baculovirus population within an individual insect host

It is becoming increasingly apparent that many pathogen populations, including those of insects, show high levels of genotypic variation. Baculoviruses are known to be highly variable, with isolates collected from the same species in different geographical locations frequently showing genetic variation and differences in their biology. More recent studies at smaller scales have also shown that virus DNA profiles from individual larvae can show polymorphisms within and between populations of the same species. Here, we investigate the genotypic and phenotypic variation of an insect baculovirus infection within a single insect host. Twenty four genotypically distinct nucleopolyhedrovirus (NPV) variants were isolated from an individual pine beauty moth, Panolis flammea, caterpillar by in vivo cloning techniques. No variant appeared to be dominant in the population. The PaflNPV variants have been mapped using three restriction endonucleases and shown to contain three hypervariable regions containing insertions of 70-750 bp. Comparison of seven of these variants in an alternative host, Mamestra brassicae, demonstrated that the variants differed significantly in both pathogenicity and speed of kill. The generation and maintenance of pathogen heterogeneity are discussed.     

Genetic variation and recombination in Penicillium miczynskii and Eupenicillium species

Reproduction in the genus Penicillium is thought to be completely asexual. Sexual reproduction, as occurs in the related genus Eupenicillium, is thought to provide evolutionary benefits because it allows for new combinations of alleles and therefore increases the amount of variation within the species. This hypothesis was tested using inter-simple sequence repeats (ISSRs) to assess the amount of intraspecific and intra-population variation within Penicillium miczynskii and the closely related Eupenicillium shearii. The data for both genera were also used to test for clonal reproduction against the null hypothesis of panmixis, using measures of genotypic diversity, linkage disequilibrium and phylogenetic tree length. The ISSR fingerprints indicated that the 70 Eupenicillium strains actually included two distinct species, Eupenicillium shearii and Eupenicillium tropicum sp. nov., each represented by populations in both Costa Rica and India. While none of the species or populations were found to be randomly recombining, the relative strength of the clonal component differed among the species. Penicillium miczynskii had the smallest clonal component, with the highest genotypic diversity, lowest Index of Association, 40 % of alleles non-randomly associated, and phylogenetic tree length closer to that of recombined data sets than to the minimum possible. Eupenicillium tropicum showed nearly complete clonal reproduction with the lowest genotypic diversity and 100 % of alleles non-randomly associated in both populations. On the other hand, it also had the greatest amount of intraspecific variation, with as little as 38 % similarity among strains. The results indicate that Penicilliumspecies may, on rare occasion, genetically recombine; the regular occurrence of meiosis in the life cycle of Eupenicilliumspecies does not facilitate recombination; and the greatest amount of genetic variation was not associated with recombination, but with clonal propagation.