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<p>Reproductive Character Displacement (RCD) often occurs when species with mating-related polymorphism come into secondary contact, leading to divergence in reproductive traits. <i>Ischnura elegans</i> and <i>Ischnura graellsii</i> have formed two independent hybrid zones in Spain where reinforcement has strengthened a mechanical barrier, and RCD has shaped mating-related structures, although reinforcement is asymmetric only in gynochrome females. This study examines the link between asymmetric reinforcement and asymmetric RCD. Using geometric morphometrics, we analyze prothorax shape and size in both female morphs and males, and male caudal appendages, to assess morphological divergence, determine whether gynochrome females show stronger divergence, and evaluate how reproductive traits respond across morphs and sexes. Our results reveal consistent patterns of size and shape variation across species and zones: in <i>I. elegans</i>, androchromes are larger and resemble males in size, with clear shape differentiation between female morphs that diminishes in hybrid zones. In contrast, <i>I. graellsii</i> shows less consistent size differences between males and morphs, and weaker shape differentiation. Our results confirm RCD in prothorax shape in <i>I. elegans</i> females from both hybrid zones, but reveal that RCD in prothorax size is asymmetric, occurring only in gynochrome females from the NC hybrid zone. These findings indicate that different reproductive traits respond asymmetrically to hybridization across morphs and species. Our results show that female polymorphism shapes the evolutionary response to hybridization by promoting asymmetric patterns of RCD and reinforcement among morphs, highlighting its role in the evolution of reproductive isolation in polymorphic systems.</p>

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Asymmetric Reproductive Character Displacement and Female Polymorphism in Ischnura Damselflies

  • 期刊论文

  • 发表日期：

    2026年5月30日

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  • Andrea Viviana Ballén-Guapacha,
  • Rosa Ana Sánchez-Guillén

摘要

Reproductive Character Displacement (RCD) often occurs when species with mating-related polymorphism come into secondary contact, leading to divergence in reproductive traits. Ischnura elegans and Ischnura graellsii have formed two independent hybrid zones in Spain where reinforcement has strengthened a mechanical barrier, and RCD has shaped mating-related structures, although reinforcement is asymmetric only in gynochrome females. This study examines the link between asymmetric reinforcement and asymmetric RCD. Using geometric morphometrics, we analyze prothorax shape and size in both female morphs and males, and male caudal appendages, to assess morphological divergence, determine whether gynochrome females show stronger divergence, and evaluate how reproductive traits respond across morphs and sexes. Our results reveal consistent patterns of size and shape variation across species and zones: in I. elegans, androchromes are larger and resemble males in size, with clear shape differentiation between female morphs that diminishes in hybrid zones. In contrast, I. graellsii shows less consistent size differences between males and morphs, and weaker shape differentiation. Our results confirm RCD in prothorax shape in I. elegans females from both hybrid zones, but reveal that RCD in prothorax size is asymmetric, occurring only in gynochrome females from the NC hybrid zone. These findings indicate that different reproductive traits respond asymmetrically to hybridization across morphs and species. Our results show that female polymorphism shapes the evolutionary response to hybridization by promoting asymmetric patterns of RCD and reinforcement among morphs, highlighting its role in the evolution of reproductive isolation in polymorphic systems.