A circular analysis of chronobiology of Schistosoma japonicum cercarial emergence from hilly areas of Anhui,China

About 46 mammal species have been suspected as reservoir hosts for Schistosoma japonicum and therefore the track of the target parasites, in relation to definitive host species, may be of great importance in terms of theoretical and practical implications. The circadian rhythm of cercariae emergence, a genetically controlled behavior for parasites to adapt to their definitive hosts, may seem to be a perfect biological marker for S. japonicum. In this study, a late (or nocturnal) cercarial emergence pattern was observed on the parasites from one hilly region in Anhui of China, where rodents serve as reservoirs, and on the first generation of the parasites. Moreover, by using the circular statistics, the homogeneity of parasites in such trait was also demonstrated. All these provide evidence for the genetically controlled biological trait, which seems essential in the investigation of macro- or micro-dynamics of parasite transmission of interest. This is particularly true in the case of S. japonicum when multiple parasite isolates or strains are more likely to exist.     

Transmission of Schistosoma japonicum in Marshland and Hilly Regions of China: Parasite Population Genetic and Sibship Structure

The transmission dynamics of Schistosoma japonicum remain poorly understood, as over forty species of mammals are suspected of serving as reservoir hosts. However, knowledge of the population genetic structure and of the full-sibship structuring of parasites at two larval stages will be useful in defining and tracking the transmission pattern between intermediate and definitive hosts. S. japonicum larvae were therefore collected in three marshland and three hilly villages in Anhui Province of China across three time points: April and September-October 2006, and April 2007, and then genotyped with six microsatellite markers. Results from the population genetic and sibling relationship analyses of the parasites across two larval stages demonstrated that, within the marshland, parasites from cattle showed higher genetic diversity than from other species; whereas within the hilly region, parasites from dogs and humans displayed higher genetic diversity than those from rodents. Both the extent of gene flow and the estimated proportion of full-sib relationships of parasites between two larval stages indicated that the cercariae identified within intermediate hosts in the marshlands mostly came from cattle, whereas in the hilly areas, they were varied between villages, coming primarily from rodents, dogs or humans. Such results suggest a different transmission process within the hilly region from within the marshlands. Moreover, this is the first time that the sibling relationship analysis was applied to the transmission dynamics for S. japonicum.     

Cercarial shedding patterns of Schistosoma bovis and S. haematobium from single and mixed infections of Bulinus truncatus

The cercarial shedding of Schistosoma bovis and S. haematobium were studied in single and mixed infections in the snail host Bulinus truncatus. The two species displayed a distinctive diurnal cercarial emergence with an earlier shedding pattern for S. bovis than S. haematobium (the average emergence peaks were respectively at 0800 h and 1200 h). In mixed infections, each species kept its own cercarial shedding rhythm with no marked alterations. The cercarial emergence pattern is proposed as a new method to identify natural mixed infections in the snail intermediate hosts. The interactions between the two parasites are discussed.     

Parasite genetic differentiation by habitat type and host species: molecular epidemiology of Schistosoma japonicum in hilly and marshland areas of Anhui Province, China

Schistosoma japonicum , a parasite of significant public health importance in parts of China and Southeast Asia, is a true generalist pathogen with over 40 species of mammals suspected as definitive host reservoirs. In order to characterize levels of parasite gene flow across host species and identify the most important zoonotic reservoirs, S. japonicum larvae (miracidia) were sampled from a range of definitive host species in two contrasting habitat types within Anhui Province, China: a low-lying marshland region, and a hilly region, where animal reservoir populations may be predicted to differ substantially. Miracidia samples were genotyped using seven multiplexed microsatellite markers. Hierarchical F -statistics and clustering analyses revealed substantial geographical structuring of S. japonicum populations within Anhui, with strong parasite genetic differentiation between habitat types. Within most villages, there was very little or no parasite genetic differentiation among host species, suggesting frequent S. japonicum gene flow, and thus also transmission, across species. Moreover, the data provide novel molecular evidence that rodents and dogs are potentially very important infection reservoirs in hilly regions, in contrast to bovines in the marshland regions. The parasite genetic differentiation between habitat types might therefore be associated with contrasting host reservoirs. The high levels of parasite gene flow observed across host species in sympatric areas have important implications for S. japonicum control, particularly in hilly regions where control of infection among wild rodent populations could be challenging.     

