An examination of the final sustenance consumed by a wolf pup approximately 14,400 years ago has furnished novel perspectives regarding the disappearance of the woolly rhinoceros from our planet.
An earlier investigation into the gastric contents of a canine specimen unearthed in the Siberian permafrost in 2011 had revealed a stomach replete with woolly rhino (Coelodonta antiquitatis) flesh, dating close to the period of the rhino’s extirpation. More recently, geneticists have successfully sequenced the rhino’s genome, uncovering no indications of a protracted demographic decline or pervasive inbreeding within the species.
These findings posit that the woolly rhino’s extinction was an abrupt and swift event, rather than a gradual attrition of a weakened population already compromised at a genetic stratum.
“The retrieval of genomes from individuals that lived immediately preceding extinction presents considerable challenges, yet it can furnish vital insights into the factors precipitating a species’ demise, which may also hold relevance for the ongoing conservation efforts for extant endangered species,” observes evolutionary biologist Camilo Chacón-Duque, who was formerly associated with the Centre for Palaeogenetics in Sweden and is now affiliated with Uppsala University.
This represents the inaugural instance where scientists have successfully sequenced the complete genome of an Ice Age animal derived from the digestive tract of another creature.
Genetic material extracted from ancient animal remnants is frequently too degraded to be suitable for genomic sequencing. Nevertheless, specimens preserved within permafrost can sometimes escape the most severe forms of decay. Moreover, thanks to sophisticated extraction and sequencing methodologies, it is now feasible to recover and analyze sufficient DNA, even in instances of moderate degradation.
Recent investigations have even demonstrated that the digestive contents of predators can serve as a surprisingly abundant reservoir of genetic material, with woolly rhino DNA having been identified in fossilized hyena excrement dating back over 30,000 years.
The wolf cub central to this research was discovered in proximity to Tumat, Siberia. Its demise occurred shortly after its final repast, ensuring that the rhino flesh had not undergone complete digestion, and the deoxyribonucleic acid within those fragments remained relatively preserved.
Crucially, the cub also lived around the epoch of the woolly rhino’s extinction, affording researchers an uncommon genetic snapshot from the species’ terminal centuries. Had any genetic predisposition contributed to the rhino’s downfall, this particular specimen would have been highly likely to exhibit evidence thereof.
Should a species undergo a protracted decline, the pool of available mates diminishes, consequently leading to a reduction in genetic variability. This phenomenon manifests in the genetic makeup of progeny resulting from repeated and intensified consanguineous pairings – a definitive marker of a gradual genetic attrition preceding extirpation.
Consequently, the research team, spearheaded by Sólveig M. Guðjónsdóttir and Edana Lord from the Centre for Palaeogenetics, engaged in the meticulous endeavor of reconstructing the woolly rhino’s genome from tissue preserved within the digestive system of the Tumat wolf cub.
“It was an immensely thrilling, albeit exceptionally challenging, undertaking to extract a complete genome from such an atypical sample,” stated Guðjónsdóttir.
Subsequently, the researchers undertook a comparative analysis of this reconstructed genome against two pre-existing woolly rhino genomes – one originating from approximately 18,500 years ago and another from around 48,500 years ago. Any genetic degradation consistent with population decline or an increase in deleterious genetic mutations would have been discernible across the temporal intervals of these samples.
The research team encountered no evidence suggesting that the woolly rhino population experienced destabilization prior to its extinction.
“Our analyses revealed a remarkably stable genetic profile, with no discernible alteration in inbreeding levels across tens of thousands of years preceding the woolly rhinos’ demise,” reported Lord.
Previous research involving the 18,500-year-old woolly rhino genome also yielded no indications of degradation characteristic of population decline. While that provided robust data from a solitary individual, the genetic information derived from the Tumat cub, dating thousands of years later, serves as a compelling corroboration.
Collectively, these findings indicate that the woolly rhino maintained robust genetic health until shortly before its extinction, thereby excluding a prolonged, gradual population collapse as the primary cause.
This inference suggests that the woolly rhinos were abruptly eradicated by an external factor. Given the species’ millennia-long coexistence with humans prior to their disappearance, and the significant climatic shifts occurring approximately 14,000 years ago, the researchers propose that an inability to adapt to these environmental transformations was the likely catalyst for their extirpation.
“Our findings demonstrate that woolly rhinos sustained a viable population for 15,000 years subsequent to the initial human ingress into northeastern Siberia,” concludes geneticist Love Dalén of the Centre for Palaeogenetics, “which points towards climatic warming, rather than anthropogenic hunting, as the probable driver of their extinction.”
