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Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly adapted organisms. Several factors constrain natural selection.

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Daily Transfers, Archiving Populations, and Measuring Fitness in the Long-Term Evolution Experiment with Escherichia coli

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Strong Bottlenecks Constrain Adaptive Coevolution in a Host-Parasite Metapopulation.

Pascal Angst^1,2, Christoph R Haag^2,3, Frida Ben-Ami^2,4

¹Department of Environmental Sciences, Zoology, University of Basel, Basel, Switzerland.

Molecular Ecology

|July 21, 2025

Summary

Host population structure significantly impacts parasite evolution. This study shows host dynamics can accelerate genetic drift in the microsporidian parasite Hamiltosporidium tvaerminnensis, leading to slower parasite evolution than previously assumed.

Keywords:

daphnia host–parasite interactions loss of heterozygosity microsporidia population structure runs of homozygosity

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Following the Dynamics of Structural Variants in Experimentally Evolved Populations

Following the Dynamics of Structural Variants in Experimentally Evolved Populations

Published on: February 3, 2023

Area of Science:

Evolutionary Biology
Parasitology
Population Genetics

Background:

Parasites adaptively evolve to exploit hosts.
Transmission bottlenecks and host population structure can induce genetic drift in parasites, limiting their adaptive evolution.
The interplay between host population dynamics and parasite evolution remains incompletely understood.

Purpose of the Study:

To investigate the influence of host population structure on the genomic evolution of the microsporidian parasite Hamiltosporidium tvaerminnensis.
To analyze the co-evolutionary dynamics between H. tvaerminnensis and its host, Daphnia magna, within a dynamic metapopulation.
To determine if host population structure accelerates genetic drift in parasite populations.

Main Methods:

Longitudinal whole-genome allele frequency tracking of 59 host (Daphnia magna) and parasite (Hamiltosporidium tvaerminnensis) subpopulations over 10 years.
Analysis of co-dispersal and isolation-by-distance patterns between host and parasite.
Identification of genetic signatures, including runs of homozygosity (ROHs), in parasite populations.

Main Results:

Both host and parasite exhibited co-dispersal and isolation-by-distance, but host allele frequencies were more dynamic, showing recurrent genetic bottlenecks.
Parasite populations displayed high shared heterozygosity but also subpopulation-specific runs of homozygosity (ROHs).
Host population structure and metapopulation dynamics leave a traceable genomic signature in the parasite, suggesting accelerated drift.

Conclusions:

Host population structure and metapopulation dynamics significantly shape parasite genomic evolution.
Host-mediated parasite population bottlenecks can lead to the fixation of deleterious ROHs in parasite subpopulations.
Contrary to expectations, parasites may evolve more slowly than their hosts, with host dynamics potentially accelerating parasite drift.