Effects of body size divergence on male mating tactics in the ground beetle Carabus japonicus

Animal body size is involved in reproduction in various ways. Carabus japonicus exhibits considerable variation in adult body size across geographical locations depending on the larval environment. To investigate the effects of body size divergence on male mating traits, spermatophore deposition and weight, copulation duration, and post-copulatory mounting were observed using male-female pairs from C. japonicus populations with different body sizes. Then, variables with high predictive power on the mating traits were identified from individual characteristics. When the male was slightly smaller than his mate, spermatophore deposition likely succeeded, suggesting that mechanical size-assortative insemination determined male body size. Although male reproductive organ size was positively correlated with male body size, spermatophore weight was not significantly affected by male body size, whereas copulation duration decreased with increasing male body size. Enlarged males, with a high cap...动物体型与繁殖过程以多种途径产生关联。日本步甲（Carabus japonicus）的成虫体型在不同地理区域间存在显著差异，且该差异受幼虫生存环境调控。为探究体型分化对雄性交配性状的影响，研究选取来自不同种群、体型存在差异的日本步甲雌雄个体进行配对，观察记录了精荚（spermatophore）的沉积情况与重量、交配时长以及交配后攀附行为。随后从个体特征中筛选出对交配性状具有高预测能力的变量。研究结果显示，当雄性体型略小于其配偶时，精荚沉积更易成功，提示机械性的体型匹配式授精决定了雄性体型的选择压力。尽管雄性生殖器官尺寸与雄性体型呈正相关，但精荚重量并未受雄性体型显著影响；而交配时长则随雄性体型增大而缩短。体型偏大的雄性，其高……