Loreen Allphin

DOES HYBRIDIZATION DRIVE THE TRANSITION TO ASEXUALITY IN DIPLOID BOECHERA

Gametophytic apomixis is a common form of asexual reproduction in plants. Virtually all gametophytic apomicts are polyploids, and some view polyploidy as a prerequisite for the transition to apomixis. However, any causal link between apomixis and polyploidy is complicated by the fact that most apomictic polyploids are allopolyploids, leading some to speculate that hybridization, rather than polyploidy, enables apomixis. Diploid apomixis presents a rare opportunity to isolate the role of hybridization, and a number of diploid apomicts have been documented in the genus Boechera (Brassicaceae). Here, we present the results of a microsatellite study of 1393 morphologically and geographically diverse diploid individuals, evaluating the hypothesis that diploid Boechera apomicts are hybrids. This genus‐wide dataset was made possible by the applicability of a core set of microsatellite loci in 69 of the 70 diploid Boechera species and by our ability to successfully genotype herbarium specimens of widely varying ages. With few exceptions, diploid apomicts exhibited markedly high levels of heterozygosity resulting from the combination of disparate genomes. This strongly suggests that most apomictic diploid Boechera lineages are of hybrid origin, and that the genomic consequences of hybridization allow for the transition to gametophytic apomixis in this genus.

Molecular Phylogenetics and Taxonomy of the Genus Boechera and Related Genera (Brassicaceae: Boechereae)

Abstract Boechera (Brassicaceae) is a diverse genus of ±70 sexual diploid species and numerous apomictic hybrids concentrated in western North America. It is the largest genus in tribe Boechereae, which also includes seven other small genera. Boechera is closely related to Arabidopsis and is becoming a model genus for diverse studies, focusing particularly on apomixis and hybrid speciation. As part of an ongoing effort to clarify the taxonomy of the group, we present phylogenetic analyses of Boechereae, including all genera of the tribe and most of the sexual diploid species of Boechera. Ten loci are used, including two plastid loci, nrDNA ITS, and seven low-copy nuclear loci. These analyses indicate that Boechera, as currently circumscribed, is polyphyletic, comprising three main clades. Eastern North American species previously assigned to Boechera form a distinct clade with the Asian taxon Borodinia macrophylla and are herein transferred to the genus Borodinia, resulting in seven new combinations (Borodinia burkii, Borodinia canadensis, Borodinia dentata, Borodinia laevigata, Borodinia missouriensis, Borodinia perstellata, and Borodinia serotina). Boechera repanda, a morphologically aberrant species endemic to the Sierra Nevada, is recognized in the new genus Yosemitea (as Yosemitea repanda). A primarily western North American clade comprising all remaining species is strongly supported and retains the name Boechera. Although resolution within Boechera sensu stricto is limited, a number of well-supported clades are identified.

DEMOGRAPHY AND LIFE HISTORY CHARACTERISTICS OF THE RARE KACHINA DAISY (ERIGERON KACHINENSIS, ASTERACEAE)

-Erigeron kachinensis is a rare endemic of the Colorado Plateau regions of southeastern Utah and southwestern Colorado. It occurs in small, isolated alcoves (recessed areas in canyon walls) at seeps arising along canyon walls in sandstone substrates. One hundred randomly selected individuals of E. kachinensis within each of six alcoves in Natural Bridges National Monument, San Juan County, Utah, were monitored for 5 yr (1990-1994). Survival of the 600 individuals was followed over the monitoring interval. Vegetative and reproductive parameters were assessed for the survivors each year. Mortality varied among the study alcoves and individual size-classes. Mortality was heavily concentrated in the smaller size-classes. Growth rate accelerated with increasing size-class. Survival rate also increased with increasing size-class. Plants are long-lived; however, longevity is still unknown since mortality was not observed in the largest size-class. Fecundity was greatest for the largest sizeclasses, yet over 80% of the annual seed production came from the three smallest size-classes due to abundance of individuals in these size-classes. Populations varied with respect to plant size and resistance to environmental stressors. Matrix analysis demonstrated a finite rate of population growth of 0.75. However, observed size-class distributions of the six study populations over 5 yr of observation have never been stable. Maintenance of viable populations of the Kachina daisy is dependent on management actions that minimize disturbances (natural or anthropogenic) in the fragile hanging gardens that support the species.

