Source attribution of campylobacteriosis in Australia, 2017-2019.

Campylobacter jejuni and Campylobacter coli infections are the leading cause of foodborne gastroenteritis in high-income countries. Campylobacter colonizes a variety of warm-blooded hosts that are reservoirs for human campylobacteriosis. The proportions of Australian cases attributable to different animal reservoirs are unknown but can be estimated by comparing the frequency of different sequence types in cases and reservoirs. Campylobacter isolates were obtained from notified human cases and raw meat and offal from the major livestock in Australia between 2017 and 2019. Isolates were typed using multi-locus sequence genotyping. We used Bayesian source attribution models including the asymmetric island model, the modified Hald model, and their generalizations. Some models included an "unsampled" source to estimate the proportion of cases attributable to wild, feral, or domestic animal reservoirs not sampled in our study. Model fits were compared using the Watanabe-Akaike information criterion. We included 612 food and 710 human case isolates. The best fitting models attributed >80% of Campylobacter cases to chickens, with a greater proportion of C. coli (>84%) than C. jejuni (>77%). The best fitting model that included an unsampled source attributed 14% (95% credible interval [CrI]: 0.3%-32%) to the unsampled source and only 2% to ruminants (95% CrI: 0.3%-12%) and 2% to pigs (95% CrI: 0.2%-11%) The best fitting model that did not include an unsampled source attributed 12% to ruminants (95% CrI: 1.3%-33%) and 6% to pigs (95% CrI: 1.1%-19%). Chickens were the leading source of human Campylobacter infections in Australia in 2017-2019 and should remain the focus of interventions to reduce burden.

Risk factors for campylobacteriosis in Australia: outcomes of a 2018-2019 case-control study.

BACKGROUND: We aimed to identify risk factors for sporadic campylobacteriosis in Australia, and to compare these for Campylobacter jejuni and Campylobacter coli infections. METHODS: In a multi-jurisdictional case-control study, we recruited culture-confirmed cases of campylobacteriosis reported to state and territory health departments from February 2018 through October 2019. We recruited controls from notified influenza cases in the previous 12 months that were frequency matched to cases by age group, sex, and location. Campylobacter isolates were confirmed to species level by public health laboratories using molecular methods. We conducted backward stepwise multivariable logistic regression to identify significant risk factors. RESULTS: We recruited 571 cases of campylobacteriosis (422 C. jejuni and 84 C. coli) and 586 controls. Important risk factors for campylobacteriosis included eating undercooked chicken (adjusted odds ratio [aOR] 70, 95% CI 13-1296) or cooked chicken (aOR 1.7, 95% CI 1.1-2.8), owning a pet dog aged < 6 months (aOR 6.4, 95% CI 3.4-12), and the regular use of proton-pump inhibitors in the 4 weeks prior to illness (aOR 2.8, 95% CI 1.9-4.3). Risk factors remained similar when analysed specifically for C. jejuni infection. Unique risks for C. coli infection included eating chicken pâté (aOR 6.1, 95% CI 1.5-25) and delicatessen meats (aOR 1.8, 95% CI 1.0-3.3). Eating any chicken carried a high population attributable fraction for campylobacteriosis of 42% (95% CI 13-68), while the attributable fraction for proton-pump inhibitors was 13% (95% CI 8.3-18) and owning a pet dog aged < 6 months was 9.6% (95% CI 6.5-13). The population attributable fractions for these variables were similar when analysed by campylobacter species. Eating delicatessen meats was attributed to 31% (95% CI 0.0-54) of cases for C. coli and eating chicken pâté was attributed to 6.0% (95% CI 0.0-11). CONCLUSIONS: The main risk factor for campylobacteriosis in Australia is consumption of chicken meat. However, contact with young pet dogs may also be an important source of infection. Proton-pump inhibitors are likely to increase vulnerability to infection.

