Ancient and modern DNA reveal dynamics of domestication and cross-continental dispersal of the dromedary

Abstract

Dromedaries have been fundamental to the development of human societies in arid landscapes and for long-distance trade across hostile hot terrains for 3,000 y. Today they continue to be an important livestock resource in marginal agro-ecological zones. However, the history of dromedary domestication and the influence of ancient trading networks on their genetic structure have remained elusive. We combined ancient DNA sequences of wild and early-domesticated dromedary samples from arid regions with nuclear microsatellite and mitochondrial genotype information from 1,083 extant animals collected across the species' range. We observe little phylogeographic signal in the modern population, indicative of extensive gene flow and virtually affecting all regions except East Africa, where dromedary populations have remained relatively isolated. In agreement with archaeological findings, we identify wild dromedaries from the southeast Arabian Peninsula among the founders of the domestic dromedary gene pool. Approximate Bayesian computations further support the "restocking from the wild" hypothesis, with an initial domestication followed by introgression from individuals from wild, now-extinct populations. Compared with other livestock, which show a long history of gene flow with their wild ancestors, we find a high initial diversity relative to the native distribution of the wild ancestor on the Arabian Peninsula and to the brief coexistence of early-domesticated and wild individuals. This study also demonstrates the potential to retrieve ancient DNA sequences from osseous remains excavated in hot and dry desert environments.anthropogenic admixture | Camelus dromedarius | demographic history | paleogenetics | wild dromedary T he dromedary (Camelus dromedarius) is one of the largest domestic ungulates and one of the most recent additions to livestock. Known as the "ship of the desert" (1), it enabled the transportation of people and valuable goods (e.g., salt, incense, spices) over long distances connecting Arabia, the Near East, and North Africa. This multipurpose animal has outperformed all other domestic mammals, including the donkey, in arid environments and continues to provide basic commodities to millions of people inhabiting marginal agro-ecological zones. In the current context of advancing desertification and global climate change, there is renewed interest in the biology and production traits of the species (2), with the first annotated genome drafts having been recently released (3, 4). SignificanceThe dromedary is one of the largest domesticates, sustainably used in arid and hostile environments. It provides food and transport to millions of people in marginal agricultural areas. We show how important long-distance and back-and-forth movements in ancient caravan routes shaped the species' genetic diversity. Using a global sample set and ancient mitochondrial DNA analyses, we describe the population structure in modern dromedaries and their wild extinct ancestors. Phylogenetic analyses of ancient and modern dro...

Reply to Marom et al.: Mitochondrial panmixia in dromedaries predates ancient caravan trading

“…With the latter not being the focus of our paper, however, we did not address this aspect in full detail but concluded that transcontinental and crosscontinental transportation of bulk goods using dromedaries would offer the most plausible explanation for the lack of patterning in our data (2). As far as we understand, the authors do not challenge our conclusions but support our argument that camel caravans played a role in dispersal and genetic admixture.…”

“…In the maternal (mitochondrial) haplotypes, for one, we see a panmixia in modern dromedaries, which certainly predates crossbreeding at central oases along the routes. At the time that large-scale human-mediated dispersal of dromedaries started, most of today's observed mitochondrial genome diversity was already present, secured and augmented from the ancestral diversity of the wild (now extinct) dromedaries (2).…”

Back to the roots and routes of dromedary domestication

“…There are lots of additional interesting observations in the work of Almathen et al (3). For instance, their microsatellite data suggested the existence of demographic collapses before domestication, some ∼5,000-8,000 ya.…”

“…In PNAS, Almathen et al (3) now rectify this anomaly by performing what is, to my knowledge, the first large-scale genetic analysis of the domestic dromedary.…”

Genetic diversity analyses of tropical goats from some countries of Middle East

“…The main route was the central Arabian Desert route (Incense Route -South-North of Arab world) of goods traveled from Southern Arabia (currently Somalia or Yemen) through the Arabian Peninsula (currently Saudi Arabia) and Damascus region (currently Jordan and Syria) to the Phoenicians on the Mediterranean Sea (Liu, 2010). On the other hand, there was a Pilgrimage Route that Muslims traveled across the globe (North-South) to reach Islam's two holiest cities -Mecca and Medina -in the Hejaz region of Saudi Arabia (Almathen et al, 2016). Thus, Saudi Arabia exposed to animal exchange network in the past while people traveled by and/or with the animals for trading or worship purposes.…”