Temporal persistence of admixed phenotypes in a damselfly hybrid zone

Abstract

In odonates, hybridization has been documented in several species pairs, yet the long-term persistence of hybrid phenotypes remains poorly understood, particularly in Neotropical systems. Here, we investigate a putative hybrid zone between Ischnura capreolus and Ischnura cyane, which overlap along an altitudinal gradient in the Colombian Andes. We combined temporal sampling across sympatric and allopatric localities with multilocus genetic analyses and geometric morphometrics of wings and male caudal appendages to evaluate patterns of admixture and phenotypic intermediacy. Morphometric analyses revealed pronounced differentiation between I. capreolus and I. cyane, especially in allopatric populations, whereas individuals from sympatric localities displayed increased morphological overlap and intermediate phenotypes. Genetic analyses based on nuclear and mitochondrial genes identified two main genetic clusters corresponding to the parental species, with evidence of admixture and shared haplotypes in sympatric localities. Patterns of differentiation varied among loci, with mitochondrial markers showing broader haplotype sharing than nuclear loci. Across sympatric localities, morphologically intermediate individuals remained consistently present through time, particularly in Anolaima, where they represented the dominant phenotype across sampling periods. These results support concordant morphological and genetic evidence consistent with persistent hybridization and introgression between I. capreolus and I. cyane in their zone of contact and suggest that incomplete reproductive isolation contributes to the long-term maintenance of admixed phenotypes in this hybrid zone.