The Build-Up of Population Genetic Divergence along the Speciation Continuum during a Recent Adaptive Radiation of Rhagoletis Flies.

New species form through the evolution of genetic barriers to gene flow between previously interbreeding populations. The understanding of how speciation proceeds is hampered by our inability to follow cases of incipient speciation through time. Comparative approaches examining different diverging taxa may offer limited inferences, unless they fulfill criteria that make the comparisons relevant. Here, we test for those criteria in a recent adaptive radiation of the Rhagoletis pomonella species group (RPSG) hypothesized to have diverged in sympatry via adaptation to different host fruits. We use a large-scale population genetic survey of 1568 flies across 33 populations to: (1) detect on-going hybridization, (2) determine whether the RPSG is derived from the same proximate ancestor, and (3) examine patterns of clustering and differentiation among sympatric populations. We find that divergence of each in-group RPSG taxon is occurring under current gene flow, that the derived members are nested within the large pool of genetic variation present in hawthorn-infesting populations of R. pomonella, and that sympatric population pairs differ markedly in their degree of genotypic clustering and differentiation across loci. We conclude that the RPSG provides a particularly robust opportunity to make direct comparisons to test hypotheses about how ecological speciation proceeds despite on-going gene flow.

Genomically correlated trait combinations and antagonistic selection contributing to counterintuitive genetic patterns of adaptive diapause divergence in Rhagoletis flies.

Adaptation to novel environments can result in unanticipated genomic responses to selection. Here, we illustrate how multifarious, correlational selection helps explain a counterintuitive pattern of genetic divergence between the recently derived apple- and ancestral hawthorn-infesting host races of Rhagoletis pomonella (Diptera: Tephritidae). The apple host race terminates diapause and emerges as adults earlier in the season than the hawthorn host race, to coincide with the earlier fruiting phenology of their apple hosts. However, alleles at many loci associated with later emergence paradoxically occur at higher frequencies in sympatric populations of the apple compared to the hawthorn race. We present genomic evidence that historical selection over geographically varying environmental gradients across North America generated genetic correlations between two life history traits, diapause intensity and diapause termination, in the hawthorn host race. Moreover, the loci associated with these life history traits are concentrated in genomic regions in high linkage disequilibrium (LD). These genetic correlations are antagonistic to contemporary selection on local apple host race populations that favours increased initial diapause depth and earlier, not later, diapause termination. Thus, the paradox of apple flies appears due, in part, to pleiotropy or linkage of alleles associated with later adult emergence and increased initial diapause intensity, the latter trait strongly selected for by the earlier phenology of apples. Our results demonstrate how understanding of multivariate trait combinations and the correlative nature of selective forces acting on them can improve predictions concerning adaptive evolution and help explain seemingly counterintuitive patterns of genetic diversity in nature.

Antimicrobial Resistance of Campylobacter spp. Causing Human Infection in Australia: An International Comparison.

The study investigates the prevalence of antimicrobial resistance in Campylobacter jejuni and Campylobacter coli in gastroenteritis patients in the eight most populous regions in Australia and compares the prevalence of antimicrobial resistance in Europe and North America. A total of 164 Campylobacter isolates were collected from patients with campylobacteriosis and tested for susceptibility to six antimicrobials using ETEST® strips and compared with reports from Europe and the United States. Genomes were sequenced on Illumina NextSeq to identify genetic determinants of resistance. Phenotypically, 1.8%, 14.0%, 14.6%, and 20.1% of isolates were resistant to erythromycin (ERY), ampicillin, tetracycline (TET), and ciprofloxacin (CIP), respectively. Comparing published phenotypic results of antimicrobial resistance in several European countries and the United States with these Australian isolates reveals that rates observed in Australia are among the lowest observed for ERY, CIP, and TET for both C. coli and C. jejuni. For each antimicrobial tested, concordance between resistance phenotype and genotype ranged from 66.6% to 100.0%. This study highlights that, among industrialized countries, Portugal and Spain have very high levels of antimicrobial resistance in C. jejuni and C. coli, especially when compared with the United Kingdom, United States, and Australia.

