David N. Zaya

Interspecific and Intraspecific Pollination Patterns of Valley Oak, Quercus lobata, in a Mixed Stand in Coastal Central California

Pollination patterns within Quercus lobata and interspecific hybridization between Q. lobata and Quercus douglasii were studied in a coastal central California mixed woodland. We first identified hybrids by means of microsatellite genotyping and assignment tests. Hybrids were rare, both among adults (4 of 190, 2.1%) and among acorns collected from Q. lobata trees (6 of 392, 1.5%). These low rates of hybridization at both early and late life history stages suggest that fertility barriers, rather than natural selection against hybrids, limit hybridization between these two species. However, hybrid adults, although rare, may facilitate gene flow between the two species. Acorns collected from a hybrid tree had both Q. lobata pollen donors (11 of 30, 37%) and Q. douglasii or hybrid pollen donors (19 of 30, 63%). After removing hybrid acorns from the analysis, we used paternity assignment to track pollination patterns within Q. lobata. Of 108 acorns, only 32 (30%) were assigned to candidate pollen donors within 200 m of the maternal tree, indicating that the majority of effective pollen travels more than 200 m. Individual trees had acorn crops with many different sires and an average effective number of pollen donors (Nep) of 219 per tree. Indirect methods using correlated paternity estimated mean pollination distances of ∼100 m and mean Nep of 5.2 per tree, values much lower than those derived directly from paternity assignments.

The anomalous Kentucky coffeetree: megafaunal fruit sinking to extinction?

The Kentucky coffeetree (Gymnocladus dioicus, Fabaceae) is an ecological paradox. A rare tree in nature in eastern and central North America, G. dioicus produces legumes that are only known to be dispersed by water, but appear similar to fruits consumed and dispersed by elephants and rhinoceros. One would expect the pods to be consumed by livestock, but the pulp and seeds are toxic to cattle and sheep. We examine the puzzle of G. dioicus dispersal in light of its other reproductive and life history characteristics and find that it probably is a botanical anachronism, in terms of both a set of dispersal agents long extinct and habitats, including what we term megafaunal disclimaxes, which have disappeared. Large seeds, the megafaunal gestault of the fruit, a dioecious mating system, and shade-intolerance combined with vigorous cloning suggest a widely dispersed pioneer of Miocene through Pleistocene habitats profoundly altered by large-mammal herbivory. As to what ate it, we can only say there were once many candidates. We hypothesize that the plant is an ecological anachronism, sinking to extinction in the wild.

Multiple causes of seedling rarity in scrub plum, Prunus geniculata (Rosaceae), an endangered shrub of the Florida scrub

Conservation of an imperiled plant often requires an understanding of its reproductive ecology. Scrub plum (Prunus geniculata) is an endangered Florida shrub endemic to pyrogenic xeric uplands. Although plants are long-lived and may flower profusely, particularly after burning, fruit yield is sparse and seedlings are rare. We investigated potential causes of seedling rarity in scrub plum by studying its floral sex and breeding systems, fruit development, and germination ecology. We also developed a flow chart based on two time-since-fire scenarios to illustrate the cumulative impact of these factors on seedling recruitment. Breeding system experiments suggested partial gametophytic self-incompatibility in this functionally andromonoecious species, with inbreeding depression in self-compatible individuals. Predispersal seed predation, the major constraint on seedling recruitment, was lower in the first postburn season. In two field experiments, seed germination was <11% irrespective of treatment. These results indicate that seedling recruitment in scrub plum may be limited by multiple factors, including sexual reproductive failure, high predispersal seed predation, and low seed germination. The chance of a bisexual flower producing a seedling ranges from 5 in 1000 to 5 in 100000, depending on the time since fire. Restoration of scrub plums historical fire regime may mitigate some of these factors.

Long-Term Trends in Midwestern Milkweed Abundances and Their Relevance to Monarch Butterfly Declines

Declines in monarch butterfly populations have prompted investigation into the sensitivity of their milkweed host plants to land-use change. Documented declines in milkweed abundance in croplands have spurred efforts to promote milkweeds in other habitats. Nevertheless, our current understanding of milkweed populations is poor. We used a long-term plant survey from Illinois to evaluate whether trends in milkweed abundance have caused monarch decline and to highlight the habitat-management practices that promote milkweeds. Milkweed abundance in natural areas has not declined precipitously, although when croplands are considered, changes in agricultural weed management have led to a 68% loss of milkweed available for monarchs across the region. Midsuccessional plant communities with few invasive species provide optimal milkweed habitat. The augmentation of natural areas and the management of existing grasslands, such as less frequent mowing and woodyand exotic-species control, may replace some of the milkweed that has been lost from croplands.

Plant genetics for forensic applications

An emerging application for plant DNA fingerprinting and barcoding involves forensic investigations. Examples of DNA analysis of botanical evidence include crime scene analysis, identifying the source of commercial plant products, and investigation of trade in illicit drugs. Here, we review real and potential applications of DNA-based forensic botany and provide a protocol for microsatellite genotyping of leaf material, a protocol that could be used to link a suspect to a victim or to a crime scene.

