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Genome Size and the Evolution of New Genes

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Updated: Sep 10, 2025

Following the Dynamics of Structural Variants in Experimentally Evolved Populations

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How Did Evolution Halve Genome Size During an Oceanic Island Colonization?

Vadim A Pisarenco^1,2, Adrià Boada-Figueras^1,2, Marta Olivé-Muñiz^1,2

¹Departament de Genètica, Microbiologia i Estadística, Universitat de Barcelona, Barcelona, Spain.

Molecular Biology and Evolution

|August 19, 2025

Summary

This summary is machine-generated.

Red devil spiders on the Canary Islands show significant genome size reduction, primarily due to transposable element loss. This evolution supports the nonadaptive mutational hazard hypothesis for genome shrinkage.

Keywords:

adaptive radiation chromosome-level assembly effective population size genome size evolution mutational hazard hypothesis nearly neutral theory

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Area of Science:

Genomics
Evolutionary Biology
Island Biogeography

Background:

The genus Dysdera, or red devil spiders, exhibit remarkable diversification on the Canary Islands.
Insular species possess genomes approximately half the size of their mainland relatives, presenting a unique model for genome size evolution studies.

Purpose of the Study:

To investigate the forces driving genome size reduction in island-dwelling Dysdera spiders.
To resolve debates on the roles of adaptive and nonadaptive mechanisms in shaping genome size.

Main Methods:

Comprehensive genomic analyses using three high-quality chromosome-level assemblies.
Comparative analysis of genomic elements, including intronic, intergenic regions, and transposable elements (TEs).

Main Results:

Significant genome size reduction observed in insular Dysdera species, affecting all genomic components.
Transposable element (TE) loss is the primary driver of genome contraction, with autosomes showing disproportionate reduction compared to the X chromosome.
Island species display paradoxically higher nucleotide diversity, recombination rates, and evidence of intensified natural selection, suggesting larger long-term effective population sizes.

Conclusions:

Genome size reduction in Canary Island Dysdera is largely driven by nonadaptive processes, specifically purifying selection against deleterious DNA and TE insertions.
Findings support the nonadaptive mutational hazard hypothesis as the main mechanism for genome size reduction in this model system.