Ecological Load and Balancing Selection in Circumboreal Barnacles.

Area of Science:

• Evolutionary biology
• Marine ecology
• Genomics

Background:

• Acorn barnacles inhabit diverse circumboreal environments, facing significant environmental variability.
• High juvenile dispersal and mortality pose challenges to maintaining adaptation in these species.
• Understanding the genetic mechanisms of adaptation in variable marine ecosystems is crucial.

Purpose of the Study:

• To investigate how acorn barnacles maintain adaptation to environmental heterogeneity.
• To identify genes under balancing selection across the species' range.
• To explore the role of genetic variation in population structure and speciation.

Main Methods:

• Genomic analysis of acorn barnacle populations.
• Identification of genes under balancing selection.
• Phylogenetic analysis to assess evolutionary history and divergence.

Main Results:

• Approximately 4% of genes in the barnacle genome are under balancing selection across their entire range.
• Many of these selected genes contain mutations conserved over 2 million years between Pacific and Atlantic populations.
• Key genes involved in ion regulation, pain reception, and heat tolerance were identified, crucial for variable environments.
• Complex population structures were revealed, influenced by historical events like the trans-Arctic interchange and glaciations.
• High divergence between Atlantic and Pacific populations suggests incipient allopatric speciation.

Conclusions:

• Balancing selection plays a significant role in maintaining functional genetic variation in acorn barnacles, enabling adaptation to environmental variability.
• This balancing selection is potent enough to preserve variation over millions of years, even with complex population dynamics.
• The findings provide insights into the evolutionary processes shaping marine species in dynamic habitats and the early stages of speciation.