Karin Gross

What is the probability that autopolyploids establish in a novel, unoccupied habitat, and how is this affected by selfing and assortative mating? Using a modelling approach, Zwaenepoel (2025) found that, following a single migration event, autopolyploids are more likely than diploids to establish under a wide range of circumstances. The author also found that, under continuous migration, the rate of migration, along with factors such as selfing and assortative mating, affects the time to autopolyploid establishment. These findings help to explain how polyploids may colonize more extreme peripheral habitats.

Polyploidy is an important driver of the evolution and diversification of flowering plants. Several studies have shown that established polyploids differ from diploids in floral morphological traits and that polyploidization directly affects these traits. However, for floral scent, which is key to many plant-pollinator interactions, only a few studies have quantified differences between established cytotypes, and the direct effects of polyploidization on floral scent are not yet known. We compared the floral scent of established polyploids and diploids from a natural mixed-ploidy population of the plant Lithophragma bolanderi (Saxifragaceae), a species pollinated by two highly specialized moth pollinators of the genus Greya (Prodoxidae). We also compared the floral scent of neopolyploids synthetically generated from diploids with the floral scent of the diploid progenitors to quantify the direct effects of polyploidization on floral scent. Established tetraploids had a higher floral scent emission rate, produced more scent compounds, and emitted a relative scent composition that differed from diploids. Neotetraploids differed in the same direction from diploids as established tetraploids from diploids, but to a lesser extent. Together, our results provide novel insights into the ways in which polyploidization reshapes floral scent, thereby potentially altering interactions between plants and pollinators.

Polyploidization is an important driver of evolution and diversification in flowering plants. Here, we assess how repeated polyploidization may have shaped diversification of floral morphology in Lithophragma bolanderi (Saxifragaceae). This species comprises multiple cytotypes and varies geographically in its interactions with specialized pollinating moths in the genus Greya (Prodoxidae). Past studies have shown that coevolution with these moths has favored particular suites of floral characters but does not fully explain local and regional floral diversification. We combined phenotypic and genomic data from more than 1,800 individuals from 40 L. bolanderi populations spread across its entire range. Flow-cytometric analyses revealed a geographic mosaic of populations comprising one to four of three dominant (diploid, tetraploid, hexaploid) and three rare (triploid, pentaploid, octoploid) cytotypes. Whole-genome resequencing of a subset of populations suggested that polyploids arose from multiple autopolyploidization events, rather than a single event and/or through hybridization, albeit with some signals consistent with low levels of introgression from the congener Lithophragma glabrum . Quantification of flower traits from plants grown in a common garden showed that cytotype explained more than 15% of the variation in floral morphology, with polyploids showing more variability than diploids. Experimental induction of neopolyploids directly induced phenotypic changes but also indicated that local selection may have favored subsequent convergence in floral morphology among cytotypes in natural populations. Collectively, this comprehensive and integrative approach provides insights into how variability generating processes, such as polyploidization integrates with selection from species interactions to shape local floral diversification.

The vast majority of flowering plants depend on animal pollinators for sexual reproduction. These plants usually provide a reward, such as nectar and/or pollen, to their pollinators, and floral scent is often key to attract them. Some plants, however, do not provide any such reward, though they advertise one. Even though it is well known that such a food-deceptive pollination strategy is particularly common in orchids, the role of floral scent in attracting pollinators in such systems is often poorly understood. In this study, we compared the floral scent of the Eurasian deceptive lady’s slipper orchid Cypripedium calceolus with six co-flowering rewarding species visited by the same pollinators. Cypripedium calceolus produced more floral scent compounds than the co-flowering rewarding species together and differed in the floral scent composition from them. However, C. calceolus shared at least one compound with each co-flowering rewarding species, including widespread and less widespread compounds among flower scents, and had more compounds in common with the co-flowering rewarding species than they had with each other. Several compounds of C. calceolus, such as the aliphatic compounds 1-octanol, octyl acetate, and decyl acetate, did not occur in co-flowering plants but are known as pheromones of pollinating bees. Together, our results suggest that C. calceolus not only emits compounds that are generally common among flowering plants and attractive to many pollinators but specifically imitates floral scent compounds of multiple co-flowering plant species/pheromones of bees. These findings provide valuable insights into the ecology and evolution of floral scent in deceptive pollination systems in orchids.

What mechanisms cause asymmetries in reproductive success in crosses between closely related species that differ in floral style length? Feller et al. (2024) found that in five Phlox species, short-styled species produced smaller pollen grains than long-styled species. The smaller pollen of short-styled species lacked the resources to grow pollen tubes long enough to reach the ovules of long-styled species. This asymmetric pollen-style-length incompatibility may considerably affect patterns of gene flow among species