Patterns and processes of larval emergence in an estuarine parasite system

Trematode parasites in intertidal estuaries experience constantly varying conditions, with the presence or absence of water potentially limiting larval transport between hosts. Given the short life spans (< or =24 h) of cercariae, emergence timing should be optimized to enhance the probability of successful transmission. In the present study, field measurements and laboratory experiments identified processes that regulate the emergence of cercariae from their first intermediate snail hosts in an intertidal marsh. Larvae emerged over species-specific temperature ranges, exclusively during daylight hours, and only when snails were submerged. The three factors operate over different temporal scales: temperature monthly, light diurnally (24-h period), and water depth tidally (12-h period). Each stimulus creates a necessary condition for the next, forming a hierarchy of environmental cues. Emergence as the tide floods would favor transport within the estuary, and light may trigger direct (downward or upward) swimming toward host habitats. Abbreviated dispersal would retain asexually reproduced cercariae within the marsh, and local mixing would diversify the gene pool of larvae encysting on subsequent hosts. In contrast to the timing of cercarial release, emergence duration was under endogenous control. Duration of emergence decreased from sunrise to sunset, perhaps in response to the diminishing lighted interval as the day progresses. Circadian rhythms that control cercarial emergence of freshwater species (including schistosomes) are often set by the activity patterns of subsequent hosts. In this estuary, however, the synchronizing agent is the tides. Together, exogenous and endogenous factors control emergence of trematode cercariae, mitigating the vagaries of an intertidal environment.     

Protecting evolutionary significant units for the remnant populations of <Emphasis Type="Italic">Berchemiella wilsonii</Emphasis> var. <Emphasis Type="Italic">pubipetiolata</Emphasis> (Rhamnaceae)

Berchemiella wilsonii var. pubipetiolata (Rhamnaceae) is an endangered tree in eastern China. Habitat destruction has resulted in fragmentation of remnant populations and extinction of local populations. AFLP and cpDNA markers were used to determine the population structure of remnant populations of B. wilsonii var. pubipetiolata. Moderate nuclear genomic diversity was found within each of the four remnant populations (H _S = 0.141–0.172), while the cpDNA haplotype diversity in each population ranged from 0.356 to 0.681. Six haplotypes were identified by a combined cpRFLP and cpSSR analysis in a total of 89 individuals. AMOVA revealed significantly AFLP genetic differentiation within and between regions (Φ_SC = 0.196, Φ_CT = 0.396, respectively), and a high cpDNA haplotype differentiation between regions (Φ_CT = 0.849). The results suggest low gene flow between populations of B. wilsonii var. pubipetiolata. Strong genetic divergence between two regional populations as revealed by both AFLP and cpDNA markers provided convincing evidence that two distinct evolutionary lineages existed, and should be recognized as ‘evolutionary significant units’ (ESUs) for conservation concerns.     

Shedding patterns of Schistosoma mansoni and Ribeiroia marini cercariae from a mixed infection of Biomphalaria glabrata

When the snail Biomphalaria glabrata is doubly infected by two species of trematode, Schistosoma mansoni and Ribeiroia marini, each species keeps its own cercarial shedding pattern. Emergence of S. mansoni cercariae occurs during the photophase while the R. marini cercariae are shed during the night. These results demonstrate the absence of interference between the mechanisms responsible for the cercarial shedding of each species. The only difference noted concerns a two-hour shift in the peak emergence of S. mansoni as a consequence of the antagonism between the two parasites.     

