Equus roundworms (Parascaris univalens) are undergoing rapid divergence while genes involved in metabolic as well as anthelminic resistance are under positive selection

Abstract

Background The evolution of parasites is often directly affected by the host's environment. Studies on the evolution of the same parasites in different hosts are of great interest and are highly relevant to our understanding of divergence. Methods Here we performed whole-genome sequencing of Parascaris univalens from different Equus hosts (horses, zebras and donkeys). Phylogenetic and selection analyses were performed to study the divergence and adaptability of P. univalens. Results At the genetic level, multiple lines of evidence indicate that P. univalens is mainly separated into two clades (horse-derived and zebra & donkey-derived). This divergence began 300–1000 years ago, and we found that most of the key enzymes related to glycolysis were under strong positive selection in zebra & donkey-derived roundworms, whereas the lipid-related metabolic system was under positive selection in horse-derived roundworms, indicating that the adaptive evolution of metabolism has occurred over the past few centuries. In addition, we found that some drug-related genes showed a significantly higher degree of selection in diverse populations. Conclusions This work reports the adaptive evolution and divergence trend of P. univalens in different hosts for the first time. Its results indicate that the divergence of P. univalens is a continuous, dynamic process. Furthermore, the continuous monitoring of the effects of differences in nutritional and drug histories on the rapid evolution of roundworms is conducive to further understanding host-parasite interactions.

The equine ascarids: resuscitating historic model organisms for modern purposes

“…parasites from the mountain zebra ( Equus zebra , Linnaeus, 1758 ), domestic horse, and wild ass ( Equus asinus , Gray, 1824) using the mitochondrial genes cox1 and nadh1 , demonstrated that the worms from E. asinus formed a distinct clade compared to specimens collected from the other two Equus species (Peng et al 2019 ). A recent whole-genome study of specimens from horses, donkeys ( Equus africanus asinus , Linnaeus, 1758 ), and zebras also indicated distinct clades for P. univalens specimens—some of which were confirmed via karyotyping—found within horses and those found in zebras and donkeys (Han et al 2022 ). Another recent study completed a phylogenetic analysis for a select group of nuclear and mitochondrial genes using almost all Parascaris spp.…”

“…One of the study populations was later karyotyped and found to consist only of P. univalens (Nielsen et al 2014 ). Additional populations in the USA (Nielsen et al 2014 ), Sweden (Martin et al 2018 ), Iceland (Martin et al 2021c ), and China (Han et al 2022 ) were karyotyped and identified as P . univalens , which taken together suggests that the main species present in domestic horses globally is P. univalens and not P. equorum .…”

Horse and donkey parasitology: differences and analogies for a correct diagnostic and management of major helminth infections

“…isolated from donkeys formed a distinct clade compared to those collected from mountain zebras and domestic horses (Peng et al ., 2019 ). Furthermore, a recent whole-genome analysis performed in horses, donkeys and zebras showed that P. univalens found in horses belong to distinct clades than those reported in donkeys and zebras (Han et al ., 2022 ).…”

Exploration of Parascaris species in three different Equus populations in China

“…Two species of roundworms, Parascaris univalens and Parascaris equorum, are found infecting Equus hosts [4][5][6]. These two species cannot be easily distinguished morphologically but differ concerning their karyotype.…”