Krissa A. Skogen

Belowground Distribution and Abundance of Botrychium Gametophytes and Juvenile Sporophytes

Abstract A significant portion of the stages of the life history of Botrychium, the gametophyte and juvenile sporophytes, are spent belowground. Surveys were conducted to determine the distribution and abundance of belowground gametophytes, juvenile sporophytes and gemmae of eight species of Botrychium. For each species, soil samples were collected in a 200 m2 area, sifted through a series of soil sieves, and centrifuged to separate the lighter plant material. Only 40% of the soil samples contained belowground structures revealing a patchy distribution. The gametophytes of B. montanum are most dense, followed by B. mormo with 738 and 728 gametophytes m−2 respectively. Botrychium hesperium also has a relatively high density of 478 gametophytes m−2. Botrychium gallicomontanum is the least dense with 10 gametophytes m−2. Botrychium campestre and B. gallicomontanum both have abundant gemmae and few gametophytes. The density of individuals in the belowground structure bank greatly exceeds the aboveground population. The size and health of the belowground structure bank is critical in sustaining the long-term aboveground population and in buffering it from extinction.

Local Topography Shapes Fine-Scale Spatial Genetic Structure in the Arkansas Valley Evening Primrose, Oenothera harringtonii (Onagraceae)

Identifying factors that shape the spatial distribution of genetic variation is crucial to understanding many population- and landscape-level processes. In this study, we explore fine-scale spatial genetic structure in Oenothera harringtonii (Onagraceae), an insect-pollinated, gravity-dispersed herb endemic to the grasslands of south-central and southeastern Colorado, USA. We genotyped 315 individuals with 11 microsatellite markers and utilized a combination of spatial autocorrelation analyses and landscape genetic models to relate life history traits and landscape features to dispersal processes. Spatial genetic structure was consistent with theoretical expectations of isolation by distance, but this pattern was weak (Sp = 0.00374). Anisotropic analyses indicated that spatial genetic structure was markedly directional, in this case consistent with increased dispersal along prominent slopes. Landscape genetic models subsequently confirmed that spatial genetic variation was significantly influenced by local topographic heterogeneity, specifically that geographic distance, elevation and aspect were important predictors of spatial genetic structure. Among these variables, geographic distance was ~68% more important than elevation in describing spatial genetic variation, and elevation was ~42% more important than aspect after removing the effect of geographic distance. From these results, we infer a mechanism of hydrochorous seed dispersal along major drainages aided by seasonal monsoon rains. Our findings suggest that landscape features may shape microevolutionary processes at much finer spatial scales than typically considered, and stress the importance of considering how particular dispersal vectors are influenced by their environmental context.

Dormancy, small seed size and low germination rates contribute to low recruitment in Desmodium cuspidatum (Fabaceae).

Abstract Plant population growth and persistence are strongly influenced by germination and recruitment, which can be dramatically affected by seed dormancy, local site conditions, seed size and seed predation. Understanding factors that limit germination can help to explain low recruitment rates and is particularly important for species of conservation concern. Desmodium cuspidatum has declined dramatically in the northeastern United States and is currently listed as historic, threatened or endangered in all five New England states where it once occurred. Remaining populations exhibit low reproductive success and low recruitment rates, even though seed viability is nearly 100%. Requirements for optimal germination, including the breakdown of physical dormancy, effect of local site characteristics, and seed mass were largely unknown. In addition, while recruitment rates in co-occuring Desmodium species are reportedly higher than those of D. cuspidatum, germination rates in these species were unavailable for comparative purposes. Lastly, the effect of pre-dispersal seed predation, commonly observed in Desmodium species, was unknown. We performed a series of three controlled experiments to assess optimal conditions for germination (D. cuspidatum), the relationship between germination rate and seed size (mass, D. cuspidatum, D. glutinosum and D. paniculatum) and the effect of pre-dispersal seed predation on germination (D. canadense and D. paniculatum). Our results suggest that low recruitment rates observed in New England populations of D. cuspidatum are related to physical dormancy and local site conditions, whereby the highest germination rates are found when seeds are placed on bare soil, regardless of whether they are covered with leaf litter. Germination rates in D. cuspidatum were generally lower than those observed for two more common Desmodium species, D. glutinosum, and D. paniculatum and were positively correlated with seed mass in all three species. Seeds grown with field-collected soil had lower germination rates but higher nodulation rates than those grown in sterilized potting soil. Seed predation by weevils had no detectable difference on germination rates in D. paniculatum and D. canadense.

