Frank M. Frey

GENETIC CONSTRAINTS ON FLORAL EVOLUTION IN A SEXUALLY DIMORPHIC PLANT REVEALED BY ARTIFICIAL SELECTION

Abstract Sexual dimorphism is one of the most widespread and recognizable patterns of phenotypic variation in the biotic world. Sexual dimorphism in floral display is striking in the dioecious plant Silene latifolia, with males making many, small flowers compared to females. We investigated this dimorphism via artificial selection on two populations to determine whether genetic variation exists within populations for flower size and the extent of the between‐sex correlation, whether a flower size and number trade‐off exists within each sex, and whether pollen and ovule production vary with flower size. We selected for decreased flower size (calyx width) in females and increased flower size in males and measured the response to selection in size and correlated responses in flower dry mass, flower number, and pollen or ovule number per flower. Four bouts of selection in each of two selection programs were performed, for a total of three selection lines to decrease size, three to increase it, and two control lines. Flower size always significantly responded to selection and we always found a significant correlated response in the sex not under selection. Selection decreased but did not eliminate the sexual dimorphism in flower dry mass and number. A negative relationship between flower size and number within each sex was revealed. Whereas ovule number showed a significant correlated response to selection on flower size, pollen number did not. Our results indicate that although substantial additive genetic variation for flower size exists, the high between‐sex genetic correlation would likely constrain flower size from becoming more sexually dimorphic. Furthermore, floral display within each sex is constrained by a flower size and number trade‐off. Given this trade‐off and lack of variation in pollen production with flower size, we suggest that sexual dimorphism evolved via sexual selection to increase flower number in males but not females.

OPPOSING NATURAL SELECTION FROM HERBIVORES AND PATHOGENS MAY MAINTAIN FLORAL-COLOR VARIATION IN CLAYTONIA VIRGINICA (PORTULACACEAE)

Abstract The maintenance of floral‐color variation within natural populations is enigmatic because directional selection through pollinator preferences combined with random genetic drift should lead to the rapid loss of such variation. Fluctuating, balancing, and negative frequency‐dependent selection mediated through pollinators have been identified as factors that may contribute to the maintenance of floral‐color variation, and recently it has been suggested that indirect responses to selection on correlated characters through agents of selection other than pollinators may substantially shape the evolution of floral traits. Here, I provide empirical support for this latter view in Claytonia virginica (Portulacaceae) through a multiseason field study, a pollen supplementation study, and an artificial herbivory experiment. These studies show that most individuals fall into one of four discrete color classes, and suggest pollinatormediated selection for increased floral redness in concurrent years. Floral color is also an indirect target of opposing directional selection via herbivores and pathogens that fluctuates through time. Taken together, these data suggest a novel mechanism by which floral‐color variation may be maintained, and illustrate the importance of an inclusive, pluralistic view of selection when investigating the evolution of complex phenotypes.

Genetic correlations with floral display lead to sexual dimorphism in the cost of reproduction.

In dioecious plants, females typically invest more biomass in reproduction than males and consequently experience stronger life‐history trade‐offs. Sexual dimorphism in life history runs counter to this pattern in Silene latifolia: females acquire less carbon and invest more biomass in reproduction, but males pay a higher cost of reproduction. The species is sexually dimorphic for many traits, especially flower number, with males producing many, small flowers compared to females. We tested whether the cost of reproduction is higher in males because flower number, which we presume to be under sexual selection in males, is genetically correlated with traits that would affect life‐history trade‐offs. We performed artificial selection to reduce the sexual dimorphism in flower size and looked at correlated responses in ecophysiological traits. We found significant correlated responses in total vegetative mass, leaf mass, leaf thickness, and measures of CO2 exchange. Individuals in the many‐and‐small‐flowered selection lines did not grow as large or invest as much biomass in leaves, and their leaves exhibited an up‐regulated physiology that shortened leaf life span. Our results are consistent with the hypothesis that genetic correlations between floral display and ecophysiological traits lead to a higher cost of reproduction for males.

