Biology subjects

Ballen-Guapacha, A. V.

Publications and source records attributed to Ballen-Guapacha, A. V..

4 recordsLinked to original sources

bioRxiv2026

Asymmetric reproductive character displacement and female polymorphism in Ischnura damselflies

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 test for morphological covariation between male traits involved in the tandem position. 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. We also detected RCD in the prothorax shape of I. elegans males from the NC hybrid zone, extending previous evidence of RCD in male caudal appendages, while morphological covariation between male cerci and the prothorax was limited to size in I. elegans. Together, these findings illustrate how hybridization may generate morph-specific patterns of reproductive divergence.

evolutionary biology↗

bioRxiv2025

Alternative reproductive strategies explain asymmetric reinforcement of reproductive isolation in two Ischnura damselfly species

Theoretical and empirical studies on reinforcement have been a central focus in speciation research. Despite its significance, reinforcement in polymorphic species has received little attention, even though morphs often exhibit differences in behavior and reproductive capacity, which could drive asymmetric reinforcement. In this study, we tested for asymmetric reinforcement between morphs in the polymorphic damselflies Ischnura elegans and Ischnura graellsii, in which female morphs exhibit alternative reproductive strategies and males show a preference for the gynochrome morph. These species have formed two independent hybrid zones where reinforcement has strengthened a mechanical barrier and reproductive character displacement has shaped mating-related structures. We compared the strength of five reproductive barriers between female morphs to assess the interplay between female-limited color polymorphism and reinforcement. We detected asymmetric reinforcement in premating and postmating barriers between morphs in both hybrid zones, likely driven by their different reproductive strategies. Additionally, we observed weakening of oviposition and fertility barriers probably associated with gene flow and purging of incompatibilities. Our findings highlight that inherent asymmetry in reproductive isolation, caused by differences in female morph reproductive strategies, drive asymmetric reinforcement between morphs. Future studies should explore the cascading effects of this process and its implications for morph speciation.

evolutionary biology↗

bioRxiv2023

Reproductive character displacement explains strengthening of mechanical barriers in damselflies

Reinforcing natural selection against maladaptive hybrids can favor the strengthening of premating reproductive isolation driving a pattern of Reproductive Character Displacement (RCD). In a recent study conducted in North-West (NW) (older) Spanish hybrid zone, was detected an asymmetric reinforcement of the mechanical isolation in the reciprocal cross direction between I. graellsii males and I. elegans females. Furthermore, in the North-Central and Mediterranean (NCM) (younger) hybrid zone was also detected a similar strengthening of the mechanical isolation, consistent with a pattern of asymmetric reinforcement in this hybrid zone as well. In this study, we did geometric morphometrics analyses, shape, and Centroid Size (CS), on male and female secondary sexual traits to investigate whether reinforcement has generated a pattern of RCD of these traits in both hybrid zones. We detected, in the NW hybrid zone, unidirectional RCD (CS) of the male caudal appendages of I. graellsii, and bidirectional RCD (shape) of the female prothorax. Consistently with the prediction that the signal of reinforcement may diminish rapidly once reinforcement ceases to operate, a stronger signal of RCD was detected in the NCM than in the NW hybrid region. In this region, was detected unidirectional RCD (CS) of the male caudal appendages which was consistent with the lock-and-key mechanism of genital coevolution, as well as RCD (shape) of the female prothorax of I. elegans. Interestingly, our study highlights the importance of using geometric morphometrics to deal with the complexity of reproductive structures and controlling for environmental and geographic factors to investigate RCD.

evolutionary biology↗

bioRxiv2023

Testing the predictions of reinforcement: long-term empirical data from a damselfly mosaic hybrid zone

Theoretical work suggests that reinforcement can cause the strengthening of prezygotic isolation in sympatry by mitigating the costs of maladaptive hybridization. However, only a handful of studies have tested all predictions of this theory in natural populations. We investigated reinforcement in a mosaic hybrid zone of the damselflies Ischnura elegans and I. graellsii. Firstly, we tested if the conditions of reinforcement were fulfilled by quantifying whether hybridization was costly, and prezygotic isolation was strengthening in sympatry compared with in allopatry. Secondly, we investigated three specific predictions of reinforcement: rarer female effect, presence of concordant prezygotic and postzygotic isolation asymmetries in sympatry, and greater premating asymmetries associated with weaker postzygotic isolation in sympatry. We found that reinforcement has strengthened mechanical isolation in one cross direction between species in sympatry. Our study details a case of reinforcement and heterospecific gene flow causing opposite effects between reciprocal heterospecific crosses and describes a natural model in which reproductive isolation is built by the simultaneous effects of reinforcement, the lock-and-key model, Bateson-Dobzhansky-Muller incompatibilities and Haldanes rule.

evolutionary biology↗