Not all small fish are the same. Some species undergo normal development and simply remain small. In this case, the term used is proportionate dwarfism. Others reach sexual maturity at an early stage of development and consequently retain many juvenile traits well into adulthood. This shortened development results in sexually mature adults having a larval-like skeleton. They are called progenetic dwarfs.
These progenetic dwarfs were the focus of a new study by the Natural History Museum of Bern and the University of Bern. The international research team studied the evolutionary history of carp-like fish and compared the size of the genome of more than 300 species. Specifically, the study focused on the genus Paedocypris, which reaches sexual maturity when its body length is less than 8 millimeters. It emerged that these dwarf fish and other genera of progenetic dwarfs all have something in common: their genome is particularly small. What is especially surprising is that these fish species have evolved independently of each other at least three times over the course of evolution. Despite this, they have not only developed similar body characteristics, but also similarly small genomes.
Evolution always finds the same solutions
“Our findings show that body size is not the only factor,” says Lukas Rüber, curator at the Natural History Museum of Bern. “The decisive factor seems to be how these small fish species develop.” The researchers conclude from this that the shortened development of these fish is closely related to changes in their genome. “It was particularly surprising that independently formed lines of progenetic dwarf fish show remarkably similar genomic changes, whereas the proportionate dwarfs do not. This suggests that, under certain conditions, evolution can achieve the same solutions over and over again,” adds Hiranya Sudasinghe, lead author of the study.
The study, which was funded by the Swiss National Science Foundation (SNSF), opens up new insights into the interactions between development, genetic make-up and evolution. The results have now been published in the journal Proceedings of the National Academy of Sciences (PNAS).
