Mutational meltdown in selfing Arabidopsis lyrata

Area of Science:

• Evolutionary biology
• Genetics
• Plant reproduction

Background:

• Many species are hermaphrodites, possessing both male and female reproductive functions.
• Hermaphrodites frequently engage in outcrossing, despite the possibility of self-fertilization.
• Outcrossing offers genetic benefits, primarily avoiding inbreeding depression and releasing from drift load.

Purpose of the Study:

• To experimentally test the hypotheses of inbreeding depression and drift load in relation to mating system shifts.
• To investigate the evolutionary maintenance of outcrossing versus self-fertilization in hermaphroditic species.

Main Methods:

• Experimental crosses of Arabidopsis lyrata plants from 18 distinct populations with varying mating systems (outcrossing, mixed, selfing).
• Offspring performance was measured over three years following self-pollination, within-population cross-pollination, and between-population cross-pollination.
• Quantification of inbreeding depression and fitness changes associated with outcrossing versus selfing.

Main Results:

• Outcrossing populations exhibited low inbreeding depression, similar to selfing populations, questioning its role in mating system evolution.
• Plants from selfing populations showed a significant fitness increase when outcrossed with individuals from different populations.
• This indicates a higher accumulation of deleterious mutations (drift load) in selfing populations.

Conclusions:

• The study supports the drift load hypothesis, suggesting that long-term accumulation of mutations leads to extinction in selfing lineages.
• Mutational meltdown, driven by genetic drift, is a more significant factor in the rarity of selfing hermaphroditic taxa than inbreeding depression.
• Understanding mating systems is crucial for predicting species' evolutionary trajectories and extinction risks.