African gamebirds are keys to understanding global avian evolution

https://theconversation.com/african-gamebirds-are-the-key-to-understanding-global-avian-evolution-54970

African gamebirds are keys to understanding global avian evolution

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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

He summarised this view succinctly:

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.