Shifts In Population Structure Research Articles

Enamel thickness per masticatory phases (ETMP): A new approach to assess the relationship between macrowear and enamel thickness in the human lower first molar

Many anthropological studies have examined the functional implications of enamel thickness in human dental crowns. Despite limitations, Enamel thickness (ET) values are still used to infer taxonomic attribution in the genus Homo, and to identify mechanisms of functional adaptation against macrowear. However, only a few studies have tried to describe the possible relationship between ET and dental wear patterns in permanent lower first molars (M1) aiming to observe whether an adaptive response to the environmental and cultural context is detectable. The present work aims to investigate a possible signal of ET adaptive response in M1 (wear stage 3; Molnar, 1971) belonging to individuals who lived between the Neolithic (early 6th millennium BCE) and the Bronze Age (second half of the 2nd millennium BCE) in Croatia to identify any signal of change in dental tissue proportions based on archaeologically documented shifts in population structure and subsistence strategies. In order to do so, we explored 3D Average Enamel Thickness (AET) of the entire crown and wear pattern distribution among individuals and across chronological groups. We then described a new method called “Enamel Thickness per Masticatory Phases” (ETMP) involving the creation of virtual sections cutting enamel and coronal dentine in three parts based on masticatory phases, and explored the distribution of 3D AET accordingly. Finally, we performed geometric morphometric analysis on dental crown to ascertain possible morphological differences between Neolithic, Eneolithic, and Bronze Age groups. Results show that Bronze Age individuals differ from previous groups due to 1) higher values of ET in both the entire crown and specifically in the buccal area, 2) to an extensive wear pattern localized on the buccal side, and 3) to the distal extension of the hypoconid together with an extended mesio-distal shape of the crown. These patterns may represent an adaptive response of dental tissue to varying functional demands (e.g. archaeologically documented dietary shift). The study of ETMP therefore offers a more nuanced method, in addition to morphology and macrowear analysis, to document biocultural processes of change over time in archaeological populations through dental tissues.

An Empirical Study on the Impact of Regional Population Age Structure on Urban and Rural Economic Growth

Whilst the shift in population structure remains one of the pivotal factors influencing urban and rural economic growth, a thorough probe into the relationship between the two is of important significance for beefing up economic growth in both urban and rural areas. On the basis of the results of literature analysis, this paper analyzes the theories related to regional population structure and urban and rural economic growth, builds an analysis model of the impact of regional population structure on urban and rural economic growth, and selects Fujian Province as the research object, combining multiple linear regression to carry out empirical analysis. Our results reveal that the shift in population structure would boost economic growth to a certain extent, yet due attention must be paid to improving the quality of population in order to avoid the decline in economic growth rate caused by the increase in old-age dependency ratio.

Temporal trends of two iconic Mediterranean gorgonians (Paramuricea clavata and Eunicella cavolini) in the climate change context

Gorgonians are iconic species of Mediterranean benthic communities. They are ecosystem engineers and their conservation is essential for the biodiversity of marine communities. Yet these long-lived species are particularly vulnerable to natural or anthropogenic disturbances. The objective of this study is to define the demographic characteristics and health status of the gorgonian forests for two species of gorgonians Paramuricea clavata (Risso, 1826) and Eunicella cavolini (Koch, 1887) over fifteen years. The potential impact of changing environmental conditions is assessed by studying, at different depths, trends in temperature and planktonic changes (phytoplankton biomass and zooplankton abundance) over the study period. Our results indicate that there is a change in population structure of the two gorgonian species with a significant decrease in recruitment in recent years. For E. cavolini, the necrosis significantly increased between 2004 and 2019 (from 9.66% to 25.63% of injured colonies and from 0.24% to 4.75% of dead colonies, respectively). For P. clavata, the population was particularly damaged in 2004 with 14.81% of dead colonies. While necrosis significantly decreased between 2004 and 2014, a significant increase is observed between 2014 and 2019 (from 1.92% to 4.44% of dead colonies). In addition, it appears that large size colonies are more affected by necrosis, and reciprocally. Our main hypothesis is that these changes could be related to the consequences of climate change. Seawater temperature recorded on the same site, over a period of 32 years, shows a significant increase of the number of marine heat waves (MHWs) per year, especially since 2008. In addition, the study of the temperature changes along depth showed fewer and shorter MHWs in deep waters. Disturbance levels observed in these two gorgonian species (shift in population structure, temporal development of necrosis) are discussed in relation to past and present human-induced threats. The quantitative information obtained in this study provides a data baseline precious for future long-term monitoring, appearing as particularly relevant in a context of climate change.

