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Summary: The evolutionary switch to hummingbird pollination exemplifies complex adaptation, requiring evolutionary change in multiple component traits. Despite this complexity, diverse lineages have converged on hummingbird‐adapted flowers on a relatively short evolutionary timescale. Here, I review how features of the genetic basis of adaptation contribute to this remarkable evolutionary lability. Large‐effect substitutions, large mutational targets for adaptation, adaptive introgression, and concentrated architecture all contribute to the origin and maintenance of hummingbird‐adapted flowers. The genetic features of adaptation are likely shaped by the ecological and geographic context of the switch to hummingbird pollination, with implications for future evolutionary trajectories. [ABSTRACT FROM AUTHOR]

The estimation of outcrossing rates in hermaphroditic species has been a major focus in the evolutionary study of reproductive strategies, and is also essential for plant breeding and conservation. Surprisingly, genomics has thus far minimally influenced outcrossing rate studies. In this article, we generalize a Bayesian inference method (BORICE) to accommodate genomic data from multiple subpopulations of a species. As an empirical demonstration, BORICE is applied to 115 maternal families of Mimulus guttatus. The analysis shows that low‐level whole genome sequencing of parents and offspring is sufficient for individualized mating system estimation: 208 offspring (88.5%) were definitively called as outcrossed, 23 (9.8%) as selfed. After mating system parameters are established (each offspring as outcrossed or selfed and the inbreeding level of maternal plants), BORICE outputs posterior genotype probabilities for each SNP genomewide. Individual SNP calls are often burdened with considerable uncertainty and distilling information from closely linked sites (within genomic windows) can be a useful strategy. For the Mimulus data, principal components based on window statistics were sufficient to diagnose inversion polymorphisms and estimate their effects on spatial structure, phenotypic and fitness measures. More generally, mating system estimation with BORICE can set the stage for population and quantitative genomic analyses, particularly researchers collect phenotypic or fitness data from maternal individuals. [ABSTRACT FROM AUTHOR]

Premise: Adaptive radiation in ecologically and morphologically diverse plant lineages presents an opportunity to investigate the rapid evolution of novel floral traits. While some types of floral traits, such as flower color, are well-characterized, other types of complex morphologies remain understudied. One example is occluded personate flowers, dorso-ventrally compressed flowers with obstructed floral passageways, which have evolved in multiple genera, but have only been characterized from snapdragon., Methods: Our study examined the morphological basis and evolutionary history of personate flowers in a clade of Penstemon species that includes three personate-flowered species. We characterized floral morphology and inferred phylogenomic relationships for 13 species in this group in order to examine the evolutionary history of personate flowers. We used phylogenomic tests for introgression to examine whether personate-flowered lineages have a history of introgression., Results: Unlike the personate flowers of snapdragon, personate flowers in Penstemon are produced by deep pleats in the ventral petal tissue that curve the ventral petal surface upwards, obstructing the floral tube opening. Our phylogenetic tree suggests that personate flowers evolved in two separate lineages. Phylogenomic analyses indicate incomplete lineage sorting and introgression between certain taxa have contributed to phylogenomic discordance, however we found little evidence of recent introgression between the two personate-flowered lineages., Conclusions: The evolution of personate flowers in Penstemon involves a distinct morphological basis than snapdragon. Personate flowers have evolved multiple times in Penstemon on a rapid evolutionary timescale. The source of genetic variation for repeated shifts may be de novo mutations or pre-existing variants., Competing Interests: CONFLICT OF INTEREST STATEMENT The authors declare no conflict of interest.

The penstemons are ornamental annual flowering plants native to the Intermountain West and Rocky Mountains and commonly used for urban landscaping. Elite commercial penstemons are generally susceptible to abiotic stresses, including drought, root rot, cold, and high salinity. Firecracker penstemon (Penstemon eatonii), however, is much more tolerant to these stresses than most elite cultivars. Importantly, firecracker penstemon has been reported to hybridize with many other penstemons and therefore provides the opportunity to develop more tolerant elite cultivars through strategic crossing. To facilitate the study and utilization of firecracker penstemon, we sequenced and annotated the genome of a P. eatonii accession collected from Utah, USA. We also performed low-coverage, whole-genome sequencing of 26 additional accessions from three different varieties of P. eatonii. This chromosome-scale genome assembly is the most contiguous and complete Penstemon genome sequenced to date., (© The American Genetic Association. 2024.)

Adaptive radiations are characterized by rapid ecological diversification and speciation events, leading to fuzzy species boundaries between ecologically differentiated species. Adaptive radiations are therefore key systems for understanding how species are formed and maintained, including the role of de novo mutations vs. pre-existing variation in ecological adaptation and the genome-wide consequences of hybridization events. For example, adaptive introgression, where beneficial alleles are transferred between lineages through hybridization, may fuel diversification in adaptive radiations and facilitate adaptation to new environments. In this study, we employed whole-genome resequencing data to investigate the evolutionary origin of hummingbird-pollinated flowers and to characterize genome-wide patterns of phylogenetic discordance and introgression in Penstemon subgenus Dasanthera , a small and diverse adaptive radiation of plants. We found that magenta hummingbird-adapted flowers have apparently evolved twice from ancestral blue-violet bee-pollinated flowers within this radiation. These shifts in flower color are accompanied by a variety of inactivating mutations to a key anthocyanin pathway enzyme, suggesting that independent de novo loss-of-function mutations underlie parallel evolution of this trait. Although patterns of introgression and phylogenetic discordance were heterogenous across the genome, a strong effect of gene density suggests that, in general, natural selection opposes introgression and maintains genetic differentiation in gene-rich genomic regions. Our results highlight the importance of both de novo mutation and introgression as sources of evolutionary change and indicate a role for de novo mutation in driving parallel evolution in adaptive radiations.