Genetic structure of Schstosoma mansoni in western Kenya: The effects of geography and host sharing

We examined the spatial structure of Schistosoma mansoni, a parasite of humans, from natural infections at two levels: across the Lake Victoria basin of Kenya and among snail hosts. Using 20 microsatellite markers we examined geographic patterns of relatedness and population structure of cercariae and found weak, but significant structure detected by some, but not all analyses. We hypothesise structure created by aggregations of clonal individuals or adherence of hosts to local transmission sites is eroded by high amounts of gene flow in the region. This finding also supports previous hypotheses concerning the evolution of drug resistance in the region. Intrasnail dynamics were investigated in the context of aggregation and kin selection theory to determine how relatedness and also sex influence host sharing and host exploitation. Cercarial production did not differ significantly between snails with one or two genotypes suggesting that mixed infections resulted in decreased individual fitness and provides a framework for reproductive competition. Coinfection patterns in snails were independent of parasite relatedness indicating that schistosomes were not aggregated according to their relatedness and that kin selection was not influencing host sharing. Additionally, host exploitation in coinfections (measured by cercarial production) was not negatively correlated with relatedness, as predicted by classical models due to increased competition and thus exploitation when parasites are unrelated. Because of the low levels of relatedness within the population, schistosomes may rarely encounter close relatives and kin selection mechanisms that influence the distribution of individuals within snails or the virulence mode of the parasites may simply have not evolved.     

Gene duplications,divergence and recombination shape adaptive evolution of the fish ectoparasite Gyrodactylus bullatarudis

Determining the molecular basis of parasite adaptation to its host is an important component in understanding host–parasite coevolution and the epidemiology of parasitic infections. Here, we investigate short‐ and long‐term adaptive evolution in the eukaryotic parasite Gyrodactylus bullatarudis infecting Caribbean guppies (Poecilia reticulata), by comparing the reference genome of Tobagonian G. bullatarudis with other Platyhelminthes, and by analysing resequenced samples from local Trinidadian populations. At the macroevolutionary timescale, we observed duplication of G‐protein and serine proteases genes, which are probably important in host–parasite arms races. Serine protease also showed strong evidence of ongoing, diversifying selection at the microevolutionary timescale. Furthermore, our analyses revealed that a hybridization event, involving two divergent genomes, followed by recombination has dramatically affected the genetic composition of Trinidadian populations. The recombinant genotypes invaded Trinidad and replaced local parasites in all populations. We localized more than 300 genes in regions fixed in local populations for variants of different origin, possibly due to diversifying selection pressure from local host populations. In addition, around 70 genes were localized in regions identified as heterozygous in some, but not all, individuals. This pattern is consistent with a very recent spread of recombinant parasites. Overall, our results are consistent with the idea that recombination between divergent genomes can result in particularly successful parasites.     

Intraspecific spatial genetic differentiation of a Daphnia species within a long narrow reservoir

Environmental gradients influence the distribution and taxonomic composition of planktonic taxa, including Daphnia. In canyon-shaped reservoirs with pronounced horizontal gradients of food supply, predation pressure and other factors, not only species and interspecific hybrids but also clones within these taxa are non-randomly distributed. Using a long-term data set from a reservoir mostly dominated by a single Daphnia species, we evaluated whether intraspecific genetic differentiation can be frequently detected between upstream and downstream reservoir regions with different environmental conditions. We analysed variation at four allozyme loci (two species-specific and two polymorphic) to assess the taxonomic composition and intraspecific variation of Daphnia collected in different years (between 1995 and 2005) and periods of the growing season. D. galeata dominated in all samples, although other species and hybrids with D. galeata were also occasionally detected. Despite limited variation at the analysed loci, D. galeata from upstream and downstream regions were significantly genetically differentiated on seven out of twelve sampling dates. Although genetic drift in geographically distant subpopulations may contribute to differentiation, we presume that the observed patterns are primarily due to different selection regimes. We predict that a significant genetic differentiation within planktonic populations also occurs more frequently in natural water bodies.     

