Neutral processes forming large clones during colonization of new areas

Area of Science:

• Evolutionary Biology
• Population Genetics
• Ecology

Background:

• Species that reproduce both sexually and asexually frequently exhibit higher clonal frequencies in recently established populations.
• Previous research suggested natural selection favoring successful genotypes in new environments drives this pattern.
• An alternative hypothesis posits neutral processes during range expansions could also explain this phenomenon.

Purpose of the Study:

• To model and investigate the role of neutral processes in clonal dominance during species' range expansions.
• To differentiate between selection-based and neutral-based mechanisms explaining clonal prevalence in new populations.
• To compare model predictions with empirical data from a post-glacial seaweed species.

Main Methods:

• Developed a mathematical model for a dioecious species capable of both sexual and asexual reproduction during range expansion.
• Simulated scenarios with equal survival rates, dispersal distances, and varying reproductive seasons.
• Incorporated neutral processes like random dispersal and demographic stochasticity.
• Compared model outputs with empirical data from *Fucus radicans*.

Main Results:

• Colonization begins with an asexual wave, even when sexual reproduction is favored long-term.
• A subsequent sexual wave reduces clonal dominance after initial colonization.
• With local dispersal and multiple reproductive seasons, a few large clones can dominate for extended periods.
• Long-distance dispersal leads to more dominant clones but reduces their persistence time.
• Neutral processes, specifically edge effects favoring uniparental recruitment where mates are scarce, drive initial clonal patterns.

Conclusions:

• Neutral processes, rather than solely natural selection, provide a strong explanation for clonal dominance in newly established populations during range expansions.
• The model's predictions align with empirical observations in the seaweed species *Fucus radicans*, supporting a neutral mechanism.
• Edge effects at the expansion front significantly influence reproductive strategies, favoring asexual reproduction in mate-limited conditions.