https://theconversation.com/african-gamebirds-are-the-key-to-understanding-global-avian-evolution-54970
African gamebirds are keys to understanding global
avian evolution
3490
Conservation reads
Much the same as for
humans, Africa is the evolutionary cradle of ‘bird-kind’, or at least of one of
its major evolutionary branches, the ‘gamebirds’. About 290 species of gamebirds form the avian
Order Galliformes - chicken-like birds. http://global.britannica.com/animal/galliform These include: drab, small and monogamous
quails and partridges in which males and females are often indistinguishable;
medium-sized, spectacularly feathered, polygamous pheasants and peafowl whose
males and females are strikingly different in appearance; and the gigantic
and promiscuous turkeys. http://animaldiversity.org/accounts/Galliformes/ In some gamebirds,
the males are ‘armed and dangerous’ with leg spurs used in male-vs-male
combat. Together with the
duck/goose-like Anseriformes, the gamebirds occupy the second oldest branch,
after the ostrich-like birds, of the avian evolutionary tree. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0064312 Gamebirds also occur on all
continents except Antarctica. This means that an understanding their evolution
could provide insight into patterns and processes of global avian evolutionary
history.
Unfortunately,
as recently as 1959, Erwin Stresseman - the most highly respected avian
evolutionary biologist at the time - published a seminal paper called The status of avian systematics and its unsolved problems
in which he lamented the failure of evolutionists to produce a scientifically
sound phylogeny (evolutionary tree) for birds.
A
major breakthrough
Then, in 1990, a molecular avian
phylogeneticist, Charles Sibley (with his colleague Jon Ahlquist), produced
what became known as The Tapestry.
This is a phylogeny for ALL major
bird groups. http://jboyd.net/Taxo1/taxo1.html It was
based on a revolutionary molecular technique known as DNA-DNA hybridization. http://www.encyclopedia.com/topic/DNA_Hybridization.aspx DNA-DNA
hybridization assesses the total genomic DNA divergence between of pairs of
species using a measure (delta T50H) of the heat needed to separate a hybrid
helix produced by joining single stands from the different species. A high delta T50H indicates a relatively close phylogenetic relationship between the
species and a low one a distant relationship. http://mbe.library.arizona.edu/data/1986/0303/9ruvo.pdf Furthermore,
since DNA mutates at a relatively constant rate over time, Sibley maintained
that differences in delta T50H (when calibrated, e.g., with fossil and
geological evidence) could also be used to estimate the timing of phylogenetic
branching. http://www.evolution.berkeley.edu/evosite/evo101/IIE1cMolecularclocks.shtml
Anatomy is adaptive and hence evolves erratically
depending on natural selection. DNA keeps the time.
https://research.amnh.org/vz/ornithology/pdfs/1987a.DNA%20hybridization%20critique.pdf
Sibley’s findings
were heralded as a major scientific breakthrough by scientists and public
intellectuals alike. In his widely-read column in Natural History magazine,
Stephen Jay Gould, a phylogeneticist from
Harvard University, even proclaimed that his discovery should be “shouted
from the parapets”.
Sadly for Sibley,
this did not happen.
Conflicting and
supporting evidence
Sibley showed me his findings regarding
the gamebirds several years before he published The Tapestry. I had been
conducting phylogenetic research on their evolution using organismal -
anatomical and behavioural/life history - evidence. My results differed from
The Tapestry, especially with regard to the placement of guineafowls, which are
a family of gamebirds confined to Africa. https://en.wikipedia.org/wiki/Guineafowl
This incensed him and he dismissed my findings as being merely based on
the subjective analysis of “a few bumps on bones”. He could be quite irascible! https://www.google.co.za/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=Charles+sibley+obituary+dick+schodde
Soon after the publication
of The Tapestry, a team at the University of California Berkeley published the
first molecular genetic phylogenetic tree for the gamebirds based on sequenced DNA. This
research analysed a short sequence from a gene found on mitochondrial DNA which
has no effect on an organism’s anatomy. One of the phylogenetic trees produced
in this study placed the guineafowls in the same tree position as The Tapestry.
This pleased Charles, and he claimed that The Tapestry was “vindicated”.
Problems
with The Tapestry
Soon after it was
published, The Tapestry was widely criticised on a number of grounds.
Chief among these was the fact that the DNA-DNA hybridization approach to
phylogeny depends on overall - both ancestral and evolutionarily derived - DNA
similarity.
Ancestral similarity, such
as the shared presence of hair or mammary glands in mammals, is of no
phylogenetic use in working out the relationships within that group since it
inherited these features unchanged from its near relatives. http://www.encyclopedia.com/topic/symplesiomorphy.aspx
Analytical approaches to phylogenetics based on overall similarity are
known as phenetics. They have been shown to produce incorrect results biased,
amongst other things, by the effects of ancestral similarity.
The now universally
accepted method of determining phylogenetic relationships is cladistics. This
determines relationships between lineages - tree branches and their intervening
connections; but only on the basis of shared derived evolutionarily novel
character similarity.
