Alien woody plants are more versatile than native, but both share similar therapeutic redundancy in South Africa

Understanding why alien plant species are incorporated into the medicinal flora in several local communities is central to invasion biology and ethnobiology. Theories suggest that alien plants are incorporated in local pharmacopoeias because they are more versatile or contribute unique secondary chemistry which make them less therapeutically redundant, or simply because they are locally more abundant than native species. However, a lack of a comprehensive test of these hypotheses limits our understanding of the dynamics of plants knowledge, use and potential implications for invasion. Here, we tested the predictions of several of these hypotheses using a unique dataset on the woody medicinal flora of southern Africa. We found that the size of a plant family predicts the number of medicinal plants in that family, a support for the non-random hypothesis of medicinal plant selection. However, we found no support for the diversification hypothesis: i) both alien and native plants were used in the treatment of similar diseases; ii) significantly more native species than alien contribute to disease treatments particularly of parasitic infections and obstetric-gynecological diseases, and iii) alien and native species share similar therapeutic redundancy. However, we found support for the versatility hypothesis, i.e., alien plants were more versatile than natives. These findings imply that, although alien plant species are not therapeutically unique, they do provide more uses than native plants (versatility), thus suggesting that they may not have been introduced primarily for therapeutic reasons. We call for similar studies to be carried out on alien herbaceous plants for a broader understanding of the integration of alien plants into the pharmacopoeias of the receiving communities.

Widespread anthropogenic translocation of the African Clawed Frog across its native range is revealed by its co-introduced monogenean parasite in a co-phylogeographic approach

1. The management of biological invasions relies upon the development of methods to trace their origin and expansion. Co-introduced parasites, especially monogenean flatworms, are ideal tags for the movement of their invasive hosts due to their short generations, direct life cycles and host specificity. However, they are yet to be applied to trace the intraspecific movement of species in their native ranges. 2. As proof of this concept, we conducted a co-phylogeographic analysis based upon two mitochondrial markers of a globally distributed frog Xenopus laevis and its monogenean flatworm parasite Protopolystoma xenopodis in both its native range in southern Africa and its invasive range in Europe. 3. Translocation of lineages was largely masked in the frog's phylogeography. However, incongruent links between host and parasite phylogeography indicated host switches from one host lineage to the other after these were brought into contact due to human-mediated translocation in the native range. Thus, past translocation of host lineages is revealed by the invasion success of its co-introduced parasite lineage. 4. This study demonstrates the concept that parasite data can serve as an independent line of evidence in invasion biology, also on the intraspecific level, shedding light on previously undetected invasion dynamics. Based upon the distribution of these invasive parasite lineages, we infer that the widespread translocation of hosts is mainly facilitated by the frog's use as live bait by the local angling communities and not via official export routes. 5. Data from co-introduced, host-specific parasites can add value to investigations in invasion biology and conservation. A better understanding of the translocation history and resulting genetic mixing of animals in their native ranges prior to introduction into new environments can inform management strategies in the invasive range. Knowledge of the intraspecific movement of different lineages of animals in their native ranges also has conservation implications, since contact between divergent lineages of hosts and parasites can facilitate host switches and altered parasite dynamics in both native and invasive populations. Therefore, we recommend the inclusion of parasite data as a more holistic approach to the invasion ecology of animals on the intraspecific level.

Tracing the invasion of a leaf-mining moth in the Palearctic through DNA barcoding of historical herbaria

Historical herbaria are valuable sources of data in invasion biology. Here we study the invasion history of the lime leafminer, Phyllonorycter issikii, by surveying over 15 thousand herbarium specimens of limes (Tilia spp.) collected in the Palearctic during last 253 years (1764-2016). The majority of herbarium specimens with the pest mines (89%) originated from East Asia (1859-2015), whereas remaining 11% of specimens with the mines came from Europe, European Russia and Western Siberia (1987-2015). These results support the hypothesis of a recent Ph. issikii invasion from Eastern to Western Palearctic. Single molecule real-time sequencing of the COI barcode region of 93 archival larvae and pupae (7-162 years old) dissected from the mines on historical herbaria allowed to distinguish between Ph. issikii and Ph. messaniella, a polyphagous species rarely feeding on Tilia, which mines were found in herbarium from Europe dated by 1915-1942. We discovered 25 haplotypes of Ph. issikii, of which 16 haplotypes were present solely in East Asia, and revealed wide distribution of the species in China. Six haplotypes shared between Eastern and Western Palearctic suggest the contribution of Ph. issikii populations from the Russian Far East, China and Japan to the westward invasion.

