Biology subjects

Farnitano, M. C.

Publications and source records attributed to Farnitano, M. C..

4 recordsLinked to original sources

bioRxiv2026

On the causes of correlated genomic ancestry across contrasting hybridization histories in a monkeyflower species pair.

Hybridization is a powerful force shaping the evolutionary trajectories of species, yet its outcomes are highly variable both across taxa and within a pair of species. In this study, we examine the processes shaping variation in the extent of hybrid ancestry, both among populations and across the genome. We use low-coverage sequencing data to infer local ancestry across the genome for 782 individuals from multiple populations across two geographic regions within the broadly overlapping range of Mimulus guttatus and Mimulus nasutus. We find that the extent of hybrid ancestry is variable across populations, supporting disparate historical patterns of hybridization. However, genomic patterns of hybrid ancestry are correlated across groups, indicating they are shaped by parallel processes. Correlations are highest in geographically proximal populations, including between sympatric and allopatric locations, providing evidence that introgression is not locally constrained but spreads via migration across the landscape. We find that features of the genome are predictive of hybrid ancestry and its correlations among populations. However, contrary to findings in some other species, these patterns are likely not driven by simple linked selection against hybrid ancestry. Genomic outliers for high hybrid ancestry are often shared among populations, suggesting a role for parallel positive selection on ancestry. However, known loci associated with reproductive isolation are poor predictors of ancestry variation across populations, indicating that selection acting in natural hybrid populations is highly polygenic and that the underlying genetic architecture varies across space. Overall, this study demonstrates how ecological, demographic, and genomic features all interact to shape the outcomes of hybridization.

evolutionary biology↗

bioRxiv2024

Fluctuating reproductive isolation and stable ancestry structure in a fine-scaled mosaic of hybridizing Mimulus monkeyflowers

Hybridization among taxa impacts a variety of evolutionary processes from adaptation to extinction. We seek to understand both patterns of hybridization across taxa and the evolutionary and ecological forces driving those patterns. To this end, we use whole-genome low-coverage sequencing of 459 wild-grown and 1565 offspring individuals to characterize the structure, stability, and mating dynamics of admixed populations of Mimulus guttatus and Mimulus nasutus across a decade of sampling. In three streams, admixed genomes are common and a M. nasutus organellar haplotype is fixed in M. guttatus, but new hybridization events are rare. Admixture is strongly unidirectional, but each stream has a unique distribution of ancestry proportions. In one stream, three distinct cohorts of admixed ancestry are spatially structured at [~]20-50m resolution and stable across years. Mating system provides almost complete isolation of M. nasutus from both M. guttatus and admixed cohorts, and is a partial barrier between admixed and M. guttatus cohorts. Isolation due to phenology is near-complete between M. guttatus and M. nasutus. Phenological isolation is a strong barrier in some years between admixed and M. guttatus cohorts, but a much weaker barrier in other years, providing a potential bridge for gene flow. These fluctuations are associated with differences in water availability across years, supporting a role for climate in mediating the strength of reproductive isolation. Together, mating system and phenology accurately predict fluctuations in assortative mating across years, which we estimate directly using paired maternal and offspring genotypes. Climate-driven fluctuations in reproductive isolation may promote the longer-term stability of a complex mosaic of hybrid ancestry, preventing either complete isolation or complete collapse of species barriers. Author SummaryHybridization between species can create genetic novelty and promote adaptation, but can also erode species barriers and dilute genetic diversity. Climatic variation likely impacts the extent and eventual outcomes of hybridization, but these impacts are difficult to predict. We use population-scale genomic sequencing of hybridizing Mimulus monkeyflowers to better understand the influence of climatic variation on hybridization. We find evidence of hybridization in multiple populations, with groups of different hybrid ancestries clustered along streams in close proximity to each other. Variation in water availability across years appears to affect hybridization between these groups, with less hybridization in drier years compared to wetter years. Paradoxically, this variation may lead to longer-term stability of the hybridization populations, by preventing complete erosion of species barriers while still allowing some gene exchange. In fact, we do see that hybrid ancestry is remarkably stable across a decade of measurements. Climate change is expected to increase the variability of climatic factors such as precipitation and heat events. Our study demonstrates one way these fluctuations could impact species.

evolutionary biology↗

bioRxiv2023

A multi-dimensional selective landscape drives adaptive divergence between and within closely related Phlox species

Natural selection shapes diversity across micro and macro-evolutionary scales. Selection causes local adaptation across populations within species and is simultaneously responsible for much of the divergence between species. However, it is unclear if either the force of or the response to selection is the same or different across these scales. Here we show that natural selection drives adaptive divergence between closely related species in a pattern that is distinct from local adaptation within a species. We use reciprocal common-garden transplant experiments across three species of Phlox wildflowers to show widespread adaptive divergence causing species to have highest fitness in their native habitats. Using provenance trials, we also find that one of these Phlox species has strong local adaptation between populations. We compare the axes of divergence and selection between these two scales of diversity and discover that one suite of traits predicts fitness differences between species and that an independent suite of traits predicts fitness variation within species across individuals. Our work reveals how forces of selection can both drive key divergence between species, allowing for and causing speciation, while simultaneously causing extensive diversity that is maintained across populations within a species. The selection landscape is complex and multidimensional

evolutionary biology↗

bioRxiv2022

Strong postmating reproductive isolation in Mimulus section Eunanus

Postmating reproductive isolation can help maintain species boundaries when premating barriers to reproduction are incomplete. The strength and identity of postmating reproductive barriers are highly variable among diverging species, leading to questions about their genetic basis and evolutionary drivers. These questions have been tackled in model systems but are less often addressed with broader phylogenetic resolution. In this study we analyze patterns of genetic divergence alongside direct measures of postmating reproductive barriers in an overlooked group of sympatric species within the model monkeyflower genus, Mimulus. Within this Mimulus brevipes species group, we find substantial divergence among species, including a cryptic genetic lineage. However, rampant gene discordance and ancient signals of introgression suggest a complex history of divergence. In addition, we find multiple strong postmating barriers, including postmating prezygotic isolation, hybrid seed inviability, and hybrid male sterility, leading to complete or substantial postmating isolation in all species pairs. Hybrid seed inviability appears linked to differences in seed size, providing a window into possible developmental mechanisms underlying this reproductive barrier. While geographic proximity and incomplete mating isolation may have allowed gene flow within this group in the distant past, strong postmating reproductive barriers today are likely to prevent any ongoing hybridization. By producing foundational information about reproductive isolation and genomic divergence in this understudied group, we add new diversity and phylogenetic resolution to our understanding of the mechanisms of plant speciation.

evolutionary biology↗