Antibacterial activity of traditional medicinal plants used by Haudenosaunee peoples of New York State

BackgroundThe evolution and spread of antibiotic resistance, as well as the evolution of new strains of disease causing agents, is of great concern to the global health community. Our ability to effectively treat disease is dependent on the development of new pharmaceuticals, and one potential source of novel drugs is traditional medicine. This study explores the antibacterial properties of plants used in Haudenosaunee traditional medicine. We tested the hypothesis that extracts from Haudenosaunee medicinal plants used to treat symptoms often caused by bacterial infection would show antibacterial properties in laboratory assays, and that these extracts would be more effective against moderately virulent bacteria than less virulent bacteria.MethodsAfter identification and harvesting, a total of 57 different aqueous extractions were made from 15 plant species. Nine plant species were used in Haudenosaunee medicines and six plant species, of which three are native to the region and three are introduced, were not used in traditional medicine. Antibacterial activity against mostly avirulent (Escherichia coli, Streptococcus lactis) and moderately virulent (Salmonella typhimurium, Staphylococcus aureus) microbes was inferred through replicate disc diffusion assays; and observed and statistically predicted MIC values were determined through replicate serial dilution assays.ResultsAlthough there was not complete concordance between the traditional use of Haudenosaunee medicinal plants and antibacterial activity, our data support the hypothesis that the selection and use of these plants to treat disease was not random. In particular, four plant species exhibited antimicrobial properties as expected (Achillea millefolium, Ipomoea pandurata, Hieracium pilosella, and Solidago canadensis), with particularly strong effectiveness against S. typhimurium. In addition, extractions from two of the introduced species (Hesperis matronalis and Rosa multiflora) were effective against this pathogen.ConclusionsOur data suggest that further screening of plants used in traditional Haudenosaunee medicine is warranted, and we put forward several species for further investigation of activity against S. typhimurium (A. millefolium, H. matronalis, I. pandurata, H. pilosella, R. multiflora, S. canadensis).

Investigating the independent evolution of the size of floral organs via G‐matrix estimation and artificial selection

Summary The attractiveness of a plant to pollinators is dependent on both the number of flowers produced and the size of the petals. However, limiting resources often result in a size/number trade‐off, whereby the plant can make either more flowers or larger flowers, but not both. If developmental genes underlying sepal and petal identity (some of which overlap) also influence size, then this shared genetic basis could constrain the independent evolution of floral size and attractiveness. Here, we determined whether the size of sepals and petals in the dioecious perennial, Silene latifolia, are developmentally independent by performing two experiments: a genetic variance–covariance experiment to estimate genetic correlations between calyx width, petal‐limb length, flower mass, and number and a four‐bout artificial‐selection experiment to alter calyx width and estimate the correlated response in petal‐limb length. In addition, we determined whether variation in petal‐limb length is the result of cell expansion or cell proliferation. The first experiment revealed that petal‐limb length is not genetically correlated with calyx width, and the second experiment confirmed this; selection on calyx width did not result in a predictable or significant change in petal‐limb length. Flower number was negatively correlated with all the floral traits measured, indicating a flower size/number trade‐off. Cell number, but not size, explained a significant amount of the variation in petal‐limb length. We conclude that the size of the two outer floral organs can evolve independently. This species can therefore increase the number of flowers produced by decreasing investment in the calyx without simultaneously decreasing petal size and the attractiveness of each individual flower to pollinators.

Seed Production and Insect Visitation Rates in Hesperis matronalis Are Not Affected by Floral Symmetry

In the past decade, field manipulation and pollinator choice experiments utilizing arrays of natural and artificial flowers have yielded mixed results with respect to whether symmetric flowers receive higher visitation rates or produce more seeds compared to asymmetric flowers. In this article, we test the hypothesis that deviations from perfect floral symmetry result in decreased seed production and reduced rates of insect visitation. We performed a floral manipulation experiment in two concurrent years with Hesperis matronalis (Brassicaceae) to investigate how seed production per fruit was linked to floral symmetry. In addition, we performed two replicated array experiments using model plants and flowers based on H. matronalis to investigate whether insects make decisions to visit plants on the basis of floral symmetry and whether insects use floral symmetry as a cue to discriminate among flowers within plants. We find no clear evidence that deviations from perfect floral symmetry affect insect visitation rates to plants or flowers within a plant and no clear association between floral symmetry and seed production. However, our array experiments suggest that insects use flower size as a primary cue to discriminate among plants but not among flowers within a plant.

MANIPULATION OF FLORAL SYMMETRY DOES NOT AFFECT SEED PRODUCTION IN IMPATIENS PALLIDA

The outcomes of past research concerning the role of floral symmetry in plant‐pollinator interactions are mixed. Field manipulations of plants, as well as experiments using artificial arrays, have found evidence for and against a direct relationship between the degree of floral symmetry and subsequent reproductive success. In this study, we test the hypothesis that deviations from perfect floral symmetry in Impatiens pallida (Balsaminaceae) result in direct fitness costs. In two field seasons, we manipulated experimentally floral symmetry in separate populations of plants and measured seed set. We did not address any possible effects of floral asymmetry on male function. We found no significant differences in seed number per fruit among control, symmetrically cut (30% on both lobes), asymmetrically cut (60% on left lobe), and severely mutilated (100% on left lobe) flowers in the field. Post hoc power analyses show that a prohibitively large sample size would be required to detect the observed differences in seed set among treatments. Moreover, the magnitude of the observed differences among treatments is biologically irrelevant. We conclude that the degree of floral symmetry does not affect female reproductive success in this system.

