Monday, 15 August 2016

A colugo genome at last

Phylogenetic placement of colugos  (Scandentia) in the lineage of primates
From Mason et al. Sci Adv 2016 (here) CC BY-NC
Used to be that tree shrews (Scandentia) were regarded as the closest relatives to primates as cogently argued by Wilfrid Le Gros Clark. Molecular phylogenetics have brought that into question with some proposing colugos  or "flying lemurs" (Dermoptera) as a better alternative. But there have several competing hypotheses (see Martin). Choosing the right one has been difficult in the absence of a colugo genome.

Now that has been rectified in a comprehensive study by Mason and colleagues (here) who sequenced the genome of a Sunda colugo and compared it with genomes from 21 mammals. The result clearly came out in favour of colugos as the closest relatives to primates, supported by  20 shared indels and 16 shared retrotransposons.

There are many morphological similarities between tree shrews and colugos but the tree constructed by Mason et al. implies these are due to convergent evolution. Within Euarchontoglires they find tree shrews as the sister to Glires (rodents and lagomorphs).

Museomics and hidden biodiversity within colugos

Colugo fetus and placenta at term; ys = yolk sac;
pat = patagonium From Hubrecht 1894 (here)
Current reference works recognize no more than two species of colugo: Sunda Colugo (Galeopterus variegates) and the Phillipine Colugo (Cynocephalus volans). Mason et al. conclude that there may be as many as 6 Sundaic species and 2 Phillipine ones. They reached this conclusion by extracting DNA from museum specimens of known provenance. As an example, the Eastern and western populations on Borneo are highly divergent consistent with topographical features creating barriers to dispersal.

Currently we are re-examining the placenta and fetal membranes of colugos. We too have had to rely on museum specimens such as those collected by A.A.W. Hubrecht.

The importance of museum collections has been highlighted before in this blog. It is nice that scientists other than morphologists have discovered their value and coined the term museomics for studies of DNA from ancient specimens. Those in the current study ranged from 28 to 121 years old. The oldest specimen from the Raffles Museum of Biodiversity Research is contemporaneous with those collected by Hubrecht for his study of the fetal membranes and now housed at Museum für Naturkunde in Berlin. 

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