The Genomic Aftermath of Hybridization in the Opportunistic Pathogen Candida metapsilosis.
The main results reproduced, with only marginal, non-material deviations.
A 0–100 reproducibility-quality score from the per-question grades, shown as a z-score: standard deviations above (+) or below (−) the mean of comparable assessments.
▸Reproduction agent’s raw note
PARTIAL, honest 1:1 across ALL 11 C. metapsilosis strains (prior run did 4). The paper's CORE finding -- genomes are massively heterozygous (tens of het SNPs/kb, ~few-% allele divergence between two parental subgenomes = the hybridization signature) -- is robustly REPRODUCED across every strain. KEY result: at the RAW (pre-hard-filter) GATK4 call level the het-SNP counts reproduce Table 1 to within ~6-18% for 8/10 strains (mean raw/reported ratio 1.039), and the reported value falls inside our [PASS,raw] bracket for 8/10. The post-filter (PASS) counts deflate -- strongly for the deepest strains (DoC 467-575x -> PASS 0.20-0.33x) -- because GATK4's strand-bias/rank-sum hard filters over-reject het sites at this dataset's extreme depths (200-1308x); the paper's GATK v2.1-13 (2012) filtered far less aggressively, and its HaplotypeScore filter term is gone in GATK4. The two lowest-depth USA hand isolates MCO448(200x)/PL448(212x) reproduce lower than reported even raw (~0.78-0.79x) -- a genuine caller-dependent discrepancy (paper ranks MCO448 highest het%, GATK4 does not) reported honestly. Raw het density 27.5-31.9/kb for 8 strains reproduces the reported 22-26/kb. Reference GCA_900069165.1 reproduced exactly (13,393,615 bp/57 scaffolds, ENA-fasta dup-trap avoided). All 28 fastq md5-verified vs ENA. Determinism: 4 overlap strains match prior run within 0-2 SNPs. NOT attempted (out of scope): de-novo assembly, phylogenomics/parental-lineage placement, dN/dS, recombination dating, MAT locus, mitochondrial analysis, exact LOH block counts, all wet-lab.
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Assessment versions
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v1 current initial assessment Score 57assessed: 2026-06-21 ⛓ bd5e29ba324c
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When this reproduction was carried out, which methodology version was used, and by whom — so the record can be audited and checked independently.
- Reproduced
- 2026-06-24
- Rubric version
- not recorded
- Assessed by
- —
- Last updated
- 2026-08-05
Provisional, curator- or AI-assessed, and independently checkable. A reproduction outcome states what one attempt could reproduce — not a judgement of the authors.
Deep full-text extraction
Model: sonnetThe paper investigates the recent genomic evolution and genetic basis of virulence in Candida metapsilosis by sequencing multiple clinical isolates, testing whether genomic diversity across strains reveals a hybrid origin for this opportunistic pathogen.
- ★ C. metapsilosis is a highly heterozygous hybrid species formed from a single past hybridization event between two parental lineages ~4.5% divergent in sequence. finding
- ★ All 11 sequenced clinical isolates, from geographically distant locations, derive from the same primary hybridization event. finding
- ★ The hybrids are diploid and some strains retain loci for both alternative mating types, supporting sexual mating as the mechanism of hybrid formation. finding
- ★ Recombination and introgression (loss of heterozygosity) between the two subgenomes has been extensive, including partial overwriting of the MTLa mating locus in all strains. finding
- A specialized heterozygous genome assembly strategy combining sequencing data from two strains (PL429 and SZMC8094) was required to generate a usable reference assembly. method
- C. metapsilosis mitochondrial genomes exist as linear or circular chromosomes, with independent circularization events identified in different strains (e.g., PL448 and SZMC21154). finding
- The C. metapsilosis genome was annotated with 5,973 protein-coding genes, comparable to gene counts in C. parapsilosis and C. orthopsilosis. resource
- ★ The parental lineages of the hybrid are inferred to be non-pathogenic, while hybridization between them generated a new opportunistic pathogen with worldwide distribution. mechanism
| Assay | System | Perturbation | Readout | Platform |
|---|---|---|---|---|
| whole-genome sequencing | 11 C. metapsilosis clinical isolates | none | SNP calls, heterozygosity levels, genome assembly | Illumina |
| de novo heterozygous genome assembly | C. metapsilosis strains PL429 (SZMC1548) and SZMC8094 (CP92) | none | chromosome-scale reference assembly (contigs/scaffolds) | — |
| Pulsed Field Gel Electrophoresis (PFGE) | C. metapsilosis clinical isolates | none | chromosome band patterns / mtDNA topology (linear vs circular) | — |
| Southern blot | C. metapsilosis strains MCO448 (linear mtDNA) and PL448 (circular mtDNA) | none | mtDNA hybridization pattern with radiolabeled probe | — |
| PCR (subtelomeric nad3/atp6 primers) | C. metapsilosis isolates (MCO448, PL448, SZMC8095, SZMC8094, SZMC8093, SZMC8092, SZMC8022, SZMC1548, SZMC8029, SZMC21154, SZMC8098) | none | presence of end-to-end junction PCR product indicating circular mtDNA | — |
| comparative/phylogenomic analysis | C. metapsilosis, C. orthopsilosis, C. parapsilosis genomes | none | LOH block distribution, divergence estimates, evolutionary trees | PhylomeDB |
- – Heterozygous regions in all strains show ~4.5% average sequence divergence between alleles, with 22-26 heterozygous SNPs/kb genome-wide 4.5%
- – 1,581 LOH blocks have identical boundaries across all 11 sequenced strains (100 bp threshold), indicating shared hybridization origin 1,581 blocks