The breeding system of Ornithopus sativus Brot. subsp. sativus

AbstractGenetic traits within Ornithopus sativus Brot. make it suitable for breeding as a forage legume in agriculture. The breeding system of O. sativus must be understood to stabilize valuable traits once developed. Hybridization between white‐flowered and pink‐flowered genotypes of O. sativus revealed the white flower colour to be inherited recessively to pink, while early flowering showed genetic dominance over late flowering (d = 0.5). The pink flower colour was always associated with red pigmentation on seedling hypocotyls, which provided a pragmatic aid in the selection process. Pollination of O. sativus is largely autogamous, but examination of hypocotyl colour of seedlings from white‐flowered trap plants placed among pink‐flowered plants in a sward indicated a xenogamic cross‐pollination rate of 25% is possible. This significant level of cross‐pollination revealed opportunities for breeding desirable traits within the species, while providing a warning that shifts in population structure could occur in response to selection pressure.

Evidence for seasonal changes in population structure of Reed Buntings (Emberiza schoeniclus) in the Lake Neusiedl Region: a stable-isotope approach

Migrating species and populations are affected by conditions existing across large geographical scales. The degree to which populations mix at stop-over sites and wintering grounds is variable and can involve important fitness consequences. Thus, the link between breeding and wintering grounds and seasonal shifts in population structure are important to understand population demographics, local adaption and diversification patterns. This work aims to infer migration patterns and population connectivity in the Reed Bunting (Emberiza schoeniclus) community of a Ramsar-designated wetland, Lake Neusiedl, Seewinkel, Austria. Stable isotope markers (hydrogen, δ2H, carbon, δ13C) in feathers were analyzed to assign individuals to a specific breeding or natal area. Based on the geographic assignment, birds were compared with respect to their ecomorphological traits and their habitat selection (large reed bed versus more open habitat at shore of an alkaline lake) during winter to assess potential ecological differences and possibly associated morphological divergence. Stable isotope data revealed that the local Reed Bunting community undergoes seasonal changes in population structure. Three different populations that vary in their δ2H signature and to some extent in morphological characteristics as well as in δ13C values were identified. Indications for differential migration related to age and/or sex were additionally found, since males and females as well as first-year birds and adults showed remarkable differences in their traits and feather isotope values. δ2H values diverged significantly between these groups in both age and sex classes and birds with highest feather δ2H values were considered to represent the local breeding population at Lake Neusiedl and possibly also Reed Buntings from close surroundings. Moreover, this group had the highest δ13C values in first-year individuals as well as in adults. In both sex classes, the assignment of Reed Buntings to different populations was ultimately possible due to differences in bill shape with residents being characterized by more massive bills than individuals belonging to populations visiting the study area only during migration or for wintering. During winter, beak shape and feather δ2H and δ13C values differed significantly between birds caught in the reed stand of Lake Neusiedl and those captured near the salt pan, hence, indicating differential habitat selection among co-occurring populations during winter. These findings suggest that morphological attributes, such as bill shape and size as well as linked adaptations to different food sources play a decisive role for niche segregation among wintering populations. The results provide evidence that different populations mix during migration and during winter at Lake Neusiedl and the extent to which they are specialized to a specific habitat varied.

Canadian polar bear population structure using genome-wide markers.

