Paternal strategies in social hierarchy: A comprehensive study on ranked bioenergetic investment and its influence on sperm quality in Nile tilapia (Oreochromis niloticus)

Nile tilapia ( Oreochromis niloticus ) maintains a stable and long-term social hierarchy in breeding tanks where the dominant male (DM) aggressively competes with subordinate males (SM) for access to the spawning site and the spawning female. An intermediate rank between DM and SM i.e. ascendant male (AM), was identified and categorized. Within this three-tiered hierarchy, we examined a rank-bioenergetic relationship to determine the group-wise energetic investment in reproductive versus metabolic functions and their implications on sperm quality. We analyzed sperm motility kinetics, fatty acids, amino acids, and ATP and its derivatives composition in DM, AM, and SM. Additionally, fatty acid composition along the brain-liver-testes axis, ATP and its derivatives in muscles, body morphometrics, and plasma hormone concentration were assessed. Sperm volume, gonadosomatic index (GSI), testes weight, and testosterone levels were significantly higher in DM than in SM. Among this, testes weight, GSI, and testosterone levels of DM were comparable to AM and collectively differed from SM. No significant difference in sperm kinetics, body morphometrics, and ATP levels in muscle and sperm was found. These results, together with analytical and effect size analysis for fatty acid, amino acid, and energy derivatives of sperm from all hierarchies confirmed our hypothesis that DM and AM preferentially allocate energy towards reproductive function, whereas SM conserve energy, maintaining sperm at a basal physiological level with energetic readiness. Moreover, distinct energy allocation strategies were evident: DM primarily relied on lipid reserves, while AM exhibited elevated levels of specific amino acids, indicating context-dependent metabolic pathways underlying reproductive investment.