Adapting to Darkness: How Behavioral and Genetic Changes Helped Cavefish Survive Extreme Environment
ScienceDaily (Sep. 15, 2010) — University of Maryland biologists have identified how changes in both behavior and genetics led to the evolution of the Mexican blind cavefish (Astyanax mexicanus) from its sighted, surface-dwelling ancestor. In research published in the August 12, 2010 online edition of the journal Current Biology, Professor William Jeffery, together with postdoctoral associates Masato Yoshizawa, and Špela Gorički, and Assistant Professor Daphne Soares in the Department of Biology, provide new information that shows how behavioral and genetic traits coevolved to compensate for the loss of vision in cavefish and to help them find food in darkness.
Except for the loss of eyes and pigment seen in the cave-dwelling form, the surface-dwelling (at top) and cave-dwelling fish (at bottom) are hard to tell apart. You can study evolution very nicely if you have both the ancestral and derived forms of evolving animals. (Credit: University of Maryland, Masato Yoshizawa)
This is the first time that a clear link has been identified between behavior, genetics, and evolution in Mexican blind cavefish, which are considered an excellent model for studying evolution.
Why Study Blind Cave Fish
Worldwide, about 80 different species of cave-dwelling fish have evolved from surface-dwelling fish, but in most cases the surface-dwelling ancestor has disappeared. "The Mexican blind cavefish is one of the only cases where a similar ancestor still exists," explains Professor Jeffery. "Except for the loss of eyes and pigment seen in the cave-dwelling form, the surface and cave-dwellers are hard to tell apart. You can study evolution very nicely if you have both the ancestral and derived forms of evolving animals."
Jeffery is a leading expert on the developmental and evolutionary genetics of the blind cavefish. His previous research provided evidence that the loss of eyes in blind cavefish is the result of natural selection, and has inspired other researchers to take up Astyanax as a model system for studying eye loss and evolution in general. Studying the evolution of cave fish may help provide clues about human forms of blindness such as macular degeneration and cataracts, and the University of Maryland team is also exploring how studies of cave fish metabolism might be used to better understand the underlying causes of obesity and diabetes in humans. "It turns out that many of the mutations in genes studied in model organisms like Astyanax are the same genes that are involved in human disease," says Jeffery. "By studying evolution, you can see what sort of mutations and genes are present in the population and how these can be selected for or against."
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Current Biology
Evolution of a Behavioral Shift Mediated by Superficial Neuromasts Helps Cavefish Find Food in Darkness
Masato Yoshizawa1, , , Špela Gorički1, Daphne Soares1 and William R. Jeffery1
1 Department of Biology, University of Maryland, College Park, MD 20742, USA
Received 17 April 2010;
revised 12 July 2010;
accepted 13 July 2010.
Published online: August 12, 2010.
Available online 12 August 2010.
Summary
How cave animals adapt to life in darkness is a poorly understood aspect of evolutionary biology [1]. Here we identify a behavioral shift and its morphological basis inAstyanax mexicanus, a teleost with a sighted surface-dwelling form (surface fish) and various blind cave-dwelling forms (cavefish) [[2], [3] and [4]]. Vibration attraction behavior (VAB) is the ability of fish to swim toward the source of a water disturbance in darkness. VAB was typically seen in cavefish, rarely in surface fish, and was advantageous for feeding success in the dark. The potential for showing VAB has a genetic component and is linked to the mechanosensory function of the lateral line. VAB was evoked by vibration stimuli peaking at 35 Hz, blocked by lateral line inhibitors, first detected after developmental increases in superficial neuromast (SN) number and size [[5], [6] and [7]], and significantly reduced by bilateral ablation of SN. We conclude that VAB and SN enhancement coevolved to compensate for loss of vision and to help blind cavefish find food in darkness.
Highlights
► Vibration attraction behavior (VAB) was characterized in blind cavefish ► VAB has a genetic basis and confers an advantage for feeding in darkness ► VAB is based on an increase in superficial neuromasts (SN) ► Coevolution of VAB and SN was likely a critical step in adaptation to cave life
Author Keywords: EVO_ECOL
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