The loss of nuptial gifts in sclerosomatid Opiliones coincides with an increase in sexual conflict-like behaviour

Nuptial gifts serve to increase donor fitness through a variety of mechanisms, including securing additional copulations, increasing sperm transfer or storage, or increasing paternity share. Coercive mating behaviour can provide similar male benefits, potentially allowing for evolutionary transitions between solicitous and coercive strategies, wherein male behavioural antagonism could function to secure mates in lieu of nuptial gifts. In temperate leiobunine harvesters (Arachnida: Opiliones), nuptial gifts have been repeatedly lost, resulting in two primary mating syndromes: an ancestral, sacculate state in which males endogenously produce high-investment nuptial gifts and females lack pregenital barriers, and a derived, nonsacculate state in which females have pregenital barriers and males produce significantly reduced, low-investment nuptial gifts. In this study, we investigated whether behavioural sexual conflict is elevated in nonsacculate harvesters by comparing pre-, peri-, and postcopulatory mating behaviour between the nonsacculate species Leiobunum vittatum and L. euserratipalpe and the sacculate species L. aldrichi and L. bracchiolum. We additionally sought to establish an automated behavioural analysis pipeline by developing analogues for metrics traditionally scored manually. Our results revealed significantly different, potentially coercive, behaviour in nonsacculate species, indicating that the loss and reduction of pre- and pericopulatory nuptial gifts may contribute to increased behavioural antagonism. Mating behaviour also differed significantly between L. vittatum and L. euserratipalpe, indicating there are multiple suites of potentially antagonistic behaviours. Together, these results suggest that multiple behavioural strategies may be effective substitutes for nuptial gifts in leiobunine Opiliones, although the mechanisms through which male fitness is increased requires further research.

婚赠礼物（nuptial gifts）可通过多种机制提升供体适合度，包括促进额外交配、增加精子传递与储存，或提高父权份额。强制交配行为（coercive mating behaviour）同样能为雄性带来类似收益，这使得殷勤策略与强制策略间可能发生进化转换，其中雄性行为拮抗作用可替代婚赠礼物以获取配偶。
在温带莱奥布尼盲蛛类（leiobunine harvesters，蛛形纲:盲蛛目（Arachnida: Opiliones））中，婚赠礼物已多次丢失，由此形成两种主要交配综合征：一类为祖先型具囊态，雄性内源产生高投入婚赠礼物，雌性无生殖前屏障；另一类为衍生型非具囊态，雌性具备生殖前屏障，雄性产生的婚赠礼物显著减少且为低投入类型。
本研究通过比较非具囊物种条纹莱奥布尼蛛（Leiobunum vittatum）、L. euserratipalpe与具囊物种L. aldrichi、L. bracchiolum的交配前、交配中及交配后行为，探究非具囊盲蛛的行为性性冲突是否更为剧烈。此外，本研究还尝试通过开发传统人工计分行为指标的等效分析指标，建立一套自动化行为分析流程。
研究结果显示，非具囊物种存在显著差异且可能属于强制交配的行为，表明交配前与交配中婚赠礼物的丢失与减少可能加剧了雄性行为拮抗作用。条纹莱奥布尼蛛与L. euserratipalpe的交配行为同样存在显著差异，说明存在多套潜在的拮抗行为组合。
综上，本研究结果表明，在莱奥布尼盲蛛类群中，多种行为策略可有效替代婚赠礼物；不过雄性适合度提升的具体机制仍需进一步研究加以阐明。