Biology subjects

Chavez-Rios, J. R.

Publications and source records attributed to Chavez-Rios, J. R..

3 recordsLinked to original sources

bioRxiv2026

From divergence to contact: demographic history and genomic context shape introgression across independent damselfly hybrid zones

Hybridisation outcomes often vary across space and time, yet the relative roles of demographic history and genomic architecture in shaping introgression remain unclear. Here, we investigate three replicated hybrid zones between the damselflies Ischnura elegans and Ischnura graellsii across Spain to test whether genomic introgression patterns are repeatable across independently formed zones. Using genome-wide data, we combined demographic modelling, genomic cline, and functional annotation of introgressed loci. Demographic inference supported three independent secondary contact events of different ages: The South-east zone forming first ([~]207 years ago), followed by the North-west ([~]73.5 years) and North-central ([~]33 years) hybrid zones. Despite similar cline steepness across autosomes, asymmetric gene flow from I. graellsii into I. elegans was observed, with a low overlap of introgressed loci between zones. These loci were mainly associated with broad regulatory and transport-related functions in both hybrid zones, indicating repeatability at the level of gene function rather than gene identity. In contrast, the X chromosome showed steeper clines, suggesting strong intrinsic genomic constraints. Together, demographic history explains geographic heterogeneity in introgression, whereas chromosome architecture imposes consistent constraints. These findings highlight how replicated hybrid zones can disentangle contingent versus repeatable genomic responses during early stages of speciation with gene flow.

evolutionary biology↗

bioRxiv2025

Hybridization outcomes reflect context-dependent reproductive isolation in two damselfly hybrid zones

Pair of species with multiple hybrid zones provide powerful systems to examine how reproductive isolation and reinforcement may depend on ecological and demographic contexts. We conducted a comparative analysis of two hybrid zones between Ischnura elegans and Ischnura graellsii in North-central (NC) and North-western (NW) Spain to evaluate how differences in reproductive barriers shape patterns of hybridization and admixture. First, we quantified five prezygotic barriers in the NC hybrid zone--where no barrier estimates previously existed--and compared them with published data from the NW hybrid zone. Second, we conducted genomic analyses using 5,702 SNPs to assess genetic structure, differentiation, and diversity between species; and 381 SNPs with species-specific alleles to characterize hybrid classes and introgression across both regions. Reproductive isolation was strongly context dependent. Mechanical reinforcement acted in the same cross direction in both hybrid zones, but the NC hybrid zone also showed stronger gametic (fertility) isolation. Consequently, total prezygotic isolation was higher in the NC hybrid zone. These differences were also observed genomically: the NC hybrid zone exhibited limited and largely unidirectional introgression, whereas the NW hybrid zone showed more extensive admixture, bidirectional gene flow, and reduced interspecific differentiation, consistent with a longer or more sustained history of hybridization. Our results demonstrate that hybridization outcomes can differ markedly between hybrid zones involving the same pair of species, underscoring the importance of evaluating spatial variation in reproductive barriers and introgression to assess the presence, asymmetry, and repeatability of reinforcement, as well as the microevolutionary processes shaping hybrid zone structure.

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↗