Comparative genomics sheds new light on the convergent evolution of infrared vision in snakes

Infrared vision is a highly specialized sensory system that evolved
independently in three clades of snakes. Apparently, convergent evolution
occurred in the transient receptor potential ankyrin 1 (TRPA1) proteins of
infrared-sensing snakes. However, this gene can only explain how infrared
signals are received, and not the transduction and processing of those
signals. We sequenced the genome of Xenopeltis unicolor, a key outgroup
species for pythons, and performed a genome-wide analysis of convergence
between two clades of infrared-sensing snakes. Our results revealed
pervasive molecular adaptation in pathways associated with neural
development and other functions, with parallel selection on loci
associated with trigeminal nerve structural organization. Additionally, we
found evidence of convergent amino acid substitutions in a set of genes,
including TRPA1 and TRPM2. Analysis also identified convergent accelerated
evolution in non-coding elements near 12 genes involved in facial nerve
structural organization and optic nerve development. Thus, convergent
evolution occurred across multiple dimensions of infrared vision in vipers
and pythons, as well as amino acid substitutions, non-coding elements,
genes, and functions. These changes enabled independent groups of snakes
to develop and utilize infrared vision.