Assessing the Value of Potential “Native Winners” for Restoration of Cheatgrass-Invaded Habitat

Abstract. Native plants that are able to persist and reproduce in highly disturbed habitats (i.e., “native winners”) may be useful to include in seed mixes when restoring similarly disturbed habitat. Establishing whether these plants produce viable seeds that germinate to a high degree under appropriate conditions is a first step to determining their utility as restoration species. We identified 10 potential native winners at sites degraded by cheatgrass (Bromus tectorum), an invasive annual grass ubiquitous in the Colorado Plateau. We assessed seed viability for each species to determine its potential to reproduce within a cheatgrass-invaded site, and conducted a series of germination and competition experiments to test how effective these species may be when restoring habitat invaded by cheatgrass. All species produced viable seed (ranging from 56% to 100% viability), and the seeds of many species had high germination under a range of fall conditions without cold stratification, which is thought to increase establishment potential in cheatgrass-dominated habitats. We selected the 5 species with the highest germination and conducted a greenhouse competition study to determine their response to cheatgrass presence. The growth of all 5 forb species was suppressed by cheatgrass. However results from germination and competition trials suggest that several species, in particular Acmispon humistratus, Cryptantha fendleri, and Machaeranthera tanacetifolia, may be beneficial for restoration of cheatgrassinvaded sites. These 3 species have higher percent germination (78%–100%) and germination tolerance (0.42–0.63), and were suppressed less by cheatgrass (relative interaction index of negative 0.28–0.49) than a commonly seeded restoration species, Penstemon palmeri. Acmispon humistratus and M. tanacetifolia, in particular, are also desirable candidates for use in restoration because of the ecosystem sendees they provide. In general, natives that grow, reproduce, and tolerate competition in degraded habitats are potential native winners and worthwhile candidates for use in restoration of similarly degraded sites.

Pollinator identity and spatial isolation influence multiple paternity in an annual plant

The occurrence and extent of multiple paternity is an important component of variation in plant mating dynamics. However, links between pollinator activity and multiple paternity are generally lacking, especially for plant species that attract functionally diverse floral visitors. In this study, we separated the influence of two functionally distinct floral visitors (hawkmoths and solitary bees) and characterized their impacts on multiple paternity in a self‐incompatible, annual forb, Oenothera harringtonii (Onagraceae). We also situated pollinator‐mediated effects in a spatial context by linking variation in multiple paternity to variation in plant spatial isolation. We documented pronounced differences in the number of paternal sires as function of pollinator identity: on average, the primary pollinator (hawkmoths) facilitated mating with nearly twice as many pollen donors relative to the secondary pollinator (solitary bees). This effect was consistent for both isolated and nonisolated individuals, but spatial isolation imposed pronounced reductions on multiple paternity regardless of pollinator identity. Considering that pollinator abundance and pollen dispersal distance did not vary significantly with pollinator identity, we attribute variation in realized mating dynamics primarily to differences in pollinator morphology and behaviour as opposed to pollinator abundance or mating incompatibility arising from underlying spatial genetic structure. Our findings demonstrate that functionally distinct pollinators can have strongly divergent effects on polyandry in plants and further suggest that both pollinator identity and spatial heterogeneity have important roles in plant mating dynamics.

