Same genes, same environment, different fitness levels

Same genes, same environment, different fitness levels

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Reproductive individualism. credit: Nature Communications (2023). doi: 10.1038/s41467-023-43069-6

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Reproductive individualism. credit: Nature Communications (2023). doi: 10.1038/s41467-023-43069-6

According to current knowledge, individuality is determined either by differences in the genome or in apparent environmental conditions. However, studies indicate that the twin research paradigm is currently collapsing.

A research team from the Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB) and the “Science of Intelligence” Cluster of Excellence (SCIoI) has discovered that cloned fish – that is, fish with identical genetic material – that are raised under almost identical conditions, differ significantly from very standard environments. Systematizes the number and size of offspring per reproductive cycle, two crucial indicators of biological fitness. The study is published in the journal Nature Communications.

The researchers studied the behavior and reproductive profiles of 34 Amazonian fish (Poecilia formosa) over a period of 280 days. These fish naturally reproduce clonally, so all offspring are genetically identical to the mother, the species consists of only females, and reproduction (i.e. maternal cloning) occurs through activation by sperm of males of similar species. The fish are born alive and there is no brood care after birth. They can therefore be kept in very identical and uniform conditions from day one.

With the help of a high-resolution automated video tracking system, the researchers recorded activity and food intake during the first month of life. They then described each individual’s reproductive profile, i.e. reproductive onset, brood size, and offspring size. These are indicators of life history productivity and, ultimately, biological fitness. The team studied 2,522 offspring from 152 broods.

Individual differences in activity and food intake

As described in a previous study (“Emergence and evolution of behavioral individualism in clonal fishes”, also published in Nature Communications), individual fish differed systematically in their activity and food intake patterns.

“Our experience confirms that behavioral individualism develops at a very early stage even without clear genetic and environmental differences,” said Max Wolf, study leader and researcher at the IGB and in the SCIoI Cluster of Excellence.

Individual differences in reproductive and productivity profiles

The researchers studied an average of four broods per individual and found that individuals consistently varied in the size of their offspring and the number of offspring they produced per brood. In other words, individuals differed in how productive they were.

“This is the first evidence that genetically identical animals growing under almost identical environmental conditions differ significantly in their biological fitness,” said Ulrike Scherer, lead author of the study, researcher in the SCIoI Cluster of Excellence and guest scientist at the IGB.

There’s a reason for this: He found that fish that spent more time feeding grew larger, and that larger fish produced larger offspring, even though those fish started reproducing later. However, food intake appeared to have no effect on brood size, and there was no correlation between individual activity levels and reproduction.

“Our study also reveals how little we yet understand about the emergence of individuality and the potential role of epigenetics, stochasticity, and subtle environmental differences,” Ulrike-Scherer said.

more information:
Ulrike Scherer et al., Reproductive individualism of clonal fish reared in near-identical environments and its association with behavioral individualism in early life, Nature Communications (2023). doi: 10.1038/s41467-023-43069-6

Magazine information:
Nature Communications

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