Strong selection for African ancestry in Madagascar

As I've long suspected, certain ancestry survives longer in certain places than others if it provides benefits in terms of adaption to the area.

See: Denis Pierron et al
"Strong selection during the last millennium for African ancestry in the admixed population of Madagascar"


https://www.nature.com/articles/s41467-018-03342-5

"While admixed populations offer a unique opportunity to detect selection, the admixture in most of the studied populations occurred too recently to produce conclusive signals. By contrast, Malagasy populations originate from admixture between Asian and African populations that occurred ~27 generations ago, providing power to detect selection. We analyze local ancestry across the genomes of 700 Malagasy and identify a strong signal of recent positive selection, with an estimated selection coefficient >0.2. The selection is for African ancestry and affects 25% of chromosome 1, including the Duffy blood group gene. The null allele at this gene provides resistance to Plasmodium vivax malaria, and previous studies have suggested positive selection for this allele in the Malagasy population. This selection event also influences numerous other genes implicated in immunity, cardiovascular diseases, and asthma and decreases the Asian ancestry genome-wide by 10%, illustrating the role played by selection in recent human history."

is this about immunity against typical African diseases?

Still searching for answers

Thank you for your interpretation of human history. I've been research the Bantu for a short time but their's so much about their historic I just had to think about genetics.
Abstract

Linguistic and cultural evidence suggest that Madagascar was the final point of two major dispersals of Austronesian- and Bantu-speaking populations. Today, the Mikea are described as the last-known Malagasy population reported to be still practicing a hunter-gatherer lifestyle. It is unclear, however, whether the Mikea descend from a remnant population that existed before the arrival of Austronesian and Bantu agriculturalists or whether it is only their lifestyle that separates them from the other contemporary populations of South Madagascar. To address these questions we have performed a genome-wide analysis of >700,000 SNP markers on 21 Mikea, 24 Vezo, and 24 Temoro individuals, together with 50 individuals from Bajo and Lebbo populations from Indonesia. Our analyses of these data in the context of data available from other Southeast Asian and African populations reveal that all three Malagasy populations are derived from the same admixture event involving Austronesian and Bantu sources. In contrast to the fact that most of the vocabulary of the Malagasy speakers is derived from the Barito group of the Austronesian language family, we observe that only one-third of their genetic ancestry is related to the populations of the Java-Kalimantan-Sulawesi area. Because no additional ancestry components distinctive for the Mikea were found, it is likely that they have adopted their hunter-gatherer way of life through cultural reversion, and selection signals suggest a genetic adaptation to their new lifestyle. (Less)
DOI: 10.1073/pnas.1321860111

Wow, a genome-wide reduction of 10% in Asian ancestry in less than ~27 generations is a BIG thing, I think. This suggests that, if the arriving population is not that adapted to the local environment, the pressures of selection against it can be really significant, almost decisive to the really long term (say, 100, 200 generations) survival of that genetic ancestry in its new homeland.

It does seem quite dramatic in evolutionary terms, but it's also interesting to think about how quickly humans can adapt to epidemics. These people had a deadly disease around, and they also had a population with the genetic protection to it right next to them. The immunity genes probably entered the Asian population very early, yet after 1000 years there are still many people there who aren't immune. Maybe the disease wasn't deadly enough to speed up the process.

Ownstyler said:

It does seem quite dramatic in evolutionary terms, but it's also interesting to think about how quickly humans can adapt to epidemics. These people had a deadly disease around, and they also had a population with the genetic protection to it right next to them. The immunity genes probably entered the Asian population very early, yet after 1000 years there are still many people there who aren't immune. Maybe the disease wasn't deadly enough to speed up the process.

Click to expand...

That's very true. It spills over into other areas as well.