Predicting the consequences of environmental changes, including human‐mediated climate change on species, requires that we quantify range‐wide patterns of genetic diversity and identify the ecological, environmental, and historical factors that have contributed to it. Here, we generate baseline data on polar bear population structure across most Canadian subpopulations (n = 358) using 13,488 genome‐wide single nucleotide polymorphisms (SNPs) identified with double‐digest restriction site‐associated DNA sequencing (ddRAD). Our ddRAD dataset showed three genetic clusters in the sampled Canadian range, congruent with previous studies based on microsatellites across the same regions; however, due to a lack of sampling in Norwegian Bay, we were unable to confirm the existence of a unique cluster in that subpopulation. These data on the genetic structure of polar bears using SNPs provide a detailed baseline against which future shifts in population structure can be assessed, and opportunities to develop new noninvasive tools for monitoring polar bears across their range.

Demographic aging and biopower

The aging of the world's population is an unprecedented recent phenomenon in human history, as for millennia - at least from the Neolithic to the mid-18th century - the age structures of human populations have changed little. The question posed by this anthropological perspective seems at first sight quite simple: how did this aging come to be? We will see that from a demographic point of view, the answer seems trivial: a basic shift in population structure is at the origin. However, we will go further by exploring the historical and political conditions of this transition by mobilizing the Foucauldian notion of biopower. We argue that this notion has the heuristic advantage of linking several core processes at work in the demographic transition. Although our analysis focuses on France to illustrate the notion of biopower in Foucault's work, we also discuss several non-western societies to explain why demographic aging is inevitable across the globe due to biopower strategies and “dispositifs”. This article also constitutes a reflexive analysis on our practices as gerontologists and on the widespread “successful aging” concept.

S22THE EFFECT OF ALCOHOL ON THE GUT MICROBIOME OF PREGNANT WOMEN

Cadmium is a persistent contaminant of surface waters. The effects of cadmium on early life stages of fish are not well understood, although they are often disproportionately affected by contaminants. The objectives of this study were to examine effects of chronic exposure to environmentally relevant concentrations on growth, development, cellular stress, and glucose metabolism of channel catfish, Ictalurus punctatus. Eggs were wet-fertilized in treatment water at concentrations of 0.4 (control), 2.2 (low), or 8.5 (high) μg L−1 and monitored through swim-up, black fry stage. Eggs and fry accumulated cadmium dose-dependently. Fertilization rates were unaffected, yet hatch rate was significantly reduced in the high treatment. Survival to black fry and overall size and condition factor were not affected; however, differences in yolk sac size, and presumably energetics of yolk fry, was detected. Physiological pathways were also affected, demonstrated by altered gene expression, most notably in genes related to carbohydrate metabolism. Elevated expression of HK and G6PD, rather than G6P and GADPH, suggests glucose may be shunted towards the pentose-phosphate pathway. Overall, observations indicate cadmium negatively affects development in early life stages of channel catfish, which could lead to shifts in population structure and life history patterns in exposed populations of wild fish.

Exposure to environmentally relevant cadmium concentrations negatively impacts early life stages of channel catfish (Ictalurus punctatus)

Cadmium is a persistent contaminant of surface waters. The effects of cadmium on early life stages of fish are not well understood, although they are often disproportionately affected by contaminants. The objectives of this study were to examine effects of chronic exposure to environmentally relevant concentrations on growth, development, cellular stress, and glucose metabolism of channel catfish, Ictalurus punctatus. Eggs were wet-fertilized in treatment water at concentrations of 0.4 (control), 2.2 (low), or 8.5 (high) μg L−1 and monitored through swim-up, black fry stage. Eggs and fry accumulated cadmium dose-dependently. Fertilization rates were unaffected, yet hatch rate was significantly reduced in the high treatment. Survival to black fry and overall size and condition factor were not affected; however, differences in yolk sac size, and presumably energetics of yolk fry, was detected. Physiological pathways were also affected, demonstrated by altered gene expression, most notably in genes related to carbohydrate metabolism. Elevated expression of HK and G6PD, rather than G6P and GADPH, suggests glucose may be shunted towards the pentose-phosphate pathway. Overall, observations indicate cadmium negatively affects development in early life stages of channel catfish, which could lead to shifts in population structure and life history patterns in exposed populations of wild fish.