Selection leading to adaptation to interactions may generate rapid evolutionary feedbacks and drive diversification of species interactions. The challenge is to understand how the many traits of interacting species combine to shape local adaptation in ways directly or indirectly resulting in diversification. We used the well‐studied interactions between Lithophragma plants (Saxifragaceae) and Greya moths (Prodoxidae) to evaluate how plants and moths together contributed to local divergence in pollination efficacy. Specifically, we studied L. bolanderi and its two specialized Greya moth pollinators in two contrasting environments in the Sierra Nevada in California. Both moths pollinate L. bolanderi during nectaring, one of them–G. politella–also while ovipositing through the floral corolla into the ovary. First, field surveys of floral visitors and the presence of G. politella eggs and larvae in developing capsules showed that one population was visited only by G. politella and few other pollinators, whereas the other was visited by both Greya species and other pollinators. Second, L. bolanderi in these two natural populations differed in several floral traits putatively important for pollination efficacy. Third, laboratory experiments with greenhouse‐grown plants and field‐collected moths showed that L. bolanderi was more efficiently pollinated by local compared to nonlocal nectaring moths of both species. Pollination efficacy of ovipositing G. politella was also higher for local moths for the L. bolanderi population, which relies more heavily on this species in nature. Finally, time‐lapse photography in the laboratory showed that G. politella from different populations differed in oviposition behavior, suggesting the potential for local adaptation also among Greya populations. Collectively, our results are a rare example of components of local adaptation contributing to divergence in pollination efficacy in a coevolving interaction and, thus, provide insights into how geographic mosaics of coevolution may lead to coevolutionary diversification in species interactions.

Two highly correlated anther traits affect pollination efficacy in a wild radish population. Does the strength and type of selection on these traits differ through male and female fitness with increased ancestral trait variation? Waterman et al. (2023) found stabilizing selection on one trait and disruptive selection on the other trait, with no difference between male and female fitness. Such quantifications of selection in populations with the increased variation that reflects ancestral trait variation provide insights into processes of trait adaptation.

Geographically structured phenotypic selection can lead to adaptive divergence. However, in flowering plants, such divergent selection has rarely been shown, and selection on floral signals is generally little understood. In this study, we measured phenotypic selection on display size, floral color, and floral scent in four lowland and four mountain populations of the nectar-rewarding terrestrial orchid Gymnadenia odoratissima in two years. We also quantified population differences in these traits and pollinator community composition. Our results show positive selection on display size and positive, negative, or absence of selection on different scent compounds and floral color. Selection on the main scent compounds was consistently stronger in the lowlands than in the mountains, and lowland plants emitted higher amounts of most of these compounds. Pollinator community composition also differed between regions, suggesting different pollinators select for differences in floral volatiles. Overall, our study is the first to document consistent regional differences in selection on floral scent, suggesting this pattern of selection is one of the evolutionary forces contributing to regional divergence in floral chemical signaling.

Background and Aims Polyploidization, the doubling of chromosome sets, is common in angiosperms and has a range of evolutionary consequences. Newly formed polyploid lineages are reproductively isolated from their diploid progenitors due to triploid sterility, but also prone to extinction because compatible mating partners are rare. Models have suggested that assortative mating and increased reproductive fitness play a key role in the successful establishment and persistence of polyploids. However, little is known about these factors in natural mixed-ploidy populations. This study investigated floral traits that can affect pollinator attraction and efficiency, as well as reproductive success in diploid and tetraploid Gymnadenia conopsea (Orchidaceae) plants in two natural, mixed-ploidy populations. Methods Ploidy levels were determined using flow cytometry, and flowering phenology and herbivory were also assessed. Reproductive success was determined by counting fruits and viable seeds of marked plants. Pollinator-mediated floral isolation was measured using experimental arrays, with pollen flow tracked by means of staining pollinia with histological dye. Key Results Tetraploids had larger floral displays and different floral scent bouquets than diploids, but cytotypes differed only slightly in floral colour. Significant floral isolation was found between the two cytotypes. Flowering phenology of the two cytotypes greatly overlapped, and herbivory did not differ between cytotypes or was lower in tetraploids. In addition, tetraploids had higher reproductive success compared with diploids. Conclusions The results suggest that floral isolation and increased reproductive success of polyploids may help to explain their successful persistence in mixed-ploidy populations. These factors might even initiate transformation of populations from pure diploid to pure tetraploid.

The crucial role of reproductive isolation in speciation has long been recognized; however, a limited number of studies quantify different isolation barriers and embed reproductive isolation in a phylogenetic context. In this study, we investigate reproductive isolation between the often sympatrically occurring orchid species,Gymnadenia conopseaandG. odoratissima. We examine the phylogenetic relationship between the two species and analyse floral isolation, fruit set and seed viability from interspecies crosses, as well as the ploidy level. Additionally, we quantify interspecies differences in floral signals and morphology. The results suggest that the two species have a sister–species relationship. In terms of reproductive isolation, we found complete floral isolation between the two species, but little to no post‐pollination isolation; the species also mostly had the same ploidy level in the studied populations. We also show clear distinctions in floral signals, as well as in floral size and spur length. We propose that respective adaptation to short‐ vs. long‐tongued pollinators was the driver of speciation in the here studiedGymnadeniaspecies. Our study supports the key role of floral isolation in orchid speciation and shows that floral isolation is not restricted to highly specialized pollination systems, but can also occur between species with less specialized pollination.