From South America to Global Spread: The Invasive Success of Toxic Toads across Continents.
The South American origin of the “amphibian success”
An investigation into invasive toads in Madagascar led to a groundbreaking reevaluation of the evolutionary history of these amphibians. A team of international scientists analyzed the DNA of 124 toad species from around the world, revealing unexpected findings.
Toxic toads first emerged in South America approximately 61 million years ago, contrary to previous beliefs that they migrated through North America and Asia. The direct dispersal to Africa from South America challenged existing theories and highlighted the key role of this region in the amphibian’s evolutionary success.
The evolution of a chemical shield
The development of parotoid glands behind the eyes of toads marked a significant turning point in their evolution. These glands produce bufotoxins, chemical compounds that serve as a defense mechanism against predators. This evolutionary adaptation enabled toads to repel or intoxicate various predators, contributing to their survival and expansion.
The diversification and expansion of toads coincided with the evolution of this chemical defense mechanism. Two potential dispersal routes are proposed, including migration through Antarctica during a temperate period and drifting on vegetation rafts, facilitating their spread to Africa and Eurasia.
Resistance, adaptation, and expansion
In addition to their chemical defense, toxic toads exhibited a resilient physiology that allowed them to survive harsh conditions. Their ability to endure long periods without water or food, supported by energy reserves in their inguinal fat bodies, enabled them to colonize diverse environments.
After a global extinction event around 33 million years ago, the Bufonidae family rapidly diversified, driven by their unique chemistry. Today, toxic toads inhabit a wide range of habitats, showcasing their evolutionary success and adaptability.
This study sheds light on the intertwined history of biology and geology, emphasizing how toxic frogs leverage chemistry as an evolutionary weapon to navigate ecological challenges and global environments.
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