Zonkey:a simple, accurate and sensitive pipeline to genetically identify equine Fl-hybrids in archaeological assemblages

Horses, asses and zebras, can produce first-generation F1-hybrids, despite their striking karyotypic and phenotypic differences. Such F1-hybrids are mostly infertile, but often present characters of considerable interest to breeders. They were extremely valued in antiquity, and commonly represented in art and on coinage. However, hybrids appear relatively rarely in archaeological faunal assemblages, mostly because identification based on morphometric data alone is extremely difficult. Here, we developed a methodological framework that exploits high-throughput sequencing data retrieved from archaeological material to identify F1-equine hybrids. Our computational methodology is distributed in the open-source Zonkey pipeline, now part of PALEOMIX (https://github.com/MikkelSchubert/paleomix), together with full documentation and examples. Using both synthetic and real sequence datasets, from living and ancient F1-hybrids, we find that Zonkey shows high sensitivity and specificity, even with limited sequencing efforts. Zonkey is thus well suited to the identification of equine F1-hybrids in the archaeological record, even in cases where DNA preservation is limited. Zonkey can also help determine the sex of ancient animals, and allows species identification, which advantageously complements morphological data in cases where material is fragmentary and/or multiple candidate equine species coexisted in sympatry

Experimental conditions improving in-solution target enrichment for ancient DNA

High-throughput sequencing has dramatically fostered ancient DNA research in recent years. Shotgun sequencing, however, does not necessarily appear as the best-suited approach due to the extensive contamination of samples with exogenous environmental microbial DNA. DNA capture-enrichment methods represent cost-effective alternatives that increase the sequencing focus on the endogenous fraction, whether it is from mitochondrial or nuclear genomes, or parts thereof. Here, we explored experimental parameters that could impact the efficacy of MYbaits in-solution capture assays of ~5000 nuclear loci or the whole genome. We found that varying quantities of the starting probes had only moderate effect on capture outcomes. Starting DNA, probe tiling, the hybridization temperature and the proportion of endogenous DNA all affected the assay, however. Additionally, probe features such as their GC content, number of CpG dinucleotides, sequence complexity and entropy and self-annealing properties need to be carefully addressed during the design stage of the capture assay. The experimental conditions and probe molecular features identified in this study will improve the recovery of genetic information extracted from degraded and ancient remains.No Full Tex