Evidence for spatial clines and mixed geographic modes of speciation for North American cherry-infesting Rhagoletis (Diptera: Tephritidae) flies.

An important criterion for understanding speciation is the geographic context of population divergence. Three major modes of allopatric, parapatric, and sympatric speciation define the extent of spatial overlap and gene flow between diverging populations. However, mixed modes of speciation are also possible, whereby populations experience periods of allopatry, parapatry, and/or sympatry at different times as they diverge. Here, we report clinal patterns of variation for 21 nuclear-encoded microsatellites and a wing spot phenotype for cherry-infesting Rhagoletis (Diptera: Tephritidae) across North America consistent with these flies having initially diverged in parapatry followed by a period of allopatric differentiation in the early Holocene. However, mitochondrial DNA (mtDNA) displays a different pattern; cherry flies at the ends of the clines in the eastern USA and Pacific Northwest share identical haplotypes, while centrally located populations in the southwestern USA and Mexico possess a different haplotype. We hypothesize that the mitochondrial difference could be due to lineage sorting but more likely reflects a selective sweep of a favorable mtDNA variant or the spread of an endosymbiont. The estimated divergence time for mtDNA suggests possible past allopatry, secondary contact, and subsequent isolation between USA and Mexican fly populations initiated before the Wisconsin glaciation. Thus, the current genetics of cherry flies may involve different mixed modes of divergence occurring in different portions of the fly's range. We discuss the need for additional DNA sequencing and quantification of prezygotic and postzygotic reproductive isolation to verify the multiple mixed-mode hypothesis for cherry flies and draw parallels from other systems to assess the generality that speciation may commonly involve complex biogeographies of varying combinations of allopatric, parapatric, and sympatric divergence.

Molecular characterization of Campylobacter spp. recovered from beef, chicken, lamb and pork products at retail in Australia.

Australian rates of campylobacteriosis are among the highest in developed countries, yet only limited work has been done to characterize Campylobacter spp. in Australian retail products. We performed whole genome sequencing (WGS) on 331 C. coli and 285 C. jejuni from retail chicken meat, as well as beef, chicken, lamb and pork offal (organs). Campylobacter isolates were highly diverse, with 113 sequence types (STs) including 38 novel STs, identified from 616 isolates. Genomic analysis suggests very low levels (2.3-15.3%) of resistance to aminoglycoside, beta-lactam, fluoroquinolone, macrolide and tetracycline antibiotics. A majority (>90%) of isolates (52/56) possessing the fluoroquinolone resistance-associated T86I mutation in the gyrA gene belonged to ST860, ST2083 or ST7323. The 44 pork offal isolates were highly diverse, representing 33 STs (11 novel STs) and harboured genes associated with resistance to aminoglycosides, lincosamides and macrolides not generally found in isolates from other sources. Prevalence of multidrug resistant genotypes was very low (<5%), but ten-fold higher in C. coli than C. jejuni. This study highlights that Campylobacter spp. from retail products in Australia are highly genotypically diverse and important differences in antimicrobial resistance exist between Campylobacter species and animal sources.

Prevalence of Campylobacter coli and Campylobacter jejuni in Retail Chicken, Beef, Lamb, and Pork Products in Three Australian States.

