Abstract
Life-history theory predicts trade-offs between offspring number and offspring size as a central mechanism shaping reproductive strategies in animals. Variation in egg size, fecundity, and parental care influences early survival and evolutionary diversification. Yet how closely related species integrate reproductive behavior and parental care with offspring size and fecundity remains poorly understood. We compared two closely related Neotropical substrate-brooding cichlids, Cryptoheros spilurus and C. cutteri, under controlled laboratory conditions to evaluate how female body mass mediates reproductive allocation. We quantified absolute and relative fecundity, egg diameter, larval size at hatching, and yolk sac volume, and conducted qualitative observations of reproductive behavior. Both species exhibited biparental care and iterative spawning, consistent with previous descriptions, but differed in offspring size while exhibiting similar fecundity–body mass scaling relationships. Clutch-level analyses revealed interspecific differences in egg diameter, but no significant relationship between female body mass and egg size in either species. C. spilurus produced larger eggs and larvae at hatching (approximately 20% greater total length), whereas C. cutteri produced smaller eggs and larvae. Both species showed comparable parental care behaviors, including fanning, cleaning, and brood defense. These findings demonstrate that closely related substrate-brooding cichlids can diverge in offspring size while maintaining conserved parental strategies.