Relative impacts of light, temperature, and reactive oxygen on thaumarchaeal ammonia oxidation in the North Pacific Ocean

AbstractThaumarchaeota are implicated as the major ammonia oxidizers in the ocean. However, the influence of various abiotic factors in determining their distribution and activity in the upper ocean remain largely unclear. Here, we examined the influence of light, hydrogen peroxide (H2O2), and temperature on ammonia oxidation rates for communities dominated by Thaumarchaeota at the nitrite maximum across two North Pacific transects. In situ ammonia oxidation was almost exclusively driven by Thaumarchaeota, as inferred from ammonia monooxygenase subunit A (amoA) genes, amoA transcripts, and inhibitor studies. A major shift in population structure near the eastern North Pacific Subtropical Front was revealed by sequence variation of amoA genes, showing different Thaumarchaeota community structure in oligotrophic gyre and temperate regions. While the most dominant OTUs were closely related, we found significant differences in physiological responses to light and temperature of incubation. At four stations in different biogeochemical regimes, the impact of sunlight intensity and temperature on activity was evaluated using 15 ‐spiked whole seawater collected from the nitrite maximum and incubated at different depths on a free floating in situ array. Ammonia oxidation was usually completely inhibited by PAR at the surface and 21–45% inhibited at 1% surface PAR, whereas a temperature effect on ammonia oxidation was observed at only two of four stations. While inhibition due to H2O2 cannot be ruled out in surface waters, our findings show that below the mixed layer, photoinhibition, and not H2O2 toxicity, had a greater influence on ammonia oxidation.

Cleaner wrasse influence habitat selection of young damselfish

The presence of bluestreak cleaner wrasse, Labroides dimidiatus, on coral reefs increases total abundance and biodiversity of reef fishes. The mechanism(s) that cause such shifts in population structure are unclear, but it is possible that young fish preferentially settle into microhabitats where cleaner wrasse are present. As a first step to investigate this possibility, we conducted aquarium experiments to examine whether settlement-stage and young juveniles of ambon damselfish, Pomacentrus amboinensis, selected a microhabitat near a cleaner wrasse (adult or juvenile). Both settlement-stage (0 d post-settlement) and juvenile (~5 weeks post-settlement) fish spent a greater proportion of time in a microhabitat adjacent to L. dimidiatus than in one next to a control fish (a non-cleaner wrasse, Halichoeres melanurus) or one where no fish was present. This suggests that cleaner wrasse may serve as a positive cue during microhabitat selection. We also conducted focal observations of cleaner wrasse and counts of nearby damselfishes (1 m radius) to examine whether newly settled fish obtained direct benefits, in the form of cleaning services, from being near a cleaner wrasse. Although abundant, newly settled recruits (<20 mm total length) were rarely (2 %) observed being cleaned in 20 min observations compared with larger damselfishes (58 %). Individual damselfish that were cleaned were significantly larger than the median size of the surrounding nearby non-cleaned conspecifics; this was consistent across four species. The selection by settlement-stage fish of a microhabitat adjacent to cleaner wrasse in the laboratory, despite only being rarely cleaned in the natural environment, suggests that even rare cleaning events and/or indirect benefits may drive their settlement choices. This behaviour may also explain the decreased abundance of young fishes on reefs from which cleaner wrasse had been experimentally removed. This study reinforces the potentially important role of mutualism during the processes of settlement and recruitment of young reef fishes.

Presence of cleaner wrasse increases the recruitment of damselfishes to coral reefs.