Genetic factors accelerate demographic decline in rare Asclepias species

We investigated the role of genetic, reproductive and demographic factors in the decline of two co-occurring milkweeds, Asclepias lanuginosa and A. viridiflora, in fragmented populations in Illinois and Wisconsin. Asclepias lanuginosa flowers but does not set seed while seed set is regularly observed in A. viridiflora. We used microsatellite genotyping to determine the extent of clonal growth, genetic diversity, and genetic structure in nine populations of A. lanuginosa and five populations of A. viridiflora. Microsatellite genotyping revealed extremely high clonality in A. lanuginosa; only 32 multilocus genotypes occurred among more than 300 ramets, compared to 118 multilocus genotypes among 124 ramets for A. viridiflora. Four A. lanuginosa populations were monoclonal. While we found no evidence for inbreeding, A. lanuginosa had significantly lower expected heterozygosity and a lower mean number of effective alleles than A. viridiflora. Population viability analysis (PVA) conducted at one site indicated a high probability of persistence, although the population was comprised of only two clones. Because PVA does not distinguish between ramets and genets, results should be interpreted with caution when conducted on highly clonal species. A nearly complete shift in the mode of reproduction, from sexual to asexual, appears to be the most immediate threat to survival of A. lanuginosa in these fragmented prairie remnants. Conservation management strategies should include actions to increase clonal diversity in remnant populations.

Drivers of synchrony of acorn production in the valley oak (Quercus lobata) at two spatial scales

We investigated spatial synchrony of acorn production by valley oaks (Quercus lobata) among individual trees at the within-population, local level and at the among-population, statewide level spanning the geographic range of the species. At the local level, the main drivers of spatial synchrony were water availability and flowering phenology of individual trees, while proximity, temperature differences between trees, and genetic similarity failed to explain a significant proportion of variance in spatial synchrony. At the statewide level, annual rainfall was the primary driver, while proximity was significant by itself but not when controlling for rainfall; genetic similarity was again not significant. These results support the hypothesis that environmental factors, the Moran effect, are key drivers of spatial synchrony in acorn production at both small and large geographic scales. The specific environmental factors differed depending on the geographic scale, but were in both cases related to water availability. In addition, flowering phenology, potentially affecting either density-independent pollination failure (the pollination Moran effect) or density-dependent pollination efficiency (pollen coupling), plays a key role in driving spatial synchrony at the local geographic scale.

Mislabeling of an Invasive Vine (Celastrus orbiculatus) as a Native Congener (C. scandens) in Horticulture

The horticultural industry is an important source of invasive ornamental plant species, which is part of the motivation for an increased emphasis on using native alternatives. We were interested in the possibility that plants marketed in the midwestern United States as the native Celastrus scandens, or American bittersweet, were actually the difficult-to-distinguish invasive Celastrus orbiculatus (oriental bittersweet) or hybrids of the two species. We used nuclear microsatellite DNA loci to compare the genetic identities of 34 plants from 11 vendors with reference plants from wild populations of known species identity. We found that 18 samples (53%) were mislabeled, and 7 of the 11 vendors sold mislabeled plants. Mislabeled plants were more likely to be purchased through Internet or phone order shipments and were significantly less expensive than accurately labeled plants. Vendors marketed mislabeled plants under five different cultivar names, as well as unnamed strains. Additionally, the most common native cultivar, ‘Autumn Revolution,’ displays reproductive characteristics that diverge from the typical C. scandens, which could be of some concern. The lower price and abundance of mislabeled invasive plants introduces incentives for consumers to unknowingly contribute to the spread of C. orbiculatus. Revealing the potential sources of C. orbiculatus is critical for controlling further spread of the invasive vine and limiting its impact on C. scandens populations. Nomenclature American bittersweet, Celastrus scandens L. oriental bittersweet, Celastrus orbiculatus Thunb

Reproductive Success of the Gynodioecious Lobelia spicata Lam. (Campanulaceae): Female Frequency, Population Demographics, and Latitudinal Patterns

Premise of research. In gynodioecious species, female plants are often at a disadvantage due to their reliance on hermaphroditic pollen donation and lower attractiveness to pollinators. They may compensate for these disadvantages through greater reproductive output and progeny fitness; however, the level of female advantage may vary based on population demographics (i.e., female frequency and gender morph density), geographic location, and abiotic conditions (i.e., temperature and precipitation). Methodology. In 2008 and 2009, data on latitude, longitude, mean temperature and mean precipitation from May to July (growing season), female frequency, female density, hermaphrodite density, reproductive output (i.e., fruit set, seed number per fruit, seed biomass), seed germination, and female advantage in reproduction were collected for 11 populations of the gynodioecious prairie species Lobelia spicata Lam. (Campanulaceae) in Illinois. Pivotal results. Female plants were found to produce greater fruit sets, greater number of seeds per fruit, and heavier, better-germinating seeds than hermaphrodites, though these gender differences in reproduction varied among populations and between sampling years. Female frequency impacted the gender-based reproductive measurements; in particular, it was negatively correlated with fruit set. Female frequency within L. spicata populations was negatively correlated with latitude, with temperature the most likely driving force. Conclusions. Abiotic conditions such as high temperatures seem to favor the success of female plants within populations of L. spicata, either directly through differential resource allocation between genders or indirectly as a covariate for some other environmental factor (e.g., pollinator abundance/behavior), though experimental data are needed to support this assertion.