Optimum Growth Temperatures of Three Species of Green Chloromonas Snow Algae from Upstate New York and the White Mountains, Arizona

ABSTRACT The optimum temperatures of three species of snow algae were studied using four strains of Chloromonas (Cr.) rosae v. psychrophila, six strains of Cr. tughillensis, and one strain of Cr. chenangoensis. These axenic strains were from Upstate New York except for two of Cr. rosae v. psychrophila from the White Mountains, Arizona. Temperatures tested were from 2.5 to 20°C. The high elevation subalpine Cr. rosae v. psychrophila from New York and Arizona grew from 4 to 20°C and had the greatest cell counts at 4 to 15°C. In contrast, the subalpine to temperate low elevation strains of Cr. tughillensis grew from 2.5 to 10°C and optimally at 2.5 or 5°C, and Cr. chenangoensis grew from 2.5 to 7.5°C and optimally at 2.5 and 5°C. Chloromonas tughillensis and Cr. chenangoensis belong to a genetic subclade with low temperature optima, whereas Cr. rosae v. psychrophila belongs to a subclade with broad temperature optima. In acclimation experiments, there were no significant differences in cell counts when acclimating two Adirondack, New York, strains of Cr. rosae v. psychrophila for two weeks prior to experiments vs. using non-acclimated strains that were moved from 4°C directly to 4, 10, 15, or 20°C. For Cr. tughillensis, four of six strains had significantly higher cell counts when grown at 2.5°C after acclimation at 7.5°C for five months. These are the first reports of temperature optima of snow algae from eastern North America.

The Optimum pH of the Green Snow Algae, Chloromonas Tughillensis and Chloromonas Chenangoensis, from Upstate New York

ABSTRACT The optimum pH of two species of snow algae from Upstate New York were assessed by studying three axenic strains of Chloromonas tughillensis in a pH range of 3.0–7.0 and three non-axenic strains of Cr. chenangoensis in a pH range of 3.0–8.0. Growth was examined at 0.5 pH intervals. Cell counts at the termination of the experiments differed among strains and among pH intervals in individual strains for both species, and strains of Cr. tughillensis responded differently to changes in pH (p < 0.001) while strains of Cr. chenangoensis did not (p  =  0.193). Cell counts and absorbance data for Cr. tughillensis indicated an optimum pH of 4.9–6.1 using regression analysis. Strains of Cr. chenangoensis exhibited higher but insignificantly different counts between pH 7.0 and 8.0 with maxima at pH 7.5, but pH optima were not determined. When the range was expanded to include pH 8.5–9.0, an optimal pH of 7.0–8.0 was determined for strain CU 722B, and this is the first snow alga reported to have an optimum alkaline pH. The highest absorbance values, however, occurred between pH 3.0–4.5 and pH 7.0–8.0. The pH values recorded in the field were 5.0–5.3 for Cr. tughillensis and 6.7–7.6 for Cr. chenangoensis.

Floral symmetry is associated with flower size and pollen production but not insect visitation rates in Geranium robertianum (Geraniaceae)

The degree to which fine-scaled variation in floral symmetry is associated with variation in plant fitness remains unresolved, as does the question of whether floral symmetry is in itself a target of pollinator-mediated selection. Geranium robertianum (Geraniaceae) is a broadly distributed species whose five-petaled flowers vary widely with respect to their degree of rotational asymmetry. In this study, we used a naturally occurring population of plants to investigate whether floral rotational asymmetry and leaf bilateral symmetry were phenotypically correlated with a series of fitness-related traits, and also used an experimental array with model flowers to investigate the preference of insect visitors for varying degrees of floral size and symmetry. We found that leaf asymmetry was not associated with any of the phenotypic traits measured, and that the degree of floral rotational asymmetry was strongly associated with decreased flower size and decreased pollen production. Our experimental arrays showed that insect visitors did not discriminate among model flowers on the basis of size or symmetry alone; however, insect visitors preferentially visited smaller, symmetric model flowers over larger, severely asymmetric model flowers. Taken together, our results suggest that floral and leaf symmetry in G. robertianum are not likely strong indicators of phenotypic quality, and that floral symmetry is unlikely to be a target of pollinator-mediated selection. However, the relationship between floral asymmetry and pollen production may provide a role for fecundity selection on symmetry in this species. These data importantly add to the growing literature on the adaptive nature of floral symmetry in the wild.