A blind fish living within a Mexican cave system’s deep, enduring darkness still maintains some ability to sense light. As the cave fish no longer seem to rely on an internal daily cycle and some sleep very little, biologist Inca Stein-dal and her colleagues were keen to see if their bodies can still regulate cyclically through time. Most animals on Earth have an internal clock for this the circadian rhythm (昼夜节律) that uses light levels to make our bodies fit in with our planet’s day and night cycles. This rhythm is then used to cycle through different biological processes that can influence our behaviour, such as our hunger cycles.
The Mexican blind cave fish live in a complex of over 30 isolated caves, within which they have each independently adjusted to the dark. Their bodies are extra sensitive to vibrations (震动), allowing them to sense changes in water currents for navigation (导航) in compensation for their limited or complete lack of sight. This adaptation occurred despite the fish from each cave evolving from the same species with fully functioning eyes. This ancestral group still lives in the surface waters in the El Albra region of Mexico and some parts of the Southwestern US.
Steindal and her team took tissue samples from the blind cave fish, from three isolated caves, and their surface relatives and tested the cells in different conditions. They detected the activation of several molecular (分子的) clock mechanisms when the cells were exposed to light, even in the cave fish cells. “Non-visual light detection is maintained at a fundamental cell-based level,” the researchers explain,although the cave fish cells did not respond as strongly as those cells from surface fish. While there were some similarities between the fish from the different caves compared to their surface relatives, there were also differences that confirm their biological clock changes each evolved independently of one another via different molecular mechanisms.
“We have provided proof that despite being blind, cells from the Mexican blind cave fish can detect light and make their clocks fit in with a light/dark cycle,” Steindal and her colleagues conclude. The team hopes these can help us learn more about the circadian rhythm and provide an easier way to study animal adaptations to dark environments.
【小题1】As to the cave fish, what did Steindal and her fellows try to find out?| A．If they have a circadian rhythm. | B．If they rely on an internal daily cycle. |
| C．If they need to sleep. | D．If they are able to sense light. |
| A．The Mexican cave fish’s ancestors had normal vision. |
| B．The Mexican cave fish’s home is in the dark deep sea. |
| C．The Mexican cave fish have adapted to darkness. |
| D．The Mexican cave fish have trouble navigating. |
| A．Cave fish’s unique molecular structures. |
| B．Non-visual light detection in cave fish cells. |
| C．The cave fish’s adjustment t0 molecular clock mechanisms. |
| D．Biological clock changes evolved independently. |
| A．Why Do the Mexican Cave fish Live in the Darken“ |
| B．A Blind Cave fish Can Still Perceive Light. |
| C．How Can the Mexican Cave fish Fit in with the Day Cycles? |
| D．The Biological Clocks of the Life in the Sen Are Constantly Changing. |
