Female-Biased Sexual Size Dimorphism and Its Potential Causes in Hairy-Winged Bats.

Sexual size dimorphism (SSD) is widespread in bats, yet its magnitude, direction, and underlying mechanisms vary substantially among species and remain incompletely understood. The hairy-winged bat (Harpiocephalus harpia) represents a particularly informative case, as pronounced female-biased SSD has historically led to taxonomic confusion, underscoring its value for exploring the mechanisms driving SSD at the species level. Here, we quantified intersexual morphological differences underlying female-biased SSD in 80 H. harpia individuals (41♂, 39♀) sampled across China. After excluding potential geographic effects, females exhibited both absolute and relative size advantages over males in multiple craniodental characteristics, whereas sexual differences in wing elements were detected only in absolute terms. Craniodental differentiation and sex-specific allometric patterns in skull morphology, particularly in regions associated with bite force and mastication, suggest that females potentially exploit larger and/or harder prey during energetically demanding reproductive stages. In contrast, wing morphology in H. harpia exhibited little evidence of sex-specific allometric growth or shape differentiation, and female wing dimensions appeared sufficient to accommodate pregnancy-related mass gain without additional compensatory enlargement. Moreover, the absence of sex-biased reduction in body-size variance provides limited support for intrasexual resource competition. Collectively, our findings indicate that SSD in H. harpia is best explained by niche divergence, with the "Big Mother" and "Resource Competition" hypotheses playing secondary roles.