# Decoding the Impacts of Mating Behavior on Ovarian Development in Mud Crab (Scylla paramamosain, Estampador 1949): Insights from SMRT RNA-seq

## TL;DR

This study explores how mating affects ovarian development in mud crabs by analyzing gene expression and splicing changes, revealing key molecular pathways involved in reproduction.

## Contribution

The study provides the first comprehensive view of transcriptional and splicing dynamics in post-mating ovarian maturation in mud crabs.

## Key findings

- Mating triggers major transcriptional reprogramming in the ovary, with serotonin and dopamine signaling acting as opposing regulators of oocyte maturation.
- Later stages of ovarian development involve energy metabolism, lipid mobilization, and extracellular matrix remodeling to support yolk accumulation.
- Enhanced antioxidant defenses are observed, indicating the importance of maintaining redox balance during rapid ovarian development.

## Abstract

In crustaceans, pubertal molting marks the shift from growth to reproduction, and mating promotes ovarian maturation. However, the molecular events driving this transition remain unclear. In this study, we used full-length transcriptome sequencing to investigate gene expression and alternative splicing changes in the mud crab (Scylla paramamosain) after mating. Our results showed that mating triggered major transcriptional reprogramming in the ovary. Early responses involved serotonin and dopamine signaling, which act as opposing regulators of oocyte maturation. Later stages were characterized by activation of energy metabolism, lipid mobilization, and extracellular matrix remodeling to support yolk accumulation and oocyte growth. We also observed enhanced antioxidant defense, indicating the importance of maintaining redox balance during rapid ovarian development. These findings provide new molecular insights into the reproductive biology of mud crabs and may support future strategies for improving broodstock management in aquaculture.

Pubertal molting represents a pivotal transition in the life cycle of crustaceans, marking the shift from somatic growth to reproductive development. In mud crabs, mating is known to facilitate this process, yet the molecular mechanisms remain poorly understood. Here, we applied full-length transcriptome sequencing to characterize changes in gene expression and alternative splicing (AS) across post-mating ovarian development. AS analysis revealed extensive transcript diversity, predominantly alternative first exon (AF) and alternative 5′ splice site (A5) events, enriched in genes linked to chromatin remodeling, protein regulation, and metabolism, underscoring AS as a fine-tuning mechanism in ovarian development. Comparative analyses revealed profound molecular reprogramming after mating. In the UM vs. M1 comparison, pathways related to serotonin and catecholamine signaling were enriched, suggesting early neuroendocrine regulation. Serotonin likely promoted, while dopamine inhibited, oocyte maturation, indicating a potential “inhibition–activation” switch. In the UM vs. M3 comparison, pathways associated with oxidative phosphorylation, ATP biosynthesis, and lipid metabolism were upregulated, reflecting heightened energy demands during vitellogenesis. ECM-receptor interaction, HIF-1, and IL-17 signaling pathways further pointed to structural remodeling and tissue regulation. Enhanced antioxidant defenses, including upregulation of SOD2, CAT, GPX4, and GSTO1, highlighted the importance of redox homeostasis. Together, these findings provide the first comprehensive view of transcriptional and splicing dynamics underlying post-mating ovarian maturation in Scylla paramamosain, offering novel insights into the molecular basis of crustacean reproduction.