Frog colour patterns shed new light on evolution

NYUAD researchers study 2,700 anurans

Ateam of researchers from NYU Abu Dhabi (NYUAD) has shared new insights into the evolution of colour patterns in frogs and toads — collectively known as anurans.

In their paper published in the journal Molecular Biology and Evolution, the researchers of the Evolutionary Genomics Lab at NYUAD completed a broadscale comparative analysis, which included over 2,700 species of anurans.

Sandra Goutte, PhD, a research associate at the Evolutionary Genomics Lab at NYUAD, said: “Our findings establish that the vertebral stripe in frogs and toads holds a great potential in the field of evolutionary biology as it represents a clear example of repeated evolution.

Vertebral stripe

“Studying this colour pattern in other species can thus help us understand to which extent evolution predictably employs the same molecular paths when identical phenotypes evolve under similar selection pressures,” she added.

NYUAD researchers found that the vertebral stripe has evolved hundreds of times and is selected for in terrestrial habitats where visual predators coming directly from above — such as mammals or birds — are more prevalent.

Many anurans have a light stripe along their back, which, when observed from above, creates the optical illusion that the animal is split in two halves and confuses visually-oriented predators. Although this colour pattern is widespread in frogs around the world, little is known regarding its evolution or genetic origin.

Evolutionary history

To understand the genetic basis of the pattern, the researchers focused on the Ethiopian grass frog species Ptychadena robeensis, which is polymorphic — meaning that it presents the vertebral stripe trait in multiple forms — wide, thin or absent.

This study is the first large-scale study of the adaptive value of the anuran vertebral stripe. It also establishes a link between the ASIP gene and a colour pattern in anurans for the first time.

ASIP is a well-studied gene in mammals, known to be linked to melanin production and colour variation. The fact that it is linked to colour patterns in frogs opens new research avenues on comparative studies across vertebrates.