Meek Males and Fighting Females: Sexually-Dimorphic Antipredator Behavior and Locomotor Performance Is Explained by Morphology in Bark Scorpions (<i>Centruroides vittatus</i>)

Sexual dimorphism can result from sexual or ecological selective pressures, but the importance of alternative reproductive roles and trait compensation in generating phenotypic differences between the sexes is poorly understood. We evaluated morphological and behavioral sexual dimorphism in striped bark scorpions (Centruroides vittatus). We propose that reproductive roles have driven sexually dimorphic body mass in this species which produces sex differences in locomotor performance. Poor locomotor performance in the females (due to the burden of being gravid) favors compensatory aggression as part of an alternative defensive strategy, while male morphology is coadapted to support a sprinting-based defensive strategy. We tested the effects of sex and morphology on stinging and sprinting performance and characterized overall differences between the sexes in aggressiveness towards simulated threats. Greater body mass was associated with higher sting rates and slower sprinting within sexes, which explained the greater aggression of females (the heavier sex) and, along with longer legs in males, the improved sprint performance in males. These findings suggest females are aggressive to compensate for locomotor costs of reproduction while males possess longer legs to enhance sprinting for predator evasion and mate finding. Sexual dimorphism in the metasoma (“tail”) was unrelated to stinging and sprinting performance and may best be explained by sexual selection.性二态性（sexual dimorphism）可由性选择或生态选择压力塑造，但替代生殖角色与性状补偿在塑造两性表型差异中的重要性仍未得到充分阐释。本研究对条纹树皮蝎（Centruroides vittatus）的形态与行为性二态性进行了评估。我们提出，生殖角色差异驱动了该物种的体型质量性二态性，进而导致了两性运动表现的差异。雌性因怀卵负担导致运动表现较差，这使得雌性演化出补偿性攻击行为作为替代防御策略；而雄性的形态则与之协同适配，以支撑基于冲刺的防御策略。本研究检验了性别与形态对螫刺与冲刺表现的影响，并刻画了两性在应对模拟威胁时的攻击性整体差异。在两性内部，更大的体型质量均与更高的螫刺速率及更慢的冲刺速度相关，这解释了雌性（体型更重的性别）攻击性更强的原因；同时结合雄性更长的腿部特征，也解释了雄性冲刺表现更优的机制。上述研究结果表明，雌性通过提升攻击性以弥补繁殖带来的运动成本，而雄性则拥有更长的腿部，以强化冲刺能力，从而更好地躲避天敌与寻找配偶。后体部（"tail"）的性二态性与螫刺及冲刺表现均无关联，其演化最可能由性选择驱动。