Derived characters are
features that are invariant within and between populations under study and
discriminate evolutionarily independent lineages - tree branches. http://www.merriam-webster.com/dictionary/synapomorphy
A second major criticism of
The Tapestry was that it excluded organismal attributes like anatomical,
behavioural, physiological and life history characteristics. Sibley believed
that such things were prone to convergent or phylogenetically misleading
evolution due to adaptation.
I am a strong proponent of
combining all evidence in phylogenetic analyses. In other words, DNA does not stand
for “don’t need anatomy”.
In the end, when large
amounts of DNA sequence data, partitioned into ancestral/derived characters,
were analysed together with similarly partitioned organismal characters using
cladistics, many of the results of The Tapestry were confirmed. Others were
refuted. Prominent among these was the
resulting tree for the gamebirds.
The ‘true’
tree for gamebirds
In 2006, I and an
international team of molecular biologists found only one phylogenetic tree for the gamebirds. This was long after Sibley’s death,
and done through through cladistic analyses of combined organismal and DNA
evidence. Calibrated with fossil evidence, the tree suggests that the evolutionary
roots of gamebirds date back to close to the mass extinction
of the dinosaurs some 65 million years ago.
This tree demonstrates that
the gamebirds originated in the southern mega-continent, Gondwana.
The oldest evolutionary
gamebird lineage diversified around 64 million years ago into the Australasian
megapodes. They use rotting vegetation and even volcanic sand to incubate their
eggs. Next, around 61 million years ago, came the cracids who have evolved and
diversified extensively in South and Central America.
Then, contrary to The
Tapestry, come Africa’s guineafowls at around 54 million years ago. No matter
where you are in sub-Saharan Africa, you can encounter at least one of the six
species of guineafowls. http://www.biodiversitylibrary.org/part/74638
Unexpected
results from Africa
Then the situation within
Africa gets fascinating. In the early 1990s, I was sent a manuscript describing
a bizarre new species as a francolin or spurfowl. This gamebird is about the
size of a partridge, and is found only in the forests of Tanzania’s Udzungwa
Mountains. But, based on its
anatomy, one thing was certain: this Udzungwa gamebird is not an African
spurfowl or francolin like Swainson’s Spurfowl and the Grey-winged Francolin.
So the discoverers of this
amazing new gamebird were forced to place it into its own single-species genus
called Xenoperdix. http://www.birdlife.org/datazone/speciesfactsheet.php?id=187
This can be loosely translated as:
I don’t know that the hell this
partridge is related to.
When Xenoperdix udzungwensis was included in the study that refuted The
Tapestry, our team found that it was unrelated to any African gamebird. Its
nearest living relatives are partridge-like gamebirds from south-eastern Asia.
Equally surprisingly, we
found that Nahan’s Francolin, also a restricted-range species which occurs only
in primary rainforest in the north-eastern Democratic Republic of Congo and
western Uganda, is also not a francolin. It is most closely related to another
evolutionarily enigmatic African gamebird. This is the Stone Partridge, which
lives in dry savannas. Until then, it was also placed in its own genus known as
Ptilopachus.
Finally, these two
sister-species are not related to any African, European or Asian gamebird.
Their nearest, but very distant, relatives are the North and South American
quails. These are even tinier gamebirds of the Family Odontophoridae.
Our
team also provided a definitive answer to the question of the evolutionary
affinities of Africa’s arguably most spectacular avian discovery of the 20th
Century, the Congo Peafowl or Afropavo
congensis. This ‘peacock’ was discovered in the 1920s. It is found only in
the Central Congolian lowland forests of the Democratic Republic of Congo and
is its national bird. It was first
thought to be distantly related to the guineafowls and that its peafowl-like
features had evolved independently from those of Asian peafowl. http://www.birdlife.org/datazone/speciesfactsheet.php?id=187
We found that it is, in fact, distantly related to Asian peafowl.
Implications
for global avian evolution
In addition to overturning
the widely accepted The Tapestry hypothesis, our research suggests the
following scenario for the evolution of gamebirds.
·
After
the guineafowl evolved in Africa, the next major gamebird lineage that split
off has its roots around 50 million years ago in Africa with the Stone
Partridge and Nahan’s Francolin.
·
An
offshoot of their common ancestor emigrated from north-western Africa through
western Europe into North America, giving rise to the New World quails.
·
Then,
around the same time there was a second emigration out of Africa, this time
from the continent’s north-east. It had roots in Xenoperdix that ultimately gave rise to the remainder of the
Eurasian and North American gamebirds. These include the grouse, turkeys,
pheasants, partridges, Asiatic francolins quails and peafowls.
Finally, much more recently
- averaging around 17 million years ago - there were multiple emigrations.
These are now from Asia back into Africa that gave rise to Afropavo and the African francolins, spurfowls and quails. So, like with modern Homo sapiens, modern gamebirds are largely evolutionary products of
out-of-Africa emigrations.
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