Young Jin Chun

The role of enemy release, tolerance and resistance in plant invasions: linking damage to performance

An explanation for successful invasion is that invasive alien species sustain less pressure from natural enemies than co-occurring native species. Using meta-analysis, we examined whether invasive species: (1) incur less damage, (2) exhibit better performance in the presence of enemies, and (3) tolerate damage more than native species. Invasive alien species did not incur less damage than native species overall. The performance of invasive alien species was reduced compared to natives in the presence of enemies, indicating the invasive alien species were less tolerant to damage than native species. However, there was no overall difference in performance of invasive alien and native species with enemies present. The damage and degree of reduction in performance of invasive alien relative to native species did not depend on relatedness to natives. Our results suggest aliens may not always experience enemy release, and enemy release may not always result in greater plant performance.

PHENOTYPIC PLASTICITY OF NATIVE VS. INVASIVE PURPLE LOOSESTRIFE: A TWO-STATE MULTIVARIATE APPROACH

The differences in phenotypic plasticity between invasive (North American) and native (German) provenances of the invasive plant Lythrum salicaria (purple loosestrife) were examined using a multivariate reaction norm approach testing two important attributes of reaction norms described by multivariate vectors of phenotypic change: the magnitude and direction of mean trait differences between environments. Data were collected for six life history traits from native and invasive plants using a split-plot design with experimentally manipulated water and nutrient levels. We found significant differences between native and invasive plants in multivariate phenotypic plasticity for comparisons between low and high water treatments within low nutrient levels, between low and high nutrient levels within high water treatments, and for comparisons that included both a water and nutrient level change. The significant genotype x environment (G x E) effects support the argument that invasiveness of purple loosestrife is closely associated with the interaction of high levels of soil nutrient and flooding water regime. Our results indicate that native and invasive plants take different strategies for growth and reproduction; native plants flowered earlier and allocated more to flower production, while invasive plants exhibited an extended period of vegetative growth before flowering to increase height and allocation to clonal reproduction, which may contribute to increased fitness and invasiveness in subsequent years.

Gene flow and population admixture as the primary post‐invasion processes in common ragweed (Ambrosia artemisiifolia) populations in France

*An improved inference of the evolutionary history of invasive species may be achieved by analyzing the genetic variation and population differentiation of recently established populations and their ancestral (historical) populations. Employing this approach, we investigated the role of gene flow in the post-invasion evolution of common ragweed (Ambrosia artemisiifolia). *Using eight microsatellite loci, we compared genetic diversity and structure among nine pairs of historical and recent populations in France. Historical populations were reconstructed from herbarium specimens dated from the late 19th to early 20th century, whereas recent populations were collected within the last 5 yr. *Recent populations showed greater allelic and genetic diversity than did historical populations. Recent populations exhibited a lower level of population differentiation, shorter genetic distances among populations and more weakly structured populations than did historical populations. *Our results suggest that currently invasive populations have arisen from active gene flow and the subsequent admixture of historical populations, incorporating new alleles from multiple introductions.

Comparison of quantitative and molecular genetic variation of native vs. invasive populations of purple loosestrife (Lythrum salicaria L., Lythraceae)

Study of adaptive evolutionary changes in populations of invasive species can be advanced through the joint application of quantitative and population genetic methods. Using purple loosestrife as a model system, we investigated the relative roles of natural selection, genetic drift and gene flow in the invasive process by contrasting phenotypical and neutral genetic differentiation among native European and invasive North American populations (QST − FST analysis). Our results indicate that invasive and native populations harbour comparable levels of amplified fragment length polymorphism variation, a pattern consistent with multiple independent introductions from a diverse European gene pool. However, it was observed that the genetic variation reduced during subsequent invasion, perhaps by founder effects and genetic drift. Comparison of genetically based quantitative trait differentiation (QST) with its expectation under neutrality (FST) revealed no evidence of disruptive selection (QST > FST) or stabilizing selection (QST < FST). One exception was found for only one trait (the number of stems) showing significant sign of stabilizing selection across all populations. This suggests that there are difficulties in distinguishing the effects of nonadaptive population processes and natural selection. Multiple introductions of purple loosestrife may have created a genetic mixture from diverse source populations and increased population genetic diversity, but its link to the adaptive differentiation of invasive North American populations needs further research.

Adaptive divergence for a fitness-related trait among invasive Ambrosia artemisiifolia populations in France

The impact of natural selection on the adaptive divergence of invasive populations can be assessed by testing the null hypothesis that the extent of quantitative genetic differentiation (QST) would be similar to that of neutral molecular differentiation (FST). Using eight microsatellite loci and a common garden approach, we compared QST and FST among ten populations of an invasive species Ambrosia artemisiifolia (common ragweed) in France. In a common garden study with varying water and nutrient levels, we measured QST for five traits (height, total biomass, reproductive allocation, above‐ to belowground biomass ratio, and days to flowering). Although low FST indicated weak genetic structure and strong gene flow among populations, we found significant diversifying selection (QST > FST) for reproductive allocation that may be closely related to fitness. It suggests that abiotic conditions may have exerted selection pressure on A. artemisiifolia populations to differentiate adaptively, such that populations at higher altitude or latitude evolved greater reproductive allocation. As previous studies indicate multiple introductions from various source populations of A. artemisiifolia in North America, our results suggest that the admixture of introduced populations may have increased genetic diversity and additive genetic variance, and in turn, promoted the rapid evolution and adaptation of this invasive species.