The aim of this study was to investigate the prevalence and distribution of Campylobacter species in a variety of fresh and frozen meat and offal products collected from retail outlets in New South Wales (NSW), Queensland (Qld), and Victoria (Vic). A total of 1,490 chicken, beef, lamb, and pork samples were collected from Australian supermarkets and butcher shops over a 2-year sampling period (October 2016 to October 2018). Campylobacter spp. were detected in 90% of chicken meat and 73% of chicken offal products (giblet and liver), with significantly lower prevalence in lamb (38%), pork (31%), and beef (14%) offal (kidney and liver). Although retail chicken meat was frequently contaminated with Campylobacter, the level of contamination was generally low. Where quantitative analysis was conducted, 98% of chicken meat samples, on average, had <10,000 CFU Campylobacter per carcass, with 10% <21 CFU per carcass. Campylobacter coli was the most frequently recovered species in chicken meat collected in NSW (53%) and Vic (56%) and in chicken offal collected in NSW (77%), Qld (59%), and Vic (58%). In beef, lamb, and pork offal, C. jejuni was generally the most common species (50 to 86%), with the exception of pork offal collected in NSW, where C. coli was more prevalent (69%). Campylobacter prevalence was significantly higher in fresh lamb (46%) and pork (31%) offal than in frozen offal (17 and 11%, respectively). For chicken, beef, and pork offal, the prevalence of Campylobacter spp. was significantly higher on delicatessen products compared with prepackaged products. This study demonstrated that meat and offal products are frequently contaminated with Campylobacter. However, the prevalence is markedly different in different meats, and the level of chicken meat portion contamination is generally low. By identifying the types of meat and offal products types that pose the greatest risk of Campylobacter infection to consumers, targeted control strategies can be developed.

Geographic and Ecological Dimensions of Host Plant-Associated Genetic Differentiation and Speciation in the Rhagoletis cingulata (Diptera: Tephritidae) Sibling Species Group.

Ascertaining the causes of adaptive radiation is central to understanding how new species arise and come to vary with their resources. The ecological theory posits adaptive radiation via divergent natural selection associated with novel resource use; an alternative suggests character displacement following speciation in allopatry and then secondary contact of reproductively isolated but ecologically similar species. Discriminating between hypotheses, therefore, requires the establishment of a key role for ecological diversification in initiating speciation versus a secondary role in facilitating co-existence. Here, we characterize patterns of genetic variation and postzygotic reproductive isolation for tephritid fruit flies in the Rhagoletis cingulata sibling species group to assess the significance of ecology, geography, and non-adaptive processes for their divergence. Our results support the ecological theory: no evidence for intrinsic postzygotic reproductive isolation was found between two populations of allopatric species, while nuclear-encoded microsatellites implied strong ecologically based reproductive isolation among sympatric species infesting different host plants. Analysis of mitochondrial DNA suggested, however, that cytoplasmic-related reproductive isolation may also exist between two geographically isolated populations within R cingulata. Thus, ecology associated with sympatric host shifts and cytoplasmic effects possibly associated with an endosymbiont may be the key initial drivers of the radiation of the R. cingulata group.

Mifepristone Treatment in Four Cases of Primary Bilateral Macronodular Adrenal Hyperplasia (BMAH).

CONTEXT: Primary bilateral macronodular adrenal hyperplasia (BMAH) is a rare form of adrenal Cushing syndrome conventionally treated with adrenalectomy. Medical treatment is often reserved for patients not eligible for surgery. However, to date there have been few studies about the efficacy of mifepristone for the treatment of BMAH associated with hypercortisolism. OBJECTIVE: To describe a series of patients with hypercortisolism due to BMAH treated with mifepristone from multiple medical practices. DESIGN: We retrospectively assessed four patients treated with mifepristone for hypercortisolism due to BMAH who had either failed unilateral adrenalectomy, declined surgery, or were poor surgical candidates. RESULTS: Mifepristone induced clinical improvement and remission of the signs and symptoms of hypercortisolism in all described patients with BMAH. The median treatment duration at the time of efficacy response assessment was 5 months (range: 3 to 18 months). Improvement in cardiometabolic parameters was observed as early as 2 weeks after treatment was started. All patients achieved improvements in glycemic control and hypertension and had significant weight loss. The most common adverse event observed with mifepristone therapy was fatigue. Increases in TSH level occurred in two patients. CONCLUSION: Mifepristone can be an effective medical alternative to surgery in patients with hypercortisolism due to BMAH.

