Stable isotopes and inferring kinship Flashcards
(23 cards)
Is carbon 14 a stable isotope?
No, C14 is not stable but instead unstable and radioactive, which we can take advantage of to data remains as far back as ~50 kya. by measuring the ratio of C14 in relation to the stable isotopes C13 and C12. C12 and C13 occur in a natural proportion of 93:1, heavy isotopes are generally more rare.
C13 is useful when looking at diet, for example to distinguish between C4 plants (common in warm areas) and C3 plants (clod and temperate env - majority of earth’s biomass) which has a difference in C13 by 12-14‰.
What is an isotope signature?
The isotope signature of organisms are the product of the ratios of heavy to light isotopes of the substrates they utilize and the physiological processes (i.e. enzymatic reactions) they employ in assimilating these substrates and discarding their products.”
How do we measure and interpret isotopes?
We measure isotopes in relation to set standard values, which for C13 is a Cretaceous belemnite sample from the Peedee formation in South Carolina, USA. Usin mass spec.
- Rsample>RStandard=”Enriched”
- Rsample<RStandard=”Depleted”
There are main three elements of interest that can be useful in archeologic and aDNA studies, which? What information do we get from them?
- Carbon (δ13C): Diet, dietary preferences, habitat type, climate
- Nitrogen (δ15N): Diet, trophic level, metabolism, aridity
- Strontium (δ87Sr): Geographic location & migration
Nitrogen isotope ratios is an indication of trophic status, why?
From one trophic level to the next in the food chain, δ 15 N-values of the consumer’s collagen become ~2-4‰ enriched. So higher δ 15 N-values in an organism can point to a diet high in marine organisms.
What factors affect isotope abundance?
Isotope abundance varies depending on:
- Temperature
- Precipitation
- Bedrock type
- Variations over time
- Age
- Human impact (e.g. carbon dioxide emissions, pollution)
This can be visualized through ”Isoscapes”, a geological map of isotope distribution.
Also, isotope abundance also differs between organs, different isotope turnover/accumulation rates (Fast turnover: Liver, kidneys, blood plasma, Slow turnover: Fat, bone). In hair for example it accumulates, so you can follow isotope changes over time.
Through plotting δ 13C-values as a function of δ 15N-values, what can you learn?
Plotting δ 13C-values as a function of δ 15N-values tells you something about what type of diet different organisms have.
- For example, herbivores fall lower on the δ15N scale, as they are eating primary produces (plants) while carnivores end up higher (higher trophy level, accumulation of 15N.
- For herbivores you can also distinguish between type of plants in their diet, on the savannah, there are more C4 plants being eaten which make them fall higher on the δ 13C scale, than in temperate forests ”Canopy effect”-lower δ13C in forests.
- If several members of a species is clustering close together, they are probably specialists, if they are more spread, they’re probably generalists.
Where a species fall on this can also be referred to as their “isotopic niche”, but there can be a bit of overlap between species so the information is limited.
How are isotopic studies relevant to research on ancient remains?
Bones preserve for a long time and are rich in collagen, in which isotopes accumulate (C14 - dating, C13 & N15 - diet and S34 - geographic location), so isotopic data can be useful proxies and provide additional layers of information to archeological finds.
δ13C can also be useful as a proxy for what?
δ13C can act as a proxy for atmospheric CO2, top predators reflect the overall picture best - useful in understanding local past climates.
Mammoths has been found to contain similar levels of nitrogen 15 as top predators, why?
Mammoths were herbivores, and should therefor not have similar levels to top predators with the highest trophy levels. One explanation could be that mammoths were recycling nitrogen by eating facies/poop, a behavior that is well recorded among elephants, their closest living relative.
So, even though isotopic data is useful, there are always exceptions - interpretation requires full picture.
Isotopic studies have provided a possible explanation of the extinction of mammoths on Wrangel island, what did they find?
Isotopic data on the Wrangel mammoths found that 34S (stable isotope of Sulphur) were accumulating towards the end, which coincided with an increase in precipitation at 5.5–4 ka. From this its theorized that the increased precipitation led to a lot of weathering and possible accumulation of toxins in their drinking water that might have contributed to their demise.
Isotopic data on cave bears and brown bears tells an interesting story, what?
Isotopic studies show that while brown bears and cave bears were both present (up until ~30 000 ya) brown bears had a higher ratio of 15N while cave bears lower, which suggests that brown bears was eating more fish while cave bears more vegetation. After the extinction of cave bears, the N15 ratios of brow bears have gone down, which indicates that they have taken over the niche occupied by cave bears earlier, more vegetative diet.
Isotopic data on wolves and megafauna?
Wolves before LGM ate megafauna and post LGM much smaller prey, could have driven the extinction of dire wolves.
What does isotopic data tell us about the diet of Neanderthals?
Neanderthals were high in N15, which suggests they ate a meat rich diet (they ate less fish and ate other neanderthals apparently - very high in N15). Ancient humans also high - more flexible in diet.
A study on Gotland ancient humans showed that two populations on Gotland had very different diets/lifestyles, one ate marine food (seal hunters) while the other were farmers.
Could isotopic data be used as evidence for domestication?
