A new understanding of reptile colouration
Snakes and mice donāt look alike. But much of what we know about skin colouration and patterning in vertebrates generally, including in snakes, is based on lab mice. However, there are limits to what mice can tell us about other vertebrates because they donāt share all of the same types of colour-producing cells, known as chromatophores. For example, snakes have a type of chromatophore called iridophores that can generate iridescent colours by reflecting light.
To gain a better understanding of the genetic basis of colouration in vertebrates, a Ā鶹AV-led research team combined a range of techniques (whole gene sequencing, gene-editing, and electron microscopy) to look more closely at colour variations and patterning in the skin shed by ball pythons bred in captivity. They were able to identify a particular gene (tfec) that plays a crucial role in reptile pigmentation generally and more specifically in a classic color variant found across vertebrates and distinguished by blotches of white, the piebald.
A small sample of variations in colouring seen in captive-bred ball pythons (Python regius). CREDIT: Ā鶹AV
Crowdsourcing biological data with the help of snake breeders
The sale of captive-bred reptiles is a $1.4 billion industry within the U.S. alone. Over 4.5 million American households keep reptiles, and close to one in five of these are snakes bred in captivity. Due to the spectacular colour variations produced through captive breeding, an individual ball python (Python regius ā originally found in West and Central Africa) can sell for tens of thousands of dollars.
āBall pythons show incredible variation in skin colouring and patterning, which is part of their appeal for hobbyists, but also makes them really useful for researchers who want to understand the genetic basis of colouration,ā says Rowan Barrett, Interim Director of Ā鶹AVās Redpath Museum, the Canada Research Chair in Biodiversity Science, and the senior author on the recent paper in . āThe pet trade has created a huge pool of colour variation that would not have existed otherwise. This provides a catalogue for us to figure out the many ways that genes produce the amazing diversity of colours, spots, and stripes we see across different animals.ā
Gene-editing confirms role of mutation in reptile colouration
To identify the genes that control a particular trait, scientists look for genetic variants that are present in animals that have the trait and absent in animals that donāt. Using shed skin collected from snake breeders, Barrettās team found that piebald snakes carried the same mutation in the tfec gene.
But a common problem for scientists is that finding a correlation between a gene and a particular trait, such as the piebaldism, does not imply causation. To make that functional link, the Ā鶹AV researchers collaborated with Doug Menkeās lab at the University of Georgia to modify tfec in a different reptile species, the brown anole lizard, using the gene-editing technology CRISPR. They found that genetically modified lizards do indeed show altered colouration, proving that mutations to tfec cause changes to color-producing cells.
āOur research advances knowledge of the genetics of vertebrate colouration generally and particularly of the development of iridescent cells, which havenāt been studied as much as other colour pathwaysā adds Alan Garcia-Elfring, a PhD student in Ā鶹AVās Biology Department and the first author on the paper. āIt also highlights the potential benefits of working with non-academic communities like ball python breeders to accelerate discoveries in fundamental science. Our job, at this point, is to figure out what other mutations underlie all this variation seen in captivity, and how these mutations interact. Itās an exciting time for both researchers and reptile hobbyists.ā
The study
āPiebaldism and chromatophore development in reptiles are linked to the tfec geneā in by Alan Garcia-Elfring et al
About Ā鶹AV
Founded in Montreal, Quebec, in 1821, Ā鶹AV is Canadaās top ranked medical doctoral university. Ā鶹AV is consistently ranked as one of the top universities, both nationally and internationally. It is a world-renowned institution of higher learning with research activities spanning three campuses, 11 faculties, 13 professional schools, 300 programs of study and over 39,000 students, including more than 10,400 graduate students. Ā鶹AV attracts students from over 150 countries around the world, its 12,000 international students making up 30% of the student body. Over half of Ā鶹AV students claim a first language other than English, including approximately 20% of our students who say French is their mother tongue.
