Researchers from the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) and the Cluster of Excellence “Science of Intelligence” (SCIoI), Germany, have found that fish with identical genetic material and reared under identical conditions still differ in the number and size of offspring, according to a study published in the journal Nature Communications.
Researchers have long believed that the genome and environmental conditions determine individuality. However, this idea is being revised with multiple studies showing that other factors may also have an impact.
For this work, the team analysed the behaviour and reproductive patterns of 34 families of Amazon mollies (Poecilia formosa) over 280 days. These fish were selected because they reproduce clonally, and all offspring are genetically identical to the mother. The species only has females, and reproduction is activated using sperm from males from similar species. The fish receive no care from the mother after birth, which means they can be kept under standard conditions from birth. Using a high-resolution tracking system, the researchers followed the fish throughout their lives. Over 2500 fish from 152 broods were included in the study.
After analysing multiple broods in each family, the team found that the fish consistently differed in how many offspring they produced and how large they were. “This is the first evidence that genetically identical animals growing up under near-identical environmental conditions differ quite substantially in their biological fitness,” said Ulrike Scherer, lead author of the study and researcher in the Cluster of Excellence SCIoI and guest scientist at IGB. “Our study also reveals how little we understand so far about the emergence of individuality and the possible role of epigenetics, stochasticity, and micro-environmental differences.”
“Our experiment confirms that behavioural individuality develops at a very early stage even without genetic and obvious environmental variation”, concluded Max Wolf, leader of the study and researcher at IGB and in the Cluster of Excellence SCIoI.
Scherer, U., Ehlman, S.M., Bierbach, D. et al. Reproductive individuality of clonal fish raised in near-identical environments and its link to early-life behavioral individuality. Nat Commun 14, 7652 (2023). https://doi.org/10.1038/s41467-023-43069-6