The Relative Effects of Resources and Genetics on Reproductive Success in the Rare Kachina Daisy, Erigeron kachinensis (Asteraceae)

In a previous study, Erigeron kachinensis, the Kachina daisy, was found to have low percentage seed set because of low fertilization rates of ovules (ca. 48%) and high abortion rates of developing seeds (ca. 56%). Therefore, we initiated field and greenhouse experiments to determine which of several factors were responsible for the observed low production of filled seeds in this species. Unmanipulated plants in the greenhouse, under pollinator exclosures, demonstrated that E. kachinensis requires an animal vector for successful pollination. Geitonogamous field and greenhouse crosses produced almost no viable seed (<1%), demonstrating that the species is self‐incompatible. The species appears to exhibit a homomorphic sporophytic type incompatibility system, as found in other composites that may be responsible for the observed low levels of ovule fertilization. Although plants exhibited developmental asymmetries both vegetatively and reproductively under resource stress, resource availability did not affect abortion rates of developing seeds. Resource availability did affect the number of flower heads produced. Seed abortion was significantly decreased when pollen came from a different population. Seed set is likely limited by the species’ inability to find compatible mates because of its self‐incompatibility system and recessive lethals exposed during sexual recombination in its small populations.

Reproductive success and genetic divergence among varieties of the rare and endangered Astragalus cremnophylax (Fabaceae) from Arizona, USA

Populations of Astragalus cremnophylax from Arizona and related A. humillimus from New Mexico were assessed for morphological, reproductive, genetic, and ecological differences. Results suggest that some of the taxa (i.e., A. cremnophylax var. cremnophylax and A. humillimus) are poor reproducers and environmental fluctuation is not likely a factor contributing to low fecundity in these species. Astragalus cremnophylax var. cremnophylax appears to have low fecundity due to inbreeding depression. Allozyme data from 18 loci show little within-population and taxon genetic variability. Most genetic variability is distributed among populations and taxa. The population of A. cremnophylax var. cremnophylax from the Grand Canyon (South Rim) was genetically depauperate, indicative of the bottleneck caused by historic trampling at this viewpoint. Cape Final, a population of A. cremnophylax var. cremnophylax on the Grand Canyon (North Rim) is genetically different from typical materials of this taxon (South Rim) and is more closely related to other taxa within this species complex. However, the other varieties of A. cremnophylax are more closely related to A. humillimus than the population at Cape Final, suggesting potential species status for Cape Final materials based on allozyme divergence.

Weaving a Tangled Web: Divergent and Reticulate Speciation in Boechera fendleri Sensu Lato (Brassicaceae: Boechereae)

Abstract Hybrid speciation is relatively common in plants compared to other well-studied groups. Polyploidy and apomixis are strongly associated with hybrid speciation, presumably due to the opportunities they provide for both reestablishing reproductive function in hybrids with incomplete chromosomal homology and creating rapid reproductive isolation in sympatry. Boechera, a species-rich genus closely related to Arabidopsis, is a particularly fertile ground for the study of hybrid speciation. Thirty-eight apomictic triploid hybrid species are currently recognized in Boechera. Recent research has shown that apomictic diploid hybrids, although very rare in angiosperms, are common in Boechera. Given this complexity, focused studies of individual species complexes are critical to understanding speciation and diagnosing biodiversity in Boechera. Here we analyze DNA sequences from seven nuclear loci and multilocus genotypes from 15 microsatellite markers in a group of closely related taxa formerly included in B. fendleri. Our results support the recognition of four species previously segregated from B. fendleri s. l., including three genetically distinct, sexual diploids (B. fendleri, B. spatifolia, and B. texana) and one apomictic triploid hybrid (B. porphyrea). We also identify four novel apomictic diploid hybrid species (B. carrizozoensis, B. centrifendleri, B. sanluisensis, and B. zephyra) and additional apomictic triploid hybrids. Our results reveal a complex network of relationships. Sexual diploid species can hybridize to form apomictic diploids, and members of these two groups can hybridize to form trigenomic, apomictic triploids.

