New research provides key clue as to why the Thylacine, or Tasmanian tiger/wolf was driven to extinction. The model indicates that loss of ancestral genes played a major role in this species’ downfall. The Thylacine, a marsupial relative of the Tasmanian devil, roamed across the Australian mainland, Tasmania, and New Guinea for millions of years. The last known Thylacine died in captivity in Hobart, Tasmania in 1936. Today, it’s hard to fathom the destruction of this model of adaptation to an increasingly adverse environment, which survived for several thousand years.
A study published in the Proceedings of the Royal Society B: Biological Sciences reveals that the Thylacine underwent notable evolutionary shifts, including an increase in size and adaptations to a hypercarnivorous diet. These adaptations were probably prompted by the aridification of the Australian environment. This transition was especially pronounced during the Middle Miocene Climatic Transition (MMCT), a period of profound ecological and climatic change.
Evolutionary Adaptations and Gene Loss
In the winter of 2010, the research team pursued a complete analysis of the Thylacine genome. Then they contrasted it with the genomes of the Tasmanian devil and related marsupials. They found that the Thylacine underwent losses of adaptive ancestral genes. This loss may have provided the species with an advantage when undergoing environmental pressures during the MMCT. This gene loss likely happened long before humans and dingoes moved into their territories.
Unique to the Thylacine were four lost genes with simple sequences SAMD9L, HSD17B13, CUZD1, and VWA7. They suspect this loss of genes happened between 1 and 13 million years ago, with specialists narrowing the time frame to between 6 and 13 million years ago.
“In line with temporal estimations of gene losses, our study provides an empirical case where we observe the coincidence in the timing of gene loss (approximately 13−6 Ma, following the Middle Miocene Climatic Transition (MMCT); approx. 15−13 Ma). This period marked significant ecological and climatic changes, during which Thylacinidae, previously small-bodied, unspecialized faunivores, underwent notable shifts such as an increase in size and developing adaptations to a hypercarnivorous diet, likely driven by the aridification of the Australian environment,” – Buddhabhushan Girish Salve et al.
Today’s story of this genetic adaptation is a classic example of species evolving to adapt to their changing environments. It begs critical questions about the long-term impacts of these adaptations.
Competition and Human Impact
The extinction of the Thylacine was about more than just the natural cruising speed of evolution. The arrival of dingoes and the dingo’s competition with humans brought hunting practices that were really serious for this species’ decline. Research indicates that disease was not a contributing factor in the thylacine’s extinction. Contrary to some popular reporting, other research found that a “canine-distemper-like” disease increased its susceptibility.
The competition for resources between Thylacines and dingoes would have increased likely due to environmental shifts and the general lack of availability of prey. The cumulative impact of these consequences made life impossible for the remaining Thylacine population.
“Although model-based population viability analyses suggest that the disease played only a minor role in thylacine extinction, other studies suggest that a ‘canine-distemper-like’ disease played a role in exacerbating its extinction. Therefore, adaptive ancestral gene loss may have provided specific advantages to the Thylacine in response to environmental pressures during the MMCT while being deleterious in the recent past.” – Buddhabhushan Girish Salve and Nagarjun Vijay
The dynamic relationship between the genetic adaptation of keystone species as well as environmental hurdles proves that species are indeed resilient and fragile.
Implications for Conservation Genetics
This unique research lays the groundwork for more in-depth studies exploring the genetics of other living and extinct species. Ancestral gene loss and other evolutionary trends reveal important details about ancestral ecologies and trait evolution, and are rich sources of phylogenetic inference. This kind of understanding can help develop successful conservation tactics for the species now facing the greatest threats.
“Similar investigations of other extant and extinct species can provide a more comprehensive understanding of their past ecologies and trait evolution, with potential implications for species survival and extinction. This research area remains underexplored in conservation genetics but will likely illuminate ancient evolutionary patterns and guide effective conservation strategies.” – Buddhabhushan Girish Salve et al.
The extinction of the Thylacine serves as a cautionary tale about the fragility of ecosystems and the importance of genetic diversity in species survival.