"In addition to the Duffy blood group gene, the chromosomal region with the highest African ancestry (>90%, 9 SDs from the mean, Table 1) also contains disease-related biomarkers known to differ greatly between African and non-African populations: (1) C-reactive protein level (linked to the CRP gene), an inflammation marker that is higher in populations with African ancestry and associated with cardiovascular disease risk28; (2) immunoglobulin E levels, associated with FCER1A (Fc fragment of immunoglobulin E (IgE)) polymorphisms, are higher in populations with African ancestry and are associated with asthma susceptibility29; and (3) low white blood cell counts (benign ethnic neutropenia) are also linked to African ancestry at the 1q23 locus30. SNPs for all of these loci exhibit large frequency differences between East Asian and African populations, and the Malagasy exhibit allele frequencies more similar to those in Africans and significantly different from frequencies predicted by admixture without selection (Fig. 5 and Table 1). "

"Moreover, this selection in favor of African ancestry decreased the Asian ancestry not just at the 1q23 locus, but also genome-wide. Indeed if selection had not occurred, Asian ancestry genome-wide in Madagascar would probably be 45–50%, as opposed to the observed 38%. This is because in the initial stages of selection, individuals with Asian ancestry at the 1q23 locus that were selected against also had high levels of Asian ancestry genome-wide. In other words, African populations coming to Madagascar might have had a significant advantage over Asian people. It is not clear whether African or Asian populations first settled Madagascar, but it is possible that when the two populations came into contact in Madagascar, fitness differences played a role in the history of the settlement of Madagascar even before the admixture. Biology can thus play a role in historical events and should be considered when discussing the settlement of a new environment such as Madagascar."

Vast continent so much to know

First it always important to thank those willing to share the journey of discovery that tweek the curiosity.
:grin:The challenge seems to be how many issues the continent of Africa has to offer. Malaria with it's Duffy positive Populations and on the other hand Duffy Negative Populations. Ethiopia and Cameroon added to Madagascar yet we've only scratched the surface.
Background
Malaria is the mostprevalent communicable disease in Ethiopia, with 75% of the country’s landmassclassified as endemic for malaria. Accurate information on the distribution andclinical prevalence of Plasmodium vivaxand Plasmodium falciparum malaria inendemic areas, as well as in Duffy-negative populations, is essential todevelop integrated control strategies.
Themalaria parasite Plasmodium vivax isknown to be majorly endemic to Asian and Latin American countries with no orvery few reports of Africans infected with this parasite. export on Since the human Duffy antigens act asreceptors for P. vivax to invade human RBCs and Africans aregenerally Duffy-negative, non-endemicity of P. vivax in Africahas been attributed to this fact. However, recent reports describing P.vivax infections in Duffy-negative Africans from West and Centralparts of Africa have been surfaced including a recent rP. vivax infectionin native Cameroonians
Malaria Is a highly infectious vector-borne disease of the tropical and subtropical countries of the globe. Almost all the African countries are endemic to malaria, contributing about 90% of the total global malaria deaths incidences [1].Apart from global effort to control malaria, this disease remains as a frontline infectious disease in Africa and in other malaria endemic regions of the globe. Relief and management of malaria majorly rely on treatment of infected patients by chemotherapy. Since as many as five different species of the genus Plasmodium (Plasmodium falciparum, P. vivax, P.ovale, P. malariae and P. knowlesi) are known to infect humans [2], [3]either singly or as mixed parasitic infections, proper diagnosis of specific malariaparasitic infection holds the key for effective treatment and management of malaria.

This is pretty interesting.

Ygorcs said:

Wow, a genome-wide reduction of 10% in Asian ancestry in less than ~27 generations is a BIG thing, I think. This suggests that, if the arriving population is not that adapted to the local environment, the pressures of selection against it can be really significant, almost decisive to the really long term (say, 100, 200 generations) survival of that genetic ancestry in its new homeland.

Click to expand...

most pressure on the asian genome probably came in the early stages when people with a disadvantage allele at 1q23 still mostly had asian genome because they were not mixed or the recombination of the chromosomes wasn't as developed. here the it may have been the arriving population that was adapted to the local environment. interessting that there was a population in madagascar related to south east asians.