Methods used to reveal genetic diversity in the colony-forming prymnesiophytes Phaeocystis antarctica, P. globosa and P. pouchetii—preliminary results

Previous work on the genetic diversity of Phaeocystis used ribosomal DNA and internal transcribed spacer (ITS) sequence analyses to show that there is substantial inter- and intraspecific variation within the genus. First attempts to trace the biogeographical history of strains in Antarctic coastal waters were based on a comparison of ITS sequences. To gain deeper insights into the population structure and bloom dynamics of this microalga it is necessary to quantify the genetic diversity within populations of P. antarctica from different locations (i.e., each of the three major gyres in the Antarctic continental waters) and to calculate the gene flow between them. Here we describe methods to quantify genetic diversity and our preliminary results for P. antarctica in comparison to two other colonial species: P. globosa and P. pouchetii. For this study of genetic diversity, two fingerprinting techniques were used. First, amplified fragment-length polymorphisms (AFLPs) were established as a pre-screening tool to assess clone diversity and to select divergent clones prior to physiological investigations. Second, the more-powerful microsatellite markers were established to assess population structure and biogeography more accurately. Results show differences in the AFLP patterns between isolates of P. antarctica from different regions, and that a wide variety of microsatellite motifs could be obtained from the three Phaeocystis species.     

Genetic variation within and among populations of a wild rice Oryza granulata from China detected by RAPD and ISSR markers

Genetic variation within and between five populations of Oryza granulata from two regions of China was investigated using RAPD (random amplified polymorphic DNA) and ISSR (inter-simple sequence repeat amplification) markers. Twenty RAPD primers used in this study amplified 199 reproducible bands with 61 (30.65%) polymorphic; and 12 ISSR primers amplified 113 bands with 52 (46.02%) polymorphic. Both RAPD and ISSR analyses revealed a low level of genetic diversity in wild populations of O. granulata. Furthermore, analysis of molecular variance (AMOVA) was used to apportion the variation within and between populations both within and between regions. As the RAPD markers revealed, 73.85% of the total genetic diversity resided between the two regions, whereas only 19.45% and 6.70% were present between populations within regions and within a population respectively. Similarly, it was shown by ISSR markers that a great amount of variation (49.26%) occurred between the two regions, with only 38.07% and 12.66% between populations within regions and within a population respectively. Both the results of a UPGMA cluster, based on Jaccard coefficients, and pairwise distance analysis agree with that of the AMOVA partition. This is the first report of the partitioning of genetic variability within and among populations of O. granulata at the DNA level, which is in general agreement with a recent study on the same species in China using allozyme analysis. Our results also indicated that the percentage of polymorphic bands (PPB) detected by ISSR is higher than that detected by RAPD. It seems that ISSR is superior to RAPD in terms of the polymorphism detected and the amplification reproducibility. Received: 29 March 2000 / Accepted: 15 May 2000     

Genetic diversity of Schistosoma mansoni within and among individual hosts (Rattus rattus): infrapopulation differentiation at microspatial scale

The distribution of genetic diversity in a local population of the trematode Schistosoma mansoni was determined within and between individual wild rats at a microspatial geographic scale of a standing water transmission site. Using RAPD markers, molecular variance and canonical correspondence analysis were performed to test the significance of genetic differentiation between infrapopulations. Of total gene diversity, 8 and 11% was partitioned between hosts trapped at few metres distance from each other. Significant temporal differentiation (2%) was also detected among schistosomes sampled at 6 month intervals with more infrapopulation pairs differentiated during the dry season of parasite transmission than during the rainy season (45 and 12%, respectively). A combination of factors such as restricted displacement of rats, patchy spatial aggregation of infected snails and limited cercarial dispersion in standing water are likely to promote the genetic differentiation observed between infrapopulations at this microgeographic scale.     

