The Genetic Load of Plenty: When Too Much Diversity Becomes a Burden

Species with small, declining populations have long been the focus of conservation efforts; however, I propose that species with historically very high population sizes, when they begin to decline, may be at even greater risk. Very high population size is theoretically expected to lead to very high genetic diversity; new mutations are primarily retained rather than being lost by random genetic drift, as would otherwise occur in smaller populations. High genetic diversity is typically seen as beneficial by increasing genetic adaptive potential, but here I challenge this view by exploring its hidden downside. I hypothesize that species with enormous population sizes accumulate huge amounts of deleterious mutations (genetic load) that become a liability when populations decline and inbreeding occurs. This may elevate extinction risk, and in species like European and American eel - primary models in this project - it may furthermore hinder domestication efforts in aquaculture.