Bottlenecks and inbreeding depression in autotetraploids

Area of Science:

• Evolutionary Biology
• Population Genetics
• Genetics

Background:

• Inbreeding depression, the reduced fitness in inbred individuals, is a key factor influencing the evolution of self-fertilization (selfing).
• While polyploids (organisms with multiple sets of chromosomes) are generally expected to have less inbreeding depression than diploids at evolutionary equilibrium, this has not been well-studied under non-equilibrium conditions like population bottlenecks.

Purpose of the Study:

• To investigate the impact of population bottlenecks on inbreeding depression in diploids and autotetraploids.
• To examine how the formation of neo-autotetraploids (new tetraploids) from unreduced gametes affects inbreeding depression.

Main Methods:

• Stochastic individual-based simulations were employed to model populations with varying ploidy levels (diploid and autotetraploid).
• A ploidy-independent dominance function, based on enzyme kinetics, was used to assess the effects of recessive and partially recessive mutations.
• Simulations considered scenarios of population bottlenecks and the formation of neo-autotetraploids.

Main Results:

• Inbreeding depression was generally lower in autotetraploids compared to diploids for recessive and partially recessive mutations.
• Population bottlenecks reduced inbreeding depression to a lesser extent in autotetraploids due to increased chromosome sampling during reproduction.
• In some cases, bottlenecks temporarily increased inbreeding depression in autotetraploids by elevating the frequency of heterozygous genotypes carrying harmful mutations.
• The formation of neo-autotetraploids by a small number of individuals dramatically reduced inbreeding depression due to effective masking of deleterious mutations.

Conclusions:

• Population bottlenecks have ploidy-dependent effects on inbreeding depression.
• Nascent neo-autotetraploids experience reduced inbreeding depression, creating a transient window conducive to the evolution of selfing.
• Understanding these dynamics is crucial for predicting the evolutionary trajectories of selfing in different ploidy levels.