Ah, there’s nothing quite like sitting out on a balmy Australian summer night sitting
to a campfire, watching the stars.
But everyone knows a good campfire needs a good campfire story, and I think I’ve got
just the one.
It’s as wild as the wilderness, as deep as our DNA, and as wide as the span of the
animal kingdom.
Best of all, it’s a true tale, but don’t worry, sometimes the truth is stranger than
fiction.
Let me describe an animal for you: Carnivorous, a head shaped like a fox, a jaw that can open
impossibly wide, nearly 90 degrees.
Stripes, but only on the back half, shaped a bit like a dingo, and it has a pouch like
a kangaroo.
These are the features of the Tasmanian tiger, or thylacine.
For those non-Australians out there, Tasmania is an island state located south of the Australian
mainland, where the eponymous Tasmanian tiger was mostly found.
The last captive thylacine died in a Tasmanian zoo in 1936, and the species was declared
extinct shortly after.
Farmers of the late 19th century loathed the Thylacine, and the species notoriety at the
time earned farmers a one pound bounty for each animal killed.
Now compared to the death of the last thylacine, the field of genetics is comparatively young.
While the idea of a gene can be dated back to Gregor Mendel in 1865, the chemical structure
of DNA, the building blocks of our genes, was only discovered in 1953, and it wouldn’t
be until the 1995 that an organism’s entire genome would be sequenced for the first time,
giving rise to the field of genomics, the study of genes and their interactions at the
level of the whole genome.
That brings us back to the thylacine, and a 2018 research article by Dr Charles Feigin
and colleagues.
The group extracted ancient DNA from a thylacine joey preserved in alcohol by Museums Victoria
and used it to compile the first full thylacine genome.
Now bear in mind, at the time of publication, the thylacine had been extinct for 82 years,
and the sample was even older –105 years old to be exact.
Now this is all well and good, but why sequence the genome of an extinct species?
One reason was to clarify where the thylacine sits in the great phylogenetic tree of life.
By identifying retroposons, short non-protein-coding sections of DNA that are inserted into the
genome over millennia and tracking the conservation of these short DNA sections between species,
the researchers were able to build the case that the thylacine was a basal lineage of
the Dasyuromorphia, which also includes the families of other extant Australian marsupials,
including the numbat in the family Myrmeocobiidae, and the quoll, dunnart, and Tasmanian devil
in the family Dasyuridae.
Secondly, thylacine is a widely regarded example of convergent evolution.
Ordinarily we think of evolution as a divergent process, where organisms become ever more
different from each other and fill various niches.
However, some species develop similar traits despite their great phylogenetic distance.
In the case of the thylacine, the group looked at skull shape compared to other Dasyuromorphia
as well as Caniformia, the suborder that includes dogs, wolves, foxes and many other “dog-like”
species.
Skull shape is an excellent predictor of feeding habits amongst both canine and marsupial species,
and the morphological variations that predict carnivorous behaviour in one similarly predict
it in the other.
However, compared to the class Carnivora to which Caniformia belongs, Dasyuromorphia are
believed to have diverged from the phylogenetic tree over 160 million years ago.
Taken alongside the fact that the geometry of the thylacine skull shares much in common
with the skull of the red fox and the grey wolf, this suggests that the thylacine has
developed a skull shape suited to carnivorous feeding independently of these species and
understanding the genetic basis of this convergence is an ongoing question.
While the group didn’t find evidence of genetic convergence in protein-coding regions
in their 2018 paper, they would go on to release a publication in 2019 describing significant
convergence in the regulatory regions of genes between the thylacine and grey wolf.
Genomics is a deep and rapidly expanding field of enquiry, and while its impact on medicine
is grand, on agriculture great, and ecology difficult to understate, I hope I’ve convinced
you that the species we’ve lost to time may yet surprise us and teach us about the
nature of life in its inconceivable grandness.
Our thylacine friend may be extinct, but she’s certainly not forgotten.