Burrowing snakes have far worse eyesight than their ancestors

Date:
December 9, 2021
Source:
University of Plymouth
Summary:
An international team of scientists has demonstrated that burrowing
snakes have undergone extensive vision gene loss over tens of
millions of years of evolutionary history.



FULL STORY ==========================================================================
The ancestor of all living snakes probably had substantially better
vision than present-day burrowing snakes, according to new research.


==========================================================================
An international team of scientists -- led by the Natural History Museum
and the University of Plymouth -- carried out the first detailed analysis
of gene sequence data for any species of the so-called "blindsnakes" (Scolecophidia), a group of small-eyed burrowers.

They found that seven of the 12 genes associated with bright-light vision
in most snakes and lizards species are not present in scolecophidians.

This, they say, demonstrates extensive vision gene loss over tens of
millions of years of evolutionary history, similar to that which has
also been observed in burrowing mammals with reduced vision.

It also challenges the hypothesis that all snakes living across the world
today evolved from extreme burrowers, because the vision genes lost in scolecophidians are present in most other living snakes. The researchers
say it would be extremely unlikely for such genetic deficiencies to have
been reversed through evolution.

Scolecophidians are dedicated burrowers and form one half of the oldest divergence in the snake tree. They comprise approximately 460 of the approximately 3,850 currently recognised living snake species, and
likely diverged from their closest living relatives (Alethinophidia,
which includes all other living snakes) more than 65 million years ago.

Scolecophidians are typically small, cylindrical, burrowing snakes with
reduced eyes and small mouths, strikingly different from the more familiar alethinophidians, which include pythons, vipers, and cobras.

For this research, published in Genome Biology and Evolution, scientists generated new gene-sequence data for the dark-spined blind snake (Anilios bicolor) and the prong-snouted blind snake (Anilios bituberculatus),
both of which are common across southern Australia.

They then compared their results with similar data for functional vision
genes among other species of snakes and lizards.

Lead author Dr David Gower, Head of the Life Sciences Vertebrates Division
at the Natural History Museum, said: "Our data and analytical results
provide clear evidence for very substantial reduction of elements of
the visual system of burrowing scolecophidian snakes. We already knew
that snakes lost some vision genes and eye structures during their
evolution from lizards, but most were nonetheless retained. It is highly unlikely that functional copies of a large number of vision genes were
lost from the ancestral snake but subsequently re-evolved in most living snakes. As a result, our study strongly suggests that the ancestor of all living snakes was unlikely to have been as extreme a burrower as living scolecophidian snakes." The same team of researchers published a study
in May 2020, which revealed that the visual systems of sea snakes have undergone remarkable adaptation to life underwater for 15 million years.

Dr Bruno Simo~es, Lecturer in Animal Biology at the University of
Plymouth, led that research and is senior author on the current study. He
said: "The nature of the ancestral snake has been highly debated. It has
been suggested that it had evolved a reduced visual system as a result of
a possible burrowing ecology. Our research provides new information on the likely ecology and environment of the ancestral snake and suggests that
the highly subterranean lives and reduced eyes of living scolecophidian
snakes likely evolved as specialisms rather than being the retention of primitive characteristics. This study also shows convergent evolution
between subterranean snakes and burrowing mammals with the loss of similar genes, especially those associated with bright-light and colour vision." ========================================================================== Story Source: Materials provided by University_of_Plymouth. Original
written by Alan Williams. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. David J Gower, James F Fleming, Davide Pisani, Freek J Vonk,
Harald M I
Kerkkamp, Leo Peichl, Sonja Meimann, Nicholas R Casewell,
Christiaan V Henkel, Michael K Richardson, Kate L Sanders, Bruno
F Simo~es. Eye- Transcriptome and Genome-Wide Sequencing for
Scolecophidia: Implications for Inferring the Visual System of
the Ancestral Snake. Genome Biology and Evolution, 2021; 13 (12)
DOI: 10.1093/gbe/evab253 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211209082611.htm

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