Data from: Interspecific aggression, not interspecific mating, drives character displacement in the wing colouration of male rubyspot damselflies (Hetaerina)

Traits that mediate intraspecific social interactions may overlap in closely related sympatric species, resulting in costly between-species interactions. Such interactions have principally interested investigators studying the evolution of reproductive isolation via reproductive character displacement (RCD) or reinforcement, yet in addition to reproductive interference, interspecific trait overlap can lead to costly between-species aggression. Previous research on rubyspot damselflies (Hetaerina spp.) demonstrated that sympatric shifts in male wing colour patterns and competitor recognition reduce interspecific aggression, supporting the hypothesis that agonistic character displacement (ACD) drove trait shifts. However, a recent theoretical model shows that RCD overshadows ACD if the same male trait is used for both female mate recognition and male competitor recognition. To determine whether female mate recognition is based on male wing coloration in Hetaerina, we conducted a phenotype manipulation experiment. Compared to control males, male H. americana with wings manipulated to resemble a sympatric congener (H. titia) suffered no reduction in mating success. Thus, female mate recognition is not based on species differences in male wing coloration. Experimental males did, however, experience higher interspecific fighting rates and reduced survival compared to controls. These results greatly strengthen the case for ACD and highlight the mechanistic distinction between ACD and RCD.

介导种内社会互动的性状在亲缘关系较近的同域物种中往往存在重叠，进而引发代价高昂的种间互动。此类互动长期以来备受进化生物学家关注，相关研究多通过生殖特征置换（reproductive character displacement, RCD）或强化作用探讨生殖隔离的演化；不过除生殖干扰外，种间性状重叠还可导致代价高昂的种间敌对行为。既往针对红痣豆娘（溪蟌属Hetaerina spp.）的研究表明，雄性翅色模式与竞争者识别的同域分化可降低种间敌对程度，这支持了敌对特征置换（agonistic character displacement, ACD）驱动性状分化的假说。然而近期的理论模型显示，若同一雄性性状同时用于雌性配偶识别与雄性竞争者识别，则生殖特征置换（RCD）的效应会掩盖敌对特征置换（ACD）的作用。为验证溪蟌属物种的雌性配偶识别是否基于雄性翅色，我们开展了表型操控实验。与对照组雄性相比，被操控翅色以模拟同域近缘种烟翅溪蟌（H. titia）的美洲红痣豆娘（H. americana）雄性并未出现交配成功率下降的情况。由此可见，雌性配偶识别并非基于雄性翅色的物种间差异。但相较于对照组，实验组雄性的种间争斗率更高，存活率则有所降低。上述结果极大地强化了敌对特征置换（ACD）的相关证据，并明确了敌对特征置换与生殖特征置换（RCD）之间的机制差异。