Genomic Differentiation during Speciation-with-Gene-Flow: Comparing Geographic and Host-Related Variation in Divergent Life History Adaptation in Rhagoletis pomonella.

A major goal of evolutionary biology is to understand how variation within populations gets partitioned into differences between reproductively isolated species. Here, we examine the degree to which diapause life history timing, a critical adaptation promoting population divergence, explains geographic and host-related genetic variation in ancestral hawthorn and recently derived apple-infesting races of Rhagoletis pomonella. Our strategy involved combining experiments on two different aspects of diapause (initial diapause intensity and adult eclosion time) with a geographic survey of genomic variation across four sites where apple and hawthorn flies co-occur from north to south in the Midwestern USA. The results demonstrated that the majority of the genome showing significant geographic and host-related variation can be accounted for by initial diapause intensity and eclosion time. Local genomic differences between sympatric apple and hawthorn flies were subsumed within broader geographic clines; allele frequency differences within the races across the Midwest were two to three-fold greater than those between the races in sympatry. As a result, sympatric apple and hawthorn populations displayed more limited genomic clustering compared to geographic populations within the races. The findings suggest that with reduced gene flow and increased selection on diapause equivalent to that seen between geographic sites, the host races may be recognized as different genotypic entities in sympatry, and perhaps species, a hypothesis requiring future genomic analysis of related sibling species to R. pomonella to test. Our findings concerning the way selection and geography interplay could be of broad significance for many cases of earlier stages of divergence-with-gene flow, including (1) where only modest increases in geographic isolation and the strength of selection may greatly impact genetic coupling and (2) the dynamics of how spatial and temporal standing variation is extracted by selection to generate differences between new and discrete units of biodiversity.

Genetic Evidence for the Introduction of Rhagoletis pomonella (Diptera: Tephritidae) into the Northwestern United States.

The apple maggot fly, Rhagoletis pomonella Walsh (Diptera: Tephritidae), is a serious quarantine pest in the apple-growing regions of central Washington and Oregon. The fly is believed to have been introduced into the Pacific Northwest via the transport of larval-infested apples near Portland, Oregon, within the last 40 yr. However, R. pomonella also attacks native black hawthorn, Crataegus douglasii Lindley (Rosales: Rosaceae), and introduced ornamental hawthorn, Crataegus monogyna Jacquin, in the region. It is, therefore, possible that R. pomonella was not introduced but has always been present on black hawthorn. If true, then the fly may have independently shifted from hawthorn onto apple in the Pacific Northwest within the last 40 yr after apples were introduced. Here, we test the introduction hypothesis through a microsatellite genetic survey of 10 R. pomonella sites in Washington and 5 in the eastern United States, as well as a comparison to patterns of genetic variation between populations of Rhagoletis cingulata Loew and Rhagoletis indifferens Curran, two sister species of cherry-infesting flies known to be native to the eastern and western United States, respectively. We report results based on genetic distance networks, patterns of allelic variation, and estimated times of population divergence that are consistent with the introduction hypothesis for R. pomonella. The results have important implications for R. pomonella management, suggesting that black hawthorn-infesting flies near commercial apple-growing regions of central Washington may harbor sufficient variation to utilize apple as an alternate host, urging careful monitoring, and possible removal of hawthorn trees near orchards.

Evolution across the Curriculum: Microbiology.

An integrated understanding of microbiology and evolutionary biology is essential for students pursuing careers in microbiology and healthcare fields. In this Perspective, we discuss the usefulness of evolutionary concepts and an overall evolutionary framework for students enrolled in microbiology courses. Further, we propose a set of learning goals for students studying microbial evolution concepts. We then describe some barriers to microbial evolution teaching and learning and encourage the continued incorporation of evidence-based teaching practices into microbiology courses at all levels. Next, we review the current status of microbial evolution assessment tools and describe some education resources available for teaching microbial evolution. Successful microbial evolution education will require that evolution be taught across the undergraduate biology curriculum, with a continued focus on applications and applied careers, while aligning with national biology education reform initiatives. Journal of Microbiology & Biology Education.

