洞窟生物の適応と遺伝子劣化
Hello everyone, SCIEN-SPOT is a podcast that shines the spotlight on the latest scientific
technology from Japan. Your host is REN from SCIEN-TALK. So, when creatures move from the
surface to underground environments, especially dark places like caves, they often undergo
remarkable revolutionary changes. For instance, as you might know, fish and insects living in
caves frequently show degradation of their eyes, or a reduction in body pigment. This happens
because in the absence of light, eyes become unnecessary, and body coloration no longer
serves a protective purpose. It's almost as if, like unused muscles, the body adapts and changes
in response to its environment. With recent advancement in genomic analysis, it's becoming
clear that this morphological degradation is closely linked to the degradation of the genes
responsible for those structures. Underground organisms are excellent subjects for studying
genome evolution because the connection between environmental factors and gene degradation is
so clear. What's even more interesting is that some closely related underground species have
視覚関連遺伝子の研究
different evolutionary origins for their subterranean colonization. By studying such
groups, researchers can explore whether gene degradation is merely a random accumulation
of changes, or if it exhibits a certain directionality when adapting to similar environments.
The focus of this study was on a group of small insects called tracing beetles,
which are only a few millimeters to about one centimeter long. Over 400 species are known in
Japan, including lineage that are believed to have independently colonized caves,
just like the ones that is here. The research team chose these tracing beetles to investigate
if there are rules governing the degradation of vision-related genes, which are linked to their
eye degradation. This research was conducted by a team including a PhD student at Hokkaido University
and Simon is now a researcher at Kyoto University. They collected a total of four
tracing beetle species from various locations across Japan. Specifically, they sampled two cave-dwelling
species with completely lost compound eyes. The four types of this beetle and in the lab,
視覚遺伝子の研究
they extracted DNA and RNA from the sample and used the state of the ad sequencer to obtain gene
and gene expression information. With this data, they estimated the evolutionary relationships
among these beetles and specifically focused on analyzing 24 vision-related genes found in insects.
A gene was considered retained if its amino acid coding region was conserved. Conversely,
a gene was deemed lost if mutations causing loss of function were detected or if the gene itself
could not be found within the genomic information. First, they confirmed the two cave-dwelling
tracing beetle species in their study belonging to different evolutionary lineages.
This finding aligns with previous morphological studies indicating that these two species did not
evolve from a common cave-dwelling ancestor but independently colonized caves.
Yet, both lost their eyes. This suggested that their similar eye degradation is a result of
parallel evolution due to the common selective pressure of living in darkness.
Next, when they examined the 24 vision-related genes, they found striking results.
視覚関連遺伝子の進化
Despite their independent cave colonization, nine genes were commonly lost in both cave species
and 12 genes were commonly retained. The commonly lost genes included those for
light reception, such as option genes, as well as IRR and TLP genes involved in signal transduction
in photoreceptor cells, and cardinal genes involved in pigment synthesis.
This indicated a high consistency in the evolutionary fate of vision-related genes
in these two tracing beetle species despite their separate evolutionary path to cave life.
Furthermore, the research team investigated what characteristics the commonly lost genes shared.
They focused on the gene multifunctionality or pleiotropy. Multifunctionality referred to
how many different types of tissues a single gene functions in. They assessed this using
gene expression data from Drosophila melanogaster as a reference. The results showed that the
commonly lost genes tended to have low multifunctionality and this means they were
typically expressed in only a limited number of tissues. Conversely, the commonly retained genes
tended to have high multifunctionality being expressed in multiple tissues. It suggested that
無眼甲虫の遺伝子劣化
even in a cave environment where eyes are no longer needed and not all vision-related genes degraded
randomly. This research highlights that the degradation of vision-related genes in cave
dwelling attrition beetles is not simply a random accumulation of changes but has a certain
directionality and one key factor determining this directionality appears to be the gene's
inherent property of multifunctionality. This discovery could pave the way for predicting which
genes are more likely to evolve or degrade across various organisms based on their
genomic information. This holds significant promise potentially even offering clues
for assessing disease risk and prevention in the human genome. That's all for today's SciencePod.
This podcast is broadcast daily on workday morning in both Japanese and English. Honestly, I'm absent
because I went to Japan and Shanghai in China. I took a rest but now I restart this broadcasting.
I'd love for you to listen to the podcast and post your notes and results with the hashtag
SciencePod. See you next time!
