TAG: GS 3: ECOLOGY AND ENVIRONMENT
THE CONTEXT: The flightless Aldabra rail went extinct over 130,000 years ago, but the species then reappeared via iterative evolution.
EXPLANATION:
- The Aldabra rail, scientifically known as Dryolimnas cuvieri aldabranus, has captivated scientists with its extraordinary evolutionary journey.
- It originated from the Aldabra atoll, a coral paradise off the southeast coast of Africa.
- This unassuming bird has not only faced extinction but has also defied the odds by evolving flightlessness not once, but twice.
- The Aldabra rail, named after the Aldabra Atoll it inhabits in the Seychelles, is the last surviving native flightless bird in the Indian Ocean region.
- It is a descendant of the flying white-throated rail that is believed to have lost its ability to fly because the lack of predators made it unnecessary.
- It’s about the size of a chicken, with a flecked gray back, a rusty red head and chest and a white throat.
- It is a subspecies of the white-throated rail (Dryolimnas cuvieri) and is the only living flightless bird in the Indian Ocean.
The Atoll’s Ancient Submersion and Initial Extinction (136,000 Years Ago)
- The Aldabra atoll, home to the Aldabra rail, experienced a dramatic event approximately 136,000 years ago when it sank beneath the waves.
- This cataclysmic submersion led to the extinction of various species, including the flightless Aldabra rail subspecies.
- The geological upheaval caused a turnover in the atoll’s fauna, marking a chapter of extinction in the bird’s evolutionary history.
Resurfacing of the Atoll and the Return of the Rail (Approximately 118,000 Years Ago)
- In a surprising turn of events, the Aldabra atoll resurfaced, allowing a recolonization by the white-throated rail (Dryolimnas cuvieri), a bird capable of flight.
- This marked the beginning of a unique evolutionary phenomenon as the white-throated rail embarked on a journey to become flightless once again.
Evidence from Fossil Records: A Window into Evolution
- A pivotal 2019 study published in the Zoological Journal of the Linnean Society provided insights into the Aldabra rail’s evolutionary saga.
- Researchers, led by a paleontologist from the Natural History Museum, London, examined the fossil record of rails on Aldabra.
- Fossils dating back to around 100,000 years ago revealed distinct changes in leg structure, suggesting a transition towards flightlessness.
The Evolutionary Process: From Flight to Flightlessness
- The study’s findings indicated that the rails on Aldabra were gradually becoming heavier and developing more robust legs around 100,000 years ago.
- This transformation was a clear sign of iterative evolution, where the white-throated rail, once again inhabiting the atoll, was losing its ability to fly.
- The researchers attributed this shift to the advantageous trait of flightlessness in the atoll’s environment, where the birds lay their eggs on the ground, necessitating strong legs for survival.
Iterative Evolution: Rising from Extinction
- The Aldabra rail’s journey stands out as a rare case of iterative evolution.
- Unlike instances where different species evolve similar traits independently, the Aldabra rail managed to evolve flightlessness not as a new species but as the very same ancestral bird that had faced extinction over 130,000 years ago.
- This phenomenon of rising from the dead through iterative evolution showcases the resilience and adaptability of the Aldabra rail.
Conclusion: Unraveling Nature’s Intriguing Mysteries
- The story of the Aldabra rail serves as a captivating chapter in the annals of evolutionary biology.
- Its ability to overcome extinction and evolve the same traits twice challenges conventional understanding and opens new avenues for exploring the intricacies of nature’s resilience.
- As scientists continue to delve into the mysteries of iterative evolution, the Aldabra rail stands as a living testament to the enduring spirit of life on Earth.