Functional differences in the hypothalamic-pituitary-gonadal axis are associated with alternative reproductive...

Area of Science:

• Evolutionary biology
• Behavioral endocrinology
• Genomics

Background:

• Genomic variation underlies behavioral diversity, but mechanisms remain unclear.
• Chromosomal inversions can influence hormone synthesis and signaling, impacting behavior.
• Male ruffs display alternative reproductive tactics (ARTs) linked to an autosomal inversion and distinct morphs.

Purpose of the Study:

• To investigate hormonal and transcriptomic differences in the pituitary and gonads between ruff morphs.
• To understand how a specific autosomal inversion affects reproductive hormone synthesis and signaling pathways.
• To identify the primary site of morph-specific hormonal regulation.

Main Methods:

• Hormonal analysis using a GnRH challenge to assess testosterone and androstenedione synthesis.
• Gene expression analysis in the pituitary and gonads to examine key hormone-related genes.
• Comparison of pituitary sensitivity, gonadotropin production, and gonadal sensitivity across different ruff morphs.

Main Results:

• Inversion carriers showed constrained testosterone synthesis but normal androstenedione production, indicating intact pituitary sensitivity to GnRH.
• No significant alterations in pituitary sensitivity, gonadotropin production, or gonadal sensitivity to LH/FSH were found.
• Reduced progesterone receptor expression in the pituitary of inversion morphs.
• Overexpression of the STAR gene in the gonads of inversion morphs, suggesting a key role in hormone synthesis.

Conclusions:

• Morph-specific differences in hormonal regulation are primarily determined by gonadal function, not pituitary sensitivity.
• The overexpression of STAR in gonads of inversion morphs highlights its importance in regulating sex hormone synthesis.
• This study elucidates the genetic and hormonal underpinnings of alternative reproductive strategies in ruffs.