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Speciation Rates

Speciation Rates

Gene Flow

Gene Flow

Gene flow is the transfer of genes among populations, resulting from either the dispersal of gametes or from the migration of individuals.

Formation of Species

Formation of Species

Speciation describes the formation of one or more new species from one or sometimes multiple original species. The resulting species are discrete from the parent species, and barriers to reproduction will typically exist. There are two primary mechanisms, speciation with and without geographic isolation—allopatric and sympatric speciation, respectively.

Genetics of Speciation

Genetics of Speciation

Speciation is the evolutionary process resulting in the formation of new, distinct species—groups of reproductively isolated populations.

Hybrid Zones

Hybrid Zones

Hybrid zones are narrow regions where two closely related species interact, mate, and produce hybrids. Relative to either parent species, hybrids may possess distinct phenotypic or genetic differences that impact their survival and reproductive success. The genetic variances introduced by hybridization influence species diversity and speciation processes within the hybrid zone.

What is a Species?

What is a Species?

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Updated: Sep 11, 2025

Determination of the Mating Efficiency of Haploids in Saccharomyces cerevisiae

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Published on: December 2, 2022

Coexistence in Sympatry With Gene Flow Before Speciation Has Completed.

Dolph Schluter¹, Thor Veen¹, Ken A Thompson^1,2

¹Zoology Department, and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada.

Molecular Ecology

|August 13, 2025

Summary

Sympatric species like stickleback fish can coexist despite hybridization, but require moderately strong selection against hybrids to maintain distinct populations. Niche differences are crucial for stability with gene flow.

Keywords:

community ecology conservation genetics fish genomics/proteomics hybridization speciation

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Area of Science:

Evolutionary Biology
Ecology
Population Genetics

Background:

Incipient species may coexist in sympatry before full reproductive isolation.
Hybridization and gene flow pose challenges to species persistence by eroding genetic differences and destabilizing populations through selection against hybrids.

Purpose of the Study:

To estimate gene flow and selection against hybrid genotypes in sympatric limnetic and benthic threespine stickleback species.
To determine the level of selection required to maintain coexistence in the face of hybridization.

Main Methods:

Comparing ancestry proportions between juvenile and adult stickleback samples.
Utilizing genomic simulation with assortative mating in an ecological model.
Estimating selection coefficients against hybrid genotypes.

Main Results:

First-generation hybrids were present at approximately 2%.
Estimated selection coefficients (S) against the least fit ancestry proportion ranged from 0.5 to 0.6.
Selection was only slightly weaker than that leading to population collapse and fusion in simulations.

Conclusions:

Sympatric stickleback species are near a coexistence boundary, requiring moderately strong selection to persist with low gene flow.
Larger niche differences are necessary to stabilize coexistence when gene flow is present.
Conspicuous ecological and phenotypic differences in hybridizing sympatric species may be a consequence of stabilizing selection.