Kategorie: News
Unusual cichlid shows how genes and behavior influence body shape
In nature, most animals are extremely symmetrical in structure. In humans, birds, and mammals, the left and right sides are often almost indistinguishable, with the two halves of the body being virtually mirror images of each other. However, there are exceptions that break this mold...
One example is the cichlid Perissodus microlepis, which is native to Lake Tanganyika in Africa and whose head—or, more precisely, its mouth—is severely shifted to one side. This unusual fish has a “crooked head” that is bent to the left or right. As it turns out, this asymmetrical head shape is not just a visual peculiarity, but is closely linked to its behavior and underlying genes.
But why would a fish have such an unusual body structure? And what significance does this phenomenon have for its survival? A team of researchers led by Axel Meyer from the University of Konstanz has investigated these questions in more detail. Their goal was to find out which genetic mechanisms are responsible for this asymmetrical body shape and how behavior and morphology influence each other. The results of their studies are impressive and shed new light on the complex relationships between genetics, behavior, and evolution.
The unusual hunting strategy of the cichlid
Perissodus microlepis feeds differently from most other fish species. It lives by biting off the scales of other fish, which it attacks from behind in a torpedo-like manner. What is special about this is that the scales are pulled off on the side where the cichlid's mouth is pointing. This means that the fish prefers to attack either from the right or from the left – a preference that is closely linked to the lateral shift of its head. Most populations consist of an almost equal mix of “right-headers” and “left-headers,” with the ratio shifting up or down every four to five years over the years, but fluctuating around half in the long term.
Scientist Xiaomeng Tian explains these fluctuations using a fascinating mechanism: if the number of left-headers is high, the prey will pay attention to the side that is attacked more by these fish – the right side of the prey fish is therefore observed and defended more intensively. This in turn gives the right-headers an advantage, and the balance between the two groups is maintained. This phenomenon is called frequency-dependent selection. It ensures that neither variant gains a permanent advantage, but rather that a dynamic equilibrium is maintained.
Why is the head shape asymmetrical in the first place?
The researchers' next step was to decipher the genetic intrigue behind the asymmetrical head shape. They analyzed 102 specimens of the cichlid, carried out comprehensive genome analyses, and used modern morphometry techniques to create 3D images of the fish. They identified 72 genetic regions associated with the lateral shift of the head.
“It used to be assumed that this phenomenon was a simple Mendelian trait,” explains Axel Meyer. But the investigations show that it is much more complex. Not just one gene, but a multitude of genes distributed throughout the genome influence the development of the asymmetrical head shape. Each individual gene has only a minimal effect, but together they lead to the distinctive lateral deviation.
Chicken or egg? Which came first?
Another exciting question was: Which came first – the asymmetrical head shape or the behavioral preference when attacking? Here, the scientists suspect that both developed simultaneously and reinforced each other. Genetic and neurobiological studies of the brain suggest that the direction of the attack preference is due to asymmetrical activation of genes in the brain. This means that genetic mechanisms influence both physical form and behavior and thus interact with each other. This close connection between body and behavior shows how complex evolutionary processes can be: they are not just the result of individual genes, but develop through the interaction of various biological factors that reinforce and adapt to each other.
Conclusion: A complex interplay between genetics and behavior
The study by Axel Meyer and his team proves that the asymmetrical head shape of the cichlid cannot be explained by a single trait. Instead, it is based on a multitude of genetic regions that together form a complex predisposition. At the same time, behavior—i.e., the preference for attacking—influences the development of this body shape. Both aspects are closely linked: genes determine how the brain works and how the body is built, while behavior shapes morphology. The research thus provides a fascinating example of the diverse ways in which biological balance and adaptation function in nature.
Overall, this example shows how evolutionary processes are based on closely interwoven genetic and behavioral factors. It is proof that body and behavior are in a dynamic exchange that helps animals adapt to their environment and maximize their chances of survival. The crooked fish head of Perissodus microlepis is thus more than just an unusual visual appearance – it is a window into the complex world of evolutionary development and genetic interactions.