Divergence along the gonadal steroidogenic pathway: Implications for hormone-mediated phenotypic evolution

Area of Science:

• Evolutionary biology
• Endocrinology
• Genetics

Background:

• Hormones regulate key traits influencing survival and reproduction.
• Mechanisms of hormone-mediated trait evolution remain unclear.
• Testosterone influences aggression, ornamentation, and body size in many species.

Purpose of the Study:

• To investigate if differential gene regulation in hormone biosynthesis drives phenotypic divergence.
• To test this hypothesis using two subspecies of junco (Junco hyemalis) that have diverged in testosterone-mediated traits.
• To identify specific genes involved in testosterone production that contribute to evolutionary changes.

Main Methods:

• Comparing gonadal gene expression in two junco subspecies in wild and captive settings.
• Analyzing the steroidogenic pathway for key regulatory genes.
• Measuring testosterone levels following exogenous stimulation to assess response dynamics.
• Mapping gene expression variation to phenotypic differences in a common garden experiment.

Main Results:

• Variation in gonadal gene expression along the steroid biosynthetic pathway correlates with phenotypic divergence within and among junco subspecies.
• The more androgenized subspecies shows a prolonged testosterone elevation after stimulation.
• Specific genes with functionally varying expression link population-level phenotypic variation.

Conclusions:

• Differential regulation of genes in the testosterone biosynthesis pathway is a mechanism for phenotypic evolution.
• Identified genes meet criteria for driving phenotypic evolution: functional variation and correlation with phenotype.
• Findings link hormones, gene expression, and phenotypic evolution, particularly in the context of subspecies divergence.