In 2008, Warren et al. published the genome of Glennie, a female platypus. Once thought to be a zoological joke, the platypus is one of 5 remaining monotremes. The platypus lays eggs and has no nipples but does produce milk that is sucked through the skin. The duck-bill and webbed feet added to its infamy. On top of that, the adult platypus lacks teeth. In short, platypuses are strange and very cool.
Evolutionary, monotremes are very significant because they diverged from mammals about 166 MYR ago. This time scale is of importance because they share a common ancestor more distant than the common ancestor of all mammals, but not nearly as distant as the split away from birds and reptiles 315 MYR ago. The common ancestor of all mammals was just 18 million years after the common ancestor ofmonotremes and mammals. Warren et al. used the genome of this relatively not-so-distant ancestor as a way of learning more about mammals as a whole.Synapsids split from sauropsids 167 million years before the mammalian lineage evolved. The monotreme group split away from mammals just 18 years before the common ancestor of all mammals.
The analysis that Warren et al. did was basically showing that this weird creature that looks like a half-bird half-mammal shares many genes with birds, many with mammals and also has a few genes unique to Monotremes. It’s great when science works out. The general premise that the reseachers used is that the majority of genes shared by mammals and monotremes are likely to have been present in the common ancestor while genes found in monotremes and sauropsids are likely to have been lost in mammals.
The platypus lactates like mammals, and it has a copy of the casein gene that is thought to cause lactation in mammals.
Monotremes have a venomous hind leg spur. The genes that create the venonom are duplications of genes common to all animals. Figure 2 shows these duplications.
The fact that platypuses lay eggs makes it a very interesting creature in itself. A comparison of genes between Glennie, our favorite platypus, and mammals in the eutherian lineage shows that many of the egg proteins present in Glennie are not present in the mammals.
In our research at the Lane Lab we are using full proteomes for a number of applications, so it is wonderful to see species like the platypus getting published. There is currently a large gap in the Rhizaria and Excavate clades, which are both just as cute as the platypus. As genbank fills up with genomes our analyses will continue to improve.
In summary, I would like to again state that platypuses are very cool. Sadly, a search of the literature for facts about Glennie was in vain, but lets assume that she is a fun loving monotreme who enjoys snails and short swims near the beach.
Warren et at. (2008). Genome analysis of the platypus reveals unique signatures of evolution. NATURE. Volume: 455 Issue: 7210 Pages: 256-256 Published: SEP 11 2008