Mutualisms affect the biodiversity, distribution and abundance of biological communities. However, ecological processes that drive mutualism-related shifts in population structure are often unclear and must be examined to elucidate how complex, multi-species mutualistic networks are formed and structured. In this study, we investigated how the presence of key marine mutualistic partners can drive the organisation of local communities on coral reefs. The cleaner wrasse, Labroides dimidiatus, removes ectoparasites and reduces stress hormones for multiple reef fish species, and their presence on coral reefs increases fish abundance and diversity. Such changes in population structure could be driven by increased recruitment of larval fish at settlement, or by post-settlement processes such as modified levels of migration or predation. We conducted a controlled field experiment to examine the effect of cleaners on recruitment processes of a common group of reef fishes, and showed that small patch reefs (61-285 m(2)) with cleaner wrasse had higher abundances of damselfish recruits than reefs from which cleaner wrasse had been removed over a 12-year period. However, the presence of cleaner wrasse did not affect species diversity of damselfish recruits. Our study provides evidence of the ecological processes that underpin changes in local population structure in the presence of a key mutualistic partner.

Revisiting Camu-camu (Myrciaria dubia): Twenty-seven Years of Fruit Collection and Flooding at an Oxbow Lake in Peruvian Amazonia

Revisiting Camu-camu ( Myrciaria dubia ): Twenty-seven Years of Fruit Collection and Flooding at an Oxbow Lake in Peruvian Amazonia Camu-camu (Myrciaria dubia HBK McVaugh; Myrtaceae) is an important riparian species in the floodplain forests of Peruvian Amazonia, and its fruits have been harvested commercially for over 30 years. We examined the population impacts of intensive fruit collection on this species by remeasuring a 1,000 m2 inventory transect that was established in 1984 in a dense stand of M. dubia along an oxbow lake. We found that regeneration rates had declined notably since the original survey, and that the number of M. dubia individuals had dropped from 693 to 161 genets. While this dramatic shift in population structure would appear to be caused by excessive fruit collection, the same decline in regeneration was noted for Eugenia inundata DC, an associated species of similar growth form and phenology that is not harvested. The life cycles of both species are closely tied to the rise and fall of the river. In addition to annual fruit collection, we suggest that the extreme hydrological events that have occurred in the Amazon Basin over the last few decades, as well as the successional development of the ox-box lake study site that has been slowly filling up with sediment, also play a role in the observed reduction in M. dubia numbers.

Dramatic Changes in the Genotypic Frequencies of Target Insecticide Resistance in French Populations of &lt;I&gt;Myzus persicae&lt;/I&gt; (Hemiptera: Aphididae) Over the Last Decade

In 2001, although target site resistance against pyrethroids was wide-spread in clonal populations of Myzus persicae on oilseed rape in France (kdr), target site resistance against carbamates was rare. Starting in 2005, control failure by carbamates appeared. The current study was designed to document changes in insecticide-resistant genotype frequencies in France during the last decade. Two resistant genotypes (RGs) were dominant in populations in 2009-2010: RG1 with the kdr 1014F allele (16%), RG2 with the MACE 431F allele and the atypical s-kdr 918L allele (83%). The widespread prevalence of RG2 suggests that a substantial shift has occurred (allele 431F in < 2% individuals in 2001) presumably in response to agrichemicals. Analysis of neutral markers revealed that 2009-2010 populations were composed of two differentiated genetic pools (instead of one in 2001) and that RG2 was found in two divergent superclones of M. persicae. Possible explanations for these observed shifts in population structure and especially for the dramatic increase of the double mutant RG2 are discussed.

Evidence for Links between Feeding Inhibition, Population Characteristics, and Sensitivity to Acute Toxicity for Daphnia magna