Escherichia coli out in the cold: Dissemination of human-derived bacteria into the Antarctic microbiome.

Discharge of untreated sewage into Antarctic environments presents a risk of introducing non-native microorganisms, but until now, adverse consequences have not been conclusively identified. Here we show that sewage disposal introduces human derived Escherichia coli carrying mobile genetic elements and virulence traits with the potential to affect the diversity and evolution of native Antarctic microbial communities. We compared E. coli recovered from environmental and animal sources in Antarctica to a reference collection of E. coli from humans and non-Antarctic animals. The distribution of phylogenetic groups and frequency of 11 virulence factors amongst the Antarctic isolates were characteristic of E. coli strains more commonly associated with humans. The rapidly emerging E. coli ST131 and ST95 clones were found amongst the Antarctic isolates, and ST95 was the predominant E. coli recovered from Weddell seals. Class 1 integrons were found in 15% of the Antarctic E. coli with 4 of 5 identified gene cassette arrays containing antibiotic resistance genes matching those common in clinical contexts. Disposing untreated sewage into the Antarctic environment does disseminate non-native microorganisms, but the extent of this impact and implications for Antarctic ecosystem health are, as yet, poorly understood.

Sequential divergence and the multiplicative origin of community diversity.

Phenotypic and genetic variation in one species can influence the composition of interacting organisms within communities and across ecosystems. As a result, the divergence of one species may not be an isolated process, as the origin of one taxon could create new niche opportunities for other species to exploit, leading to the genesis of many new taxa in a process termed "sequential divergence." Here, we test for such a multiplicative effect of sequential divergence in a community of host-specific parasitoid wasps, Diachasma alloeum, Utetes canaliculatus, and Diachasmimorpha mellea (Hymenoptera: Braconidae), that attack Rhagoletis pomonella fruit flies (Diptera: Tephritidae). Flies in the R. pomonella species complex radiated by sympatrically shifting and ecologically adapting to new host plants, the most recent example being the apple-infesting host race of R. pomonella formed via a host plant shift from hawthorn-infesting flies within the last 160 y. Using population genetics, field-based behavioral observations, host fruit odor discrimination assays, and analyses of life history timing, we show that the same host-related ecological selection pressures that differentially adapt and reproductively isolate Rhagoletis to their respective host plants (host-associated differences in the timing of adult eclosion, host fruit odor preference and avoidance behaviors, and mating site fidelity) cascade through the ecosystem and induce host-associated genetic divergence for each of the three members of the parasitoid community. Thus, divergent selection at lower trophic levels can potentially multiplicatively and rapidly amplify biodiversity at higher levels on an ecological time scale, which may sequentially contribute to the rich diversity of life.

Hybridization and the spread of the apple maggot fly, Rhagoletis pomonella (Diptera: Tephritidae), in the northwestern United States.

Hybridization may be an important process interjecting variation into insect populations enabling host plant shifts and the origin of new economic pests. Here, we examine whether hybridization between the native snowberry-infesting fruit fly Rhagoletis zephyria (Snow) and the introduced quarantine pest R. pomonella (Walsh) is occurring and may aid the spread of the latter into more arid commercial apple-growing regions of central Washington state, USA. Results for 19 microsatellites implied hybridization occurring at a rate of 1.44% per generation between the species. However, there was no evidence for increased hybridization in central Washington. Allele frequencies for seven microsatellites in R. pomonella were more 'R. zephyria-like' in central Washington, suggesting that genes conferring resistance to desiccation may be adaptively introgressing from R. zephyria. However, in only one case was the putatively introgressing allele from R. zephyria not found in R. pomonella in the eastern USA. Thus, many of the alleles changing in frequency may have been prestanding in the introduced R. pomonella population. The dynamics of hybridization are therefore complex and nuanced for R. pomonella, with various causes and factors, including introgression for a portion, but not all of the genome, potentially contributing to the pest insect's spread.

