Approximating the Coalescent Under Facultative Sex

Area of Science:

• Evolutionary Biology
• Population Genetics
• Genomics

Background:

• Facultative sexual species reproduce both sexually and asexually, presenting unique evolutionary dynamics.
• Understanding the genomic evolutionary history of these species is crucial for evolutionary biology.
• The applicability of standard coalescent theory to facultative sexuals remains unclear.

Purpose of the Study:

• To determine the conditions under which standard coalescent approximations are valid for facultative sexual species.
• To investigate the existence and nature of a coalescent effective population size (Ne) in these species.
• To inform optimal sampling strategies for studying the evolutionary history of mixed reproductive mode organisms.

Main Methods:

• Theoretical analysis of population genetics models incorporating sexual and asexual reproduction.
• Investigation of genealogical properties under varying frequencies of sexual reproduction and gene conversion.
• Mathematical derivation of coalescent approximations and effective population size (Ne) under different scenarios.

Main Results:

• When sexual reproduction is frequent (>>1/N), the standard coalescent approximation is valid, with Ne ≈ N.
• When sex is rare (<<1/N), pairwise coalescent times are influenced by sex and gene conversion frequencies, not directly by N.
• Under rare sex conditions, a standard coalescent effective population size (Ne) does not emerge.

Conclusions:

• The evolutionary history of facultative sexuals can be approximated by standard coalescent theory only when sex is frequent.
• Rare sexual reproduction and gene conversion significantly alter genealogical patterns, precluding simple coalescent Ne estimations.
• Findings guide the development of effective sampling strategies for studying the population genomics of mixed reproductive mode species.