A population experiment with Daphnia magna tested the hypothesis that short-term feeding inhibition provokes a shift in population structure that will vary with conspecific pressure (e.g., pressure occurring from individuals of the same species due to competition for food and space) and increases population sensitivity to a xenobiotic exposure due to size-dependent toxicity (e.g., decreasing sensitivity with increasing body length). Populations were exposed for one week to a feeding inhibitor (imidacloprid, 0.15 or 12.0 mg/L) followed by one week of recovery and one day of exposure to an acute toxin (carbaryl, 0.0098 mg/L). Identical exposure under low and high conspecific pressure was studied by delaying the start of exposure for half of the populations by two weeks; thus populations were in a different stage of population development when exposure occurred. Feeding inhibition of 97% (12.0 mg/L imidacloprid) caused a shift in population structure toward smaller individuals but also reduced population abundance by up to 56 ± 7% with a strong influence of conspecific pressure. Increased population sensitivity to carbaryl was observed after feeding inhibition of 97% as hypothesized. Carbaryl exposure for one day resulted in population decline of up to 23 ± 6% when populations were not previously exposed to imidacloprid. Identical carbaryl exposure provoked a four times stronger decline in population abundance when exposure occurred following feeding inhibition of 97%. In conflict with the hypothesis, this was at least in part due to changes in the reproductive strategy of daphnids following exposure to imidacloprid rather than driven by the shift in population structure. The differences in population sensitivity to additional stress (carbaryl) occurring one week after feeding inhibition caused by exposure to imidacloprid adds a further challenge to understanding potential impacts from multiple stressors as occurring in the field at the population level.

Urban parakeets in Northern Illinois: A 40-year perspective

Monk parakeets (Myiopsitta monachus) are the most abundant and widely distributed of the naturalized parrots in the United States. We summarize monk parakeet population data from 1970 to 2010 for northern Illinois, one of the best-known populations. Throughout the 1970s, parakeets were seen in small numbers at scattered locations, but none of the nesting sites persisted and the birds either died or moved elsewhere. The species became established in the Hyde Park neighborhood of Chicago in 1979 and this population grew exponentially and expanded over the next 25 years, doubling in size every 2 to 3 years. In the mid to late 1990s parakeets became established in many other localities in the Chicago region. The population in Hyde Park began to rapidly decline in 2005, a trend also exhibited in national counts. The reasons for this decline are unknown but we suggest that the decline is more apparent than real and that the decline in Hyde Park is the result of shifts in population structure from a few dense aggregations to progressively more spatially separated smaller groups. As evidence for this, the population of parakeets in the greater Chicago region does not appear to have declined but is still growing in size and distribution. Monk parakeets are a novel addition to many urban ecosystems, with a neutral impact to most other bird species but an increasingly complex interaction with human residents in urban areas.

Genetic variation on the rocks - the impact of climbing on the population ecology of a typical cliff plant

1. Rock climbing enjoys enormous popularity world-wide. As a consequence, the anthropogenic pressure on the vegetation of formerly undisturbed cliff ecosystems is continuously increasing. 2. The impact of rock climbing on population structure and genetic variation of the rare plant species Draba aizoides was investigated representatively for many other typical central European cliff plants. Populations from eight climbed and from eight pristine cliffs were compared through the use of vertical transect analyses and molecular markers. 3. Population structure differed between climbed and pristine cliffs. Individuals of D. aizoides were significantly smaller and less frequent on climbed compared with pristine cliffs. On plateau sites, the species’ occurrence was unaffected by climbing activities; it was significantly less frequent on the faces, but more frequent on the tali of climbed in comparison with pristine cliffs. 4. Genetic variation was greater in populations from climbed compared with pristine cliffs, and genetic differentiation was stronger between subpopulations from pristine cliffs than between subpopulations from climbed cliffs. 5. Synthesis and applications. Rock climbing clearly affects population structure and genetic variation of D. aizoides. Seed dispersal is presumably enhanced by rock climbers but climbers remove and drop plant individuals from cliff faces, which causes a downward shift in population structure. This shift in turn reduces genetic differentiation between upper and lower subpopulations. In mountain regions that attract sport climbing, conservation management plans should therefore always ensure the provision of completely unclimbed cliffs to protect the native vegetation.

Genetic Consequences of Habitat Fragmentation in Long-Lived Tree Species: The Case of the Mediterranean Holm Oak (Quercus ilex, L.)