Phoretic mite infestations associated with Rhynchophorus palmarum (Coleoptera: Curculionidae) in southern California

The South American palm weevil, Rhynchophorus palmarum (Coleoptera: Curculionidae), established in San Diego County, California, USA sometime around 2014. Attached to the motile adults of this destructive palm pest, we identified three species of uropodine mites (Parasitiformes: Uropodina), Centrouropoda n. sp., Dinychus n. sp. and Fuscuropoda marginata. Two of these species, Centrouropoda n. sp. and Dinychus n. sp. are recorded for the first time in the USA and were likely introduced by R. palmarum. Several species of mites, primarily of Uropodina, have previously been recorded as phoretic on Rhynchophorus spp. In this study, we examined 3,035 adult R. palmarum trapped over a 2.5-year period, July 2016 to December 2018, and documented the presence of and species composition of phoretic mites and their relationship with weevil morphometrics (i.e., pronotum length and width). The presence and species composition of mites on weevil body parts changed over the survey period. No mites were found under weevil elytra in 2016 and mite prevalence under elytra increased over 2017–2018 due to an increased abundance of Centrouropoda n. sp per individual beetle. Mite occurrence levels were significantly correlated with reduced pronotum widths of male weevils only. The significance of this finding on male weevil fitness is unknown. Potential implications of phoretic mites on aspects of the invasion biology of R. palmarum are discussed.

The Genomic Processes of Biological Invasions: From Invasive Species to Cancer Metastases and Back Again

The concept of invasion is useful across a broad range of contexts, spanning from the fine scale landscape of cancer tumors up to the broader landscape of ecosystems. Invasion biology provides extraordinary opportunities for studying the mechanistic basis of contemporary evolution at the molecular level. Although the field of invasion genetics was established in ecology and evolution more than 50 years ago, there is still a limited understanding of how genomic level processes translate into invasive phenotypes across different taxa in response to complex environmental conditions. This is largely because the study of most invasive species is limited by information about complex genome level processes. We lack good reference genomes for most species. Rigorous studies to examine genomic processes are generally too costly. On the contrary, cancer studies are fortified with extensive resources for studying genome level dynamics and the interactions among genetic and non-genetic mechanisms. Extensive analysis of primary tumors and metastatic samples have revealed the importance of several genomic mechanisms including higher mutation rates, specific types of mutations, aneuploidy or whole genome doubling and non-genetic effects. Metastatic sites can be directly compared to primary tumor cell counterparts. At the same time, clonal dynamics shape the genomics and evolution of metastatic cancers. Clonal diversity varies by cancer type, and the tumors’ donor and recipient tissues. Still, the cancer research community has been unable to identify any common events that provide a universal predictor of “metastatic potential” which parallels findings in evolutionary ecology. Instead, invasion in cancer studies depends strongly on context, including order of events and clonal composition. The detailed studies of the behavior of a variety of human cancers promises to inform our understanding of genome level dynamics in the diversity of invasive species and provide novel insights for management.

Some reflections on current invasion science and perspectives for an exciting future