Distribution of genes and recombination on wheat homoeologous group <Emphasis Type="Italic">6</Emphasis> chromosomes: a synthesis of available information

Presence of genes in gene-rich regions on wheat chromosomes has been widely reported. However, there is a lack of information on the precise characterization of these regions with respect to the distribution of genes and recombination. We attempted to critically analyze the available data to characterize gene-rich regions and to study the distribution of genes and recombination on wheat homoeologous group 6 chromosomes which are a reservoir of several useful genes controlling traits of economic importance. Consensus physical and genetic linkage maps were constructed for homoeologous group 6 using physical and genetic mapping data. Five major gene-rich regions were identified on homoeologous group 6 chromosomes, with two on the short and three on long arm. More than 90% of marker or gene loci were present in these five gene-rich regions, which comprise about 30% of the total physical chromosomal length. The gene-rich regions were mainly present in the distal 60% regions of the chromosomes. About 61% of the total loci map in the most distal regions which span only about 4% of the physical length of the chromosome. A range of sub-microscopic regions within each gene-rich region were also identified. Comparisons of the consensus physical and genetic linkage maps revealed that recombination occurred mainly in the gene-rich regions. Seventy percent of the total recombination occurred in the two most distally located regions that span only 4% of the physical length of the chromosomes. The relationship of recombination to the gene-rich region is not linear with distance from the centromere, especially on the long arm. The kb/cM estimates for group 6 chromosomes ranged from 146 kb in the gene-rich to about 10 Mb in the gene-poor region. The information obtained here is vital in understanding wheat genome structure and organization, which may lead in developing better strategies for positional cloning in wheat and related cereals.This revised version was pubished online in April 2005 with corrections to the page numbering.     

The distributions of autumn picoplankton in relation to environmental factors in the reservoirs along the Wujiang River in Guizhou Province,SW China

Autumn picoplankton (Synechococcus, picoeukaryotes and heterotrophic bacteria) and environmental factors have been investigated in a series of reservoirs along the Wujiang River in Guizhou Province, SW China. The average abundances of Synechococcus, picoeukaryotes and heterotrophic bacteria was 10⁴, 10² and 10⁶ cells ml⁻¹, respectively. In autumn meso-eutrophic reservoirs, thermal stratification was clear and abundances of different picoplankton groups in release water was low; whereas these phenomena were not obvious in autumn hypereutrophic reservoir. Picoplankton numbers decreased with increasing water depth and showed a positive correlation with water temperature, which reflected the importance of light and temperature on the picoplankton growth. Contribution of Synechococcus to total phytoplankton production and contribution of picoeukaryotes to total phytoplankton production asynchronous changed with varying trophic states. Synechococcus preferred meso-eutrophic reservoirs over hypereutrophic reservoir and picoeukaryotes showed no preference for the investigated reservoirs in autumn. Handling editor: L. Naselli-Flores     

Schistosoma mansoni and Schistosoma haematobium: Emergence of schistosome cercariae from snails with darkness and illumination

Biomphalaria glabrata and Bulinus globosus were infected with Schistosoma mansoni and Schistosoma haematobium, respectively, and the effect of different illumination conditions at 25 C on cercarial output was observed for 4 days. In both species, a dark period of 10–14 hr on Day 2 of the observation period resulted in an emergence pattern on Day 3 similar to the regular pattern recorded for Day 1. Total cercarial output on Day 3 was within 30% of the control (Day 1) output. A dark period of between 0 and 8 hr resulted in suppression of cercarial emergence and in abolishment of the regular hourly emergence pattern on Day 3. A dark period of 16–20 hr resulted in an emergence pattern with two peaks, the first occurred at Hour 1, and the other at Hour 5 of the subsequent light period. Interjection of a 1-hr dark period during the light period of Day 3, following short (2–8 hr) exposure to dark on the preceding day, produced an increase in cercarial shedding of S. mansoni immediately after restitution of the light conditions. On the other hand, in S. haematobium, cercarial output was stimulated during the interposed dark period itself.     

