{
  "id": 18485528,
  "title": "Sexing carnivores from faecal metagenomes: calibrating Rx for stone marten and red fox",
  "url": "https://urgent.news/2026/11/06/sexing-carnivores-from-faecal-metagenomes-calibrating-rx-for-stone",
  "topic": "science",
  "section": "Science",
  "published": "2026-11-06T00:00:00.000Z",
  "source": {
    "name": "bioRxiv",
    "slug": "biorxiv",
    "url": "https://www.biorxiv.org/content/10.64898/2026.11.04.764345v1?rss=1"
  },
  "original_language": "en",
  "account": "Determining the sex of an animal based on its fecal matter can enhance non-invasive monitoring techniques, yet existing read-ratio sexing methods were originally designed for human ancient DNA. Researchers investigated the applicability of these methods in shotgun metagenomes derived from seven stone marten (Martes foina) and red fox (Vulpes vulpes) scats. They first removed human DNA from each library using competitive mapping against a host assembly and the human reference genome. Next, they utilized the Skoglund Ry metric on the marten samples, which yielded 0 to 25 Y-mapping reads per sample. However, this approach failed to identify the two animals as male according to the Rx metric developed by Mittnik et al. To address this limitation, the researchers reimplemented the X-to-autosome ratio Rx as an open-source, species-agnostic Python tool.\n\nTo assess the tool's performance, the researchers simulated both female and male genomes for both species and created 200 replicate subsamples at various depths ranging from 1,000 to 100,000 mapped reads. Out of 11,200 replicates, only 9 were incorrectly assigned to the wrong sex, all of which occurred when the sample depth was below 2,000 mapped reads. Above that threshold, the tool only failed to assign sex in under 5% of replicates at depths greater than 7,500 reads and under 1% at depths exceeding 15,000 reads.\n\nWhen applied to the actual scat samples, the Rx tool successfully identified four females and two males. One sample with 596 host-assigned reads remained unassigned. Importantly, after implementing competitive removal of human reads, the tool demonstrated its usability for monitoring these carnivores.",
  "summary": "Knowing the sex of the animal that deposited a scat adds value to non-invasive monitoring, but read-ratio sexing methods were developed for human ancient DNA. We examined their use in shotgun metagenomes of seven stone marten (Martes foina) and red fox (Vulpes vulpes) scats. Human DNA, present in every library, was removed by competitive mapping against the host assembly and the human reference.…",
  "key_points": [],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}