Insights into the genetic basis of bilat­eral head asymme­try in a scale-eating cichlid fish

Xiaomeng Tian, Young Researcher of the Hector Fellow Academy, is first author of the paper “Insights into the genetic basis of bilat­eral head asymme­try in a scale-eating cichlid fish”, published in Science Advances in July 2025. She conducted this work together with Hector Fellow Axel Meyer and co-author Ming Li.

The study focuses on the scale-eating cichlid Peris­so­dus microlepis from Lake Tanganyika, also known as the scale-eater. Some fish develop a left-bending head, while others develop a right-bending head. This enables them to attack differ­ent sides of their prey. This unusual polymor­phism is stably maintained at a 50:50 ratio through negative frequency-depen­dent selec­tion, whereby the rarer morph temporar­ily gains an advantage.

To uncover the genetic basis of this trait, the researchers created the first chromo­some-level refer­ence genome for the species, sequenced 102 wild individ­u­als, and examined their skull morphol­ogy with high-resolu­tion micro-CT scans. They identi­fied 72 genomic regions linked to cranio­fa­cial devel­op­ment, nervous system function, and early left–right asymmetry.

Their findings show that head asymme­try is controlled not by a single gene, but by many inter­act­ing loci and behav­ior. These results provide insight into how evolu­tion maintains genetic diver­sity through ecolog­i­cal inter­ac­tions. Beyond evolu­tion­ary biology, these results may also help us under­stand congen­i­tal cranio­fa­cial malfor­ma­tions and neuro­log­i­cal disor­ders in humans, in which left-right asymme­try plays an impor­tant role.