Shared Features Underlying Compact Genomes and Extreme Habitat Use in Chironomid Midges.

Area of Science:

• Evolutionary Biology
• Genomics
• Ecology

Background:

• Nonbiting midges (Chironomidae) inhabit diverse environments and tolerate harsh conditions, possessing compact genomes.
• The molecular basis and evolutionary history of these traits in Chironomidae remain largely unknown.

Purpose of the Study:

• To investigate the shared molecular basis for compact genomes and habitat tolerances in nonbiting midges.
• To reconstruct the evolutionary history of these traits within the Chironomidae family.

Main Methods:

• Generated high-quality genome assemblies for Tanytarsus gracilentus and Parochlus steinenii.
• Constructed a time-calibrated phylogenomic tree for Chironomidae using available assemblies and Diptera outgroups.
• Analyzed genome structure, gene family evolution, and positive selection in relation to environmental tolerances.

Main Results:

• Compact genomes in Chironomidae likely evolved in their common ancestor with Ceratopogonidae, primarily through reduction of noncoding DNA.
• Expanded gene families in Chironomidae are associated with stress tolerance, including temperature homeostasis and trehalose transport.
• Identified several genes under positive selection, such as sulfonylurea receptor and CREB-binding protein, potentially contributing to adaptation.

Conclusions:

• The study elucidates the evolutionary pathways leading to compact genomes and enhanced stress tolerance in nonbiting midges.
• Findings provide insights into the molecular mechanisms enabling Chironomidae's widespread distribution and survival in extreme habitats.