Seed germination ecology of Polymnia canadensis (Asteraceae), a monocarpic species of the North American Temperate Deciduous Forest

The seed germination of Polymnia canadensis was studied in relation to its wide variation in life history and its ecology as a mostly facultative biennial, a life cycle type that is rare in stable forest habitats in eastern North America. The seed dormancy and germination characteristics of P. canadensis were like some other herbaceous woodland species of diverse life cycle types. That is, its seeds have physiological dormancy, and they (1) germinated to higher percentages after cold stratification, (2) germinated better in light than in darkness and (3) formed a persistent soil seed bank. Since its seed dormancy and germination characteristics are not uncommon and are not particularly associated with any one life cycle type in woodlands, those properties do not contribute to the rarity of its life cycle type in deciduous forests. These properties are also found in many facultative biennials of open, disturbed habitats and in other Asteraceae of various life cycle types. In addition, the germination phenology of P. canadensis differed between mesic and dry field sites in central Kentucky. At the dry sites, most of the yearly germination occurred in fall, while at the mesic sites most germination occurred in the spring due to being inhibited during fall. A reciprocal seed transplant experiment conducted in two different years demonstrated that the cause of this difference was environmental and that there was no source x site interaction; i.e., no difference between sources in phenotypic plasticity for germination phenology. Absence of genetic effects was also shown by no consistent pattern in the few differences between seed sources in seed incubation laboratory experiments and in a germination phenology experiment in glasshouse flats. Exposure of seeds to a high ratio of far-red/red light prior to or during incubation did not inhibit germination. Neither did changes in leaf litter thickness qualitatively alter germination phenology in field quadrats or in glasshouse flats. Thus, germination in fall at mesic sites was inhibited by other unknown factor(s), perhaps interacting with the effects of closed tree canopy and/or thick leaf litter.     

Ecological life history of Polymnia canadensis,a monocarpic species of the North American Temperate Deciduous Forest: Demography

A demographic investigation was conducted to assess variation in life history of Polymnia canadensis (Asteraceae), a geographically-widespread, herbaceous species of deciduous forests in eastern North America. During 1985-1994, 23,063 seedlings of P. canadensis were monitored at five central Kentucky study sites. Numbers at the end were: biennials, 554; triennials, 142; winter annuals, 16; monocarpic perennials, 2; tricarpic perennials (three years), 3; and dicarpic perennials (some skipped years) that matured in the first year of life, 23; in the second year, 60; and in the third year, 9. Weekly cohorts of P. canadensis generally exhibited Deevey Type III survivorship with highest seedling mortality in summer associated with low soil moisture. Wide spatial variation in life history was displayed by the fact that fall germination cohorts at dry sites generally had greater germination and survivorship than at mesic sites during seedling establishment, while the reverse was true for spring cohorts. This led to more reproductive individuals in fall germination cohorts than spring cohorts at dry sites and generally the opposite case at mesic sites. Forest shade in mesic sites caused slower growth and a greater frequency of longer-lived reproductive individuals than in open, dry sites, but it also resulted in higher survivorship than at dry sites during moderate drought. Annual population growth rate averaged across four years was not significantly different between a dry site and mesic site, indicating that despite forest shade, P. canadensis persisted in the mesic site as well as it did in the dry site. Population structure varied among years, seasons, and study sites; at two study plots, a 2-year flowering cycle of mass seeding and senescence persisted for 4 years. At a smaller scale, there was little difference in survivorship between study plots within sites or between quadrats within study plots, while in a few instances there were large differences in the number of reproductive individuals. Weekly cohorts that germinated early within seasonal cohorts had greater number of reproductive individuals than later weekly cohorts, but not consistently greater survivorship. Several droughts induced temporal variation that was as important as spatial variation. During these droughts, the population size of all cohorts that germinated prior to the droughts declined to zero at all sites, and biennials were the longest lived type of reproductive individuals. During drought, Deevey Type I survivorship was prevalent, and lack of seed rain led to dependence on persistent seed banks for recruitment in some seasonal cohorts.     