Two-year field study shows little evidence that PPO-transgenic rice affects the structure of soil microbial communities

There is global concern about the environmental consequences associated with transgenic crops. Their effects on the soil ecosystem are of special interest when assessing ecological safety and integrity. Although many efforts have been made to develop crops genetically modified to have resistance to protoporphyrin oxidase (PPO)-inhibiting herbicides, little is known about their influence on soil microbial communities. We conducted a 2-year field study and an analysis via terminal restriction fragment length polymorphism (T-RFLP) to assess the impacts of PPO-transgenic rice on bacterial and fungal communities. In the first year we sampled the rhizosphere and surrounding bulk soil, while in the second year we sampled rhizosphere soil only. No differences were observed in the diversity indices and community composition of microbial communities between transgenic rice and its parental non-transgenic counterpart (cultivar Dongjin). Instead, community variation was strongly dependent on growth stage and year. Therefore, we observed no adverse effects by these crops of modified rice on the microbial community composition in paddy soils.

Co-Channel Interference Cancellation Using Single Radio Frequency and Baseband Chain

We present a new architecture for multi-antenna receivers that cancels the co-channel interference (CCI) using a single radio frequency (RF) and baseband (BB) chain, while still achieving nearly the same bit error rate that can be provided by the conventional receiver architecture requiring multiple RF/BB chains. The proposed receiver architecture enables multiple transmitter-receiver pairs to simultaneously communicate in the same frequency band without additional bandwidth, thereby increasing the spectral efficiency or capacity, with significantly reduced receiver complexity and power consumption.

High Genetic Differentiation in Endangered Sedum ussuriense and Implications for Its Conservation in Korea

Sedum ussuriense Kom. (Crassulaceae) is a succulent perennial herb localized to rocky valleys in southeastern Korea. Although it is an important natural resource with high economic value as an ornamental plant, it is currently endangered because of land-use changes and illegal exploitation. To initiate a proper conservation plan, we selected four populations (Juwang, Okgye, Jeolgol, and Haok) around Mt. Juwang, characterized their phenotypic traits, and evaluated patterns of random amplified polymorphic DNA variation. Despite its small population size, Okgye had the greatest proportion of flowering plants and higher seed production than from the other populations. This population also harbored the greatest genetic diversity. However, recent fragmentation between Okgye and Haok appeared to cause genetic divergence, leading to close genetic relationships of Okgye to Juwang vs. Haok to Jeolgol. In the long term, this raises concerns about the loss of genetic variation and the possibility of a demographic crash in those fragmented populations. Because our results indicated a high degree of divergence among populations, we suggest that conservation activities should focus on maintaining and propagating all populations throughout this species’ range.

Log-likelihood-ratio ordered successive interference cancellation in multi-user, multi-mode MIMO systems

Log-likelihood-ratio (LLR) ordered successive interference cancellation (SIC) scheme is analyzed in multi-user, multi-mode, multi-input multi-output (MIMO) systems in which each user may choose between two operation modes: spatial multiplexing or beamforming. The main idea is to detect and cancel the user signal in order of LLR which provides a posteriori information about the reliability of detection. The simulation results indicate that LLR-ordered SIC provides 1 ~ 3 dB gain over the conventional SNR-ordered SIC in multiuser MIMO system and the gain increases with increasing number of users.

Reliability-Rate Tradeoff in Large-Scale Multiple Access Relay Networks

We consider random network coding in noisy large-scale multiple-access relay networks in which the source packets that are correctly received at a relay are linearly combined with randomly chosen coefficients and forwarded to the destination. We derive the union bound on the average probability of decoding error at the destination with the maximum likelihood decoding, averaged over all possible node locations and relay encoding rules. The union bound provides an upper bound to the probability of decoding error with the best network coding scheme and enables us to determine the error exponent. From the error exponent, we determine the reliability-rate tradeoff and the achievable rate at the high node density regime. The high node density analysis is useful for understanding the performance of large-scale multiple access relay networks. The energy saving at a source node offered by the energy expenditure at a relay node and the optimum constellation size that minimizes the energy per information bit (Eb/N0) are investigated as a function of reliability, rate, and node density. The effect of MIMO transmit modes at the relay nodes, when they are equipped with multiple antennas, on the network-wide reliability-rate tradeoff is investigated. The insight provided by the analysis is useful for understanding of the fundamental limit and tradeoffs in large-scale multiple-access relay networks with network coding.