Horse Ancestors Need Re-examination

[Gast]

VETERINARY FEATURE
HORSE ANCESTORS NEED RE-EXAMINATION
The horse’s family tree should
be redesigned according
to an international team
of scientists. Ancient DNA
recovered from extinct horse
species from around the world
has challenged the fossil record
of the horse family.
Only the modern horse, zebras,
wild asses and donkey survive
today, but many other lineages
have become extinct over the
last 50,000 years.
Before the advent of DNA
analysis, fossils were grouped
according to their morphological
characteristics. Now analysis of
DNA fragments isolated from
ancient bones has prompted
scientists to reassess the
relationships between some
of the ancient and modern
members of the horse family.
The study involved an international team of researchers. They
examined 35 equid fossils from around the world (South America,
Europe, Southwest Asia, and South Africa). Ancient mitochondrial
DNA (aDNA) was identified in 22 of the specimens.
The DNA samples were extracted, amplified, and sequenced in
specialist laboratories in Lyon and Adelaide.
Professor Alan Cooper, Director of the Australian Centre for Ancient
DNA (ACAD) based at the University of Adelaide, says despite an
excellent fossil record of the Equidae, there are still many gaps in
our evolutionary knowledge. “Our results change both the basic
picture of recent equid evolution, and ideas about the number and
nature of extinct species.”
The study used bones from caves to identify new horse species in
Eurasia and South America. It also revealed that the Cape zebra,
an extinct giant species from South Africa, was simply a large
variant of the modern Plains zebra. The Cape zebra weighed up to
400 kilograms and stood up to 150 centimeters at the shoulder
blades.
“The Plains zebra group once included the famous extinct quagga,
so our results confirm that this group was highly variable in both
coat color and size.”
Lead author of the paper, Dr Ludovic Orlando from Ecole Normale
Supérieure of Lyon says the group discovered a new species of
the distinct, small hippidion horse in South America.
“Previous fossil records suggested this group was part of an
ancient lineage from North America but the DNA showed these
unusual forms were part of the modern radiation of equid
species,” Dr Orlando says.
A new species of ass was also detected on the Russian Plains
and appears to be related to European fossils dating back more
than 1.5 million years. Carbon dates on the bones reveal that this
species was alive as recently as 50,000 years ago.
“Overall, the new genetic results suggest that we have underestimated
how much a single species can vary over time and
space, and mistakenly assumed more diversity among extinct
species of megafauna,” Professor Cooper says.
“This has important implications for our understanding of
human evolution, where a large number of species are currently
recognized from a relatively fragmentary fossil record.
“It also implies that the loss of species diversity that occurred
during the megafaunal extinctions at the end of the last Ice Age
may not have been as extensive as previously thought.
In contrast, ancient DNA studies have revealed that the loss of
genetic diversity in many surviving species appears to have been
extremely severe,” Professor Cooper says. “This has serious
implications for biodiversity and the future impacts of climate
change.”
The study was published in the Proceedings of the National Academy of Sciences. See: PNAS December 22, 2009 vol. 106 no. 51 21754-21759

[Ramzes]

http://www.innovations-report.de/html/berichte/biowissenschaften_chemie/neue_erkenntnisse_genforschung_145509.html

Da wird noch vieles neu interpretiert werden müssen !
Die Forschung steht ja erst am Anfang !

...für mich natürlich auch die Sparte Agrarwissenschaften interessant z.B. Boden

http://www.agroscope.admin.ch/recherche-equine/index.html?lang=de

[carlo]

Hervorragende Sendung hier on www.PBS.org ,dann links unten:NOVA,dann :"What Darwin never knew"
Viel ueber neueste Erkenntnisse in Genetik;what they "SWITCHES" !

Zumindest DVD sollte bestellbar sein!

Waere interessant zu wissen,ob in IRE in diese Richtung,was geschieht (Dublin,Trinity College, did DNAresearch )

see:http://www.tbheritage.com/GenMarkers.html

One principal discovery in the study demonstrated that Thoroughbred foundation mares share mtDNA haplotypes (variants) far more than has been observed in other horse populations. Researchers determined that a number of Thoroughbred maternal lines or families, formerly thought to spring from unrelated mares, have common female founders, and that Thoroughbreds have a much higher frequency of "sharing" female lines than do other breeds that have been studied. Thoroughbreds, as historians of the breed have said for decades, spring from a small number of original mares, probably even fewer than previously thought.

The study identified only seventeen variants in the nineteen family lines studied; since two of the variants were due to a single difference, or de novo mutation, in the DNA sequence, it is probable the number of unique haplotypes, indicating different founding mares, is actually fifteen, within the nineteen families.

Because mtDNA does not vary over long periods of time -- the rate of mutation suggests 10,000 years or more -- the variants found in the Hill study can also be found in horse breeds from Europe, the Far East, and Near East. The Animal Geneticsarticle includes a chart, which shows a phylogenetic tree mapping the mtDNA haplotypes geographically, to which readers are referred. The genetic discoveries of the Hill study, then, must be interpreted within the framework of recorded history -- pedigrees and other historical records -- to examine the impact on the thoroughbred.