Review of the biology and ecology of a ragweed leaf beetle,Ophraella communa (Coleoptera: Chrysomelidae), which is a biological control agent of an invasive common ragweed,Ambrosia artemisiifolia (Asterales: Asteraceae)

A ragweed leaf beetle, Ophraella communa (Coleoptera: Chrysomelidae), has been highlighted as a potential biological control agent of Ambrosia artemisiifolia. O. communa and A. artemisiifolia are native in North America and alien species in East Asia and Europe. As an invasive weed, A. artemisiifolia causes severe economic losses as reducing agricultural production as well as producing severe allergenic pollen. As an herbivore insect, O. communa has strong host preference on A. artemisiifolia. All the developmental stages of O. communa can be found on A. artemisiifolia and it attacks a single plant in repeated and extended manners. With few individuals on A. artemisiifolia, O. communa can completely defoliate before pollen production. Therefore, O. communa had been focused as a biological control of this invasive weed, but its introduction was denied because of possible damage on an important crop, Helianthus annuus. O. communa was accidentally introduced in East Asia and Europe in 1990s and 2010s, respectively. Fortunately, O. communa population was well established to suppress A. artemisiifolia in the introduced areas. Following detailed field surveys and host specificity tests of O. communa were conducted and proved a strong potential of O. communa as a biological control agent of A. artemisiifolia. Moreover, O. communa has been investigated in physiological and evolutionary studies. In this study, the potential of O. communa as a biological control agent and a study organism are reviewed.     

AFLP and breeding system studies indicate vicariance origin for scattered populations and enigmatic low fecundity in the Moroccan endemic Hypochaeris angustifolia (Asteraceae), sister taxon to all of the South American Hypochaeris species

We used Amplified Fragment Length Polymorphism markers (AFLP) and breeding system studies to investigate the population structure and reproductive biology of Hypochaeris angustifolia (Asteraceae: Cichorieae). This species is endemic to altiplanos of the Atlas Mountains (Morocco) where it occurs in scattered populations, and it is the sister species to c. 40 species of this genus in South America. PCoA, NJ, and Bayesian clustering, revealed that the populations are very isolated whilst AFLP parameters show that almost all populations have marked genetic divergence. We contend that these features are more in accord with a vicariance origin for the scattered populations of H. angustifolia, rather than establishment by long-distance dispersal. The breeding system studies revealed that H. angustifolia is a self-incompatible species, with low fecundity in natural and in experimental crosses, probably due to a low frequency of compatible phenotypes within and between the populations.     

Resurrection of Rabdophaga salicivora Shinji (Diptera: Cecidomyiidae), a Japanese gall midge formerly misidentified as a North American species, Rabdophaga rigidae (Osten Sacken), with observations on the phylogenetic relationships of its populations in Japan and the Russian Far East

Intercontinental biotic connections between Eurasia and North America are common in many gall midge genera (Diptera: Cecidomyiidae), but only a few species have been recorded from both continents. In Japan, four gall midge species had been previously considered to be identical to North American species, but three of these cases have already been disproved. We examined the remaining species, Rabdophaga rigidae, which had been originally described from Japan as Rabdophaga salicivora in 1938, later recorded from the Russian Far East in 1967, and synonymized with a North American species, R. rigidae, in 1982. Morphological features and partial sequence data of the mtDNA cytochrome oxidase subunit I (COI) region suggested that the Japanese species is a distinct species and is identical to the species recorded from the Russian Far East. We therefore apply the original name, R. salicivora, to the Japanese and the Russian species. In addition, on the basis of a molecular phylogenetic analysis, we conclude that R. salicivora possibly came to the Japanese Archipelago through the Korean Peninsula and established itself first in the southern parts of Japan. Then, it expanded its distribution range to northern parts of Honshu, but could not reach Hokkaido, probably because of the Tsugaru Strait between Honshu and Hokkaido.