Searching for Diamonds in the Apomictic Rough: A Case Study Involving Boechera lignifera (Brassicaceae)

Abstract The genus Boechera is one of the most difficult species complexes in North America, with about 70 sexual diploids and hundreds of apomictic taxa representing diverse combinations of nearly every known sexual genome. In this study, we set out to clarify the taxonomy of Boechera lignifera, which currently includes a small number of sexual diploid populations in addition to the widespread apomictic diploid upon which the name is based. Using data from cytological studies, microsatellite DNA analyses, geography, and morphology, we demonstrate that the apomictic populations are genetically quite divergent from the sexual diploids. We propose the name Boechera kelseyana to accommodate the sexual diploid taxon, which occurs entirely south of the geographic range of B. lignifera. Boechera kelseyana is consistently separable from B. lignifera based on pollen and seed morphology, the length and proximal orientation of fruiting pedicels, differences in the branching and orientation of trichomes on the lowers stems, and the number of flowers and cauline leaves on unbranched fertile stems.

GENETIC DIVERSITY AND LOW REPRODUCTIVE SUCCESS IN ISOLATED POPULATIONS OF UTAH JUNIPER (JUNIPERUS OSTEOSPERMA, CUPRESSACEAE)

Abstract Utah juniper (Juniperus osteosperma) has greatly expanded its historical range in the western United States. Management plans for the species have focused on curtailing its encroachment into sagebrush and grassland communities. These plans often include burning or other methods of elimination. These methods may result in subdivision or fragmentation of existing juniper stands. We initiated a study at Dugway Proving Ground, a U.S. Army facility, to examine the effects of fragmentation on the reproductive success of Utah juniper in isolated populations. We used enzyme electrophoresis to quantify genetic variability in isolated populations. We also determined population reproductive success by examining juniper fruits for evidence of seed abortion and/or presence of insect parasites. We compared reproductive and genetic variability in isolated populations at Dugway to 2 nonisolated and encroaching Utah juniper populations. The Dugway populations exhibited reduced seed set due to high seed abortion and/or insect seed parasitism, and a loss of genetic variability in comparison to the nonisolated populations. Additionally, there was a significant correlation between reproductive success and genetic variability.

The Discovery of Great Basin Bristlecone Pine, Pinus Longaeva, in the Tushar Mountains of the Fishlake National Forest in Central Utah, USA

Abstract. In this paper, we provide the first documented evidence of Pinus longaeva from the Tushar Mountain range in central Utah. The P. longaeva trees, initially noticed at the end of September, and further surveyed during the first week of October 2016 are present on 6 small sites on the north-facing slopes of the North Fork of North Creek in the Tushar Mountains of the Fishlake National Forest. We estimate that there are currently up to 179 live individuals that range in age from seedlings to approximately 1400 years. Our data indicate these are particularly slow-growing specimens on very steep sites, in soil of igneous origin. Though many of the trees are infested with dwarf mistletoe, there is little indication that the population is currently at risk from fire, bark beetle attack, or many other common pathogens characteristic of other Pinus species. Nonetheless, there may be reasons for concern associated with future changes to the climate of southern Utah, as well as the impact of invasive species such as white pine blister rust (Cronartium ribicola). We see opportunities for additional research on this unique population and its associated plant community. We also see the need for management strategies to conserve these P. longaeva stands, as well as a possible need to preserve its seeds and/or other genetic materials.

Seed production estimation for mountain big sagebrush (Artemisia tridentata ssp. vaseyana)

ABSTRACT Seed production is an essential component of postdisturbance recovery for mountain big sagebrush (Artemisia tridentata Nutt, ssp vaseyana [Rydb] Beetle; MBS). We tested a method for rapid estimation of MBS seed production using measurements of inflorescence morphology. We measured total stem length, stem length from first branchlet to stem tip, stem diameter, fresh weight, and number of stem branchlets for 750 inflorescences collected from five central and southern Utah sites. Florets per inflorescence were counted to provide an estimate of seed production potential. We used regression analysis to assess associations between morphological traits and potential seed production and evaluated the efficiency and scalability of each measure for field application. Site means for morphological measures varied ∼2 to 11-fold while mean number of florets per inflorescence varied ∼ 8-fold. Inflorescence weight was the best predictor of seed production potential (P < 0.0001, r2 = 0.897), although correlations for all tested variables were highly significant. Among-site differences in regression equations for this relationship were not significant (P = 0.226), suggesting that a single conversion factor may have broad application. However, validation will require additional testing across a broader range of sites and field conditions. Scalable methods for efficient estimation of sagebrush seed production potential, such as those evaluated in this study, could be useful for managers charged with assessing variability in sagebrush community stability.