Maybe! A study on reindeer found that they had higher N15 levels when fed during the winter, so higher N15 could be a proxy for domestication.
How can strontium isotopes be useful? example?
Strontium levels are different in different locations (kind of unique) which can be helpful in determining is a remain is local or not. It can give us an idea of human migration. For example, from cemeteries in Sigtuna, we have been able to see the likely origin of people buried there, which showed that many were not local.
Also ”The Egtved girl” Bronze Age (1400 BC) had enamel that originated outside Denmark (were her remains were found), Hair: δ13C & δ15N indicate terrestrial diet w. seasonal variation and Elevated Sr signatures both 13-23 months & 4-6 months before death - clear case of migrating humans. Together with other proxies her origin is thought to have been the black forest (southwestern Germany.
There are two kinship types, which?
The two types of kinship are:
- Genetic (biological) kinship: A group of people are genetically related by blood (birth) and share DNA segments inherited from their recent common genetic ancestor (descent)
- Social kinship: Refers to relationships between individuals who are not connected by blood or birth and do not share DNA, but instead construct kin-ties through cultural, social, or religious patterns, i.e., burial practices and co-residence. In some ancient societies there is evidence suggesting that social kinship was more important than genetic.
Why is it relevant to study genetic kinship in ancient humans? five main points.
Knowing kinship relations between individuals in archaeological contexts is of great importance to anthropologists and archaeologists:
- To understand the mobility and inheritance rules of past human populations (e.g., patrilocality or matrilocality)
- To identify genetic relationship between multiple burials or mass graves
- To understand the social organization and patterns of a community, settlement or cemetery, combining genetic with archaeological data, e.g., if they are socially related rather than genetic kin-ties.
- To understand if there was any kin-relationships among the individuals that lived in the house series: Houses were built on top of the old ones and this continuity on the buildings is called as “house series” (~1000 years of continuity) in Aşıklı Höyük (Anatolia).
- To exclude close relatives in population genetic and demographic analyses: in pop. gen. we want diversity, and close relatives can cause bias.
Which genetic markers are used to identify kinship?
Uniparental markers:
- Mitochondrial DNA (mtDNA) haplogroup (hpg) is inherited maternally
-Y chromosome haplogroup is inherited paternally
- STRs (short tandem repeats): short repeated sequences of DNA, 2-6 bp repetitive units) The number of repeat units is highly variable among individuals
NGS methods:
- SNPs (Single Nucleotide Polymorphisms): Thanks to NGS methods (whole genome shotgun sequencing and target SNP capture), we can produce a large number of comparable loci from several samples to study genetic kinship.
Why is SNP capture so useful in kinship studies?
With shotgun sequencing we don’t necessarily get coverage of the same SNPs, SNP capture allows for getting the same target SNPs from all different individuals, which is useful in population genetics.
Give two examples where genetic kinship estimation have been useful.
- Identification of the Romanov family (Russias last Tsar): Nine skeletons in a mass grave, was the Tsar’s family among them? DNA was extracted and analysis of mtDNA, DNA based sexing and STRs together with comparison to living relatives of the Tsar and Tsarina showed that five of the skeletons were the Tsar, tsarina and three of their five children (one daughter and one son missing). The missing children was later found and confirmed in 2007 by the same methods with the original family remains as reference.
- Birger Jarl/birger magnusson grave: Found that the three individuals in the grave had different mtDNA haplogroup - Birger Jarl, his son and Birger’s wife (not the mother of the son).
- Late neolithic (5000 year old) 15 person mass grave in Poland, all with violence against the head, were they related? The study used SNPs as a genetic marker and found that all 15 buried individuals belonged to the same extended family, some first degree, second degree and third degree. The relative position of the bodies was in accordance with kin relationship, revealing that, after a violent death, someone who knew these people, took care of their burial.
- Anatolia and kinship burials: Pre-neolithic HG lifestyle = little kinship, communal lifestyle, Early neolithic (small villages with initial sedentary lifestyle)= More genetic kinship-centered communities, Late Neolithic (full-scale farming and herding) = More socially related rather than genetic kin-ties.
What genetic and anthropological information is needed to identify pedigree relationships?
- X-chromosomal kinship coefficient (θ): Since the X chromosome is inherited maternally (75% of Ne) the θ is different for different types of first degree kinship relationships, e.g sister 0,375 and mother daughter 0,25 even though autosomal kinship coefficient is the same for all.
- mtDNA and Y-chromosome haplogroups: Can help building the pedigree as they need to follow from mother and father.
- Age-at-death estimate: Even if a kinship is unclear, a baby/child cannot be a parent, good extra layer of info.
- Consistency of radiocarbon dates: Two siblings should not date over 100 years apart for example.
One measure of relatedness is abbreviated “IBD” what does it stand for?
IBD stands for Identical-by-descent: Shared DNA segments inherited from recent common genetic ancestors. Two individuals that are genetically related share alleles that are Identical-By-Descent.
Along the genomes of a pair of diploid individuals, there are 9 IBD states possible at any given locus. Six of these states can only occur if the individuals are the result of inbreeding, besides that, they can share one or both the alleles maternally of paternally, or none. If they are unrelated, the probability that they will have alleles that are 0, but the closer related they are the higher the probability that they share alleles that are IBD.