Species spreading beyond their native ranges are important study objects in ecology and environmental sciences and research on biological invasions is thriving. Along with an increase in the number of publications, the research field is experiencing an increase in the diversity of methods applied and questions asked. This development has facilitated an upsurge in information on invasions, but it also creates conceptual and practical challenges. To provide more transparency on which kind of research is actually done in the field, the distinction between invasion science, encompassing the full spectrum of studies on biological invasions and the sub-field of invasion biology, studying patterns and mechanisms of species invasions with a focus on biological research questions, can be useful. Although covering a smaller range of topics, invasion biology today still is the driving force in invasion science and we discuss challenges stemming from its embeddedness in the social context. Invasion biology consists of the building blocks ‘theory’, ‘case studies’ and ‘application’, where theory takes the form of conceptual frameworks, major hypotheses and statistical generalisations. Referencing recent work in philosophy of science, we argue that invasion biology, like other biological or ecological disciplines, does not rely on the development of an all-encompassing theory in order to be efficient. We suggest, however, that theory development is nonetheless necessary and propose improvements. Recent advances in data visualisation, machine learning and semantic modelling are providing opportunities for enhancing knowledge management and presentation and we suggest that invasion science should use these to transform its ways of publishing, archiving and visualising research. Along with a stronger focus on studies going beyond purely biological questions, this would facilitate the efficient prevention and management of biological invasions.

Solutions in microbiome engineering: prioritizing barriers to organism establishment

Microbiome engineering is increasingly being employed as a solution to challenges in health, agriculture, and climate. Often manipulation involves inoculation of new microbes designed to improve function into a preexisting microbial community. Despite, increased efforts in microbiome engineering inoculants frequently fail to establish and/or confer long-lasting modifications on ecosystem function. We posit that one underlying cause of these shortfalls is the failure to consider barriers to organism establishment. This is a key challenge and focus of macroecology research, specifically invasion biology and restoration ecology. We adopt a framework from invasion biology that summarizes establishment barriers in three categories: (1) propagule pressure, (2) environmental filtering, and (3) biotic interactions factors. We suggest that biotic interactions is the most neglected factor in microbiome engineering research, and we recommend a number of actions to accelerate engineering solutions.

Genealogical structure changes as range expansions transition from pushed to pulled

Range expansions accelerate evolution through multiple mechanisms, including gene surfing and genetic drift. The inference and control of these evolutionary processes ultimately rely on the information contained in genealogical trees. Currently, there are two opposing views on how range expansions shape genealogies. In invasion biology, expansions are typically approximated by a series of population bottlenecks producing genealogies with only pairwise mergers between lineages—a process known as the Kingman coalescent. Conversely, traveling wave models predict a coalescent with multiple mergers, known as the Bolthausen–Sznitman coalescent. Here, we unify these two approaches and show that expansions can generate an entire spectrum of coalescent topologies. Specifically, we show that tree topology is controlled by growth dynamics at the front and exhibits large differences between pulled and pushed expansions. These differences are explained by the fluctuations in the total number of descendants left by the early founders. High growth cooperativity leads to a narrow distribution of reproductive values and the Kingman coalescent. Conversely, low growth cooperativity results in a broad distribution, whose exponent controls the merger sizes in the genealogies. These broad distribution and non-Kingman tree topologies emerge due to the fluctuations in the front shape and position and do not occur in quasi-deterministic simulations. Overall, our results show that range expansions provide a robust mechanism for generating different types of multiple mergers, which could be similar to those observed in populations with strong selection or high fecundity. Thus, caution should be exercised in making inferences about the origin of non-Kingman genealogies.

Biological invasion risk assessment of Tuta absoluta: mechanistic versus correlative methods

The capacity to assess invasion risk from potential crop pests before invasion of new regions globally would be invaluable, but this requires the ability to predict accurately their potential geographic range and relative abundance in novel areas. This may be unachievable using de facto standard correlative methods as shown for the South American tomato pinworm Tuta absoluta, a serious insect pest of tomato native to South America. Its global invasive potential was not identified until after rapid invasion of Europe, followed by Africa and parts of Asia where it has become a major food security problem on solanaceous crops. Early prospective assessment of its potential range is possible using physiologically based demographic modeling that would have identified knowledge gaps in T. absoluta biology at low temperatures. Physiologically based demographic models (PBDMs) realistically capture the weather-driven biology in a mechanistic way allowing evaluation of invasive risk in novel areas and climes including climate change. PBDMs explain the biological bases for the geographic distribution, are generally applicable to species of any taxa, are not limited to terrestrial ecosystems, and hence can be extended to support ecological risk modeling in aquatic ecosystems. PBDMs address a lack of unified general methods for assessing and managing invasive species that has limited invasion biology from becoming a more predictive science.