In the paper published in the journal Molecular Biology and Evolution, the researchers of the Evolutionary Genomics Lab at NYUAD completed a broad-scale comparative analysis, which included over 2,700 species of anurans, to further the understanding of the evolutionary history of the vertebral stripe. They 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. In contrast, the pattern was lost significantly more often in arboreal lineages -- those living in trees -- than in other habitats. While beneficial to frogs living on the ground, this color pattern may thus be disadvantageous to frogs living in trees.
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. They found that the gene ASIP is linked to the stripe pattern in that species. This genetic variation affects the level of expression of ASIP in the different morphs, a higher expression leading to a wide stripe and a lower expression leading to a thin stripe. They also compared the genes of closely-related species of frogs and found that, while they present the same stripe patterns, they do not share the genetic variation found in P. robeensis. This led the researchers to the conclusion that the stripe alleles found in P. robeensis evolved recently. The researchers further conclude that the vertebral stripe evolves rapidly in anurans, which may allow species to adapt to environmental changes or variable conditions.
