Unexpected male choosiness: Female aggressiveness as a criterion for mate choice preference in the red swamp crayfish.

As a core manifestation of sexual selection, mate choice preference has traditionally been studied primarily in the context of female assessment and selection of male traits, whereas active male choice for female phenotypic characteristics remains rarely reported in crustaceans. Among the various factors influencing mate choice outcomes, animal personality types-particularly aggressiveness-serve as key behavioural indicators of an individual's competitive ability and physiological condition. Here, using the red swamp crayfish (Procambarus clarkii), we investigated whether female aggressiveness influences male mate choice preference. After confirming sex effects on aggressiveness, we used a two-choice assay to examine the influence of female aggressive interactions and their outcomes on male preference. We found that sex affected fighting frequency: male-male pairs fought more frequently than female-female pairs, with male-female pairs intermediate. Male observers spent more time and made more entries into the winner zone than the loser zone and showed a positive standardized strength of preference (SOP), whereas female observers showed no such preference. Female aggression scores were positively correlated with male observers' duration in the preference zone. These findings suggest that male red swamp crayfish can assess the outcomes of fighting encounters between two females and prefer those females with a highly aggressive phenotype, revealing a reversal of conventional sex roles and providing new behavioral evidence for non-canonical sexual selection mechanisms in crustaceans.