More Like this

1. Olfaction and reproductive isolation in birds

   https://doi.org/10.1016/j.anbehav.2025.123076  

   Van_Huynh, Alex; Rice, Amber M (April 2025, Animal Behaviour)

   Olfaction is an important sense that has contributed to reproductive isolation and speciation in many taxa. However, in birds, olfaction and its potential role in communication has historically been neglected. Thus, what role olfaction plays in avian speciation is mostly unknown. Here, we aim to guide future research by highlighting the likely potential for olfaction to contribute to reproductive isolation and speciation in birds. First, we detail the best-understood example found thus far that is consistent with reproductive isolation by olfaction in birds: black-capped and Carolina chickadees. These species show interspecific differences in preen oil chemistry and conspecific odour preferences within their natural hybrid zone. We then suggest a number of promising avenues for future research and the kinds of systems, approaches and evidence that would help to advance this severely understudied area. In sum, the growing body of research into the chemical ecology of birds suggests an important role of olfaction in many areas of avian life. Future research will be necessary to determine to what extent olfaction contributes to the formation and maintenance of species boundaries in birds. 

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2. Strong postmating reproductive isolation in Mimulus section Eunanus

   https://doi.org/10.1111/jeb.14219  

   Farnitano, Matthew C.; Sweigart, Andrea L. (October 2023, Journal of Evolutionary Biology)

   Abstract 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 analyse 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. M. brevipes and M. fremontii have substantial but incomplete postmating isolation. For all other tested species pairs, we find essentially complete postmating isolation. 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 have likely played a key role in preventing ongoing introgression. 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. Abstract Hybrid seed inviability and other postmating reproductive barriers isolate species in Mimulus section Eunanus. Variation in seed size may help explain hybrid seed failure. Whole-genome sequencing indicates a complex history of divergence, including signals of ancient introgression and cryptic diversity. 

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3. Sexual selection promotes reproductive isolation in barn swallows

   https://doi.org/10.1126/science.adj8766  

   Schield, Drew R; Carter, Javan K; Scordato, Elizabeth_S C; Levin, Iris I; Wilkins, Matthew R; Mueller, Sarah A; Gompert, Zachariah; Nosil, Patrik; Wolf, Jochen_B W; Safran, Rebecca J (December 2024, Science)

   Despite the well-known effects of sexual selection on phenotypes, links between this evolutionary process and reproductive isolation, genomic divergence, and speciation have been difficult to establish. We unravel the genetic basis of sexually selected plumage traits to investigate their effects on reproductive isolation in barn swallows. The genetic architecture of sexual traits is characterized by 12 loci on two autosomes and the Z chromosome. Sexual trait loci exhibit signatures of divergent selection in geographic isolation and barriers to gene flow in secondary contact. Linkage disequilibrium between these genes has been maintained by selection in hybrid zones beyond what would be expected under admixture alone. Our findings reveal that selection on coupled sexual trait loci promotes reproductive isolation, providing key empirical evidence for the role of sexual selection in speciation. 

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4. Predicting how pollinator behavior causes reproductive isolation

   https://doi.org/10.1002/ece3.8847  

   Hopkins, Robin (April 2022, Ecology and Evolution)

   Abstract Pollinator behavior is an important contributor to plants speciation, yet how variation in pollinator behavior causes variation in reproductive isolation (RI) is largely uncharacterized. Here I present a model that predicts how two aspects of pollinator behavior, constancy and preference, contribute to a barrier to reproduction in plants. This model is motivated by two observations: most co‐occurring plants vary in frequency over space and time, and most plants have multiple pollinators that differ in behavior. Thus, my goal was to understand how relative frequencies of plants and pollinators in a community influence ethological RI between co‐occurring plants. I find that RI for a focal plant generally increases with increasing relative plant frequency, but the shape of this relationship is highly dependent on the strength of pollinator behavior (constancy and preference). Additionally, when multiple pollinators express different behavior, I find that pollinators with stronger preference disproportionately influence RI. But, I show that RI caused by constancy is the average RI predicted from constancy of each pollinator weighted by pollinator frequency. I apply this model to examples of pollinator‐mediated RI inPhloxand inIpomopsisto predict the relationships between plant frequency and ethological RI in natural systems. This model provides new insights into how and why pollinator specialization causes RI, and how RI could change with changing biological communities. 

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5. Odor preferences in hybrid chickadees: implications for reproductive isolation and asymmetric introgression

   https://doi.org/10.1007/s00265-021-03069-2  

   Van Huynh, Alex; Rice, Amber M. (September 2021, Behavioral Ecology and Sociobiology)

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