A Global Review of Ligustrum Lucidum (OLEACEAE) Invasion

High Propagule Pressure and Patchy Biotic Resistance Control the Local Invasion Process of the Tree Ligustrum lucidum in a Subtropical Forest of Uruguay

The tree Ligustrum lucidum (W. T. Aiton, Oleaceae), native to East Asia (China), has become an aggressive invader of subtropical and temperate forests around the world. To understand how its local small-scale spread is controlled, we studied (48 plots of 4 m-2), in a subtropical forest of Uruguay, the distribution and survival of seedlings, saplings, and poles to assess the effects of dispersal from mother trees (distance), microsite type (forest stands defined by dominant species), and past control measures. The propagule pressure of L. lucidum, estimated through seedlings density, was between 100 and 1000 times higher than that of other species of the community and was concentrated around mother trees (<10 m of distance). Spatial variability of seedlings, saplings, and poles densities were explained by the interaction between distance to mother trees and forest stands. Significative lower densities were observed in the forest patches (stands) dominated by Jodina rhombifolia, and a field survival experiment confirmed lower survival of poles at Jodina stands, demonstrating that some resistance mechanism is operating there. We propose two biotic mechanisms of resistance: herbaceous competition and/or roots hemiparasitism by J. rhombifolia, reducing seedling and sapling survival. We concluded that a high propagule pressure, small-scale dispersal from mother trees, and patchy biotic resistance at Jodina stands control the local spread and domination process of the tree L. lucidum in the studied forest.

The gap-free genome assembly and multi-omics analyses illustrate the evolutionary history and the synthesis of medicinal components of Ligustrum lucidum

Ligustrum lucidum, an important ornamental and medicinal plant in the Oleaceae family, has become a globally notorious invasive species because of its high adaptability. However, the lack of a high quality genome has hindered the understanding of the genetic basis for its broad adaptability and the mechanisms of its medicinal component synthesis. In this study, we successfully assembled a gap free telomere to telomere genome of L. lucidum. Through the reconstruction of the phylogenetic tree, we presented evidence that Jasmineae diverged from Oleaceae earlier than Forsythieae, which challenges the existing phylogenetic relationships within Oleaceae. Comparative genomics has found that two rounds of gene family expansions in L. lucidum significantly increased the number of genes related to its biotic and abiotic stress resistances, which may lay the genetic foundation for its broad adaptability. Among the L. lucidum fruits from January to March in our investigation, the results of metabolome show that March may be the optimal harvesting time. By integrating genomic, transcriptomic, and metabolomic data, we identified candidate genes involved in the synthesis of compounds, such as specnuezhenide, salidroside, and oleanolic acid. This study provides valuable genomic resources for comparative genomics studies within Oleaceae and for the genetic research of L. lucidum.

Established populations of Ixodes silvanus (Acari: Ixodidae) in the Chaco Serrano, Argentina

The aim of the study was to report the occurrence of Ixodes silvanus outside its distribution range, in the Chaco Serrano vegetation unit of the Chaco Phytogeographic Province, central Argentina. Ticks were collected from vegetation and on birds between November 2021 and December 2023. A possible seasonal activity was observed in the immature stages of I. silvanus, with larvae in autumn-winter and nymphs in spring-summer, consistent with a behavioral diapause. A total of 937 ticks were identified as I. silvanus and confirmed molecularly, 741 host-seeking and 196 parasitizing 49 passerine birds (of 9 species, 6 genera and 5 families). All host-seeking ticks were found in leaf litter in forests dominated by the invasive tree Ligustrum lucidum, suggesting a possible link between environmental changes and the establishment of I. silvanus in this region. The prevalence of I. silvanus on birds was 27.4%, with significant participation of the Turdus genus and new host associations documented. The findings suggest that I. silvanus may be expanding its range, potentially facilitated by environmental modifications, the movement of austral migratory birds (Turdus nigriceps, Synallaxis frontalis and Zonotrichia capensis), and the range expansion of other bird species (Turdus amaurochalinus, Turdus chiguanco and Turdus rufiventris). Therefore, I. silvanus may represent a biological invasion and a potential threat to wild bird populations as a vector of pathogenic microorganisms. Future studies are required to determine the implications this could have.

Frugivorous birds disperse seeds of Ligustrum lucidum, seed-feeding weevils, and parasitic wasps of weevils via endozoochory

Seed dispersal by frugivorous birds is a famous plant-animal interaction. However, we demonstrated that frugivorous birds can disperse seeds of Ligustrum lucidum, and its seed parasite weevils and the parasitic wasps from the weevils in this study. The cryptic tetrad of Ligustrum-disperser-weevil-wasp may be an overlooked phenomenon in seed dispersal syndrome.

Economic impact of invasive alien species in Argentina: a first national synthesis

Invasive alien species (IAS) affect natural ecosystems and services fundamental to human well-being, human health and economies. However, the economic costs associated with IAS have been less studied than other impacts. This information can be particularly important for developing countries such as Argentina, where monetary resources for invasion management are scarce and economic costs are more impactful. The present study provides the first analysis of the economic cost of IAS in Argentina at the national level, using the InvaCost database (expanded with new data sources in Spanish), the first global compilation of the reported economic costs of invasions. We analyzed the temporal development of invasions costs, distinguishing costs according to the method reliability (i.e. reproducibility of the estimation methodology) and describing the economic costs of invasions by invaded environment, cost type, activity sector affected and taxonomic group of IAS. The total economic cost of IAS in Argentina between 1995 and 2019 was estimated at US$ 6,908 million. All costs were incurred and 93% were highly reliable. The recorded costs were mainly related to terrestrial environments and the agricultural sector, with lack of costs in other sectors, making it difficult to discuss the actual distribution of invasion costs in Argentina. Nevertheless, the reported costs of IAS in this country are very high and yet likely much underestimated due to important data gaps and biases in the literature. Considering that Argentina has an underdeveloped economy, costs associated with biological invasions should be taken into consideration for preventing invasions, and to achieve a more effective use of available resources.