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Elaboration and degeneration of complex traits: The visual systems of lizards and snakes

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Looking into how complex eyes of lizards and snakes evolved

Snakes and lizards have amazingly flexible visual systems linked to the range of habitats they live in – from pitch-dark to dazzling desert sunshine. EU researchers have investigated their evolution.

Fundamental Research

With greater variation in eye morphology and photoreceptors than all other vertebrates combined, lizards and snakes (squamates) show exceptional diversity. “My Marie Skłodowska-Curie (MSC) funding enabled me to investigate links between genome and eye structure variation in the visual systems of squamates,” outlines Bruno Simoes, a fellow in the Evol-Eyes project. Taking a broader look at the evolution of complex traits in vertebrates, Simoes applied recently developed omics technologies as well as integrated molecular data to eye anatomy and physiology. Specifically, he addressed three lines of investigation: extent of flexibility in the genomic machinery underlying these highly diverse visual systems, their adaptation to ecological transitions, and whether a complex visual system can be regained following evolutionary loss.

Genetic patterns emerge that mirror ecological niches

“Some results are still being worked on and awaiting publication, and we are currently analysing huge amounts of genomic data,” Simoes comments. However, he reports an emerging pattern during this project – the visual system of squamates is highly diverse, reflecting the high number of ecological niches occupied by this lineage. Snakes and geckos that have undergone ecological transitions between nocturnality (active at night) and diurnality (day) have reshaped their visual systems losing vision genes. “However, following occupation of new ecological niches there were changes in the light sensitivity of visual pigments responsible for colour vision as well as changes in the cell composition of some snake retinae,” Simoes adds. Interestingly, sea snakes also developed novel sensory abilities such as being able to detect light on their tails to avoid predation.

Genetics and evolution persist despite borders and funding requirements

“Each Australian state has its own permits and some parks are co-managed with Aboriginal communities, making the process bureaucratic,” the fellow relates. However, with the undying support of the host in Adelaide, local herpetologists, Aboriginal rangers, and Wildlife and Natural Parks departments, Simoes managed to secure all permits required for fieldwork. “The project also became more expansive, and expensive, than initially expected!” However, small grants from the Environment Institute University of Adelaide and the awarding of a Discovery Grant from the Australian Research Council made sure the project was completed as well as significantly extended. Evol-Eyes research was able to include lineages with huge ecological diversity, such as Australian skinks, some South American gymnophthalmid lizards and sea snakes. Moving forward, “we are currently integrating other methods such as in situ hybridisation, microscopy and computed tomography scanning to understand other aspects of visual evolution in squamates,” he adds. Simoes emphasises that the MSC fellowship has a huge focus on making their fellows independent. “I acquired independence by writing successful grants, and supervising honours and PhD students as well as research assistants.” Sorting fieldwork permits, experimental design and lab work as well as managing budgets and collaboration with an extensive network of scientists increased organisational skills. Dissemination included valuable participation in some public engagement activities in schools as well as radio interviews and nature TV shows. He concludes on a very positive note: “Having reached some maturity in my research career as a result of this fellowship, I have since been appointed as a Lecturer at the University of Plymouth.”

Keywords

Evol-Eyes, snakes, visual system, lizards, evolution, eyes, squamates, vertebrates, omics

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