An Argentine discovery challenges a century-old genetic dogma about inbreeding

For more than a century, biology has largely explained inbreeding depression through defective recessive genes inherited from a shared ancestor. An Argentine-led study now challenges that explanation, finding that the damage can persist even when genetic variation is almost absent.

The research was led by Nicolás Bonel, a CONICET scientist at the Center for Renewable Natural Resources of the Semi-Arid Zone, in collaboration with Patrice David of France’s Centre d’Écologie Fonctionnelle et Évolutive. Published in Evolution Letters, the study offers experimental evidence that other mechanisms, probably epigenetic ones, may play a decisive role.

The team worked with Physa acuta, a freshwater hermaphroditic snail widely used in inbreeding research. Researchers subjected specimens to 28 generations of self-fertilization, producing experimental lines with almost no genetic variation. They then compared offspring produced through self-fertilization, sibling mating and cousin mating.

Classical theory would predict similar biological performance because the groups shared essentially the same genotype. Instead, self-fertilized offspring had lower survival, smaller bodies and reduced reproductive success than the other groups. The researchers used simulation models to test whether new mutations arising during the experiment could explain the results. Known mutation rates were too low to account for the size of the effect.

The strongest explanation therefore points toward epigenetics. Chemical marks on DNA can activate or silence genes without changing the underlying genetic sequence. Bonel said the experiment was designed to ask what would happen if genetic variation were almost eliminated while differences in genealogical relatedness remained. The observed effects persisted, casting doubt on the idea that shared harmful genes alone explain inbreeding depression.

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We sought to answer a fundamental question: what would happen to inbreeding depression if genetic variation between individuals were almost completely eliminated without changing their degree of relatedness?