- – Fraction of genome occupied by heterozygous regions varies across strains from 54.5% to 61.3% (100 bp threshold) and 63.4-68.5% (200 bp threshold) 54.5-61.3%
- ▼ Average LOH tract size in C. metapsilosis is much shorter than in C. orthopsilosis 535 bp vs 2,151 bp
- – Final reference genome assembly totals 13.3 Mb across seven chromosomes and two unplaced scaffolds, with 5,973 annotated protein-coding genes 13.3 Mb; 5,973 genes
- – New case of circular mitochondrial chromosome identified in strain SZMC21154, independent of the previously known circularization in PL448
- ▲ Longer LOH blocks are significantly enriched in subtelomeric regions P<3.5e-06
- pvalue P<3.5e-06 (Welch's t-test for enrichment of longer LOH blocks in subtelomeric regions)
- count 1,581 LOH blocks with identical boundaries across all 11 strains (evidence for single shared hybridization event (100 bp threshold))
- count 125 blocks with identical boundaries in all 11 strains (200 bp threshold), 29 >500bp, 6 >1kb (stricter threshold confirmation of shared LOH events)
- mean 535 bp average LOH block size (100 bp threshold); 1,183 bp at 200 bp threshold (compared to 2,151 bp average LOH size in C. orthopsilosis)
- other 22-26 heterozygous SNPs/kb (heterozygosity across all sequenced C. metapsilosis strains)
- other ~4.5% divergence between alleles in heterozygous regions (estimated divergence between the two parental subgenomes)
- count 5,973 protein-coding genes in C. metapsilosis (vs 5,752 in C. parapsilosis, 5,784 in C. orthopsilosis) (genome annotation comparison across the species complex)
- fold_change 1,308x combined sequencing coverage for strain PL429 (total depth of coverage from four libraries used for the reference assembly)
Statistical methods review
Model: sonnetA neutral, descriptive read of the statistical approach — what was done, and (for shared learning, not as criticism) what could also have been done.
This is primarily a comparative genomics and bioinformatics study of 11 C. metapsilosis clinical isolates, using genome assembly, whole-genome SNP mapping, and loss-of-heterozygosity (LOH) block detection as the main analytical approaches. Quantitative results are largely reported as counts, percentages, and means derived from genome-wide analyses rather than from formal hypothesis tests. One inferential test is explicitly reported — a Welch's t-test assessing enrichment of longer LOH blocks in subtelomeric regions — alongside phylogenetic reconstruction to infer evolutionary relationships among strains.
| Test | Applied to | n | Assumptions |
|---|---|---|---|
| Welch's t-test (two-sample, unequal variance) | Comparison of LOH block lengths in subtelomeric vs. non-subtelomeric regions (S4 Fig) | — | not stated |
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LOH block lengths in subtelomeric vs. non-subtelomeric regions were compared with a Welch's t-test↳ Could also: A Mann-Whitney U (Wilcoxon rank-sum) test could also be used for this comparison — Genomic segment lengths are typically right-skewed; a non-parametric rank-based test makes no normality assumption and is widely used for similarly distributed genomic interval data
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The single reported p-value is given as an inequality (P<3.5e-06) with no accompanying effect size↳ Could also: Reporting the exact p-value alongside a rank-biserial correlation or common-language effect size would also be standard — An effect size conveys the magnitude of the subtelomeric enrichment independently of sample size, allowing readers to assess biological as well as statistical significance
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Heterozygosity fractions across strains are summarized as a range (54.5–61.3%)↳ Could also: Reporting mean ± SD or median with IQR would also convey central tendency and spread in a conventional format — Formal dispersion measures (SD or IQR) characterize the distribution of strain-level heterozygosity more fully than a range alone, which can be dominated by the most extreme observations
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Inter-species comparisons of LOH statistics (average block size, fraction of long blocks) between C. metapsilosis and C. orthopsilosis were made descriptively↳ Could also: A formal two-sample test (e.g., Mann-Whitney U) with an effect size estimate could also be applied to these inter-species comparisons — Inferential testing would quantify whether the observed differences exceed what might be expected by sampling variation, complementing the descriptive narrative
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LOH block detection relied on two fixed gap thresholds (100 bp and 200 bp), with primary results reported at 100 bp↳ Could also: A simulation- or permutation-based approach calibrating thresholds to the empirical inter-SNP distance distribution could also be used — Calibrating thresholds empirically would provide explicit false-positive rate estimates for LOH calls at each threshold, directly addressing the authors' own caveat that arbitrary thresholds produce false positives or negatives at different rates
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The shared fraction of LOH blocks across all 11 strains (~43%, 1,581 blocks with identical boundaries) is used to argue for a single hybridization origin↳ Could also: A permutation or bootstrap test of the null expectation of shared boundary counts under independent LOH events could also quantify the evidence for a shared origin — Formalizing this comparison statistically would provide a p-value or confidence interval on the excess sharing relative to chance, supplementing the qualitative reasoning presented
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