# Navigating sex and sex roles: deciphering sex-biased gene expression in a species with sex-role reversal (Syngnathus typhle)

## TL;DR

This study explores how genes are expressed differently in a species where males carry offspring, shedding light on how sex roles and biological sex influence gene activity.

## Contribution

The study provides novel insights into sex-biased gene expression in a species with reversed sex roles, distinguishing between sex and sex role effects.

## Key findings

- Some genes are linked to sex roles like stress resistance and immune defense.
- Other genes are influenced by biological sex, such as those regulating energy and lipid storage.
- Gene expression varies by organ and age, highlighting complex regulatory patterns.

## Abstract

Sexual dimorphism, the divergence in morphological traits between males and females of the same species, is often accompanied by sex-biased gene expression. However, the majority of research has focused on species with conventional sex roles, where females have the highest energy burden with both egg production and parental care, neglecting the diversity of reproductive roles found in nature. We investigated sex-biased gene expression in Syngnathus typhle, a sex-role reversed species with male pregnancy, allowing us to separate two female traits: egg production and parental care. Using RNA sequencing, we examined gene expression across organs (brain, head kidney and gonads) at various life stages, encompassing differences in age, sex and reproductive status. While some gene groups were more strongly associated with sex roles, such as stress resistance and immune defence, others were driven by biological sex, such as energy and lipid storage regulation in an organ- and age-specific manner. By investigating how genes regulate and are regulated by changing reproductive roles and resource allocation in a model system with an unconventional life-history strategy, we aim to better understand the importance of sex and sex role in regulating gene expression patterns, broadening the scope of this discussion to encompass a wide range of organisms.