A Cross-Course Investigation of Integrative Cases for Evolution Education.

Evolution is a cornerstone theory in biology, yet many undergraduate students have difficulty understanding it. One reason for this is that evolution is often taught in a macro-scale context without explicit links to micro-scale processes. To address this, we developed a series of integrative evolution cases that present the evolution of various traits from their origin in genetic mutation, to the synthesis of modified proteins, to how these proteins produce novel phenotypes, to the related macro-scale impacts that the novel phenotypes have on populations in ecological communities. We postulated that students would develop a fuller understanding of evolution when learning biology in a context where these integrative evolution cases are used. We used a previously developed assessment tool, the ATEEK (Assessment Tool for Evaluating Evolution Knowledge), within a pre-course/post-course assessment framework. Students who learned biology in courses using the integrative cases performed significantly better on the evolution assessment than did students in courses that did not use the cases. We also found that student understanding of evolution increased with increased exposure to the integrative evolution cases. These findings support the general hypothesis that students acquire a more complete understanding of evolution when they learn about its genetic and molecular mechanisms along with macro-scale explanations.

Draft Genome Sequence of Enterococcus faecalis Strain PF3, Isolated from Adelie Penguin Feces from Antarctica.

Enterococcus faecalis is one of the leading causes of nosocomial infections and is a common commensal organism in humans and other animals. In this study, we report a draft genome sequence for the E. faecalis strain PF3, isolated from Adélie penguin feces collected from Warriner Island, Antarctica.

Assessment of student learning associated with tree thinking in an undergraduate introductory organismal biology course.

Phylogenetic trees provide visual representations of ancestor-descendant relationships, a core concept of evolutionary theory. We introduced "tree thinking" into our introductory organismal biology course (freshman/sophomore majors) to help teach organismal diversity within an evolutionary framework. Our instructional strategy consisted of designing and implementing a set of experiences to help students learn to read, interpret, and manipulate phylogenetic trees, with a particular emphasis on using data to evaluate alternative phylogenetic hypotheses (trees). To assess the outcomes of these learning experiences, we designed and implemented a Phylogeny Assessment Tool (PhAT), an open-ended response instrument that asked students to: 1) map characters on phylogenetic trees; 2) apply an objective criterion to decide which of two trees (alternative hypotheses) is "better"; and 3) demonstrate understanding of phylogenetic trees as depictions of ancestor-descendant relationships. A pre-post test design was used with the PhAT to collect data from students in two consecutive Fall semesters. Students in both semesters made significant gains in their abilities to map characters onto phylogenetic trees and to choose between two alternative hypotheses of relationship (trees) by applying the principle of parsimony (Occam's razor). However, learning gains were much lower in the area of student interpretation of phylogenetic trees as representations of ancestor-descendant relationships.

Survival, sublethal injury, and recovery of environmental Burkholderia pseudomallei in soil subjected to desiccation.

Environmental Burkholderia pseudomallei isolated from sandy soil at Castle Hill, Townsville, in the dry tropic region of Queensland, Australia, was inoculated into sterile-soil laboratory microcosms subjected to variable soil moisture. Survival and sublethal injury of the B. pseudomallei strain were monitored by recovery using culture-based methods. Soil extraction buffer yielded higher recoveries as an extraction agent than sterile distilled water. B. pseudomallei was not recoverable when inoculated into desiccated soil but remained recoverable from moist soil subjected to 91 days' desiccation and showed a growth response to increased soil moisture over at least 113 days. Results indicate that endemic dry tropic soil may act as a reservoir during the dry season, with an increase in cell number and potential for mobilization from soil into water in the wet season.