Variance effective population size is affected by census size in sub-structured populations.

Area of Science:

• Population Genetics
• Evolutionary Biology
• Conservation Genetics

Background:

• Effective population size (Ne) is crucial for understanding population dynamics and genetic diversity.
• The temporal method, estimating variance effective size (NeV), is widely used but its accuracy in sub-structured populations is debated.
• NeV is often used as a proxy for inbreeding effective size (NeI) in genetic management.

Purpose of the Study:

• To investigate the influence of census size (Nc) on the variance effective size (NeV) of local subpopulations within a metapopulation.
• To determine how migration rates (m) interact with Nc to affect NeV.
• To clarify the relationship between local NeV, metapopulation NeV, and other effective size measures (NeI, NeLD).

Main Methods:

• Derivation of explicit mathematical expressions for NeV under an island migration model.
• Verification of analytical results using high-resolution computer simulations.
• Comparison of local NeV with metapopulation NeV, NeI, and NeLD.

Main Results:

• Local NeV is influenced by both migration rate (m) and census size (Nc), with the effect of Nc being most pronounced at high migration rates.
• The relationship between NeV and m can be positive or negative depending on the isolated Ne and Nc.
• Metapopulation NeV, NeI, and NeLD are independent of Nc, unlike local NeV.

Conclusions:

• Census size (Nc) is a significant factor affecting local effective population size estimates (NeV) in sub-structured populations.
• The findings offer a potential explanation for the wide variation in Ne/Nc ratios observed in empirical studies.
• Metapopulation NeV should be prioritized over local NeV as a more reliable proxy for inbreeding effective size (NeI) in genetic management.