Biology subjects

Heyda, C.

Publications and source records attributed to Heyda, C..

3 recordsLinked to original sources

bioRxiv2026

Adaptive coupling of chromosomal inversions with multilocus ecological, mating-bias, and hybrid-incompatibility genotypes facilitates sympatric speciation

Chromosomal inversions (CIs) are widespread structural variants that suppress recombination and maintain favorable allele combinations as tightly linked supergenes. They are increasingly recognized for their contributions to local adaptation and speciation, yet their role in sympatric speciation under ongoing gene flow remains unresolved. Here, we develop mathematical models and computer simulations to examine how polygenic architectures and CI invasion jointly shape the evolution of reproductive isolation (RI) in a two-niche model under disruptive ecological selection. Extending previous frameworks, we incorporate multilocus ecological traits, multilocus mating-bias traits, and multilocus hybrid-incompatibility genotypes, and evaluate the invasion fitness and evolutionary consequences of CIs capturing different combinations of locally adaptive alleles. We show that the evolutionary impact of CI invasion depends critically on how polygenic trait structure influences hybrid production and the strength of barrier mechanisms. Increasing the number of ecological or hybrid-incompatibility loci strengthens disruptive ecological selection and postzygotic incompatibility selection by generating more unfit hybrids, whereas increasing the number of mating-bias loci weakens premating selection because mating-bias hybrids remain viable within the same niche. Accordingly, CIs capturing ecological or hybrid-incompatibility alleles tend to reduce the effective number of loci, diminish hybrid loss, and weaken existing RI, whereas CIs capturing mating-bias alleles strengthen premating isolation by reducing the effective number of mating-bias loci. Importantly, CIs that couple alleles across distinct barrier mechanisms exhibit elevated invasion fitness and generate synergistic reinforcement and positive feedback among premating isolation, postmating isolation, and ecological divergence. These findings reconcile contrasting theoretical predictions by demonstrating that CIs can either facilitate or constrain sympatric speciation depending on how they reshape effective locus number and barrier coupling, and provide a unified framework for understanding how structural genomic variants interact with polygenic architectures to influence the origin and stability of reproductive isolation.

evolutionary biology↗

bioRxiv2025

Coupling of habitat-preference barriers leads to reproductive isolation in sympatric speciation

Habitat preference is a widely recognized mechanism of reproductive isolation, yet its role in initiating premating barriers and coupling with other barrier mechanisms to establish robust and irreversible reproductive isolation (RI) in sympatric speciation remains unclear. In this study, we developed mathematical models and computer applications to investigate one- and two-allele models of habitat-preference barriers in sympatric populations under disruptive ecological selection. We examined two spatial arrangements: an open-space model inspired by sympatric cichlid fishes that meet in open water with niche habitats that are small relative to lake size, and a no-open-space model inspired by sympatric hawthorn and apple maggot flies that move directly between trees without lingering in midair. Next, we examined coupling between habitat-preference barriers and a two-allele mating-bias barrier developed in a prior study to analyze how their invasion and coupling dynamics could lead to stronger RI. Our findings confirm that habitat preference is an independent mechanism capable of establishing initial premating barriers in sympatric speciation. Moreover, it can couple with additional barriers, such as those based on mating-trait discrimination, to enhance overall RI. Because habitat preference is an adaptive barrier mechanism, its invasion and coupling are driven by selection pressures arising from maladaptive hybrid loss, and it is readily reversed when disruptive ecological selection weakens. The one-allele model is easier to evolve than the two-allele model because it is immune to recombination by gene flow. Habitat-preference barriers can facilitate the emergence of mating-bias barriers. Open-space systems provide fewer opportunities for inter-niche encounters and tend to result in stronger RI compared to no-open-space systems. By elucidating the habitat-preference mechanism, our study reinforces the important role of habitat-preference barriers in sympatric speciation. It also provides insights into a wide range of premating isolating mechanisms--temporal, behavioral, and mechanical--that function similarly by reducing mating encounters.

evolutionary biology↗

bioRxiv2025

Computer Simulations and Analyses of Coupling Among Reproductive Barriers in Late-Stage Sympatric Speciation

The mechanisms driving sympatric speciation remain an unresolved challenge in evolutionary biology. In nature, closely related "good" species are observed to possess multiple different barriers in their genomes that collectively generate strong and irreversible reproductive isolation (RI). Theorists hypothesize that early-stage mechanisms responsible for establishing an initial reproductive barrier differ from those driving the coupling of barriers in later stages of sympatric speciation. In a prior study, we developed a two-allele mathematical model of mating-bias traits to demonstrate how initial premating RI can arise in a sympatric population under disruptive ecological selection. Here, we extend this model to investigate how different pre- and post-mating barriers can couple with such an initial barrier and with one another during late-stage sympatric speciation to establish strong and irreversible RI. We developed computer applications to examine the properties of various barrier mechanisms and the conditions required for their invasion and coupling. Early-stage, adaptive premating barriers, driven by maladaptive hybrid loss, are effective in establishing initial RI and coupling with other barriers but are easily reversed if disruptive ecological selection weakens. Late-stage barriers, by contrast, often rely on earlier barriers to create an environment of reduced gene flow to facilitate their invasion and coupling. Mutations reducing hybrid viability are underdominant in inter-niche matings and can only invade by hitchhiking with barriers conferring a fitness advantage. Chromosomal inversions, an adaptive late-stage mechanism, can combine different barrier properties into a supergene and gain a net fitness advantage to invade and couple with other barriers to create strong and less reversible RI. Late-stage nonadaptive Bateson-Dobzhansky-Muller (BDM) barriers evolve more slowly but confer the strongest and least reversible RI. Our findings reveal a positive feedback loop in which early-stage barriers facilitate the establishment of late-stage barriers, while late-stage barriers strengthen and secure early-stage barriers. This positive reinforcement progressively strengthens overall RI until it becomes irreversible. By examining the properties and invasion dynamics of various barrier mechanisms, this study complements our previous study to propose a comprehensive process of sympatric speciation that explains how barriers emerge and couple to complete the speciation process.

evolutionary biology↗