In snake genes, study finds they evolved 3x faster than other reptiles

In snake genes, study finds they evolved 3x faster than other reptiles

Subject: Science and tech

Section: Msc

Context:

• In the earth’s distant past, many species went through bursts of evolutionary innovation, taking giant leaps and incorporating extraordinary diversity in their population, while others were left behind.

Unexplained bursts of change:

• The enduring mystery in evolutionary biology revolves around why some species experience sudden, significant evolutionary changes, known as quantum leaps. While the Darwinian theory suggests that evolution occurs gradually through natural selection, fossil records indicate a more complex narrative.
• These records reveal not only a constant rate of transformation but also instances of rapid evolution, leading to new species’ emergence or the extinction of existing ones.
• This discrepancy between the slow, incremental changes proposed by Darwin and the sudden bursts of evolution documented in the fossil record highlights the complexity and variability of evolutionary processes on Earth.

A tree of snakes and lizards:

• Approximately 100-150 million years ago, during the era when dinosaurs inhabited the Earth, a significant evolutionary event occurred leading to the transformation of ordinary lizards into snakes, now considered some of the most highly adapted predators globally.
• This transition involved the loss of legs, enabling snakes to navigate various terrains effortlessly.
• Snakes also developed intricate chemical sensory systems for tracking prey, flexible jaws capable of consuming large animals, and diverse methods of attack, including venom production.

Study findings:

• A recent study, published in the journal Science on February 22, conducted by an international team with leading researchers from the University of Michigan, aimed to decipher the genetic sequence of over 1,018 snake and lizard species.
  • This effort resulted in the creation of the most extensive and detailed evolutionary tree of snakes and lizards to date.
  • By combining new genetic data with previous studies, the research uncovered that snakes have been evolving at a rate nearly three times faster than lizards and other reptiles.
  • This rapid evolution allowed snakes to exploit new environmental niches that appeared following the dinosaurs’ extinction, contributing significantly to their diversification and success across the globe.

A clock in the body’s molecule:

• The concept of a molecular clock is based on the observation that DNA and protein sequences evolve at a relatively constant rate over time, regardless of the species. This consistency allows scientists to use genetic variations between two species to estimate the time elapsed since their last common ancestor, providing insights into the pace of their evolution.
• Essentially, genetic sequences act as a molecular clock, enabling the determination of ‘evolutionary distances’ between different organisms.
• This mechanism has revealed not only the rapid evolution of snakes but also similar adaptations in many lizards, which developed snake-like features such as limb loss and body elongation.
• The Australian scincid lizard (Lerista), part of the Squamata clade (which includes both lizards and snakes), exemplifies this evolutionary trend.
• Lerista shows a remarkable range of limb configurations across its more than 75 species, from full-limbed to completely limbless, due to at least 10 separate limb-reduction events over millions of years.
• However, despite these adaptations, snakes have evolved much faster than lizards, leading to a significant diversification known as the “singularity of snakes”.
• This concept is likened to the Big Bang theory in cosmology, suggesting that snakes underwent a series of rapid evolutionary changes that, although distinct, occurred so closely together in time that they appeared as a single, transformative event in evolutionary history.

Availability of prey:

• The current diversity of snakes, with approximately 4,000 species thriving in various habitats—including on land, in trees, underground, and in water—can be attributed to their adaptability and varied hunting strategies and diets.
• A recent comprehensive study involving the analysis of stomach contents from over 60,000 snakes and lizards revealed that snakes primarily consume small vertebrates, demonstrating a specialization in their dietary preferences, while lizards generally eat insects and invertebrates, indicating a less specific diet.
• However, the diversity of snakes cannot be solely explained by the availability of prey. The underlying cause of the evolutionary “singularity” that led to the rapid diversification of snakes remains elusive.
• A significant aspect of snake evolution involves their unique mode of movement, facilitated by their elongated spinal column and specialized vertebrae, which allow for efficient gliding.
• Despite having a similar genetic blueprint to lizards and humans, snakes possess over 300 vertebrae, significantly more than their counterparts.
• This morphological distinction is partly due to variations in the Sonic hedgehog gene, a critical gene in limb development.
• Previous research has identified snake-specific changes in a limb-enhancer of this gene, which is present in primitive snakes like pythons and boas but not in modern snakes.
• Experiments replacing the limb-enhancer gene in mice with the snake-specific version resulted in severe limb reduction in the mice.
• This finding suggests that such evolutionary developments could have occurred multiple times, not just once.
• Understanding these evolutionary bursts is crucial for comprehending the Earth’s ecological future.

Source: TH