FIDDL: depth-matched negative controls distinguish genuine interspecific introgression from competitive-mapping artifact

Verdict. Using strains that cannot contain the ancestry being detected, we show this design generates substantial false-positive signal through two mechanisms with opposite phylogenetic-distance signatures. It primarily advances mechanistic understanding rather than explicit pathology endpoints.

What the authors report

Interspecific introgression is routinely detected by competitively mapping reads to a concatenated multi-species reference and calling regions where a non-focal species recruits coverage. Genuine cross-species sequence conservation inflates the most closely related donor.

Key results stated in the abstract include the following. Using strains that cannot contain the ancestry being detected, we show this design generates substantial false-positive signal through two mechanisms with opposite phylogenetic-distance signatures. Standard nuclear assemblies omit the mitochondrion and 2-micron plasmid, leaving high-copy cytoplasmic reads without a legitimate target; completing the reference preferentially removes signal from the most divergent donor. Because the discriminating information is below single-read resolution, no read-level filter separates artifact from introgression; we show three that fail.

Why it matters for mitochondrial biology

Within mitochondrial research, this work maps primarily to redox biology. The abstract does not lean heavily on pathology language; the contribution appears more mechanistic or systems-level than clinical. Causal language appears in the abstract; such claims should be treated as provisional until design details (loss-of-function, rescue, dose-response) are verified. Server: biorxiv. Posted 2026-08-07. Synthesis confidence is bounded by abstract completeness.

Study design (abstract-level)

Genuine cross-species sequence conservation inflates the most closely related donor. The floor grows with sequencing depth (1.19% of callable positions at 50x, 2.02% at 147x, 3.85% at 393x in a pure strain), is not mitigated by long reads, and appears at sub-diploid dosage - three properties widely read as evidence of authenticity.

Principal findings

1. Using strains that cannot contain the ancestry being detected, we show this design generates substantial false-positive signal through two mechanisms with opposite phylogenetic-distance signatures.
2. Standard nuclear assemblies omit the mitochondrion and 2-micron plasmid, leaving high-copy cytoplasmic reads without a legitimate target; completing the reference preferentially removes signal from the most divergent donor.
3. Because the discriminating information is below single-read resolution, no read-level filter separates artifact from introgression; we show three that fail.
4. We package the comparative controls as FIDDL (False Introgression Detection via Depth-matched controls and Loci-recurrence), an open-source tool, withdraw two of our own analysis-ready calls, and show re-analysis of published wild isolates reduces low-confidence introgression by ~53% while leaving high-confidence signal intact.

Limitations of this brief

• This Mitos brief is an abstract-level synthesis of a preprint; it is not peer review and not a substitute for reading the full paper.
• Preprint status: findings may change with revision or journal review.
• Effect sizes, n numbers, statistics, and full experimental controls are typically incomplete at abstract resolution.
• Primary source: biorxiv DOI 10.64898/2026.08.06.743240 (posted 2026-08-07).

Open scientific questions

• Which specific experimental panels in the full paper establish the strongest causal claim, and how robust are the controls?
• How do these findings sit relative to prior literature on the same pathway—replication, contradiction, or incremental extension?

Bottom line

For mitochondrial biologists focused on redox biology, this preprint is optional follow-up. Abstract-level takeaway: Using strains that cannot contain the ancestry being detected, we show this design generates substantial false-positive signal through two mechanisms with opposite phylogenetic-distance signatures. Confirm methods, effect sizes, and controls in the full PDF before citing the result as established.

Bibliographic record

Abstract-based editorial synthesis by Mitos. Not peer review.