Microsatellite primers in Oenothera harringtonii (Onagraceae), an annual endemic to the shortgrass prairie of Colorado

PREMISE OF THE STUDY Microsatellite markers were developed in the annual herb, Oenothera harringtonii, to investigate patterns of genetic diversity, gene flow, and parentage within and among populations of this Colorado endemic. METHODS AND RESULTS Ten polymorphic loci were identified in O. harringtonii and tested in four populations sampled across the range of the species. These loci contained trinucleotide repeats with 7-29 alleles per locus. Nine of the 10 loci also amplified in O. caespitosa subsp. macroglottis, O. caespitosa subsp. marginata, and O. caespitosa subsp. navajoensis. In addition, we optimized three markers developed for O. biennis and provide reports of their effectiveness in all four taxa. CONCLUSIONS These results indicate the utility of these markers in O. harringtonii for future studies of genetic structure, gene flow, and parentage as well as their applicability in other members of the O. caespitosa species complex.

Herbivory as an important selective force in the evolution of floral traits and pollinator shifts

The diversity of floral forms in angiosperms is frequently attributed to pollinators but herbivores can be just as important. Here we examine the role of a flower-feeding caterpillar, Mompha, in driving floral trait evolution and subsequent pollinator-shifts in a recently radiated clade of flowering plants, Oenothera sect. Calylophus (Onagraceae). Longer-tubed, hawkmoth flowers had substantially greater damage compared to smaller bee-pollinated flowers. Momphas preference for longer-tubed flowers, which is evident even within populations of some species, may have played an important role in driving the morphological changes associated with shifts from hawkmoth to bee pollination.

Microsatellites for Oenothera gayleana and O. hartwegii subsp. filifolia (Onagraceae), and Their Utility in Section Calylophus

Premise of the study: Eleven nuclear and four plastid microsatellite markers were screened for two gypsum endemic species, Oenothera gayleana and O. hartwegii subsp. filifolia, and tested for cross-amplification in the remaining 11 taxa within Oenothera sect. Calylophus (Onagraceae). Methods and Results: Microsatellite markers were tested in two to three populations spanning the ranges of both O. gayleana and O. hartwegii subsp. filifolia. The nuclear microsatellite loci consisted of both di- and trinucleotide repeats with one to 17 alleles per population. Several loci showed significant deviation from Hardy–Weinberg equilibrium, which may be evidence of chromosomal rings. The plastid microsatellite markers identified one to seven haplotypes per population. The transferability of these markers was confirmed in all 11 taxa within Oenothera sect. Calylophus. Conclusions: The microsatellite loci characterized here are the first developed and tested in Oenothera sect. Calylophus. These markers will be used to assess whether pollinator foraging distance influences population genetic parameters in predictable ways.

Characterization of Microsatellite Loci in Castilleja sessiliflora and Transferability to 24 Castilleja Species (Orobanchaceae)

Premise of the study: Microsatellite primers were developed in the hemiparasitic perennial forb Castilleja sessiliflora to investigate patterns of gene flow and genetic diversity within and among populations. Methods and Results: Twelve polymorphic loci were identified in C. sessiliflora and tested on three populations (32 individuals each) sampled across the range of the species. The loci amplified di- and trinucleotide repeats with 3–14 alleles per locus. To assess cross-amplification, primer pairs were also tested on 24 additional Castilleja species that represent the morphological and geographic diversity of the genus. We provide reports of their effectiveness in all 25 taxa. Conclusions: These results indicate the utility of these primers in C. sessiliflora for future studies of genetic structure and gene flow, as well as their widespread applicability in other members of the diverse and complex genus Castilleja.

Characterization of Microsatellite Loci inCastilleja sessilifloraand Transferability to 24CastillejaSpecies (Orobanchaceae)

Premise of the study: Microsatellite primers were developed in the hemiparasitic perennial forb Castilleja sessiliflora to investigate patterns of gene flow and genetic diversity within and among populations. Methods and Results: Twelve polymorphic loci were identified in C. sessiliflora and tested on three populations (32 individuals each) sampled across the range of the species. The loci amplified di- and trinucleotide repeats with 3–14 alleles per locus. To assess cross-amplification, primer pairs were also tested on 24 additional Castilleja species that represent the morphological and geographic diversity of the genus. We provide reports of their effectiveness in all 25 taxa. Conclusions: These results indicate the utility of these primers in C. sessiliflora for future studies of genetic structure and gene flow, as well as their widespread applicability in other members of the diverse and complex genus Castilleja.