Global divergence of the human follicle mite Demodex folliculorum : Persistent associations between host ancestry and mite lineages

Abstract

Microscopic mites of the genus Demodex live within the hair follicles of mammals and are ubiquitous symbionts of humans, but little molecular work has been done to understand their genetic diversity or transmission. Here we sampled mite DNA from 70 human hosts of diverse geographic ancestries and analyzed 241 sequences from the mitochondrial genome of the species Demodex folliculorum. Phylogenetic analyses recovered multiple deep lineages including a globally distributed lineage common among hosts of European ancestry and three lineages that primarily include hosts of Asian, African, and Latin American ancestry. To a great extent, the ancestral geography of hosts predicted the lineages of mites found on them; 27% of the total molecular variance segregated according to the regional ancestries of hosts. We found that D. folliculorum populations are stable on an individual over the course of years and that some Asian and African American hosts maintain specific mite lineages over the course of years or generations outside their geographic region of birth or ancestry. D. folliculorum haplotypes were much more likely to be shared within families and between spouses than between unrelated individuals, indicating that transmission requires close contact. Dating analyses indicated that D. folliculorum origins may predate modern humans. Overall, D. folliculorum evolution reflects ancient human population divergences, is consistent with an out-of-Africa dispersal hypothesis, and presents an excellent model system for further understanding the history of human movement.Demodex | phylogeography | symbiosis | coevolution H uman evolution did not take place in isolation but instead occurred alongside that of many closely associated species. Phylogeographic studies of human-associated species-such as lice and rodents, as well as certain bacteria and viruses-have suggested, eliminated, and confirmed hypotheses about human history (1-10). For example, these studies have provided details about the timing and nature of the original human migration out of Africa, the spread of humans within and among continents, and the domestication of large vertebrates.Mites of the genus Demodex live in the hair follicles and sebaceous glands of humans and provide a promising system with which to explore further the details of human evolution. The association between Demodex and Homo sapiens is likely to be an ancient one: The broad distribution of these mites across mammal species (11), coupled with the ancient date of divergence estimated between the two species known to be found on humans (12), suggests that Demodex originated and diversified with early mammals. Furthermore, Demodex seem likely to have been carried along whenever their hosts migrated, because they are ubiquitous inhabitants of human skin (13,14). Finally, in comparison with the other human associates that have been studied to date, Demodex mites are more tightly associated with human bodies than are lice, while their generation times are slower than those of bacteria and virus...

Afoxolaner and fluralaner treatment do not impact on cutaneous Demodex populations of healthy dogs

“…Under normal circumstances, they appear to live as commensals, feeding on their host's sebum and are only opportunistically pathogenic . It is possible that the presence of Demodex mites may confer a mutualistic host benefit by ingesting bacteria or other organisms, or by having some positive effect on the innate immune system, considering the long history of this association, lasting for millions of years according to one study …”

Detection, Prevalence and Phylogenetic Relationships of Demodex spp and further Skin Prostigmata Mites (Acari, Arachnida) in Wild and Domestic Mammals

“…Although mites are host-specific and usually do not cross-infest, transmission between individuals within the same colony may occur during allogrooming, breeding, fighting, aggregating, or from mother to offspring during birth or nursing [21,68–71]. Transmission does not necessarily result in an individual developing a disease (e.g.…”

“…Demodex mites have been described (both morphologically and genetically) in both groups, reflecting the constancy of the hair follicle niche or the high transmissibility of Demodex mites between and within placental mammal species [5,14–20]. We have an extraordinary example of parasitic parallelism in the Demodex genus [6,12,21,22]. …”

“…In addition, a 930 bp fragment of the mitochondrial Demodex genome was used to evaluate the genetic diversity and phylogeography of D . folliculorum [21]. However, one of the most effective genes known to detect, determine and classify Demodex mites is the mitochondrial 16S rRNA gene (16S rDNA).…”

Phylogeography of a migratory songbird across its Canadian breeding range: Implications for conservation units

“…However, cryptic genetic structure in such apparent panmixia can often be identified using parasites, mutualists, and commensals. Symbionts of birds have been shown to be useful biological markers for resolving host evolutionary history, population structure, and migratory patterns because of their shorter generation time compared to their hosts (Bruyndonckx, Biollaz, Dubey, Goudet, & Christe, 2010;Palopoli et al, 2015;Whiteman, Kimball, & Parker, 2007). Variation in symbiont assemblages or in genetic structure of particular species of symbionts can potentially provide finer resolution of host structure than the hosts themselves.…”