Large-scale forest fragmentation can increase interpopulation genetic differentiation and erode the genetic variability of remnant plant populations. In this study, we analyze the extent of clonality and the genetic variability and structure within a holm oak (Quercus ilex) population from Central Spain at 3 patches showing different degrees of fragmentation. For this purpose, we have typed 191 individuals (105 adults and 86 saplings) at 9 microsatellite loci. Microsatellite markers revealed an extensive clonal structure in this species, with most analyzed clumps constituting a single "genet", which in some cases extended over a considerable area (up to 318 m(2)). The maximum distance between "ramets" tended to be higher in the extremely fragmented patch, suggesting that intensive management and environmental perturbation has favored clonal propagation. We have also found evidence that fragmentation has contributed to reduce genetic variability and increase genetic differentiation in holm oak saplings, indicating that the younger cohorts are suffering some negative genetic consequences of long-term population fragmentation. Finally, analyses of fine spatial genetic structure have revealed significant kinship structures up to 20-50 m that were particularly patent in the 2 less fragmented patches. Overall, our findings point to long-term genetic shifts in population structure of holm oaks in fragmented landscapes; however, further research is required on pollen dispersal and gene flow in this species.

Striped weakfish ( Cynoscion guatucupa) population structure in waters adjacent to Rio de la Plata, environmental influence on its inter-annual variability

The springtime temporal variations of striped weakfish ( Cynoscion guatucupa) population structure available to the commercial fishery and its relationship to environmental factors were evaluated in the Uruguayan coastal zone (35° −33.4°S), from 86 stations sampled in 1994, 98, 99 and 2003. We examined the inter-annual variability of age-class structure over four years under different oceanographic conditions: (1) 1998 (El Niño year) was characterized by elevated water temperature; (2) 1999 (La Niña year) was characterized by decreased water temperature; and (3) 1994 and 2003 were ‘typical years’ with intermediate values in those parameters. To determine whether or not major shifts in population structure occurred between years we used ANOSIM and SIMPER analysis to determine which age-class typified and discriminated between years. A canonical correspondence analysis (CCA) was used to define the temporal pattern of age-class structure of C. guatucupa and to estimate its associations with environmental factors (depth, temperature, salinity, vertical stratification, and zonal and meridional component of the wind). The C. guatucupa population structure showed significant difference between 1998 and 1999 and 1994–2003. During 1998 and 1999, the population structure was dominated by adults (between 4 and >7 age-class), while that in 1994 and 2003 was dominated by juveniles (between 0 and 3 age-class). CCA results indicated that zonal wind and salinity has a major influence on the temporal pattern of C. guatucupa population structure. Juvenile population structure was associated with low salinities and occurred when the wind field forced an inflow of freshwater into the marine coastal area from the Rio de la Plata estuary, while the adult structure, associated with high salinities, occurred when the area was dominated by a wind driven inflow of higher salinity shelf water. These results support the hypothesis that the short-term environmental synoptic condition has a greater influence on the distribution and population structure of C. guatucupa than long-term environmental variability.

The emergence of meticillin-resistant Staphylococcus aureus among injecting drug users

To quantify an observed increase in meticillin-resistant Staphylococcus aureus (MRSA) infections in injecting drug users (IDUs) and, using genetic analysis and clinical presentation, contrast findings with those from previous studies in Brighton to further understanding of the clinical epidemiology and underlying molecular biology associated with the increase. From 2006 to 2008, isolates of S. aureus were collected, together with clinical details from infected IDUs. Isolates were characterised using antibiotic susceptibilities, multilocus-sequence typing (MLST) and spa typing. The molecular epidemiology and patterns of clinical presentation were compared with results from 1999-2000 to 2000-2003. From 2006 to 2008, 18/37 (49%) of clinical isolates from IDUs were MRSA compared with 4/59 (7%) in 2000-2003 and 0/48 (0%) in 1999-2000. Despite this increase, hospital attendances by IDUs for treatment of infection dropped from 3.2 to 1.1 patients per month. MLST showed a shift in population structure towards a single MRSA clone, ST1, rather than epidemic hospital-associated strains. In IDUs between 2000-2003 and 2006-2008, an increase occurred in the percentage of community-associated S. aureus isolates showing meticillin-resistance, but hospital attendances decreased. IDUs may act as a focus for the emergence of resistant S. aureus strains.