The Freshwater Animal Diversity Assessment: an overview of the results

The geographic genetic structure of two common encrusting sponges, Hymeniacidon sinapium and Hymeniacidon flavia (family Halichondriidae), was investigated using two DNA markers, Internal Transcribed Spacers (ITS) of nuclear ribosomal DNA and NADH dehydrogenase subunit 5 (nad5) of mitochondrial DNA. In the ITS analyses, multiple sequence types were identified within each species. Geographic distribution patterns of sequence types showed higher diversity in the western than eastern areas in both species. However, intraspecific genetic diversity of the two species in Japan differed markedly. Hymeniacidon flavia had far more diverse sequence types, and several genetic differentiations between localities were detected. In contrast, H. sinapium had only four sequence types in Japan, and two Atlantic Hymeniacidon species had sequence types similar to this species. In comparison to ITS, nad5 showed very low genetic diversity in both species, with two haplotypes identified in each species. In H. flavia, frequency of haplotype changed gradually from north to south. In H. sinapium, one haplotype was predominant in most regions, and another haplotype was minor and distributed only in the Korean and Tsushima populations. Based on the unique distribution patterns of sequence types around Shikoku and Kyushu, geographical history and ocean currents were assumed to affect the generation of genetic structure. The geographic genetic structure of H. flavia suggests low dispersal ability of pelagic larvae, whereas higher larval dispersal ability and a far broader distribution range are suggested in H. sinapium. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: C. Sturmbauer     

Allozyme variation in the diploid (A genome) populations ofScilla scilloides (Hyacinthaceae)

Allozyme variation at eleven loci encoding seven enzyme systems were examined in 20 populations of diploid (genome AA, 2n = 16)Scilla scilloides in China. In comparison with the average species of seed plants studied, populations of this species display a high amount of genetic variation (A = 2.0, P = 58.6%, H_o = 0.172, and H_e = 0.185). Allozyme variation pattern revealed predominant outcrossing within populations and considerable differentiation (F_ST = 0.314) among populations as well as between the subtropic and temperate regions. The wide distribution, long existence and outcrossing are presumably the main factors responsible for the high genetic diversity within populations. But the gravity dispersal of seeds and pollination by small insects set limits to the increase of genetic variation within populations and promote differentiation between populations and regions. In addition, allozyme variation does not distinguishS. scilloides var.albo-viridis and suggests that subtropic populations may be considered as a genetic entity.     

Variation in life history and genetic traits of Hawaiian mosquitofish populations

Mosquitofish (Gambusia affinis) were collected from 17 reservoirs on three islands in Hawaii, USA. Genetic and life history traits for adult females from these populations were used to evaluate hypotheses concerning short-term evolutionary divergence of populations recently established from a common ancestral source. The effects of founder events and drift on genetic variability and population differentiation were also examined. Significant differences in life history characteristics, allele frequencies, and multi-locus heterozygosities (H) were found among fish populations collected from different reservoirs and between reservoirs classified as stable or fluctuating on the basis of temporal fluctuation in water level. Females from stable reservoirs exhibited greater standard length (35.1 vs 32.8 mm), lower fecundity (11.9 vs 15.2 embryos), lower reproductive allocation (18.2% vs 22.8%), but larger mean embryo size (1.95 vs 1.67 mg) than females from fluctuating reservoirs. Consistency in means among replicates of each reservoir class and concordance in direction and magnitude of differences reported here and results of sampling conducted from these same locations 10 years previously (Stearns, 1983a) suggest that ecological factors intrinsic to these two environments are important in determing population life history traits. Females from stable reservoirs exhibited lower heterozygosity than females from fluctuating reservoirs (0.134 vs 0.158, respectively). Levels and direction od differences in heterozygosity, the high proportion of polymorphic loci and lack of fixation of alternative alleles argue against a purely stochastic explanation for genetic and life history variation among reservoir populations. Levels of genetic variability and interpopulation differentiation were similar to those observed in mainland populations of this species. A high proportion of the genetic diversity was apportioned between populations and within populations due to differences between juveniles and adults. Significant genotypic differences between adult and juvenile age classes suggest that the genetic divergence of local populations may occur over short periods of time.